Identification of a novel retrovirus expressed in rat Sertoli cells and granulosa

Differential display reverse transcriptase-polymerase chain reaction (DDRT- PCR) was used to identify a novel retrovirus, designated SC1, that is expre ssed at high levels in rat granulosa cells and prepubertal Sertoli cells. T he initial DDRT-PCR screen was performed using RNA from cultured prepuberta l rat Sertoli cell, liver, and brain samples. SC1 was detected in the prepu bertal rat Sertoli cell samples but not in those from liver and brain. SCI cDNA was 6 kilobases in length and contained regions encoding for the gag, pol, and env retroviral proteins. Northern blot analysis failed to detect e xpression of the SC1 gene in total RNA isolated from adult brain, heart, sp leen, lung, liver, skeletal muscle, kidney, prostate, and epididymis. Simil arly, Northern blot analysis of testes from rats at various ages of develop ment showed that high-level expression of the SCI gene was limited to prepu bertal testis samples. In situ hybridization analysis localized the SCI mRN A to the seminiferous tubules of prepubertal testes and at a much lower lev el in Sertoli cells of adult testes. Northern blot analysis of total RNA is olated from Sertoli cells from 20-, 27-, and 35-day-old rat Sertoli cells a nd type A spermatogonia, pachytene spermatocytes, and round spermatids show ed expression of the SCI gene to be restricted to 20- and 27-day-old Sertol i cells, with no expression detected in germ cells. Furthermore, Northern b lot analysis also showed expression of the SCI gene in rat ovaries, and the level of expression was affected during eCG/hCG-induced ovulation. Express ion of SCI mRNA was localized by in situ hybridization of eCG-treated ovari es to the granulosa cell layer in developing follicles. Southern blot analy sis showed SC1 to be endogenous in the rat and absent in mouse and human ce ll genomes. Transient transfection assays using the SC1 promoter region sho wed high promoter activity in MSC-1 and cultured prepubertal rat Sertoli ce lls, and no activity in 3T3 or MCF-7 cell lines.