The Ultrastructure of Immature Sertoli Cells. Maturation-Like Changes During Culture and the Maintenance of Mitotic Potentiality

Cell aggregates dissociated from 10-day-old rat testes form epithelial colonies in culture. These epithelial cells have been identified as supporting cells (immature Sertoli cells) by the close similarity between the nuclear and cytoplasmic structures of the cultured cells and those of supporting cells in vivo . The cultured supporting cells undergo maturation-like changes in serum-enriched media containing follicle stimulating hormone (FSH). These changes include a change in the pattern of chromatin condensation, the development of large nucleoli and nuclear infoldings, a progressive predominance of the smooth over the rough endoplasmic reticulum and the appearance of luminal (apical) differentiations. The differentiations of the luminal surface consist of finger-like cytoplasmic extensions, a regional accumulation of microfilaments and microtubules and the junctional complexes between neighboring cells near the lumen. In the presence of FSH there is a low but sustained mitotic activity in the population of cultured supporting cells. This FSH-dependent mitotic activity was observed from Day 4-15 in culture. It is suggested that while several structural differentiations of the supporting cells develop under these conditions in vitro , the luminal region of these cells does not differentiate in the same way as the apical region of Sertoli cells in vivo .