Ultrastructural morphodynamics of human Sertoli cells during testicular differentiation.

Our study reviews and ultrastructurally characterises human pre-Sertoli cells between the 6th and the 20th week of gestation by means of integrated light microscopy, transmission electron microscopy and high resolution scanning electron microscopy (standard or following ODO maceration). The morphofunctional differentiation of Sertoli cells defines testicular differentiation. These somatic cells are mostly of mesonephric origin and can be first morphologically recognised in 7 week-old embryos altogether with the formation of testicular cords. The latter organise as primordial germ cells surrounded by pre-Sertoli cells. Due to the great synthetic activity of pre-Sertoli cells the rough endoplasmic reticulum develops. The basal lamina of the cords becomes distinguishable at 7 to 8 weeks of gestation. Both prespermatogonia and pre-Sertoli cells actively proliferate but the latter greatly outnumber prespermatogonia. Many interdigitations and cytoplasmic processes are observed between neighbouring pre-Sertoli cells. Due to cell proliferation a sort of compartmentalisation is established inside the cords in which pre-Sertoli cells tend to localise closer to the basal membrane embracing prespermatogonia with long and thin cytoplasmic processes. One of the main typical features of differentiating pre-Sertoli cells is the irregular nucleus and the prominent nucleolus. When the embryo is 14 to 20 weeks-old pre-Sertoli cells maintain their general morphology whereas the most significant change is the maximum development of Leydig cells. Testicular cords do not show any lumen at all so they cannot be termed "tubules".