Redistribution of Bax is an early step in an apoptotic pathway leading to germ cell death in rats, triggered by mild testicular hyperthermia

Programmed cell death occurs spontaneously during spermatogenesis and can b e induced in a cell- and stage-specific manner by mild testicular hyperther mia. Studies using transgenic mice suggest the involvement of Bcl-2 protein s in regulating germ cell apoptosis. To delineate further the pathways invo lved, we examined the temporal changes in proapoptotic Bax and antiapoptoti c Bcl-2 in rat testes after transient exposure to heat (43 degreesC for 15 min). Germ cell apoptosis, involving exclusively early (I-IV) and late (XII -XIV) stages, was activated within 6 h. Initiation of apoptosis was precede d by a redistribution of Bax from a cytoplasmic to perinuclear localization within 0.5 h of heating as assessed by immunocytochemical methods. In cont rast, Bcl-2 is distributed both in the cytoplasm and nucleus in those cell types susceptible to heat-induced apoptosis. Despite the striking redistrib ution, Bax levels remained unchanged as determined by Western analysis; Bcl -2 levels increased significantly by 6 h after heat exposure. Reverse trans cription polymerase chain reaction analysis indicated no change in either B ax or Bcl-2 mRNA levels in response to heat, suggesting the involvement of post-transcriptional rather than transcriptional mechanisms mediating their activity. The marked subcellular redistribution of Bax prior to activation of apoptosis and the increase in Bcl-2 suggest an involvement of Bcl-2 fam ily members in heat-induced apoptotic death of germ cells.