When a cell divides – a process called mitosis – its chromosomes must be separated and distributed evenly in the newly created daughter cells. Although this is known to be extremely complicated and that there are a number of cellular components, many details are still unclear, which has hampered the efforts to develop treatments for when mitosis goes wrong.
A new study is reported in the newspaper nature Cell Biology has gained insight into this process by revealing the details of how protein complexes coincide at the center of chromosomes in places called centromerrals. At these sites, the protein complexes function as anchors through which cellular structural organizers can redistribute chromosomes in the cell.
These protein complexes on centromeres are known as kinetochores, to which long, thin, cylindrical structures called microtubules are attached. In cell division, microtubules can physically manipulate the chromosomes, pull half of each chromosome for transposition into a daughter cell and half in the other.
In this new study, Osaka University-led team focused on the various components that form and bind to kinetochores. Such a group is the CCAN proteins present at the centrometer through the cell cycle and acts as a binding site for other microtubular associating proteins only when cell division occurs. This work demonstrates that a subset of the CCAN proteins, which form the CENP-T pathway, dominates to ensure successful cell division by binding to a protein complex called the Ndc80 complex, which allows microtubules to attach to chromosomes.
"We mainly investigated whether the CENP-T pathway or the approximately the same CENP-C pathway is essential for mitotic progression by selectively removing portions of these proteins that bind to the Ndc80 complex," said the corresponding author Tatsuo Fukagawa. "CENP-T mutants lacking domains for binding to Ndc80, but not similar to CENP-C mutants, revealed a failure of chromosomes to segregate, prevent cells from dividing and ultimately leading to cell death. "
In order to confirm the results and reveal more about CENP-T's essential role to promote cell division through the Ndc80 complex, the group also constructed chimeric constructs that consisted partly of CENP-T and partly by CENP-C. This validated the discovery that CENP-T and the molecules that bind to it are crucial to mitosis. They also revealed that phosphorylation plays an important role in regulating binding between the Ndc80 complex and CENP-T and obtained further direct evidence of their findings by measuring the traction exerted by microtubules in the mitotic spider.
"Our work disappears from a previous consensus by demonstrating that it is CENP-T, not CENP-C, which acts through the Ndc80 complex for successful cell division by ensuring proper and fast chromosome segregation," says principal author Masatoshi Hara. "The results can lead to therapeutic alternatives for the treatment of dysfunction in kinetochores and mitotic progression, including cancer. "
Two-step process supports the maintenance of key protein in cell division
Masatoshi Hara et al. Several phosphorylations control the recruitment of the KMN network on kinetochores, nature Cell Biology (2018). DOI: 10,1038 / s41556-018-0230-0