Male Germ Cell Proliferation Research Articles

Spermatogonial Cell Proliferation in Organ Culture of Immature Rat Testis1

Regulatory mechanisms of male germ cell proliferation in mammals were investigated by using in vitro organ culture of immature rat testis. Nutritional and hormonal requirements for maintenance and differentiation of germ cells in vitro were first characterized by testing different culture conditions. FSH was essential for the progression of type A spermatogonia up to the stage of pachytene spermatocytes after 3 wk of in vitro culture, while vitamins A, C, and E, LH, and testosterone were not effective. The proliferative activity of Sertoli cells markedly declined after 1 wk of in vitro culture, irrespectively of the presence of FSH in the medium. In addition, basal testosterone production by Leydig cells was maintained after 1 wk of culture, provided that FSH was present in the medium. The appearance of differentiating type I and type B spermatogonia and meiotic cells in the seminiferous cords throughout culture was accompanied by a significant reduction in the number of undifferentiated spermatogonia. Moreover, a similar labeling index of undifferentiated spermatogonia was observed in both unstimulated and FSH-stimulated testis fragments at all culture times considered. Therefore, FSH did not influence the mitotic activity of undifferentiated spermatogonia, suggesting a differential role of this gonadotropin during the mitotic phase of spermatogenesis. These results indicate that the organ culture system of immature rat testis represents a useful experimental model for studying regulatory mechanisms of spermatogonial cell proliferation.

REVIEW The genetic control and germ cell kinetics of the female and male germ line in mammals including man*

The female germ line (germ cell lineage, Keimbahn) is provided with only one proliferation wave, the oogenic, whereas male gametogenesis involves two successive waves: prespermatogenic, which corresponds to the female proliferation wave, and spermatogenesis, which is responsible for the immense number of male gametes produced in mature testes. Both male proliferation systems are linked by the transitional or T prospermatogonia. Using the reverse percentage of labelled metaphases method, it has been shown that the first differences between female and male germ cells can be identified by the end of the first wave, when oogonia and multiplying or M prospermatogonia are proliferating. This prenatal first wave of proliferation of male germ cells was also demonstrated in man and ceases around the 22nd week of pregnancy. Spermatogenesis involves a stock of stem cells (stem spermatogonia), a flexibly reacting pool of undifferentiated spermatogonia and several generations of differentiating spermatogonia, which proliferate almost exponentially. Furthermore, it consists of spermatocytes and haploid spermatids transforming into spermatozoa. The oocytes pass through the preleptotene stage, synthesizing DNA, and thereafter traverse the meiotic prophase up to the diplotene stage. In mammals they act as 'pre-embryos' in a similar but to a lesser degree than oocytes of amphibia and insects. The maternal chromosomes are largely responsible for the development of the embryo, the paternal genome for the development of the extra-embryonic tissue. The synthesis of transgenic animals is a powerful weapon in the armoury of geneticists, as has recently been demonstrated: a 14 kb genomic DNA fragment (Sry) is sufficient to induce testis differentiation and subsequent male development when introduced into chromosomally female mouse embryos.

Intercellular bridges between germ cells in the immature golden hamster testis: evidence for clonal and non-clonal mode of proliferation

Intercellular bridges of prespermatogonia and of the first A-spermatogonia in the maturing testes of newborn to 17-day-old golden hamsters have been studied by electron microscopy. Incomplete cytokinesis of dividing M- and T2-prespermatogonia and A-spermatogonia produces these bridges, which undergo different developmental fates. Bridges of the first A-spermatogonia are stable beyond subsequent mitoses of these cells; this gradually leads to the formation of bridge-connected groups of synchronously developing germ cells. Thus, the clonal mode of male germ cell proliferation is already established in this period of testis maturation. During mitoses, pre-existing bridges reversibly develop structural modifications, i.e., considerable elongation and formation of a bridge-partitioning complex. In contrast, intercellular bridges of prespermatogonia are mostly severed and become lost during subsequent mitoses of the cells involved; this results in separation of the germ cells and represents a mainly non-clonal mode of M- and T2-prespermatogonial proliferation. Here, too, pre-existing bridges elongate and develop the bridge-partitioning complex during subsequent mitoses of the joined cells, but this is superposed and interrupted by the simultaneous process of disconnection of the bridges.