Postnatal development of bovine Sertoli cells.

The fine structure of bovine Sertoli cells was studied from the 4th to the 40th week post natum in order to correlate the progressive acquisition of normal adult morphology with functional development. The considerable increase in tubular size during the first 20 weeks is due to the proliferation of both presumptive Sertoli and germ cells. Aside from this, the presumptive Sertoli cells are seen to expand radially and lengthen considerably. From then on however, the observed increase in tubular diameter during the later period of postnatal development is solely due to the great increase in the number of germ cells. Presumptive Sertoli cells undergo morphological differentiation to mature Sertoli cells during the first 28 weeks of proliferative development. The maturation process includes distinct changes in cell shape, nucleus and cellular organelles, as well as an increase in and differentiation of Sertoli cell surface specializations. At 24 weeks the development of inter-Sertoli cell junctions has reached a point of differentiation where, in our opinion, a functional blood-testis barrier can be expected. During the first 8 weeks an extensive development of rough endoplasmic reticulum and a well-developed Golgi apparatus can be observed, which suggests a high secretory activity in the presumptive Sertoli cells at this time. We speculate that these secretory activities may play a role in the formation of the basal lamina which is extremely well developed during early postnatal life. The subsequent reduction of the basal lamina correlates well with diminished secretory activity in the Sertoli cells.