033. IMPORTIN α2 MEDIATES SUBNUCLEAR TARGETING OF THE CAJAL BODY COMPONENT COILIN; A KEY ROLE IN SPERMATOGENESIS?

Abstract

Spermatogenesis, the progressive maturation of immature germ cells to form spermatozoa, requires nucleocytoplasmic shuttling of nuclear factors to implement changes in gene transcription, as well as the storage and alternative splicing of mRNA transcripts in the nucleus that is vital for fertility. The key cellular mediators of nuclear entry are members of the importin (IMP) superfamily, of which the five different IMPα proteins in mouse testis are expressed dynamically throughout spermatogenesis, consistent with roles in transporting distinct, specific cargoes critical to gamete maturation. We identified the central Cajal body (CB) component Coilin as a specific testicular binding partner of IMPα2 in a yeast 2-hybrid screen and confirmed this interaction by coimmunoprecipitation from testis lysates. CBs are small nuclear inclusions that can associate with histone genes and facilitate histone pre-mRNA processing by recruiting RNA processing factors; intriguingly, expression of IMPα2 but not other IMPαs can regulate the number and size of CBs, as shown in cell culture experiments. Immunohistochemical analysis revealed that Coilin is predominantly in spermatocytes and in round and elongating spermatids in the rodent testis. The physiological importance of its role is indicated by the fact that Coilin knockout mice have reduced fertility, smaller testes and aberrant spermatogenesis. Our future work will focus on the testicular functions of Coilin and IMPα2 during spermatogenesis, and their roles in coordinating the pre-assembly, storage and targeting of transcription complexes to RNA processing machinery in the nucleus.