STEM-CELL FACTOR AND LEUKEMIA INHIBITORY FACTOR PROMOTE PRIMORDIAL GERM-CELL SURVIVAL BY SUPPRESSING PROGRAMMED CELL-DEATH (APOPTOSIS)

Proliferating primordial germ cells (PGCs) isolated from mouse embryos soon after their arrival in the genital ridges would only survive in vitro at temperature of less than 30-degrees-C (De Felici, M. and McLa ren, A. (1983). Exp. Cell. Res. 144,417-427; Wabik-Sliz, B. and McLare n, A. (1984). Exp. Cell. Res. 154, 530-536) or when co-cultured on cel l feeder layers (Donovan, P. J., Stott, D., Godin, I., Heasman, J. and Wylie, C. C. (1986). Cell 44, 831-838; De Felici, M. and Dolci, S. (1 991). Dev. Biol. 147, 281-284). In the present paper we report that mo use PGC death in vitro occurs with all the hallmarks of programmed cel l death or apoptosis. We found that after 4-5 hours in culture many PG Cs isolated from 12.5 dpc fetal gonads assumed a nuclear morphology an d produced membrane bound fragments (apoptotic bodies) typical of apop totic cells. In addition, PGCs in culture accumulated high level of ti ssue transglutaminase (tTGase; an enzyme that is induced and activated during apoptosis) and showed extensive degradation of DNA to oligonuc leosomal fragments, which is characteristic of apoptosis. The physiolo gical relevance of this mechanism of PGC death is supported by the fin ding that some PGCs undergoing apoptosis, as revealed by the high leve l of tTGase expression, were detected in the embryo. Most importantly, we show that the addition of stem cell factor (SCF) or leukemia inhib itory factor (LIF) to the culture medium, two cytokines known to favou r PGC survival and/or proliferation in vitro, markedly reduced the occ urrence of apoptosis in PGCs during the first hours in culture. These last results suggest a novel mechanism by which these two cytokines ma y affect the in vitro as well possibly in vivo development of mammalia n PGCs.