Pregnancy-specific beta 1-glycoprotein messenger ribonucleic acid and immunoreactive protein in the rat testis

Human pregnancy-specific beta 1-glycoprotein (PS beta G) is synthesized in large quantities by syncytiotrophoblasts of the placenta. Recent studies using a partial cDNA of PS beta G isolated from human term placenta detected the presence of mRNA highly homologous to placental PS beta G in a number of extraplacental tissues, including human and rat testis. The present study determined in the rat that the amount of PS beta G mRNA based on percentage of total tissue RNA was greatest in the testis of mature rats, followed by senescent and prepubertal rats. In experiments using rats with testicular feminization syndrome (Tfm) which exhibit end-organ insensitivity to androgen stimulation, slot blot analysis of testicular RNA showed reduced levels of PS beta G mRNA in Tfm rats compared to normal rats. Northern blot analysis of rat testicular RNA probed with a human placental PS beta G cDNA demonstrated the presence of a single mRNA species of 1.65 kilobases. Subsequent studies investigated whether proteins immunologically similar to PS beta G were present in the testes from normal and Tfm rats. The rat testes were perfused with fixative, and sections from paraffin-embedded tissues were treated with rabbit anti-human PS beta G, followed by the avidin-biotin-peroxidase complex. Testes from the normal rat showed intense immunostaining in late spermatids (steps 16, 17, 18, and 19 of spermiogenesis), residual bodies, as well as cytoplasm of Leydig cells. Spermatozoa within the epididymis also demonstrated intense immunolabeling. Paraffin sections of the testes from the Tfm rat showed light diffuse cytoplasmic immunostaining in cells of the seminiferous tubules. Since spermiogenesis does not proceed normally, and no spermatids were seen, it was not possible to accurately stage the seminiferous tubules of the Tfm rat. The Leydig cells of the Tfm testes stained intensely, however, as was observed in the testes of the normal rat. These data suggest that the rat may provide an animal model for the investigation of the biological function and regulation of PS beta G in the testis.