EXPRESSION AND DISTRIBUTION OF ANDROGEN-BINDING PROTEIN SEX HORMONE-BINDING GLOBULIN IN THE FEMALE RODENT REPRODUCTIVE-SYSTEM/

Androgen-binding protein (ABP)/sex hormone-binding globulin gene expre ssion has been described in the rat testicular Sertoli cell and brain, The extracellular protein is thought to regulate the bioavailability of sex steroids, but may have a more complex function as a hormone or growth factor, Transgenic mice were developed with a 5.5-kilobase (kb) rat DNA fragment containing the ABP gene with all 8 exon sequences an d 1.5 kb upstream of the transcription start site. Expression of the g ene was observed in the testis and brain, but not in other examined ti ssues of the transgenic mice, In this paper we describe ABP gene expre ssion in ovaries of transgenic mice that contain the rat gene; a lower level of ABP mRNA was also detected in the transgenic uterus. Norther n blot analysis also detected ABP mRNA in rat ovary. The hybridizing s pecies in the rat and transgenic mouse ovaries and uteri were the size of testicular ABP mRNA (1.7 kb). Except in the transgenic mouse brain , there was no detectable hybridizing RNA in the other transgenic tiss ues examined. The plasma, ovary, and uterus of the transgenic mice all contained elevated ABP (dihydrotestosterone [DHT]-binding) activities as compared to those of wild-type littermates; other wild-type and tr ansgenic tissues were negative for DHT binding. Immunohistochemistry r evealed increased immunoreactivity in the transgenic oviduct and uteru s, but not the ovary, in the oviduct, the intense immunoreactivity was associated with the epithelium, whereas in the uterus it was primaril y associated with the luminal epithelium and glands. Phenotypic abnorm alities of the homozygous transgenic mice included reduced fecundity r esulting in small litters, We conclude that ABP may function in the fe male reproductive system to increase the local concentrations of sex s teroids or to sequester them in key target organs, Studies in the fema le will aid in elucidating the functions of ABP in male and female rep roduction.