spermiogenesen

Spermiogenesis is the final stage of spermatogenesis in which haploid round spermatids are transformed into mature spermatozoa. It occurs within the seminiferous tubules of the testis and is supported by Sertoli cells. The process involves dramatic cellular remodeling, chromatin condensation, and the development of the sperm tail.

The transformation proceeds through four consecutive phases. In the Golgi phase, proacrosomal vesicles derived from the trans-Golgi network coalesce at the anterior of the nucleus to form a single acrosomal vesicle, while the distal centriole migrates to the anterior pole. In the cap phase, the acrosomal vesicle spreads to form an acrosomal cap over part of the nucleus as the head begins to elongate. In the acrosome phase, the nucleus condenses and elongates further, the acrosome expands, and the axoneme begins to assemble from the distal centriole to form the base of the flagellum. Mitochondria accumulate around the proximal flagellum to form the mitochondrial sheath of the midpiece. In the maturation phase, excess cytoplasm is extruded as residual bodies and phagocytosed by Sertoli cells, while DNA undergoes drastic condensation by replacing histones with transition proteins and protamines, yielding highly compact chromatin.

The final product is a structurally mature spermatozoon with a condensed head, a midpiece containing mitochondria, and a long flagellum for motility. Spermiogenesis ends with spermiation, the release of mature spermatozoa into the lumen of the seminiferous tubules, after which they are transported to the epididymis where they acquire full motility and fertilizing capability. In humans, spermiogenesis generally lasts about 24 days per spermatid.