FUNCTIONS OF AURORA- · Deciphering the functions of the Aurora-B in the molecular mechanisms of chromosome segregation and the epigenetic program of male germ cells

Final Activity Report Summary - FUNCTIONS OF AURORA- (Deciphering the functions of the Aurora-B in the molecular mechanisms of chromosome segregation and the epigenetic program of male germ cells)

Essential meiotic function of the Aurora-B kinase in mammalian spermatogenesis Aneuploidy arising in the germline can be attributed to the majority of human reproductive loss, and is a characteristic of malignant tumour cells. The Aurora-B kinase has been implicated in oncogenesis and in the alignment and segregation of chromosomes during mitosis. An outstanding question is its role in mammalian meiosis. During meiotic division, there are two rounds of chromosome segregation after a single round of DNA synthesis, giving rise to haploid gametes. To achieve haploidy, sister chromatid cohesion is maintained in meiosis I, making it fundamentally different from meiosis II and mitosis. Our objectives were to determine the function of the Aurora-B kinase in mammalian meiosis. At the commencement of this study we knew that Aurora-B kinase was essential for chromosome segregation in mitotic cell division but its role in meiosis, a more complicated form of cell division was unknown. Our first step was to characterise the cell and stage specific distribution of Aurora-B kinase during spermatogenesis in mice. We found that this chromatin modifying protein is highly expressed in meiotic cells suggesting that it will be important in the chromatin dynamics of meiosis. Next we created transgenic mice using a meiotic-specific promoter driving the expression of wild-type Aurora-B, or of an inactive form carrying two single-aminoacid mutations in the ATP-binding site and in the DEAD-box. We then proceeded to characterise the phenotype of these mice and determine the functions of Aurora-B in spermatogenesis. Our results demonstrate that Aurora-B is crucial for mammalian meiosis and spermatogenesis. These Aurora-B TG-m (transgenic mutant mice) had reduced fertility and histological analysis showed that spermatogenesis was severely impaired. Observations at the chromosome level indicated that in the TG-m mice there were severe defects in chromosome segregation leading to aneuploid cells. Using in vitro kinase assays we identified new meiotic specific substrates of Aurora-B, synaptonemal complex protein 3 and the meiotic cohesion rec8. Our genetic data show that the Aurora-B kinase is required for mammalian meiosis and that it is a crucial protein for chromosome stability. The identification of Aurora-B kinase as part of the regulatory processes required for meiotic chromosome dynamics provides an attractive link to the signalling pathways that govern male germ cells. In this respect, Aurora-B may act as an interface control between physiological signals and structural components of the meiotic machinery.

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