Interactions of RBM, a candidate human spermatogenesis factor

Development can be seen as the consequence of alternative gene expression in different cell types. The focus of this study is the hierarchy of gene expression that controls the process of spermatogenesis, at the RNA level. RBM is an RNA-binding protein (encoded by the Y chromosome) thought to be important for the production of sperm. Its primary structure is reminiscent of SR protein splicing factors and it colocalises with them in the nucleus of germ line cells in the testes. If RBM were involved in splicing it should interact with components of the splicing machinery, so a yeast two-hybrid screen was employed and several candidate RNA-binding proteins were retrieved. These included two testes-specific novel proteins with ubiquitous known homologues. Overall the prey fell into three functional categories: signal transducers and RNA processors (STAR proteins), general heterogeneous ribonucleoproteins (hnRNPs) and SR protein splicing factors. This suggests a global theory for RBM function, that it relays signals from the cytoplasm to effect key changes in gene expression at the level of splicing. Evidence was obtained that these proteins colocalise in vivo and bind in vitro in a phosphorylation-dependent manner that could be the key to its essential regulation in nature.