From syncytium to sperm: Coordinated membrane and cytoskeletal remodeling in Drosophila spermiogenesis

Male infertility has increased in the recent past, with declining sperm counts affecting many couples. Critically, its genetic and cellular causes remain only partially understood. Contributing to male sterility are defects in sperm production, structure, function, and seminal fluid quality, with sperm abnormalities also negatively impacting pregnancy and fetal development. Spermatogenesis is a highly complex, multistep process requiring germline-somatic interactions and the coordination of cell division with the remodeling of the cytoskeleton and with enormous growth of membranes. Regulated by a plethora of genes, spermatogenesis is particularly vulnerable to genetic and epigenetic disruptions. These complexities make the identification and functional validation of genes orchestrating male gametogenesis particularly challenging. Model organisms such as Drosophila melanogaster provide powerful systems to study gene function, and this review thus focuses on spermiogenesis in flies, the post-meiotic process with the most extensive structural changes necessary for the production of functional sperm.