[The development of the horse testis].

This research article discusses the development of a horse’s testis, detailing the origin and growth of various components, particularly noting the role of Leydig cells and seminiferous tubules. It further reveals that the growth of seminiferous tubules influences the size of the rete in the testis during sexual maturity.

Origin of Testicular Components

• The study found that seminiferous tubules, important structures responsible for producing sperm in the testes, originate from the sex cords of the coelomic epithelium. The coelomic epithelium is the innermost layer of the coelom, which is a fluid-filled cavity that covers some of the internal organs in the body.
• Meanwhile, Leydig cells, which produce testosterone in the testes, are believed to come from the proximal parts of mesonephric nephrons. Nephrons are the basic structural and functional units of the kidney involved in the process of filtering blood and forming urine.
• The rete and ductuli efferentes, two parts of the testis involved in the transport of sperm, are said to derive from the intermediate and distal parts of the mesonephric tubules. The latter are parts of kidneys in the embryological or fetal stage.

Leydig Cells and PMSG Role

• The research highlights that during the development of the horse’s testis, Leydig cells experience significant proliferation, driven by the secretion of Pregnant Mare’s Serum Gonadotropin (PMSG) in the mare (female horse).
• This extensive proliferation of Leydig cells inhibits the deep penetration of the rete into the medulla of the testis, explaining why the rete is not observed to extend deeply into it.
• Despite the initial proliferation, around 80% of these Leydig cells degenerate during the final third of pregnancy in horses.

Seminiferous Tubules and Rete Size

• The growth of seminiferous tubules during the horse’s sexual maturity played a major role in reducing the size of the rete to the extremitas capitata of the testis.
• The extremitas capitata is a term used to refer to the end part of the testis. This implies that as seminiferous tubules grow and multiply to optimize sperm production during sexual maturity, they essentially limit the space for the rete within the testis.