Multiple protein phosphatases are required for mitosis in Drosophila

I have asked which protein phosphatases or subunits (PPs) have cell-cycle roles through systematic RNAi. I found that progression through G2 into M requires Puckered, the JNK MAP-kinase inhibitory phosphatase and PP2C in addition to String/Cdc25. Strong mitotic arrest and failure in chromosome congression occurred after down-regulation of Pp1-87B. Chromosome alignment/segregation defects also occurred after knock-down of PP1-Flapwing, not previously thought to have a mitotic role. Reduction of several non-receptor tyrosine phosphatases gave defects in spindle and chromosome behaviour, and for corkscrew, premature chromatid separation. RNAi of the dual specificity/lipid phosphatase, Myotubularin, or the related Sbf “anti-phosphatase” resulted in aberrant mitotic chromosome behaviour. In addition to the survey of Drosophila PPs that are required for cell division cycle, I have investigated the functions of PP2A in considerably more detail than the other enzymes. Knock-down of the catalytic or A subunits led to bipolar monoastral spindles; of the Twins/Aar B subunit, bridged and lagging chromosomes; and of the B’Widerborst subunit, scattering of all mitotic chromosomes. The Widerborst B’ subunit was associated with MEI-S332 (Shugoshin) and was required for its normal localization to kinetochores. Finally, by developing a controlled gene regulation system in Drosophila male meiosis, I identified a novel requirement for PP2A activity in cytokinesis. Conclusions: I have identified cell-cycle roles for 22 of 117 Drosophila PPs. Involvement of several PPs in G2 suggests multiple points for its regulation. Major mitotic roles are played by PP1 with tyrosine PPs and Myotubularin-related PPs having significant roles in regulating chromosome behaviour. Finally, depending upon its regulatory subunits, PP2A regulates spindle bipolarity, kinetochore function, progression into anaphase, and cytokinesis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo