Ultrastructural morphodynamics of human Sertoli cells during testicular differentiation

Our study reviews and ultrastructurally characterises human pre-Sertoli cel ls between the 6(th) and the 20(th) week of gestation by means of integrate d light microscopy, transmission electron microscopy and high resolution sc anning electron microscopy (standard or following ODO maceration). The morp hofunctional differentiation of Sertoli cells defines testicular differenti ation. These somatic cells are mostly of mesonephric origin and can be firs t morphologically recognised in 7 week-old embryos altogether with the form ation of testicular cords. The latter organise as primordial germ cells sur rounded by pre-Sertoli cells. Due to the great synthetic activity of pre-Se rtoli cells the rough endoplasmic reticulum develops. The basal lamina of t he cords becomes distinguishable at 7 to 8 weeks of gestation. Both presper matogonia and pre-Sertoli cells actively proliferate but the latter greatly outnumber prespermatogonia. Many interdigitations and cytoplasmic processe s are observed between neighbouring pre-Sertoli cells. Due to cell prolifer ation a sort of compartmentalisation is established inside the cords in whi ch pre-Sertoli cells tend to localise closer to the basal membrane embracin g prespermatogonia with long and thin cytoplasmic processes. One of the mai n typical features of differentiating pre-Sertoli cells is the irregular nu cleus and the prominent nucleolus. When the embryo is 14 to 20 weeks-old pr e-Sertoli cells maintain their general morphology whereas the most signific ant change is the maximum development of Leydig cells. Testicular cords do not show any lumen at all so they cannot be termed "tubules".