Every time a eukaryotic cell divides, its duplicated chromosomes must be distributed with extraordinary accuracy between the two daughter cells. A failure in this process can produce cells with missing or extra chromosomes, a condition known as aneuploidy that is associated with developmental disorders, infertility and cancer. At the center of this process is the kinetochore, a large protein assembly that forms on each chromosome and creates the physical interface between chromosomal DNA and spindle microtubules.

The kinetochore is not a single molecular machine but a layered structure containing many different proteins. Its inner region is anchored to centromeric chromatin, while the outer region extends toward the mitotic spindle and interacts directly or indirectly with microtubules. This organization allows the kinetochore to convert the identity of a specific chromosomal site into a controlled mechanical connection capable of bearing tension, sensing attachment and helping correct errors before chromosomes separate.

The review focuses particularly on the inner kinetochore, the region that links specialized centromeric DNA and nucleosomes to the larger kinetochore network. Understanding this layer has been challenging because it is assembled from numerous proteins that interact dynamically rather than forming a rigid, permanent structure. Recent structural studies, including high-resolution imaging and biochemical reconstitution, have nevertheless begun to reveal how these components are arranged and how their interactions support kinetochore assembly.

A defining feature of many eukaryotic centromeres is the histone H3 variant known as centromere protein A, or CENP-A. Histones package DNA into nucleosomes, the repeating units that organize the genome into chromatin. CENP-A-containing nucleosomes are molecularly distinct from conventional H3 nucleosomes and provide an epigenetic signal that helps specify where the kinetochore will form. In this context, “epigenetic” means that centromere identity is maintained through chromatin features and inheritance rather than being determined solely by a unique DNA sequence.

The role of CENP-A is more complex than simply marking a point on the chromosome. Its presence influences the local organization, accessibility and physical properties of centromeric chromatin, creating a platform for the recruitment of inner-kinetochore proteins. The review discusses how scientists are using structural biology to determine the precise organization of CENP-A nucleosomes and how those nucleosomes connect to the protein network above them. These connections help explain how a chromatin-based identity becomes a functional attachment site for chromosome segregation.

Centromeric DNA itself is also receiving renewed attention. In many organisms, centromeres contain repetitive sequences that were historically difficult to assemble and analyze with conventional genome-sequencing methods. Improvements in long-read sequencing and chromosome-scale genome assembly are now making it possible to examine centromeric regions in greater detail. The review considers how centromeric sequences, together with their epigenetic chromatin state, contribute to kinetochore formation and whether sequence composition alone can explain the location and behavior of a centromere.

Researchers are also studying centromeres as three-dimensional structures rather than as simple linear stretches of DNA. Centromeric chromatin can fold and organize within the nucleus, creating spatial relationships that may influence the density, orientation and assembly of kinetochore components. The review brings together evidence on both the two-dimensional arrangement of chromatin along the chromosome and its three-dimensional organization in space. These perspectives are important because the kinetochore must operate under force: spindle microtubules pull on chromosomes, and the centromeric region must transmit that tension without losing its identity or structural integrity.

The emerging picture is one of a flexible, multiscale system. CENP-A-containing nucleosomes help establish a specialized chromatin environment; inner-kinetochore proteins recognize and organize that environment; and the resulting platform supports the outer kinetochore, which engages with spindle microtubules. Rather than acting as an immovable clamp, the kinetochore appears to be a dynamic assembly capable of remodeling as chromosomes attach, experience tension and correct improper connections. The review emphasizes that understanding this behavior requires combining molecular structures, cell biology, genetics and quantitative imaging.

Important questions remain unresolved. Scientists still need to determine precisely how centromere identity is established and preserved across cell generations, how CENP-A is deposited and distributed during the cell cycle, and how variations in centromeric DNA influence chromatin organization. It is also unclear how the inner kinetochore coordinates with the outer kinetochore during attachment and error correction, or how defects in these systems contribute to chromosome instability in disease. By outlining these open problems, the review presents the centromere and inner kinetochore not as a finished molecular blueprint, but as an active research frontier where genome sequence, epigenetic information and mechanical force meet.

Subject of Research: Structure and function of the centromere and inner kinetochore in chromosome segregation.

Article Title: Structure and function of the centromere and inner kinetochore

Article References: Brown, R.R., Huis in ’t Veld, P.J., Musacchio, A. et al. “Structure and function of the centromere and inner kinetochore.” Nature Reviews Molecular Cell Biology (2026). https://doi.org/10.1038/s41580-026-00989-7

Image Credits: AI Generated

DOI: 10.1038/s41580-026-00989-7

Keywords: centromere, inner kinetochore, CENP-A, chromosome segregation, mitosis, centromeric chromatin, microtubules, epigenetics, genome organization

Proper chromosome segregation during mitosis is essential for accurate cell proliferation. Errors in this process often result in chromosomal instability, a hallmark of many cancers that fuels tumor progression and resistance to treatments. Central to this segregation process is the kinetochore, a multi-protein complex assembled on the centromere of each chromosome, which serves as the attachment site for spindle microtubules, facilitating chromosome movement. Deciphering the molecular interactions that govern kinetochore function has been challenging due to the redundancy and overlap among numerous involved proteins.

Employing a genome-wide CRISPR-Cas9 screening approach, the researchers focused on cells harboring a mild mutation in the CENP-C gene, which encodes an essential kinetochore protein responsible for recruiting other kinetochore components. The screen identified KIF18A, a kinesin family motor protein, as a synthetic lethal partner to the CENP-C mutation. Loss of KIF18A function in this compromised cellular context led to lethality, indicating a previously unappreciated genetic interaction critical for cell viability under kinetochore stress.

Further mechanistic investigations revealed that the CENP-C mutation indirectly caused a reduction in CENP-E activity, another motor protein at the kinetochore involved in guiding chromosome movement. Importantly, KIF18A and CENP-E were shown to act cooperatively to facilitate the congression of chromosomes to the metaphase plate, a crucial step ensuring that chromosomes are aligned before segregation. Each motor can partially compensate for the other; however, their simultaneous inhibition results in catastrophic failure of chromosome alignment.

This cooperative motor activity is of particular relevance in the context of cancer biology. Certain cancer cell lines were identified to naturally express low levels of CENP-E, rendering them especially vulnerable to KIF18A inhibition. The study demonstrated that targeting KIF18A in these cancer cells triggered selective cell death, exploiting a synthetic lethality that spares normal cells with intact CENP-E function. This selective vulnerability offers a promising therapeutic window to develop targeted cancer treatments with reduced off-target toxicity.

The research team leveraged a cell model with a partially defective kinetochore apparatus to uncover these vulnerabilities, exemplifying the power of combining genetic perturbations with high-throughput screening technologies to dissect complex cellular processes. The finding that KIF18A and CENP-E act downstream of CENP-C integrates prior knowledge of kinetochore assembly with functional motor cooperation, revealing the layered regulation required for mitotic fidelity.

At the molecular level, KIF18A and CENP-E serve distinct yet overlapping functions in chromosome movement. KIF18A primarily regulates microtubule dynamics and dampens chromosome oscillations, while CENP-E drives poleward movement of chromosomes along spindle microtubules. Their joint activity orchestrates the precise spatial positioning of chromosomes, facilitating proper microtubule attachments and checkpoint satisfaction, thus ensuring reliable chromosome segregation.

Cancer cells often harbor deregulated mitotic machinery, and this study underscores how subtle variations in motor protein expression can be exploited for therapeutic purposes. By quantifying CENP-E protein levels, clinicians might identify tumors predisposed to respond favorably to KIF18A-targeted therapies. Furthermore, the prospect of combination treatments inhibiting both motors could potentiate efficacy, potentially circumventing resistance mechanisms common in monotherapies.

Beyond immediate therapeutic implications, this work exemplifies the critical need for molecular-level investigations to illuminate novel cancer vulnerabilities. Professor Tatsuo Fukagawa, the senior author, emphasizes that translating basic mitotic biology into clinical strategies mandates a foundational understanding of the cellular machinery, as demonstrated in this elegant work that links motor protein cooperation to selective cancer cell killing.

The implications of this study extend to understanding the broader landscape of kinetochore function in health and disease. It encourages further exploration of mitotic motor redundancies as pharmacological targets, a frontier that may yield increasingly refined cancer therapies. Given the essential role of chromosome alignment in genomic stability, dissecting these redundancies may also uncover reasons behind tumor heterogeneity and differential drug susceptibilities.

Moreover, the synthetic lethality observed with impaired KIF18A and CENP-E activity presents a conceptual advance for cancer treatment design, harnessing specific genetic and proteomic contexts of tumor cells to achieve selective eradication. This precision strategy aligns with contemporary trends aiming to shift from broad-spectrum cytotoxic agents to targeted molecular interventions.

In conclusion, the study published in Cell Reports on November 10, 2025, heralds a new understanding of mitotic regulation through the cooperative actions of KIF18A and CENP-E motor proteins downstream of CENP-C. This discovery opens innovative avenues for cancer therapy by exploiting inherent weaknesses in cancer cells while preserving normal cell function. The collaboration between The University of Osaka and MIT demonstrates how cutting-edge molecular biology, genomics, and cancer research converge to produce clinically translatable knowledge.

Subject of Research: Cells

Article Title: KIF18A promotes chromosome congression in cooperation with CENP-E downstream of CENP-C

News Publication Date: 10-Nov-2025

References: 10.1016/j.celrep.2025.116515

Image Credits: Original content by Tatsuo Fukagawa

Keywords: Life sciences, Health and medicine, Cell biology, Molecular biology, Cancer cells, Centromeres, Kinetochores