Lamellar germ cell processes: structures for possible interaction between germs cells and Sertoli cells during spermatogonial differentiation and early meiotic prophase.

The recent finding of a stage-dependent topographical relationship of basally located germ cells to Sertoli-Sertoli interspaces in the rat testis ( Ulvik 1983a ) has suggested a focal interaction between Sertoli cells and early germ cells at the sites where 2 Sertoli cells meet over a basal germ cell. Focal, stage-dependent interaction between Sertoli cells and germ cells may require specializations of the germ cell membrane. Therefore, in the present work the surface of spermatogonia and spermatocytes has been studied under the electron microscope throughout the cycle of the seminiferous epithelium. Lamellar processes, 1-3 micron long, were found to emerge from germ cells and protrude into the spaces between the overlying Sertoli cells. The processes appeared on differentiating type A spermatogonia after stage VI, on intermediate and type B spermatogonia, and on leptotene, zygotene, and early pachytene spermatocytes; however, they were not found on type A spermatogonia prior to stage VII or on preleptotene spermatocytes at stage VII. The lamellar processes are thus stage-specific and may be sites of focal interaction with the Sertoli cells. Since the cell processes always protrude into the Sertoli-Sertoli interspaces this finding supports the hypothesis of focal, stage-dependent interaction between early germ cells and Sertoli cells via the narrow Sertoli-Sertoli interspaces.