Polo kinases are an evolutionarily conserved subfamily of Ser/Thr protein kinases that play pivotal roles in cellular proliferation. Outer Dense Fiber 2 (ODF2) was initially identified as a major component of sperm tail cytoskeleton, and was later suggested to be a centrosomal scaffold important for the recruitment of various proteins to somatic centrosomes. Here, we showed that a splicing variant of hODF2 called hCenexin1, but not hODF2, efficiently localized to somatic centrosomes via a splice-generated C-terminal extension and recruited a mitotic polo-like kinase 1 (Plk1) through a Cdc2-dependent phospho-S796 motif within the extension. The S796-dependent hCenexin1-Plk1 interaction and Plk1 activity were critical for the recruitment of pericentrin and gamma-tubulin, generation of microtubule organizing centers, and formation of proper bipolar spindles. Early in the cell cycle, hCenexin1, but not hODF2, also contributed to normal ninein recruitment and primary cilia formation but independently of Plk1 binding. These findings provide an unparalleled example of how a splice-generated C-terminal extension of a sperm tail-associating protein can mediate unanticipated phospho-dependent and independent centrosomal events at distinct stages of the somatic cell cycle. To understand the in vivo function of ODF2 and Cenexin1 in an animal model, we generated transgenic mice expressing either ODF2 or Cenexin1 to carry out comparative analyses.
The aim of this study is to understand the differential functions of two-related proteins, ODF2 and Cenexin1. Studies show that ODF2 is abundantly expressed in sperm tails, whereas Cenexin1 is exclusively expressed in somatic cells. Loss of ODF2/Cenexin1 leads to a preimplantation lethality, suggesting that either one or both of these proteins play a critical role during early stages of mouse development. Recent studies in cultured cells showed that Cenexin1 associates with centrosomes and plays a critical role for the recruitment of a mitotic polo-like kinase 1(Plk1) to this site. Deregulation of the Cenexin1-Plk1 interaction results in improper chromosome segregation and aneuploidy, an event that promotes tumorigenesis. In addition, Cenexin, but not ODF2, appears to be required for proper ciliogenesis, a process whose defect results in various diseases called ciliopathy. However, the physiological function of Cenexin1 and ODF2 and the significance of Cenexin1-dependent Plk1 recruitment during mitosis and ciliogenesis are not understood. To investigate differential functions of Cenexin1 and ODF2, we plan to generate mice expressing either one of them in the absence of both ODF2 and Cenexin1. To this end, we will first generate transgenic mice expressing either ODF2 or Cenexin1, or CenexinS796A defective in interacting with Plk1, and then mate them with heterozygote ODF2/Cenexin1 +/- mice. Generation and characterization of these ODF2-less or Cenexin1-less mice will allow us to understand the specific functions of each protein during mouse development and the physiological significance of the Cenexin1-Plk1 interaction in preventing genetic instability and tumorigenesis.
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