The faithful transmission of genetic material relies upon the connection between chromosomes and the mitotic spindle. Errors can result in aneuploidy with consequent cell/organism death or the formation of cancer. Chromosome segregation is achieved by the interaction between the spindle microtubules and the kinetochores at the centromeres. Mammalian centromeres are defined epigenetically by nucleosomes containing CENP-A, which marks the place of kinetochore assembly. Proper chromosome segregation is achieved by fine regulation of Kinetochore-Microtubule (K-MT) interactions and a correct activity of activators/inhibitors at specific stages of mitosis. Despite it s importance, how kinetochores are assembled, regulated and function during chromosome segregation is not yet fully understood.

With this project we aim to advance our knowledge of the mechanisms for chromosome segregation, particularly the regulation of K-MT association. On preliminary work to this project we found an uncharacterized human gene to be a new essential element for correct chromosome segregation. Importantly, we have also found that CENP-A is lost from mitotic kinetochores. Our paralel Zebrafish work confirmed this gene as essencial, required for cell proliferation. Therefore, not only have we found a new essencial mitotic player, but the results also raise the interesting possibility that a new key control mechanism to maintain centromeric chromatin epigenetic state was discovered We aim to further advance this results and define the molecular functions of the gene, elucidating his role on the structure of centromeric chromatin in human cells, as well as how and why is required for chromosome segregation. In addition, we will explore the possible correlation of this gene and tumorigenesis, by testing cell transformation and tumor cell supression capacities. Finally, we will generalize our findings in a relevant biological context by studying the gene in a vertebrate model (Zebrafish) in the early stages of development.

Specifically, we will determine whether the loading of centromeric CENP-A is affected or whether the stable centromeric CENP-A pool is lost from the centromeres. Because many centromeric proteins are not dependent on CENP-A for proper localization, the other centromere and kinetochore proteins will be tested. K-MT dynamics will be studied for alterations, and if they are responsible for the chromosome segregation errors. Finally, we will also address the ultrastructure of the kinetochore by electronic microscopy.

Overall, we expect to significantly advance our understanding of chromosome segregation (an essencial basic cell process) by characterizing a new essencial element, both in culture cells and in a vertebrate organism.