GSE108064
Cyclin Cyc2 is required for elongation of meiotic micronucleus in Tetrahymena thermophila
Meiosis occurs in all sexually reproducing unicellular and multicellular eukaryotes. Bouquet formation is indispensible for homologous pairing or recombination during meiotic prophase I, but the regulatory mechanism of this process remain largely unknown. Cyclins regulate the precise meiosis progression by activating cyclin-dependent kinases. We therefore investigated the functional contribution of cyclin Cyc2p during bouquet (named crescent in Tetrahymena) formation in Tetrahymena thermophila. As a conjugation specific gene, CYC2 expression is significantly upregulated at 2-4 h after the initiation of conjugation and Cyc2p mainly localized in cytoplasm as well as weakly in the meiotic micronucleus (Mic). CYC2 knockout mutants failed to form elongated crescent structure and aborted meiotic development. Mic DNA double-strand breakage (DSB) decreased in ?CYC2 cells as shown by ?-H2A.X staining, consistent with the finding that expression level of SPO11, DMC1, and RAD51 decreased in ?CYC2 cells. However, ?CYC2 cells failed to form crescent structure when artificial DSBs were induced, indicating that the inability to enter crescent phase was not completely due to the lack of DSBs. The localization of tubulin showed that impaired structure of nuclei and nuclear membrane may contribute to the blocked Mic elongation. This is further supported by the observation that expression levels of two microtubule associated kinesin genes, KIN11 and KIN141, were significantly downregulated in ?CYC2 cells. Interestingly, scnRNA accumulation seemed intact in ?CYC2 cells whereas the intensity of the heterochromatin marker H3K23me3 was abnormally increased. Together, these results showed that cyclin Cyc2p is required for micronuclear meiosis by controlling meiotic prophase chromosome breakage and the microtubule movement of nuclei in Tetrahymena. Overall design: Examination of transcriptional variation associated with deletion of CYC2 gene