Spermiogenese

Spermiogenesis, also called spermiogenese in some languages, is the final stage of spermatogenesis in which haploid round spermatids differentiate into mature spermatozoa. It occurs within the seminiferous tubules of the testis and is supported by Sertoli cells. It follows meiosis and precedes spermiation.

The process is traditionally divided into three phases: Golgi, acrosomal, and maturation. During the Golgi phase, proacrosomal vesicles derived from the trans-Golgi fuse to form the acrosomal cap at one pole of the developing spermatid. In the acrosomal phase, the acrosome spreads over the nucleus, the nucleus condenses, and a flagellum begins to form; the manchette, a transient microtubular structure, helps shape the head and organize the tail. In the maturation phase, most cytoplasm is discarded as residual bodies, mitochondria reorganize into a midpiece around the proximal portion of the flagellum, and chromatin undergoes extensive remodeling with histones replaced by protamines to produce a highly condensed genome.

The result is a morphologically distinct spermatozoon with a condensed head containing the acrosome, a midpiece rich in mitochondria, and a tail composed of the axoneme and supporting structures. The mature sperm is released from the Sertoli cell in a process known as spermiation, marking the completion of spermiogenesis.

Spermiogenesis is regulated by Sertoli cell signaling and hormonal inputs, and its duration varies among species and individuals. Disruptions in spermiogenesis can contribute to male infertility, often manifesting as abnormal sperm morphology or reduced motility.