From Stem Cell to Complex Sperm in the Rhabditophoran Macrostomum lignano

Abstract

Macrostomum lignano posesses a unique stem cell system (neoblasts) responsible for tissue-turnover growth, regeneration, and germ line formation. Its somatic gonads as well as the germ line formation in M.lignano. We mainly focused on the differentiation of primordial germ line stem cells to sperm using different techniques such as a light microscopical analysis and a transmission electron microscopic study mainly of the adult testis. 3D reconstructions were made based on TEM sections. The spermatozoa have a complex morphology with bristles, a terminal brush and an undulating shaft. It is still unclear how these morphological features develop. We found new intracellular structures associated with the bristles, which are transiently developed through spermiogenesis. Spermiogenesis of M. lignano will be discussed and compared to data on spermiogenesis in other species of Macrostomum and other platyhelminth taxa. More specifically, the developmental implications of bristle formation will also be discussed.