Prespermatogenesis and spermatogoniogenesis in the bovine testis

The bovine male germ cell population was studied over the entire period fro m testicular differentiation in the embryo through onset of spermatogenesis in the pubertal calf. Germ cells were identified by protein gene product 9 .5 immunohistochemistry and characterized by their ultrastructure. The prol iferation pattern of germ cells was studied with immunohistochemical anti-K i 67 and anti-proliferating cell nuclear antigen reactions. Germ cells with a high proliferation rate are observed from day 50 p.c. to day 80 p.c. The se cells are in transition from primordial germ cells to prespermatogonia. From day 80 p.c. until approximately the 15th postnatal week the germ cells present are identified as prespermatogonia. From day 80 p.c. to day 200 p. c. germ cell multiplication decreases continuously; then the prespermatogon ia enter a phase of relative mitotical quiescence that lasts until the 4th postnatal week. Between the 4th and the 15th postnatal week, testicular tub ular diameters grow from 40 to 80 mu m and the prespermatogonia resume thei r proliferation. In seminiferous tubules with diameters between 80 and 120 mu m, found in animals between 18 and 27 weeks of age, a central lumen is n ormally still absent. During this period germ cell proliferation reaches a second maximum. The cells involved represent the members of the spermatogon ia stem and precursor cell line kinetically interpolated between the prespe rmatogonia and the first differentiating A-spermatogonia. This second phase of prepubertal germ cell multiplication coincides with the period when the pre-Sertoli cells transform into adult-type Sertoli cells and enter the G( 0)-phase for the rest of life.