Effects of Transfected Human and Mouse SRY/Sry Genes upon the Expression of Hypothetical SRY-Cascade Genes in Cultured Mouse Sertoli Cell Line, TM-4

In mammals, the SRY (the sex determining region on the Y; Sry in the mouse) gene is responsible for the function of TDF (testis determining factor; Tdy in the mouse) locus, and plays a key role in the sex determination. In the mouse, the Sry open reading frame (ORF) is flanked at either end by a large inverted repeat, causing the formation of untranslatable circular transcripts; the linear transcripts have so far been known to be expressed only in the genital ridge between 10.5 and 12.5 d.p.c. In past attempts to examine the effects of expression of Sry exogenously introduced into cultured cells, the transfected Sry generated only the circular transcripts. In our experiments, cells from a cultured mouse Sertoli cell line, TM-4, which do not express endogenous Sry, were transfected with either human SRY or mouse Sry DNA where the inverted repeats responsible for the formation of circular transcripts were deleted. The expression of linear Sry transcripts was confirmed in the Sry-transfected TM-4 cell lines (TMHm series). Curiously, in TMHm cells, the gene coding for P450 aromatase (P450arom) was expressed, while P450arom was not expressed in the non-transfected TM-4 cells. No expression of P450arom was induced in the TM-4 cells transfected with the human SRY (hSRY) DNA. Although WT-1 promoter has been shown to possess a SRY binding motif, no evidence for the Sry- or hSRY-induced WT-1 expression was obtained in the transfected cell lines of either TMHm or TMHh series. MIS, another putative target gene of Sry, is expressed in non-transfected TM-4 cells, confirming the previous reports indicating that Sry expression is not a prerequisite for the MIS expression.