spermatid

Spermatid is a haploid male germ cell that forms during spermatogenesis in the testes. It is produced when secondary spermatocytes complete meiosis II and divide into spermatids. Spermatids reside in the adluminal compartment of the seminiferous tubules and, during early development, remain connected by cytoplasmic bridges, which allow sharing of gene products among cells in a cohort.

Spermatids undergo spermiogenesis, a differentiation process that transforms round haploid cells into motile spermatozoa. Morphologically, spermatids progress from a round form to an elongated cell with a condensed nucleus. The acrosome forms from Golgi-derived vesicles and covers the anterior nucleus, while the axoneme of a flagellum begins to assemble and mitochondria become organized into a midpiece. During maturation, most cytoplasm is discarded as residual bodies and the nucleus becomes highly condensed via replacement of histones with protamines. In mature spermatozoa, the head contains the condensed genome and the acrosome, the midpiece houses mitochondria, and the tail provides motility.

Functionally, spermatids themselves are not yet motile and must complete spermiogenesis to become functional sperm cells capable of fertilization. They represent a critical transition between meiotic germ cells and mature sperm, and abnormalities in spermiogenesis can contribute to male infertility. The process is tightly coordinated within the seminiferous epithelium and is a key component of spermatogenesis in mammals, including humans.