Male germ cells regulate transcription of the cathepsin L gene by rat sertoli cells

It is well known that male germ cells regulate the steady state levels of n umerous transcripts expressed by Sertoli cells. To date, however, there has been no direct test of whether this regulation reflects changes in gene tr anscription and/or transcript stability. This study used two experimental a pproaches to test the hypothesis that germ cells regulate transcription of the cathepsin L gene by rat Sertoli cells. We examined this gene because, i n vivo, steady state levels of cath L messenger RNA in Sertoli cells change in a stage-specific manner as the surrounding germ cells progress through the 14 stages of the cycle of the seminiferous epithelium. In the first exp erimental approach, seminiferous tubules at stages VI-VII and stages TX-XII were incubated for 1 h in 4-thiouridine, and the amount of metabolically l abeled cath L messenger RNA was quantified. The results demonstrate that tr anscription of the cath L gene by Sertoli cells is 7-fold higher at stages VI-VII than at stages IX-XII. The second experimental approach examined the ability of germ cells to regulate the activity of cath L reporter construc ts in mature Sertoli cells. Before these studies, we isolated a cath L geno mic clone and demonstrated that this clone contains the transcription start site of the cath L gene expressed by Sertoli cells. Transient transfection analysis then demonstrated that two reporter constructs, containing 244 an d about 2.1 kb of sequence upstream from the transcription start site, had similar activities in mature Sertoli cells. However, germ cells only affect ed the activity of the larger construct in Sertoli cells, which was reduced by 30%. We conclude that ger m cells regulate transcription of the cath L gene by Sertoli cells and that repressive effects of germ cells are mediate d by elements upstream from nucleotide -244 of this gene.