Changes in the cells of the Sex Cords and Seminiferous Tubules during the development of the Testis of the rat and mouse.

Abstract

The sex cords of the testis of the foetal rat and mouse are made up of two types of cell- the gonocytes and the indifferent cells. During foetal and early postnatal life, the former undergo a process of maturation involving principally an increase in size and in number of cytoplasmic inclusions. Nuclear enlargement is accompanied by a diminution in staining intensity. Gonocytes are more centrally placed within the sex cords than indifferent cells, and in the later stages of foetal development they cease to divide. In the first week of postnatal life, however, they resume mitotic activity and migrate to the basement membrane of the sex cords. Gonocytes as such disappear and are replaced by smaller daughter cells, the immature type A spermatogonia. The appearance of the latter is followed by the onset of spermatogenesis. As the tubules gradually become filled with the layers of cells of the spermatogenic line, the daughter cells of the gonocytes become flattened against the basement membrane, and come to resemble the type A spermatogonia found in the adult. Indifferent cells, which are always cytologically distinct from gonocytes and spermatogonia, exist as mononucleate units. The pattern of change of these cells during the development of the testis is different from that of the germ cells. Unlike the gonocytes, the indifferent cells continue to divide during foetal and early postnatal life. Little change takes place in these cells until after the onset of spermatogenesis, when they gradually increase in size and become Sertoli cells. The latter are principally mononucleate in form.