Spermatogenesis

Definition

The complete sequence of germ-cell proliferation and differentiation by which diploid spermatogonia give rise to haploid, motile spermatozoa. In arthropods the process varies markedly: most insects undergo cystic spermatogenesis, wherein germ cells remain interconnected by cytoplasmic bridges and synchronously progress through meiosis within a somatic cyst, whereas many arachnids and crustaceans show asynchronic or non-cystic patterns. The conserved stages—mitotic amplification of spermatogonia, two meiotic divisions yielding spermatids, and spermiogenesis (structural remodeling into sperm)—are modulated by taxon-specific hormones, temperature, and nutritional state.

Etymology

Greek sperma (seed) + genesis (origin)

Example

In Drosophila melanogaster, spermatogenesis proceeds within the apical tip of the testis: germline stem cells divide asymmetrically to produce gonialblasts that undergo four transit-amplifying mitoses, enter meiosis as 16-cell cysts, and complete spermiogenesis coiled within the testis, with individualization complexes stripping away excess cytoplasm to yield 64 mature sperm per cyst.

Related Terms

• spermiogenesis
• Oogenesis
• Spermatogonia
• Spermatocyte
• Spermatid
• Testis
• germline stem cell
• Meiosis
• cystic spermatogenesis

Usage Notes

Distinguished from spermiogenesis, which is strictly the post-meiotic morphological maturation of spermatids into spermatozoa. In entomological literature, 'spermatogenesis' often encompasses both meiotic and post-meiotic phases unless specified otherwise. Arthropod researchers should note that cystic versus non-cystic organization affects experimental accessibility and genetic screening strategies.