Metaphase-specific cell death in meiotic spermatocytes in mice

Apoptosis of male germ cells is a widespread but little-understood phenomenon in many animal species. The elucidation of its mechanisms could be useful in the understanding of male infertility. We have examined the distribution of dying cells with the terminal transferase-mediated nick-end labeling (TUNEL) method and by an electron-microscopic procedure in the testes of 10 mouse strains, viz., C57BL/10 (B10), SL/NiA (SL), C57BL/6 (B6), C3H/He (C3H), BALB/c (BALB), DBA2 (DBA), CBA/J (CBA), MRL/MpJ(-)+/+ (M+), MRL/MpJ-lpr/lpr (lpr), and wild-type NJL mice (Mus musculus musculus). In the testes of the B10, NJL, SL, B6, C3H, BALB, DBA, and CBA mice, very few TUNEL-positive cells are distributed in the seminiferous tubules, whereas in the testes of the M+ and lpr mice, many TUNEL-positive cells, which are restricted to stage XII seminiferous tubules, have been identified. The most important finding is that many metaphases of meiotic spermatocytes show a marked TUNEL-positive reaction. Some metaphases show apoptotic morphology electron-microscopically. These results suggest that the testes of MRL strains will provide a useful model for the study of the mechanism of metaphase-specific apoptosis in meiotic spermatocytes.