[Regulation of growth and survival of germ cells]

Growth and survival of germ cells seem to be strictly regulated by a number of environmental and intrinsic factors. One of the most important factor is Steel factor, which is necessary not only for the rapid proliferation and survival of primordial germ cells(PGCs) in embryos, but also for the development of spermatogonia and oocytes in adult gonads. Other growth factors which are linked to different signaling pathway collaboratively support PGC growth with Stecl factor. Therefore, synergistic action of different signal transduction pathway seems to be important for PGC growth. In adult testis, a large part of spermatogonia undergoes cell death, but the physiological significance and molecular mechanisms of this process are largely unknown. We have investigated the effect of misexpressing Bcl-2 in spermatogonia in transgenic mice. And we found that ectopically expressed Bcl-2 in spermatogonia inhibited their normal apoptosis. In addition abnormally accumulated spermatogonia fail to undergo further differentiation and survival, and they were just deleted from testis. These results indicate that spermatogonial apoptosis is part of the normal program of mammalian spermatogenesis and is regulated by a pathway affected by Bcl-2.