Identification and activity of new regulators of cell division.

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Protein kinase Cdk1, complexed with its activator Cyclin B, is a master-regulator of mitosis. In a recent screen (Hegarat et al. 2018), we identified 125 specific substrates of Cyclin B/Cdk1. Among them were factors controlling essential mitotic pathways, such as Chromosome Passenger Complex (aka Aurora B complex), Ki67, and kinetochore assembly components. Findings of known Cdk1 targets among the previously unidentified substrates assured us about the validity of our approach. Since most of the Cyclin B dependent phosphorylations by Cdk1 indeed are critically important for mitotic progression, we hypothesised that the novel proteins identified in this screen have essential mitotic functions. We will test this by the siRNA depletion and mitotic phenotype analysis of the panel of Cyclin B/Cdk1 substrates. We will study the effects of the RNAi-based depletion of eight uncharacterised targets of an unknown function. Additionally we will analyse three proteins involved in the "cell cycle regulation", four "kinetochore organisation" regulators, two "nuclear lamina" components, and two "protein phosphatases", as well as the selection of rather unexpectedly identified targets: three members if the "actin organisation" network, two proteins involved in the "endoplasmic reticulum organisation" and two from the "ribosome biogenesis" group. From among those 26 different targets, we will chose the most promising and interesting candidates to be studied further. Realistically, the student will be able to dissect the role of up to three new mitotic regulators, which will lead to the identification of new regulatory mechanisms that control mitosis. From the strategical point of view, it will be a genuine, real collaborative effort, which brings our research units together and allows for the accumulation of exciting, top quality data that will be used for preparing an application for a project grant (or grants) submitted to BBSRC or MRC.