The initial phases of testicular organogenesis in the rat. An electron microscopy study.

The paper is devoted to the study of the very first stages of testicular organogenesis in the rat, i.e. to the study of the initial stages of formation of the seminiferous cords. It takes over and extends the results of a previous histological study (Jost, 1972). The tissues were fixed with glutaraldehyde or glutaraldehyde-paraformaldehyde and post-fixed with osmium tetroxide. Examination with the optical microscope of semi-thick sections confirms that the differentiation begins at the stage of 13 days after fertilization; an increasing number of primitive Sertoli cells appear, first in the depth of the gonad, join each other and form the seminiferous cords. Study with the electron microscope reveals three characteristic criteria of the early differentiation of the Sertoli cells, namely : 1) an abundant cytoplasm, only slightly dense to electrons and containing short laminae or vesicles of rough endoplasmic reticulum; 2) complex contact zones involving infoldings and interdigitations of the membranes; 3) a layer of microfilaments beneath the flattened surface of the cells, that limits the outer surface of the seminiferous cords. These differentiation processes taking place at the stage of 13 days, are described.