When cells divide – a process known as mitosis – its chromosomes must be separated and evenly divided into newly formed daughter cells. Although it is known to be very complex and marks a series of mobile components, many of its data remain obscure, which has delayed efforts to develop treatment when the mitosis is exaggerated.
The new study is reported in the journal Natural Cell Biology has given a deeper insight into this process by revealing details of how protein complexes gather in chromosome centers in places known as centromeres. In these places, the protein complex acts as an anchor through which the organizers of the cell structure can redistribute the chromosome in the cell.
These protein complexes for centromers are known as kinetochores, with long, thin, cylindrical structures, called microtubules. By cell division, microwaves can be physically manipulated with chromosomes, motivating half of each chromosome to be included in one daughter's cell and half in another.
In this new study, the Osaka University team focused on the various components that make up and bind to kinetochores. One such group is CCAN proteins located in the centromer throughout the cell cycle and acts as a binding site for other microtubule binding proteins only when cell division occurs. This work shows that the CCAN protein subtype that forms the CENP-T pathway is dominated by the successful cell division by linking it with a protein complex called the Ndc80 complex, allowing the microtubules to join the chromosomes.
"We have mainly investigated whether the CENP-T pathway, or approximately the same CENP-C pathway, is essential for the progression of mitosis by selectively removing some of these proteins that bind to the Ndc80 complex," says Tatsuo Fukagawa. "CENP-T mutants with domain deficiencies linked to Ndc80, but not similar CENP-C mutations, revealed chromosomal failure, preventing cells from sharing and ultimately leading to cell death."
In order to confirm their results and to more reveal the important role of CENP-T in promoting cell division through the Ndc80 complex, the team also created chimeric structures, partly consisting of CENP-T and partly from CENP-C. This confirms the conclusion that CENP-T and its related molecules are vital for mitosis. They also found that phosphorylation plays an important role in regulating the relationship between the Ndc80 complex and the CENP-T, as well as obtaining additional direct evidence of their findings by measuring the migration force generated by the microtubules in the mitotic shaft.
"Our work overturns the previous consensus, showing that it is CENP-T instead of CENP-C, which works with the Ndc80 complex for successful cell division, providing precise and timely chromosome segregation," says Masatoshi Hara. "These discoveries could have therapeutic potential in the treatment of diseases associated with dysfunctional kinetochores and mitotic progression, including cancer."
The two-stage process is based on maintenance of the main proteins by cell division
Masatoshi Hara et al., Several phosphorylation controls the collection of KMN networks on kinetochores, Natural Cell Biology (2018). DOI: 10.1038 / s41556-018-0230-0