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, differentiation, and proliferation, but their role in spermatogenesis has remained obscure. Two transgenic mouse lines (K2 and K15) that overexpress the human ornithine decarboxylase (ODC) gene coding for a rate-controlling enzyme in polyamine biosynthesis and, hence, contain high levels of tissue putrescine have been used to study the stage-specific role of ODC in spermatogenesis. In K2 mice with 30-fold testicular ODC overexpression, [3H]thymidine incorporation at stages I-VI of the cycle of the seminiferous epithelium was significantly above the control level. This may reflect a specific stimulation of DNA synthesis in type A4, intermediate, and type B spermatogonia. The K15 mice that have about 70-fold ODC overexpression showed an elevation of DNA synthesis only at stage V of the cycle, suggesting a specific dependence of type B spermatogonia on putrescine. In K15 mice, [3H]thymidine incorporation of stage VIII tubule segments was decreased, suggesting that excess amounts of putrescine selectively inhibit meiotic DNA synthesis. We propose that putrescine has strictly selective local stimulatory and inhibitory actions during spermatogenic DNA synthesis, and that its excess amounts ultimately may lead to decreased fertility.