During spermiogenesis (the final stage of sperm production), elongation,nuclear reshaping and other morphological changes convert round spermatids into motile sperm. But what controls spermiogenesis? On , Zhou and colleagues report that the novel, conserved protein RIM-BP3 (a member of a family of multidomain proteins that probably function as adaptors during vesicle fusion and release) is essential for spermiogenesis in mice. The researchers show that RIM-BP3 is a testis-specific protein and that its expression is associated with the manchette, a transient microtubular structure that is required for spermatid morphogenesis. Targeted deletion of RIM-BP3, they report, causes the production of sperm with abnormal heads and male infertility. They also report that RIM-BP3 interacts with Hook1(another manchette-associated protein involved in sperm head morphogenesis)and suggest that this interaction might correctly position the manchette. Because infertility in male mammals is often associated with the production of sperm with abnormal heads, these results suggest that dysfunctions in the pathways that involve RIM-BP3 might underlie some forms of human male infertility.
