Spermatogenesis

Spermatogenesis
Seminiferous tubule with maturing sperm. H&E stain.
A mature human Spermatozoon
Identifiers
MeSHD013091
Anatomical terminology
Normal spermatogenesis, testis biopsy.
High-power view of a seminiferous tubule with normal spermatogenesis.

Spermatogenesis is the process by which haploid spermatozoa develop from germ cells in the seminiferous tubules of the testicle. This process starts with the mitotic division of the stem cells located close to the basement membrane of the tubules.[1] These cells are called spermatogonial stem cells. The mitotic division of these produces two types of cells. Type A cells replenish the stem cells, and type B cells differentiate into primary spermatocytes. The primary spermatocyte divides meiotically (Meiosis I) into two secondary spermatocytes; each secondary spermatocyte divides into two equal haploid spermatids by Meiosis II. The spermatids are transformed into spermatozoa (sperm) by the process of spermiogenesis. These develop into mature spermatozoa, also known as sperm cells.[2] Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa and four haploid cells.[3]

Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis, of which the female equivalent is oogenesis. In mammals it occurs in the seminiferous tubules of the male testes in a stepwise fashion. Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. DNA methylation and histone modification have been implicated in the regulation of this process.[4] It starts during puberty and usually continues uninterrupted until death, although a slight decrease can be discerned in the quantity of produced sperm with increase in age (see Male infertility).

Spermatogenesis starts in the bottom part of seminiferous tubes and, progressively, cells go deeper into tubes and moving along it until mature spermatozoa reaches the lumen, where mature spermatozoa are deposited. The division happens asynchronically; if the tube is cut transversally one could observe different maturation states. A group of cells with different maturation states that are being generated at the same time is called a spermatogenic wave.[5]

  1. ^ de Kretser, D. M.; Loveland, K. L.; Meinhardt, A.; Simorangkir, D.; Wreford, N. (1998-04-01). "Spermatogenesis". Human Reproduction. 13 (suppl_1): 1–8. doi:10.1093/humrep/13.suppl_1.1. ISSN 0268-1161. PMID 9663765.
  2. ^ Sharma S, Hanukoglu A, Hanukoglu I (2018). "Localization of epithelial sodium channel (ENaC) and CFTR in the germinal epithelium of the testis, Sertoli cells, and spermatozoa". Journal of Molecular Histology. 49 (2): 195–208. doi:10.1007/s10735-018-9759-2. PMID 29453757. S2CID 3761720.
  3. ^ "The Spermatozoön, in Gray's Anatomy". Retrieved 2010-10-07.
  4. ^ Song, Ning; Liu, Jie; An, Shucai; Nishino, Tomoya; Hishikawa, Yoshitaka; Koji, Takehiko (2011). "Immunohistochemical Analysis of Histone H3 Modifications in Germ Cells during Mouse Spermatogenesis". Acta Histochemica et Cytochemica. 44 (4): 183–90. doi:10.1267/ahc.11027. PMC 3168764. PMID 21927517.
  5. ^ Schulze, W. (24 April 2009). "Evidence of a Wave of Spermatogenesis in Human Testis". Andrologia. 14 (2): 200–207. doi:10.1111/j.1439-0272.1982.tb03124.x. PMID 7103139. S2CID 42304875.