Meiosis is essential for the creation of genetic variation and the accurate transmission of genetic material in sexually reproducing organisms. Throughout this process, chromosomes undergo complex structural rearrangements whose relationship to universally conserved meiotic processes is poorly understood. The
him-3 gene encodes a meiosis-specific structural component of chromosome cores and is required for several crucial meiotic events including chromosome pairing, the nuclear reorganization that accompanies the onset of homolog alignment, synapsis, and recombination 1 ,2 . Three paralogs of
him-3 , known as the h im - t hree p aralogs ( htp -1, 2, and 3), have been identified, raising the possibility that they constitute a family of genes involved in mediating chromosome structure and behaviour . We are investigating the localization and function of HTP-3, one of these paralogs , and its interaction with the him -3 family of proteins. Yeast two-hybrid screening data suggests that HTP-3 interacts directly with both HIM-3 3 and HTP-1 4 . Stainings with anti-HTP-3 antibodies have revealed that HTP-3 localizes to all germ line nuclei. HTP-3 is diffusely present within the nucleoplasm of mitotic nuclei, but like HIM-3, HTP-3 localizes to chromosome axes in meiotic nuclei. HTP-3 localization is independent of both HIM-3 and HTP-1. However, consistent with an interaction between HTP-3 and HIM-3, HTP-3 is required for the localization of HIM-3 to meiotic chromosome cores. Additionally,
htp-3 ( RNAi ) hermaphrodites exhibit the most severe meiotic defects of
him-3 mutants. Given these results, HTP-3 is hypothesized to have a primary meiotic function in direct recruitment of HIM-3 to chromosome axes. However, due to the mitotic localization of HTP-3 and other meiotic defects in the
htp-3 ( RNAi ) background unique from
him-3 mutants, HTP-3 likely has additional roles. Further cytological and genetic analyses of HTP-3 are in progress and will be presented. Our goal is to ultimately understand how HTP-3, in conjunction with its paralogs , mediates these essential meiotic processes as well as other germ line events. Supported by NSERC and CIHR. 1 Zetka et al . 1999. Genes and Dev. 12 : 2258, 2 Couteau et al . . 2004. Curr Biol. 14 : 585 3 Zetka , unpublished results, 4 Walhout , et al . 2002. Curr Biol. 12 : 1952