Spermiogenesis

Spermiogenesis is the final stage of spermatogenesis, the process by which spermatogonia mature through meiosis to haploid spermatids and then to mature spermatozoa. It occurs in the seminiferous tubules of the testes within the Sertoli cell environment and involves transformation of round, non-motile spermatids into elongated, highly specialized spermatozoa without further cell division. During spermiogenesis, developing cells are still connected by cytoplasmic bridges, though these bridges eventually disappear during spermiation.

Morphological changes during spermiogenesis include nuclear remodeling with progressive chromatin condensation as histones are replaced by transition proteins and protamines, producing a compact haploid genome. Acrosome formation arises from Golgi-derived vesicles that cap the anterior nucleus. The nucleus becomes elongated and its shape is sculpted by the manchette. The flagellum develops from the basal body/centrioles to form the axoneme, with associated structural elements. Mitochondria reorganize into a midpiece around the axoneme, and most cytoplasm is shed as a residual body.

Regulation and context involve signaling from Sertoli cells and local factors, with hormones such as testosterone and follicle-stimulating hormone playing supporting roles. Spermiogenesis proceeds after meiosis within the seminiferous epithelium, and the resulting mature spermatozoa are released into the lumen during spermiation. Post-testicular maturation in the epididymis confers motility and fertilizing capability. Defects in spermiogenesis, including problems with chromatin condensation or acrosome formation, can lead to abnormal sperm morphology and reduced fertility.