ONTOGENY OF FOLLICLE-STIMULATING-HORMONE RECEPTOR GENE-EXPRESSION IN THE RAT TESTIS AND OVARY

The ontogeny of the follicle-stimulating hormone (FSH) receptor (R) gene expression was studied in the rat testis and ovary between day 12.5 or 14.5 of fetal life (f), respectively, and adulthood. In Northern blots hybridized with a cRNA probe corresponding to a part of the extracellular domain of the FSHR, specific hybridization to testicular RNA was detected from day f18.5, and to ovarian RNA from postnatal day 7 onwards. The main transcripts in the testis were at all ages 7.0 kb and 2.5 kb in;size. In the ovary, the main transcript was always 2.5 kb in size. In order to increase the sensitivity of mRNA detection, the FSHR gene expression was also analyzed using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique with primer pairs corresponding to the near full-length FSHR mRNA or to its extracellular domain. The specificity of the PCR products was verified by Southern hybridization using a nested P-32-labeled cDNA probe. The results indicated that the expression of the extracellular domain of the FSHR was first detected on day f14.5 in the testis and on day f20.5 in the ovary. The full-length mRNA appeared in both sexes 2 days later, which is in agreement with earlier measurements of appearance of FSHR binding in the rat testis (day f17.5) and ovary (day 3 post partum). In situ hybridization using an antisense cRNA probe for FSHR demonstrated that, as early in development as specific hybridization was detected, it was confined to the Sertoli cells in the testis and to granulosa cells in the ovary. When compared with the developmental onset of the LHR gene expression (our earlier data), a major difference was observed in the ovary; the message encoding the extracellular LHR domain appeared >10 days earlier than that corresponding to the full-length LHR message. In the case of mRNAs for the testicular LHR, and for FSHR of both sexes, the difference between the developmental appearance of the truncated and full-length RNA forms was only 2 days.