POLYAMINES AND REGULATION OF SPERMATOGENESIS - SELECTIVE STIMULATION OF LATE SPERMATOGONIA IN TRANSGENIC MICE OVEREXPRESSING THE HUMAN ORNITHINE DECARBOXYLASE GENE

Polyamines are believed to participate in the induction of cell growth , differentation, and proliferation, but their role in spermatogenesis has remained obscure. Two transgenic mouse lines (K2 and K15) that ov erexpress the human ornithine decarboxylase (ODC) gene coding for a ra te-controlling enzyme in polyamine biosynthesis and, hence, contain hi gh levels of tissue putrescine have been used to study the stage-speci fic role of ODC in spermatogenesis. In K2 mice with 30-fold testicular ODC overexpression, [H-3]thymidine incorporation at stages I-VI of th e cycle of the seminiferous epithelium was significantly above the con trol level. This may reflect a specific stimulation of DNA synthesis i n type A(4), intermediate, and type B spermatogonia. The K15 mice that have about 70-fold ODC overexpression showed an elevation of DNA synt hesis only at stage V of the cycle, suggesting a specific dependence o f type B spermatogonia on putrescine. In K15 mice, [H-3]thymidine inco rporation of stage VIII tubule segments was decreased, suggesting that excess amounts of putrescine selectively inhibit meiotic DNA synthesi s. We propose that putrescine has strictly selective local stimulatory and inhibitory actions during spermatogenic DNA synthesis, and that i ts excess amounts ultimately may lead to decreased fertility.