The role of Rok and its substrate Cmb the male germline Traditionally, Rho kinase (ROCK, Rok in flies) functions as effector of the non-canonical Wnt/Frizzled PCP pathway during gastrulation and neural tube formation. It also affects epithelial barrier formation and is required for cell migration and metastases formation. Unsurprisingly, both the up- and downregulation of Rok activity can cause severe developmental defects. However, a function for Rok in the male germline has never been addressed. Here, we have identified a novel function for Rok and its substrate Combover (Cmb) in the male germline in Drosophila, where both are required for spermiogenesis and proper sperm separation and packaging. Our proposal addresses the hypothesis that, downstream of Rok, Combover orchestrates a novel transition checkpoint between axoneme elongation and sperm individualization. In particular, our preliminary data suggest that Cmb coordinates the cytoskeleton with the plasma membrane, thus ensuring proper growth and resolution of the syncytial spermatids into functional sperm that are encapsulated by their own plasma membrane. Our identification of Rok and Cmb as critical components necessary for male gametogenesis will have wide-ranging implications for sperm development beyond Drosophila: syncytial mammalian spermatids have to individualize during spermiation, a process that, although different in detail in mammals, nevertheless, as in flies, requires tight encapsulation of the sperm tail with its membrane while shedding unnecessary cytoplasm. The biomedical significance of sperm individualization is further exemplified by the presence of multiciliate spermatozoa and spermatids with unresorbed cytoplasm in infertile men.