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

The ontogeny of the follicle-stimulating hormone (FSH) receptor (R) ge ne 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 b lots hybridized with a cRNA probe corresponding to a part of the extra cellular domain of the FSHR, specific hybridization to testicular RNA was detected from day f18.5, and to ovarian RNA from postnatal day 7 o nwards. 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 i n size. In order to increase the sensitivity of mRNA detection, the FS HR gene expression was also analyzed using the reverse transcriptase-p olymerase chain reaction (RT-PCR) technique with primer pairs correspo nding to the near full-length FSHR mRNA or to its extracellular domain . The specificity of the PCR products was verified by Southern hybridi zation using a nested P-32-labeled cDNA probe. The results indicated t hat the expression of the extracellular domain of the FSHR was first d etected 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 agre ement with earlier measurements of appearance of FSHR binding in the r at testis (day f17.5) and ovary (day 3 post partum). In situ hybridiza tion using an antisense cRNA probe for FSHR demonstrated that, as earl y in development as specific hybridization was detected, it was confin ed to the Sertoli cells in the testis and to granulosa cells in the ov ary. When compared with the developmental onset of the LHR gene expres sion (our earlier data), a major difference was observed in the ovary; the message encoding the extracellular LHR domain appeared >10 days e arlier 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 f ull-length RNA forms was only 2 days.