The Genetics of Postmeiotic Male Germ Cell Differentiation from Round Spermatids to Mature Sperm

After meiotic divisions, postmeiotic haploid spermatids are faced with the challenge of undergoing a dramatic morphological transformation to form mature, highly specialized spermatozoa. The main processes required for the development of functional spermatozoa include the formation of an acrosome and a flagellum, and compaction of sperm chromatin and nuclear shaping. The haploid differentiation program (spermiogenesis) is governed by the well-coordinated expression of a wide variety of genes required for the morphological and metabolic changes. It is clear that disturbances at any given point of spermiogenesis lead to a reduced ability to conceive offspring due to either a reduced number or abnormal morphology and function of spermatozoa. Defective spermatozoa are often observed in infertile males, including sperm with an abnormal morphology (teratozoospermia), defective motility (asthenozoospermia), or lowered number of sperm in the semen (oligozoospermia). Male infertility is often a multifactorial disorder, which hinders our understanding of the causal factors. However, genetic studies have revealed several genes affected in infertile males with spermiogenic defects. Furthermore, genetically modified mouse models have provided valuable information about the important genes required for haploid germ cell-specific processes.