CELL-INTERACTIONS IN TESTIS DEVELOPMENT - OVEREXPRESSION OF C-MOS IN SPERMATOCYTES LEADS TO INCREASED GERM-CELL PROLIFERATION

Possible functions of the c-mos proto-oncogene during spermatogenesis were investigated through perturbations of its expression in transgeni c mice. Two promoters, one from the pre-meiotic male germ cell-specifi c mouse phosphoglycerate kinase 2 gene, and the other from the post-me iotic male germ cell-specific rat RT7 gene were used to direct express ion of c-mos. Northern blot analysis of testis RNA from transgenic PGK -c-mos mice indicated elevated levels of c-mos RNA in spermatocytes an d spermatids compared to controls. No transgene expression was detecte d in any other tissue examined, suggesting that the mouse PGK2 promote r, like the previously used human PGK2 promoter, confers correct cell- specific expression onto c-mos. The promoter from a newly characterize d rat gene, RT7, was shown to direct expression specific to post-meiot ic spermatids. Transgenic mice carrying an RT7-lacZ construct displaye d immunoreactive bacterial beta-galactosidase as well as enzyme activi ty in round spermatids. The cellular specificity for beta-galactosidas e expression observed in RT7-lacZ transgenic animals was in agreement with endogenous RT7 transcript expression. Northern blot analysis of t estis RNA of RT7-c-mos transgenic mice showed elevated levels of c-mos in spermatids, but not in other cells or tissues examined. Western bl ot analysis demonstrated elevated levels of p43(c-mos) in spermatids o f both PGK-c-mos and RT7-c-mos transgenic animals, but only PGK-c-mos transgenics had increased p43(c-mos) levels in spermatocytes. Both RT7 -c-mos and PGK-c-mos transgenic mice are fertile and show no tendency toward transformation. RT7-c-mos mice have no discernible phenotype as sociated with the c-mos overexpression in spermatids. However, PGK-cmo s transgenic males exhibited a significant increase in germ cell numbe r, as determined by cell counts using total germ cells and germ cells fractionated by centrifugal elutriation. Because mitotic divisions of germ cells occur prior to PGK-c-mos transgene expression, our observat ions suggest that c-mos overexpression in spermatocytes causes an alte ration in cell-cell interactions, (C) 1995 Wiley-Liss, Inc.