Fact-checked by Grok 2 weeks ago

Kinetochore

The kinetochore is a large, multilayered that assembles on the centromeric region of eukaryotic chromosomes and serves as the primary site for attachment during and , facilitating the precise segregation of to daughter cells and thereby maintaining genomic stability. It functions as a dynamic interface that couples dynamics to chromosome movement, generates or transduces mechanical forces, and monitors attachment fidelity through the spindle checkpoint (SAC) to prevent errors in division. Structurally, the kinetochore is organized into inner and outer layers: the inner kinetochore interacts directly with centromeric chromatin via the histone H3 variant CENP-A, while the outer kinetochore forms a fibrous corona and connects to spindle . The outer kinetochore's core is the KMN network, a conserved assembly comprising three subcomplexes—KNL1 (Knl1/Zwint), MIS12 (Mis12/Dsn1/Nsl1/Pmf1), and NDC80 (Ndc80/Nuf2/Spc24/Spc25)—that together form a rigid, prong-shaped scaffold approximately 300 long, as revealed by recent cryo-electron microscopy (cryo-EM) structures. This architecture positions microtubule-binding calponin-homology (CH) domains of NDC80 outward, enabling end-on attachments to 15–25 per kinetochore in human cells, while MIS12 and KNL1 anchor to the inner kinetochore via interactions with CENP-C and CENP-T. Accessory components, such as the Ska complex, Dam1 ring (in yeast), and motor proteins like and CENP-E, further stabilize attachments and contribute to congression and error correction. Functionally, kinetochores orchestrate biorientation by binding from opposite poles, with Aurora B activity destabilizing improper attachments through of KMN components. The , scaffolded by KNL1, recruits checkpoint proteins like Bub1 and Mad1 to halt until all kinetochores are properly attached, averting . In addition to force coupling and signaling, kinetochores regulate polymerization/depolymerization via associated enzymes such as MCAK and XMAP215, ensuring bi-oriented chromosomes align at the plate. Dysfunctions in kinetochore assembly or regulation are implicated in chromosomal instability and diseases like cancer.

Overview

Definition and Location

The kinetochore is a large proteinaceous structure composed of over 100 distinct proteins that assembles on the of eukaryotic to mediate their attachment to the . This multiprotein complex functions as the primary site for binding during segregation in . The is the specialized chromosomal region that maintains sister until and serves as the locus for kinetochore formation to ensure proper segregation of sister to daughter cells. The kinetochore assembles specifically on this centromeric , forming a multi-layered disc perpendicular to the axis. Its inner layer is embedded within the centromeric , while the outer layer extends toward the to facilitate interactions with components. In vertebrates, this disc-like structure typically measures approximately 145 nm (120-170 nm) in diameter and accommodates 15-25 per kinetochore.

Role in Cell Division

The kinetochore serves as the primary interface between chromosomes and the mitotic spindle, linking to to enable their bipolar attachment and subsequent equal segregation to cells during . This attachment ensures that each cell receives an identical set of chromosomes, maintaining genomic stability through the process of equatorial division. In , kinetochores facilitate chromosome segregation in a reductional manner during meiosis I, where homologous chromosomes separate, and in an equational manner during meiosis II, akin to , to produce haploid gametes. By coordinating with spindle components, kinetochores generate pulling forces through microtubule depolymerization, which can reach up to 700 pN per chromosome, while simultaneously sensing the status of microtubule attachments. This sensing mechanism activates the spindle assembly checkpoint (SAC) to halt cell cycle progression until all chromosomes achieve proper bipolar alignment at the metaphase plate, thereby preventing premature anaphase onset. Such coordination is crucial in both mitosis and meiosis to avoid errors in chromosome distribution. Dysfunction in kinetochore function leads to chromosomal instability, a hallmark of cancer, where improper attachments result in and missegregation events that promote tumorigenesis. For instance, defects in kinetochore-microtubule interactions have been observed to increase rates in cancer cells, contributing to disease progression. Similarly, in meiotic contexts, kinetochore errors can lead to aneuploid gametes, underscoring the structure's role in preventing heritable genomic imbalances.

Discovery and History

Early Observations

The term "kinetochore" was first introduced in 1934 by botanist Lester W. Sharp in his textbook Fundamentals of Cytology, derived from the Greek roots kinesis (motion) and choros (place or space), to describe the chromosomal region responsible for directed movement during mitosis as observed through light microscopy. Sharp's usage stemmed from contemporary studies visualizing chromosome congression and segregation, where the structure appeared as a distinct locus facilitating attachment to the mitotic spindle. In 1936, cytogeneticist Cyril D. Darlington further formalized the concept in his analysis of mechanics, explicitly describing the kinetochore as the precise "point of attachment" for fibers, particularly in observations of spermatocytes where it enabled oriented pulling. Darlington's work built on prior light microscopy evidence, emphasizing the kinetochore's role in ensuring bipolar orientation and faithful segregation. Throughout the early , fixed and live-cell imaging techniques provided key evidence of fiber connections to chromosomes, notably during when fibers shortened to draw poleward, as documented in studies of and cells. Pioneering observations, such as those by Franz Schrader in using light microscopy on cells, confirmed the physical continuity between fibers and specific chromosomal sites, solidifying the kinetochore's implication in force transmission. Despite these advances, early light microscopy suffered from resolution limitations, often blurring the kinetochore with the broader centromeric region and hindering precise morphological delineation until electron microscopy emerged in the 1960s. This technological gap restricted initial descriptions to gross attachments rather than details.

Molecular and Structural Milestones

In the 1960s, electron microscopy provided the first detailed views of kinetochore in mammalian cells, revealing a trilaminar organization. biologist Pentti T. Jokelainen's 1967 study on mitotic cells described the kinetochore as a composite disk approximately 2000–2450 in diameter, comprising an electron-dense inner layer contiguous with the centromeric , a central dense plate, and an outer dome-like layer projecting toward the poles. This trilaminar model was corroborated by subsequent work from Bill Brinkley and colleagues, who observed similar plate-like features in mammalian somatic cells, establishing the kinetochore as a multilayered proteinaceous structure essential for segregation. The 1980s and 1990s marked a shift toward molecular identification of kinetochore components, driven by autoantibodies from patients with scleroderma, particularly the CREST subset. In 1985, William Earnshaw and Neville Rothfield used these sera to identify a family of centromere proteins (CENPs), including CENP-A, a 17 kDa antigen localized exclusively to kinetochores and later confirmed as a centromere-specific variant of histone H3 that replaces conventional H3 in centromeric nucleosomes. This approach yielded additional CENPs, such as CENP-B (an 80 kDa DNA-binding protein) and CENP-C (involved in inner kinetochore organization), with over a dozen antigens mapped by the mid-1990s through immunofluorescence and biochemical fractionation, providing the first protein-level insights into kinetochore composition. Advancing into the 2000s, biochemical and genetic studies delineated modular networks within the outer kinetochore, culminating in the discovery of the KMN complex—a core assembly of the KNL1, Mis12, and Ndc80 subcomplexes that bridges centromeric to . The human Mis12 complex, a heterotetramer essential for kinetochore assembly, was characterized in 2006 for its role in recruiting Ndc80 and stabilizing attachments. Concurrent proteomic efforts, including of isolated kinetochores, identified approximately 125 centromeric and kinetochore-associated proteins by 2010, expanding from the initial CENPs to include regulators of attachment and checkpoint signaling. The 2020s have brought high-resolution structural breakthroughs via cryo-electron microscopy (cryo-EM), illuminating the inner kinetochore's architecture. In 2022, structures of the human constitutive centromere-associated network (CCAN)—a multi-subunit assembly including CENPs-L, M, N, T, and others—were resolved at near-atomic resolution when bound to CENP-A nucleosomes, revealing how CCAN clamps DNA and orients the kinetochore for outer layer recruitment. Building on this, a 2025 cryo-EM study in budding yeast delineated dual force transmission pathways through the inner kinetochore, with the Mif2 protein (orthologous to human CENP-C) and the Okp1/Ame1 heterodimer (part of the COMA complex) independently channeling mechanical loads from to centromeric , thereby enhancing stability under tension.

Structure

Inner Kinetochore

The inner kinetochore constitutes the stable, chromatin-proximal layer of the kinetochore, serving as a foundational platform embedded within centromeric chromatin. It is primarily composed of the constitutive centromere-associated network (CCAN), a multi-subunit complex comprising 16 centromere proteins (CENPs) that remain associated with the centromere throughout the cell cycle. Key components include CENP-A nucleosomes, which form the epigenetic mark defining centromeric chromatin, as well as CENP-C, which acts as a central scaffold for CCAN assembly, and the CENP-H/I/K/L/M/N/O subcomplex, which stabilizes interactions with centromeric DNA. These proteins collectively ensure the inner kinetochore's persistence across interphase and mitosis, providing a constitutive interface for higher-order kinetochore structures. Structurally, the inner kinetochore organizes into an approximately 70 nm thick inner plate that integrates directly with the underlying centromeric . This plate is anchored by arrays of CENP-A octamers, which replace canonical in nucleosomes to create a specialized environment that recruits and positions CCAN components. Cryo-electron studies reveal that CCAN modules, such as the CENP-L/N and CENP-T/W/S/X complexes, encircle and grip the emerging from CENP-A nucleosomes, forming robust, edge-on attachments that embed the structure within the fiber. This organization not only tethers the inner kinetochore to the but also orients it for load-bearing during chromosome . The inner kinetochore interfaces with specific modifications that contribute to specification and maintenance. In particular, trimethylation of at 9 (H3K9me3) in pericentromeric helps delineate the boundaries of centromeric domains, promoting the focused deposition of CENP-A and stabilizing CCAN occupancy. This epigenetic landscape ensures the inner kinetochore's fidelity in defining kinetochore assembly sites amid repetitive α-satellite DNA sequences. Recent insights from cryo-electron tomography have highlighted how centromeric forms distinct "clearings"—regions depleted of dense nucleosomes—that precisely demarcate sites for inner kinetochore assembly. These clearings, spanning 20-25 nm and containing nucleosome-associated CCAN complexes, are maintained by CENP-C and CENP-N, which organize fibers to create accessible platforms for kinetochore formation during . This mechanism underscores the inner kinetochore's role in translating architecture into precise attachment points for microtubule-binding components.

Outer Kinetochore

The outer kinetochore constitutes the dynamic, microtubule-interacting layer of the kinetochore, built upon the stable inner kinetochore platform. It primarily comprises the conserved KMN network, a ten-subunit assembly divided into three subcomplexes: the KNL1 complex (including Knl1 and Zwint1), the Mis12 complex (Mis12C), and the Ndc80 complex (Ndc80C). The Mis12C serves as a bridging that connects the KMN network to the inner kinetochore, while the Ndc80C provides the primary interface for binding through its calponin-homology (CH) domains at the N-terminal ends of Ndc80 and Nuf2 subunits, enabling end-on attachments. Additional proteins enrich the outer kinetochore's functionality, including the kinesin-like motor CENP-E, which localizes to the fibrous and aids in initial capture, and cytoplasmic , which is recruited via the RZZ complex and contributes to poleward transport. In vertebrates, the outer kinetochore organizes into a fibrous —a transient meshwork extending from the outer plate—and features 15–35 attachment sites per kinetochore, allowing for multiple end-on connections. The outer plate itself forms a flexible network of fibers that embed plus-ends, while the fibrous , prominent on unattached kinetochores, spans approximately 100 nm and facilitates initial lateral interactions before maturation to end-on attachments. This layer undergoes dynamic assembly and disassembly throughout : it expands in early to form the extended fibrous , enhancing capture efficiency, and compacts upon attachment in . Recent studies from 2025 have revealed the outer kinetochore's intricate, flexible architecture, incorporating over 100 proteins whose interactions are finely tuned by events, such as those on Mis12C components that modulate projection and stability.

Assembly

Cell Cycle Regulation

The assembly of kinetochores is tightly synchronized with the cell cycle to ensure accurate chromosome segregation. In the G1 phase, new CENP-A nucleosomes are deposited at centromeres to establish the foundation for the inner kinetochore, a process mediated by the specific histone chaperone HJURP, which forms a complex with CENP-A and H4 for targeted chromatin incorporation. This deposition is restricted to early G1 and inhibited during S, G2, and M phases by cyclin-dependent kinases (CDKs) such as CDK1 and CDK2, maintaining centromeric identity across cell divisions. As cells progress into and , outer kinetochore components are rapidly recruited to the inner kinetochore, peaking during to facilitate interactions. This recruitment is predominantly driven by phosphorylation from the cyclin B-CDK1 complex, which modifies key proteins like CENP-T at specific and serine residues (e.g., Thr11, Thr85, and Ser201), enabling the binding of up to three NDC80 complexes and one MIS12 complex per CENP-T molecule. Polo-like kinase 1 () further contributes by phosphorylating the Mis18 complex in G1 to prime this mitotic assembly, ensuring timely maturation. Kinetochore disassembly commences at anaphase onset, triggered by the ubiquitin-mediated degradation of cyclin B and securin by the anaphase-promoting complex/cyclosome (APC/C), which inactivates CDK1 and allows the spindle assembly checkpoint (SAC) to be silenced, permitting progression beyond metaphase. This leads to dephosphorylation of CDK1 substrates by protein phosphatase 2A (PP2A), particularly the B55α subunit, which reverses mitotic phosphorylations and promotes the dissociation of outer kinetochore proteins like NDC80. A 2022 review highlights additional layers of regulation, including Ran-GTP gradients that generate spatial cues for protein localization around kinetochores during , and PLK1's role in coordinating timing through targeted s that prevent ectopic assembly. Feedback loops integrate attachment status to modulate kinetochore maturation; for instance, unstable attachments sustain states that exclude premature outer kinetochore stabilization via competitive protein , thereby preventing erroneous segregation until bi-orientation is achieved.

Key Protein Networks

The constitutive centromere-associated network (CCAN) forms the foundational inner kinetochore scaffold, comprising multiple proteins that anchor the kinetochore to centromeric DNA and recruit outer kinetochore components. Central to this network, CENP-C acts as a key recruiter by directly binding the Mis12 complex (Mis12C), which in turn facilitates the attachment of the Ndc80 complex (Ndc80C), thereby bridging the inner and outer kinetochore domains. Complementing this pathway, the CENP-T/W/X/S subcomplex provides an alternative tethering mechanism, with CENP-T directly interacting with histone-fold proteins CENP-W and CENP-X to establish stable connections to centromeric and nucleosomes, independent of CENP-A. These interactions ensure the CCAN's role as a persistent platform for kinetochore assembly throughout the . The KMN network, consisting of the Knl1, Mis12, and Ndc80 complexes, represents the core outer kinetochore assembly that interfaces with . This ten-subunit structure adopts an elongated, oligomeric configuration, where the Ndc80 complex's calponin-homology-like domains and internal loops enable multivalent binding to microtubule protofilaments, promoting stable attachment through cooperative oligomerization along lattices. Mis12C serves as a critical adaptor within the KMN, linking CENP-C from the CCAN to both Knl1 and Ndc80, while its phosphorylation-sensitive interactions fine-tune assembly dynamics. The oligomeric of Ndc80C, forming arrays that track microtubule ends, underscores its primary role in load-bearing connections. Beyond the conserved CCAN and KMN, additional protein networks contribute to kinetochore functionality, particularly in microtubule coupling and chromosome movement. In yeast, the DASH (Dam1) complex assembles into oligomeric rings that encircle , enhancing processivity and force transmission in coordination with Ndc80, thereby facilitating end-on attachments during segregation. In metazoans, the kinesin-like CENP-E forms a distinct network at kinetochores, driving congression by transporting mono-oriented along toward the plate. Regulatory interactions, such as B of Ndc80's N-terminal tail, modulate these networks by destabilizing erroneous attachments and promoting dynamic remodeling. Overall, the kinetochore incorporates over 100 proteins across these networks, with many of their functions still poorly understood, highlighting ongoing challenges in dissecting their contributions.

Microtubule Interaction

Attachment Mechanisms

The search-and-capture model describes the initial interaction between kinetochores and spindle , where dynamic explore the intracellular space to locate and bind kinetochores on . In this process, kinetochores first form lateral attachments to sides, facilitated by plus-end tracking proteins () such as EB1 and CLIP-170, which accumulate at growing ends and promote initial contacts. These lateral interactions then transition to stable end-on attachments at ends, enabling force generation for alignment. The Ndc80 , a key component of the outer kinetochore, plays a central role in mediating these end-on attachments by directly binding microtubule plus ends. Its calponin-homology domains in the Hec1 subunit, along with flexible structures, allow the complex to grip and track depolymerizing microtubule ends, stabilizing attachments through multivalent interactions. Each kinetochore can support varying numbers of , typically one in budding yeast but 20 or more in mammalian cells, reflecting differences in kinetochore size and across species. Initial capture of often involves motor proteins to enhance efficiency. , recruited to the kinetochore corona, mediates sliding of laterally attached toward the plus end, transporting chromosomes poleward to facilitate subsequent end-on . Additionally, the kinesin-like protein CENP-E captures chromosomes from the periphery, using its motor to congress them toward the equator via interactions. These attachments generate mechanical forces essential for chromosome movement, with each microtubule-kinetochore connection producing approximately 1 of tension under load. This force arises from microtubule coupled to kinetochore gripping, balancing attachment stability across species where kinetochores handle single while mammalian ones manage multiple attachments to achieve similar per-fiber tension.

Bi-orientation and Tension Sensing

Bi-orientation refers to the stable attachment of sister kinetochores to emanating from opposite poles, ensuring proper during . This configuration generates pulling forces that stretch the kinetochores and centromeric , with intra-kinetochore distances increasing by approximately 20 nm between inner components like CENP-A and outer elements such as Ndc80 under tension. This tension stabilizes amphitelic attachments while distinguishing them from erroneous configurations, such as syntelic (both sisters to one pole) or merotelic (one kinetochore to both poles) orientations. The primary mechanism for sensing this tension involves the spatial separation of , localized at the inner , from its substrates in the outer kinetochore. In the absence of , remains proximal to these substrates (e.g., Ndc80 complex proteins), promoting their and thereby weakening binding affinity. Upon bi-orientation, the applied elongates the kinetochore structure, increasing the distance—estimated at around 80 nm based on the INCENP tether length—between and its targets, which reduces levels and stabilizes correct attachments. This "dog leash" model underscores how mechanical forces directly regulate enzymatic activity without requiring additional signaling cascades. When tension is low, as in erroneous syntelic or merotelic attachments, sustained Aurora B proximity leads to persistent of outer kinetochore components, which decreases microtubule plus-end rates and enhances . This promotes the detachment and turnover of incorrectly bound , facilitating error correction and the search for bi-oriented configurations. Experimental from and micromanipulation studies confirms that artificially reducing tension stabilizes such errors, while restoring it triggers rapid destabilization. A recent study in budding yeast has revealed that force transmission through the inner kinetochore occurs via two parallel pathways—the Mif2-dependent route and the Okp1/Ame1 (OA) complex route—both of which are crucial for bi-orientation stability. Using chimeric centromeric DNA constructs, researchers demonstrated that centromeric sequences in Cse4 nucleosomes specifically enhance OA-mediated force propagation, leading to stronger microtubule attachments and reduced detachment under load. This dual-pathway mechanism ensures robust tension generation and maintenance, minimizing segregation errors.

Regulatory Roles

Spindle Assembly Checkpoint

The spindle assembly checkpoint () is a critical surveillance mechanism at kinetochores that delays the onset of until all achieve proper bipolar attachments, thereby ensuring accurate chromosome segregation during . Unattached kinetochores serve as the primary signal generators for activation, recruiting checkpoint proteins to initiate a diffusible inhibitory signal that propagates throughout the cell. This process prevents premature separation of , which could lead to genomic instability. SAC activation begins when unattached kinetochores recruit the Mad1-Mad2 complex via the KMN network component KNL1. Specifically, the kinase Mps1 phosphorylates MELT motifs on KNL1, enabling binding of Bub1-Bub3, which in turn recruits the Mad1-Mad2 core complex to the kinetochore. This kinetochore-localized Mad1-Mad2 acts as a template to catalyze the conversion of cytosolic open-Mad2 (O-Mad2) to closed-Mad2 (C-Mad2), which binds Cdc20 to form an intermediate complex. This intermediate then associates with BubR1-Bub3 to assemble the mitotic checkpoint complex (MCC), consisting of Mad2, BubR1, Bub3, and Cdc20. The MCC diffuses from the kinetochore to inhibit the anaphase-promoting complex/cyclosome (APC/C) in the cytoplasm, a E3 ubiquitin ligase that targets securin and cyclin B for degradation; this inhibition blocks the activation of separase and the degradation of cyclin B1, respectively, thereby maintaining high cyclin B-Cdk1 activity and arresting the cell in metaphase. Even a single unattached kinetochore can generate sufficient diffusible MCC to sustain the wait-anaphase signal across the cell. SAC silencing occurs upon microtubule attachment to kinetochores, which displaces the Mad1-Mad2 complex and halts MCC production. Microtubule occupancy leads to the recruitment of protein phosphatase 1 (PP1), which dephosphorylates KNL1's MELT motifs, stripping Bub1-Bub3 and Mad1-Mad2 from the kinetochore; additionally, dynein-mediated transport and intra-kinetochore stretching contribute to this disassembly. With the loss of the Mad1-Mad2 template, MCC levels decline, allowing APC/C activation, securin degradation, separase-mediated cohesin cleavage, and anaphase progression. This attachment-dependent silencing ensures the checkpoint is satisfied only when all kinetochores are properly engaged. The is essential for preventing , as its dysfunction allows missegregation and genomic instability. Defects in SAC components, such as mutations in BUB1B (encoding BubR1) or TRIP13, are associated with chromosomal instability syndromes like mosaic variegated and increased tumorigenesis risk in various cancers, including colorectal and breast tumors. For instance, partial loss of SAC function promotes -driven cancer progression by permitting cells with unbalanced genomes to proliferate.

Error Correction

Error correction in kinetochores ensures the fidelity of chromosome segregation by destabilizing improper attachments, such as syntelic or merotelic orientations, while stabilizing bi-oriented attachments that generate inter-kinetochore tension. This process relies on spatial and tension-dependent of and activities at the kinetochore, preventing during . The primary effector of error correction is Aurora B kinase, a component of the chromosomal passenger complex (CPC) localized to the inner centromere. Aurora B phosphorylates key outer kinetochore proteins, including the Ndc80 complex and KNL1, which reduces their affinity for microtubules and promotes detachment of low-tension attachments. These phosphorylation events occur preferentially at attachments lacking tension, as the distance between the inner centromere-localized Aurora B and outer kinetochore substrates increases under tension, limiting kinase access. Opposing this, protein phosphatases PP1 and PP2A dephosphorylate these sites when tension is applied, stabilizing correct bi-oriented attachments by enhancing microtubule-binding affinity. Additional contributors include microtubule-depolymerizing enzymes like MCAK (mitotic centromere-associated ), a -13 family member that localizes to kinetochores and accelerates of incorrectly attached ends. MCAK's activity complements B by directly shortening , facilitating detachment and recycling of for new attachment attempts. A 2025 study in revealed that the Spc105/Kre28 complex recruits Ipl1 (the homolog of B) and its activator Sli15 to the outer kinetochore, enhancing local and error correction efficiency independent of inner localization. Error correction operates through iterative cycles of attachment formation, tension sensing, destabilization of errors, and reattachment until stable bi-orientation is achieved. This process is gated by a tension threshold of approximately 4–6 pN per kinetochore-microtubule attachment, below which erroneous configurations persist and are corrected. Recent insights from 2025 highlight how inner kinetochore complexes, such as the COMA network (including Mif2 and Okp1/Ame1), enhance force transmission from centromeric DNA to the outer kinetochore, improving the sensitivity and efficiency of tension-dependent error correction. This structural reinforcement ensures that even subtle tension differences effectively modulate Aurora B activity, reducing the time required for bi-orientation.

Comparative Aspects

In Yeast

In budding yeast (Saccharomyces cerevisiae), kinetochores assemble at point centromeres, which are compact DNA sequences of approximately 125 base pairs that specify a single site for kinetochore formation on each chromosome. These point centromeres are defined by a single nucleosome containing the centromere-specific histone variant Cse4 (the yeast homolog of CENP-A), which wraps the central 80 base pairs of the centromeric DNA and serves as the foundational platform for kinetochore assembly. Unlike more complex centromeres in other organisms, this minimalist configuration results in each kinetochore attaching to just one microtubule, facilitating precise chromosome segregation in the yeast's small mitotic spindle, which measures about 1-2 micrometers in length. The kinetochore structure in budding is notably simpler than in higher eukaryotes, lacking a fibrous corona layer and relying on a streamlined set of protein complexes for interaction. Key outer kinetochore components include the conserved Ndc80 complex, which binds through its calponin-homology domains in the Ndc80 and Nuf2 subunits, and the Mtw1-containing complex (with Mtw1 as the yeast homolog of Mis12), which bridges the inner and outer kinetochore layers to recruit Ndc80. A distinctive feature is the Dam1/ complex, a ten-subunit ring that oligomerizes to encircle lattices, enabling processive kinetochore movement along depolymerizing and stable attachment under tension. This ring structure, coupled with Ndc80, allows for rapid capture and attachment in the confined space of the yeast , supporting efficient biorientation and segregation of the 16 chromosomes. Error correction in budding yeast kinetochores is mediated by the Aurora B Ipl1, which phosphorylates outer kinetochore proteins like Dam1 and Ndc80 to destabilize improper attachments lacking tension. A recent discovery revealed that Ipl1 is recruited to the outer kinetochore via direct between its activator Sli15 and the Spc105/Kre28 (a component of the KMN network), enabling tension-sensitive error correction at the attachment site. This outer recruitment mechanism enhances the kinase's local activity, promoting detachment of syntelic or merotelic attachments and reorientation toward stable bi-orientation. In fission yeast (Schizosaccharomyces pombe), kinetochores form at regional centromeres spanning 35-110 kilobases, which incorporate multiple Cse4 nucleosomes (typically 3-5 per ) and attach to 1-3 , providing a slightly more elaborate but still simplified model compared to multicellular organisms. Core components like Ndc80 and the Mtw1 homolog Mis12 contribute to binding, while Ipl1/ B performs analogous error correction roles, though lacking an essential Dam1 ring; processivity is achieved through Ndc80 complex oligomerization and plus-end tracking proteins such as Mal3 (the EB1 homolog), with the Sim4 complex contributing to inner kinetochore assembly. Both species offer exceptional advantages for kinetochore due to their genetic tractability, allowing precise manipulations via temperature-sensitive mutants and editing, and their absence of a corona layer, which simplifies and dissection of core assembly pathways.

In Metazoans and Plants

In metazoans, particularly vertebrates, kinetochores assemble on regional centromeres characterized by repetitive DNA sequences spanning 10-100 kb, which facilitate the recruitment of centromeric proteins like CENP-A. These kinetochores typically attach to 15-35 per kinetochore, enabling robust chromosome-to-spindle connections during . A distinctive feature is the fibrous corona, a transient outer layer visible on unattached kinetochores that aids in initial capture through proteins such as CENP-E and ZW10. In plants, kinetochore organization varies between monocentric and holocentric types; for instance, exhibits monocentric kinetochores where CENH3, the plant-specific histone H3 variant analogous to CENP-A, localizes to centromeric regions for precise attachment. Holocentric kinetochores, observed in species like , distribute CENH3 along the length, allowing diffuse attachments without a single constriction point. As of 2025, structural studies have defined the plant KMN network, revealing adaptations in CENH3 structure and anastral geometry lacking centrosomes, which differ from spindles in metazoans and support flexible alignment in diverse plant architectures; evolutionary analyses indicate divergence through KMN component expansions enhancing tolerance. Key differences between metazoan and plant kinetochores include the absence of a prominent fibrous in , compensated by unique plus-end tracking proteins (+TIPs) such as EB1 homologs that stabilize plus ends at attachment sites. correction mechanisms in rely on -like kinases, which destabilize improper attachments similar to metazoan Aurora B, but with adaptations for polyploid genomes. Functionally, kinetochores often manage higher numbers—typically 8–18 per kinetochore in meiotic spindles of species like —reflecting the demands of expansive spindles in tissues. This scalability supports tolerance, where robust kinetochore- interfaces prevent during rapid cell divisions in development and stress responses.

References

  1. [1]
  2. [2]
    Structure of the human outer kinetochore KMN network complex
    Mar 8, 2024 · Kinetochores are large macromolecular complexes that couple the forces of microtubule depolymerization to chromosome movement during mitosis and ...
  3. [3]
    Functions of the centromere and kinetochore in chromosome ...
    Accurate chromosome segregation requires each chromosome's centromere to build a kinetochore, a complex structure containing at least 100 different proteins ...
  4. [4]
    The Path of DNA in the kinetochore - PMC - NIH
    The kinetochore is the protein-DNA complex at eukaryotic centromeres that functions as the attachment site for spindle microtubules.Missing: definition | Show results with:definition
  5. [5]
  6. [6]
    The life and miracles of kinetochores | The EMBO Journal
    The primary function of kinetochores is to create load‐bearing attachments between chromosomes and microtubules in a dividing mother cell.
  7. [7]
    The dynamic kinetochore-microtubule interface
    Nov 1, 2004 · The inner kinetochore normally forms on highly repetitive DNA sequences and assembles into a specialized form of chromatin that persists ...Animal Kinetochore Structure · Chromosomal Passengers And... · Proteins Influencing...
  8. [8]
    A super-resolution map of the vertebrate kinetochore - PNAS
    May 15, 2010 · Considering that the kinetochore diameter determined by serial-sectioning electron microscopy is 145 ± 27 nm (n = 48; Fig. S1) in SMC2ON ...
  9. [9]
    The outer plate in vertebrate kinetochores is a flexible network ... - NIH
    4). As most vertebrate kinetochores bind 15–30 microtubules, we estimate that on average 3–8 microtubules are laterally associated with every vertebrate ...
  10. [10]
    CENcyclopedia: dynamic landscape of kinetochore architecture ...
    Aug 18, 2025 · It functions as a versatile platform for microtubule assembly, diligently monitors microtubule binding fidelity, and acts as a force coupler.
  11. [11]
    The functions and consequences of force at kinetochores
    Mar 4, 2013 · The kinetochore plays key roles throughout mitosis, both to mediate direct attachments between microtubules and centromeric DNA (Fig. 1) and as ...
  12. [12]
    Establishing Correct Kinetochore-microtubule Attachments in Mitosis ...
    In this review, we discuss multiple molecular pathways that localize Aurora B and Aurora C to the inner centromere and kinetochore in both mitosis and meiosis.
  13. [13]
    A Brief History of Research on Mitotic Mechanisms - MDPI
    Research on mitosis began in the 19th century, with early work by Flemming, and advanced with microscopy, electron microscopy, and biochemistry, and genetics.
  14. [14]
    The external mechanics of the chromosomes I—The scope of enquiry
    The external mechanics of the chromosomes I—The scope of enquiry. Cyril Dean Darlington ... Published:04 December 1936https://doi.org/10.1098/rspb.1936.0064 ...Missing: CD | Show results with:CD
  15. [15]
    The kinetochore uncoiled - PMC - NIH
    Bill Brinkley had first described the kinetochore in the 1960s. He saw, by electron microscopy, a trilaminar, proteinaceous disc structure that flanked the ...Missing: review 1968
  16. [16]
    Structure of the human inner kinetochore bound to a centromeric ...
    Apr 14, 2022 · We describe cryo–electron microscopy structures of the human inner kinetochore constitutive centromere associated network (CCAN) complex bound ...
  17. [17]
    Structure of the human inner kinetochore CCAN complex and its ...
    May 5, 2022 · The final model of CENP-16 has a molecular mass of ∼450 kDa and consists of ∼25,000 atoms, encompassing 14 of the 16 subunits. CENP-S and CENP-X ...Missing: CENPs | Show results with:CENPs
  18. [18]
    Three-dimensional localization of CENP-A suggests a complex ...
    Dec 29, 2008 · In this study, we describe the three-dimensional localization of CENP-A at the inner kinetochore plate ... Section thickness: A, 70 nm; B–D, 60 nm ...
  19. [19]
    Critical histone post-translational modifications for centromere ...
    Recent studies suggest that centrochromatin has specific histone modifications that mediate centromere specification and kinetochore assembly.<|control11|><|separator|>
  20. [20]
    H3K9me3 maintenance on a human artificial chromosome is ...
    Summary: Pericentric heterochromatin is dispensable for centromere epigenetic memory, but is required to stabilize centromere protein levels and accurate.
  21. [21]
  22. [22]
  23. [23]
    The Conserved KMN Network Constitutes the Core Microtubule ...
    The intact KMN network is incorporated into the outer kinetochore plate to form the repeating microtubule-binding sites of eukaryotic kinetochores (Figure 7E).
  24. [24]
    Molecular determinants of the Ska-Ndc80 interaction and their ...
    Dec 5, 2019 · At one end of Ndc80, two closely interacting calponin-homology (CH) domains near the N-terminal ends of NDC80 and NUF2 form a globular ...Aurora B Does Not Disrupt... · Aurora B Kinase Activity... · Materials And Methods
  25. [25]
    Kinetochore dynein is sufficient to biorient chromosomes and ...
    Oct 21, 2024 · CENP-T provides a structural platform for outer kinetochore ... CENP-E form an integrated platform to recruit dynein to the kinetochore corona.
  26. [26]
    A farnesyl-dependent structural role for CENP-E in expansion of the ...
    Nov 7, 2023 · The fibrous corona is a meshwork that temporarily covers the outer kinetochores during early mitosis and meiosis and assists in spindle assembly ...
  27. [27]
    The vertebrate cell kinetochore and its roles during mitosis - PMC
    In most organisms, kinetochores range between 0.1–0.5 μm in diameter and bind 10–45 MTs. This article focuses on the roles kinetochores play during mitosis in ...
  28. [28]
    The outer plate in vertebrate kinetochores is a flexible network with ...
    We demonstrate that individual kMTs in PtK(1) cells are attached to the kinetochore outer plate by several fibres that either embed the microtubule plus-end ...Missing: corona | Show results with:corona
  29. [29]
    [PDF] Dynamic kinetochore size regulation promotes microtubule capture ...
    The outer layer of kinetochores transiently expands in early mitosis to form a fibrous corona, and compacts following microtubule cap- ture. Here we show that ...
  30. [30]
    Dynamic phosphorylation of MIS12 ensures accurate kinetochore ...
    Jul 17, 2025 · Phosphorylation of MIS12 expands the projection of the outer kinetochore, known as the fibrous corona, thus facilitating the attachment of ...
  31. [31]
    Dynamics of kinetochore structure and its regulations during mitotic ...
    Feb 12, 2020 · 2a) [10, 24, 26, 36–40]. This prominent fibrous structure extending over 100 nm to the cytoplasm is diminished in the kinetochores that attach ...
  32. [32]
    Assembly in G1 phase and long-term stability are unique intrinsic ...
    Jan 30, 2013 · CENP-A and H4 are coassembled during G1 phase. Prenucleosomal CENP-A forms a complex with H4 and HJURP, the CENP-A–specific histone chaperone ( ...
  33. [33]
    Cell cycle control of kinetochore assembly - PMC - PubMed Central
    Aug 29, 2022 · This review focuses on recent progress on our understanding of how the kinetochore assembly is cell cycle regulated.
  34. [34]
    Molecular basis of outer kinetochore assembly on CENP-T - eLife
    Dec 24, 2016 · We show here that CENP-T binds one MIS12:NDC80 and two NDC80 complexes upon phosphorylation by the mitotic CDK1:Cyclin B complex at three distinct CENP-T sites.
  35. [35]
    CDK-dependent phosphorylation and nuclear exclusion ...
    Mar 25, 2013 · Kinetochore disassembly begins at anaphase onset when APC/C activity is high. To test the requirements for kinetochore protein degradation to ...<|separator|>
  36. [36]
  37. [37]
    Regulation of kinetochore–microtubule attachments through ... - NIH
    Kinetochore proteins respond to microtubule attachment stability to send signals to the interactive core control network, which is composed of the spindle ...
  38. [38]
    Direct binding of Cenp-C to the Mis12 complex joins the inner and ...
    Overall, these results indicate that Cenp-C binds directly to Mis12C, and that the interaction is compatible with additional interactions of Mis12C with Ndc80C ...
  39. [39]
    CCAN makes multiple contacts with centromeric DNA to ... - PubMed
    Dec 12, 2008 · Our analysis indicates that CENP-T/CENP-W and CENP-C provide distinct pathways to connect the centromere with outer kinetochore assembly.
  40. [40]
    Structure of the human inner kinetochore CCAN complex and its ...
    May 5, 2022 · To gather evidence for DNA binding by CENP-16, we immobi- lized a maltose-binding protein (MBP)-CENP-T fusion protein complexed with CENP-W and ...
  41. [41]
    Structure of the human KMN complex and implications for regulation ...
    Mar 8, 2024 · Kinetochores, large layered structures built on specialized chromosome loci named centromeres, promote biorientation by binding and sensing ...<|control11|><|separator|>
  42. [42]
    The MIS12 complex is a protein interaction hub for outer kinetochore ...
    Sep 6, 2010 · The NDC80, MIS12, and KNL1 complexes form the core of the KMN network. We recently reported the structural organization of the human NDC80 ...
  43. [43]
    The Ndc80 kinetochore complex forms oligomeric arrays along ...
    The Ndc80 complex is a member of the conserved KMN kinetochore network, which also includes the KNL-1 and Mis12 complexes. The Ndc80 complex is the key site for ...Missing: adaptor review
  44. [44]
    Cooperation of the Dam1 and Ndc80 kinetochore complexes ...
    May 17, 2010 · In this study, we show that the Dam1 complex is a processivity factor for the Ndc80 complex, enhancing the ability of the Ndc80 complex to form load-bearing ...The Dam1 And Ndc80 Complexes... · The Dam1 Complex Enhances... · Ipl1 Phosphorylation...
  45. [45]
    Leaving no-one behind: how CENP-E facilitates chromosome ...
    Apr 29, 2020 · Recent work has revealed how CENP-E cooperates with chromokinesins and dynein to mediate chromosome congression and highlighted its role at aligned chromosomes.
  46. [46]
    Aurora B phosphorylates spatially distinct targets to differentially ...
    Here, we demonstrate that Aurora B kinase phosphorylates three spatially distinct targets within the conserved outer kinetochore KNL1/Mis12 complex/Ndc80 ...
  47. [47]
    Review Captivating Capture: How Microtubules Attach to Kinetochores
    May 27, 2003 · Here we discuss current progress in determining how kinetochores assemble and attach to MTs during mitosis as well as how they correct errors.
  48. [48]
    Kinetochore–microtubule interactions in chromosome segregation
    Oct 18, 2017 · +TIPs are a structurally and functionally diverse group of proteins that selectively localize to and track the growing plus ends of microtubules ...
  49. [49]
    Thirty years of search and capture: The complex simplicity of mitotic ...
    A model that considers the formation of end-on attachments in a spindle environment dominated by lateral microtubule interactions predicts that the enlargement ...
  50. [50]
    Ndc80 complex, a conserved coupler for kinetochore-microtubule ...
    Sep 3, 2025 · (B) Ndc80c binds microtubule wall with the toe of the Hec1 calponin-homology domain (CHD) with a pronounced tilt toward the microtubule plus end ...
  51. [51]
    Orientation and structure of the Ndc80 complex on the microtubule ...
    The four-subunit Ndc80 complex, comprised of Ndc80/Nuf2 and Spc24/Spc25 dimers, directly connects kinetochores to spindle microtubules.
  52. [52]
    Dynein at the kinetochore - Company of Biologists journals
    Mar 2, 2023 · CENP-E is implicated in sorting randomly oriented short microtubules nucleated at the corona such that their plus-ends can be incorporated into ...
  53. [53]
    Tension can directly suppress Aurora B kinase-triggered release of ...
    Apr 20, 2022 · Mps1 also phosphorylates Ndc8039, so Ndc80 was partially phosphorylated even in the absence of exogenous AurB*, along with other kinetochore ...Optical Trap Assay For... · Phosphorylation At... · Aurora B Activity Releases...<|control11|><|separator|>
  54. [54]
    Mechanical coupling coordinates microtubule growth - eLife
    Aug 10, 2023 · Thus, each microtubule generally experiences between 1 and 7 pN of tension, close to the estimated average of 4 to 6 pN experienced by ...
  55. [55]
    Aurora B Tension Sensing Mechanisms in the Kinetochore Ensure ...
    Intra-kinetochore stretch is the deformational distance produced within a kinetochore under tension and is facilitated via stretching and conformational change ...Aurora B Tension Sensing... · 6. Aurora B Tension-Sensing... · 6.3. Kinetochore...<|control11|><|separator|>
  56. [56]
    Kinetochore–microtubule interactions: steps towards bi-orientation
    As a result of amphitelic attachment, sister KTs 'bi-orient'; that is they are connected to the opposite spindle poles. Merotelic attachment: one sister KT ...
  57. [57]
    Sensing centromere tension: Aurora B and the regulation of ...
    The spatial separation model explains how chromosome bi-orientation can be sensed through changes in tension across the centromere, which is a critical ...
  58. [58]
    Force transmission through the inner kinetochore is enhanced by ...
    May 29, 2025 · This work revealed two paths of force transmission through the inner kinetochore: through Mif2 and through the Okp1/Ame1 complex (OA). Here ...
  59. [59]
    Spindle assembly checkpoint activation and silencing at kinetochores
    Abstract. The spindle assembly checkpoint (SAC) is a surveillance mechanism that promotes accurate chromosome segregation in mitosis.Missing: paper | Show results with:paper
  60. [60]
    Review The Spindle Assembly Checkpoint - ScienceDirect.com
    Nov 20, 2012 · The spindle assembly checkpoint acts to maintain genome stability by delaying cell division until accurate chromosome segregation can be guaranteed.Missing: paper | Show results with:paper
  61. [61]
  62. [62]
  63. [63]
  64. [64]
    Kinetochore-catalyzed MCC formation: A structural perspective - PMC
    Dec 14, 2022 · In response to unattached kinetochores, the SAC activates its effector, the mitotic checkpoint complex (MCC), which delays mitotic exit until ...Missing: dephosphorylation | Show results with:dephosphorylation
  65. [65]
  66. [66]
  67. [67]
    The spindle checkpoint, aneuploidy, and cancer - PubMed - NIH
    Mar 15, 2004 · Defects in a cell cycle surveillance mechanism called the spindle checkpoint contribute to chromosome instability and aneuploidy.
  68. [68]
    Kinetochore life histories reveal an Aurora-B-dependent error ...
    The major error correction mechanism in pre-anaphase cells is mediated by the Aurora B kinase, a component of the chromosome passenger complex (CPC), which ...
  69. [69]
    KNL1 facilitates phosphorylation of outer kinetochore proteins by ...
    Dec 16, 2013 · Aurora B kinase phosphorylates kinetochore proteins during early mitosis, increasing kinetochore–microtubule (MT) turnover and preventing ...
  70. [70]
    Kinetochore–microtubule error correction for biorientation
    Feb 2, 2024 · In this review article, we discuss the mechanisms of kinetochore–MT interaction, error correction and biorientation. We focus mainly on recent insights from ...
  71. [71]
    Kinesin 13s in Mitosis: Key Players in the Spatial and Temporal ...
    Kinesin-13 proteins induce depolymerization uniquely from both ends of the microtubule. This activity coincides with their cellular localization and with their ...
  72. [72]
    The Spc105/Kre28 complex promotes mitotic error correction by ...
    Apr 25, 2025 · This study reveals a novel and essential recruitment mechanism of the yeast Aurora kinase Ipl1 to the outer kinetochore via an interaction between Sli15 and ...
  73. [73]
    Chromosome biorientation produces hundreds of piconewtons at a ...
    Oct 20, 2016 · The application of opposing forces to this bioriented configuration produces tension that stabilizes kinetochore–microtubule (kt–MT) attachments ...
  74. [74]
    Force transmission through the inner kinetochore is enhanced by ...
    May 29, 2025 · This work revealed two paths of force transmission through the inner kinetochore: through Mif2 and through the Okp1/Ame1 complex (OA). Here, ...
  75. [75]
    The Four Causes: The Functional Architecture of Centromeres and ...
    Nov 30, 2022 · Here we outline the current blueprint for the assembly of a kinetochore, how functions are mapped onto this architecture, and how this is shaped ...
  76. [76]
    Nanoscale structural organization and stoichiometry of the budding ...
    Jan 27, 2023 · In this study, we use single-molecule localization microscopy to visualize individual kinetochore complexes in situ in budding yeast. For major ...
  77. [77]
    The Ndc80 complex bridges two Dam1 complex rings - eLife
    Feb 13, 2017 · The Dam1 and Ndc80 complexes are the main microtubule-binding components in the budding yeast kinetochore. The Ndc80 complex connects the Dam1 ...
  78. [78]
    The requirement for the Dam1 complex is dependent upon the ... - NIH
    The Dam1 (DASH) complex is comprised of 10 proteins and has important roles in maintaining the connection between kinetochore proteins and spindle microtubules ...
  79. [79]
    Unraveling the kinetochore nanostructure in Schizosaccharomyces ...
    Jan 27, 2023 · In this study, we investigate the architecture of the regional KT of the fission yeast S. pombe. We created a strain library of fluorescent ...
  80. [80]
    Kinetochore composition and its function: lessons from yeasts
    We review the current understanding of the assembly, functions, and regulation of kinetochores revealed mainly through studies on fission and budding yeast.Kinetochore Composition And... · Inner Kinetochore Proteins · Outer Kinetochore Proteins<|control11|><|separator|>
  81. [81]
    Bridging the gap: unravelling plant centromeres in the telomere‐to ...
    Sep 27, 2024 · In satellite centromeres, repeat monomers typically range from 100 to 200 bp in length, supporting individual CENH3 nucleosomes. For example, in ...
  82. [82]
    Kinetochore Fiber Maturation in PtK 1 Cells and Its Implications for ...
    Kinetochore microtubules (kMts) are a subset of spindle microtubules that bind directly to the kinetochore to form the kinetochore fiber (K-fiber).<|separator|>
  83. [83]
    Recent advances in plant kinetochore research - PMC
    Jan 22, 2025 · This review summarizes recent insights into plant kinetochore biology, compares plant kinetochores with those of animals and fungi, and highlights key open ...Missing: total | Show results with:total
  84. [84]
    Disruption of the standard kinetochore in holocentric Cuscuta species
    In this species, the chromosomes restrict CENH3 to only one to three heterochromatin bands, despite being attached to the mitotic spindle along their entire ...
  85. [85]
    Recent advances in plant kinetochore research - Frontiers
    Jan 21, 2025 · This review summarizes recent insights into plant kinetochore biology, compares plant kinetochores with those of animals and fungi, and highlights key open ...
  86. [86]
    Arabidopsis α-Aurora kinase plays a role in cytokinesis through ...
    May 6, 2024 · The α-Aurora kinase is a crucial regulator of spindle microtubule organization during mitosis in plants. Here, we report a post-mitotic role ...
  87. [87]
    Plant kinetochore complex: composition, function, and regulation
    It participates in connecting sister chromatids and facilitating chromosome segregation during mitosis and meiosis (Sundararajan and Straight, 2022; Evatt et al ...Missing: paper | Show results with:paper