Sexually dimorphic DNA demethylation inthepromoter oftheSlp (sex-limited protein) geneinmouseliver

MouseSlp, aduplicate ofthefourth comple- mentcomponent (C4) gene, exhibits EDTA-independent com- plement activity withahepatic expression thatismalespe- cific. Toprovide anunderlying mechanism forthemale- specific expression, wehaveanalyzed thepromoter activity of thevarious 5'-flanking sequences andCpGdemethylation of theSlpgene. Transient transfections using HepG2cells indi- catethattheelement TTCCGGGC(nt-124to-117)regu- lates thepromoter activity. Moreover, CpGatposition -121 ofthis regulatory element isdemethylated toamuchhigher degree inmales thaninfemales. Thissexually dimorphic DNA demethylation isconsistent withthemale-specific expression oftheSlpgeneinDBA/2males. Theregulatory element binds tothedifferent TTCCGGGC-specific nuclear proteins de- pending onthemethylation oftheCpGsite. Incontrast, the corresponding CpGatposition -119oftheC4gene, whichis expressed inbothmales andfemales, isdemethylated atequal andhighlevels inbothsexes. We therefore propose thatthe DNAdemethylation andmethylation-sensitive transcription