Mechanism for the Formation of Seminiferous Tubules in Mammals

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The seminiferous epithelium in the developing mice was studied by light and transmission electron microscopy to elucidate the origin of Sertoli cells. In the testis of fetal mice from day 12 to day 14 pc, PAS-positive substances were detected exclusively throughout the cytoplasm of Sertoli cells in C57BL/6 mice. On day 12 pc, pre-Sertoli cells formed irregular and cord-like arrangements around germ cells, and the arrangements were not associated with the coelomic epithelium. This suggests that Sertoli cells are originated from the mesonephric tissues. Next, the changes in lectin binding of developing fetal mouse testis were examined to clarify the mechanism of seminiferous tubule formation. out of three lectins, which, showed the characteristic binding pattern during the testicular development, BS-I and BPA preferentially bound to the plasma membrane and small dense bodies of germ cells during 12 to 14 day pc. However, in the fetal testis on day 16 pc, the reaction with these two lectins completely disappeared. The reaction with GS-II was restricted to Sertoli cells from 12 to 14 day pc, and thereafter disappeared on day 16 day pc. The striking changes in lectin binding pattern suggest that certain glyco-conjugates containing D-galactose and N-acetyl-D-galactosamine residues are expressed during the period of 12 to 14 dpc, and the changes in function and structure may take place during 14 to 16 dpc, in association with testicular development.