Spermatogonial cell proliferation in organ culture of immature rat testis.

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.

Different action of MMS and EMS in UV-sensitive strains of Aspergillus nidulans.

The repair of methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS) damages has been investigated in the fungus Aspergillus nidulans. 4 UV-sensitive mutants, namely uvsB, uvsD, uvsF and uvsH have been tested for their sensitivity and mutability to the above-mentioned agents. The results obtained show that: (1) uvsB and uvsD mutants are no more sensitive than the wild-type strain to the lethal action of EMS. In contrast, they are more sensitive to MMS; (2) uvsF and uvsH mutants are more sensitive than the wild type to EMS at 37 degrees C but not at 20 degrees C. However, they are more sensitive than the wild type to MMS at 37 degrees C as well as at 20 degrees C; (3) the mutation frequencies after treatment with either MMS or EMS plotted against survival are not altered in the UV-sensitive strains compared to the wild-type strain. From these data it may be concluded that the repair of lethal lesions induced by ethylating and methylating agents is under the control of different pathways. Furthermore the mutants tested are not involved in the mutagenic process.