Rete Testis: Structure, Cell Biology and Site for Stem Cell Transplantation

Seminiferous tubules of testis open into a continuous chamber of flattened and irregular-shaped anastomosing channels called the rete testis. Positioned at one pole of the testis (hilus), the rete is adjacent to the connective tissue capsule covering of the testis, known as the tunica albuginea. The hilus is also the location where blood vessels penetrate the capsule. The rete testis serves as a conduit and point of exit for newly released spermatozoa and seminiferous fluids derived from testicular seminiferous tubules. Emerging from the rete are many efferent ductules serving to transport sperm and fluids into the epididymis, the highly convoluted, tubular organ resting on the back of the testis and functioning in the storage and maturation of sperm. In rodents, the rete testis is situated primarily next to the tunica albuginea, while in man and large mammals it extends approximately 1/3–1/2 into the testis proper. The squamous to short cuboidal epithelium is highly active in endocytosis, where several proteins derived from the lumen of seminiferous tubules are taken up and degraded by lysosomes. Some of these proteins are secretory products of Sertoli cells that may interact with sperm as they are formed in the testis, but which are of limited functional importance as they head to the epididymis. The rete appears to be a clearing station for some proteins derived from the testis. Thus while a seemingly passive passageway, the rete has important roles in fine-tuning the lumen for sperm as they enter the efferent ducts. It may also serve in obstructions of the efferent ducts to expand and prevent disruption of the blood–testis barrier. Of clinical significance, the rete testis has over the past decade been used as an appropriate site to inject stem cells into the lumen of seminiferous tubules to restore a deficient or reduced spermatogenesis.