CHARACTERIZATION OF A CHICKEN LUTEINIZING-HORMONE RECEPTOR (CLH-R) COMPLEMENTARY DEOXYRIBONUCLEIC-ACID, AND EXPRESSION OF CLH-R MESSENGER-RIBONUCLEIC-ACID IN THE OVARY

Studies were conducted to characterize the chicken ovarian LH receptor (cLH-R) cDNA and to evaluate expression of cLH-R mRNA in follicles at different stages of development. A total of 1.89 kb of nucleic acid s equence corresponding to the cLH-R (1.79 kb of the predicted coding re gion) was isolated by a combination of reverse transcription-polymeras e chain reaction and cDNA library screening techniques. Also of intere st was the finding that two of three positive clones isolated from the hen ovarian cDNA library contained an 86-bp insert located in the ext racellular domain within 69 bp of the putative transmembrane domain. T his insert contains an inframe TCA stop codon, suggesting that an alte rnatively spliced transcript results in translation of a truncated pro tein corresponding to the extracellular domain of the cLH-R. Consideri ng all protein domains thus far characterized, the deduced amino acid sequence of the cLH-R shares 73.2% and 74.2% identity with the rat and porcine LH-R sequences, respectively, with highest homology occurring within the seven transmembrane spanning regions (86-88% identity vs. mammalian sequences). Northern blot analysis determined that cLH-R mRN A levels in the theca layer tend to increase through follicle developm ent to the second largest (F2) preovulatory follicle (p = 0.084), and to decrease in the largest preovulatory (F1) follicle (p < 0.02 vs, F2 ). By comparison, cLH-R mRNA levels are nondetectable (by Northern blo t analysis) in granulosa cells from prehierarchal (3-8-mm diameter) fo llicles. Constitutive expression of cLH-R mRNA in granulosa cells is f irst detectable at the 9-12-mm diameter stage of follicle development, and levels are Further increased in cells from large preovulatory (F1 , F2, and F3) follicles (p < 0.01 vs. 9-12-mm stage). Collectively, th ese results are consistent with previous observations that granulosa c ells from prehierarchal follicles fail to produce cAMP or steroids in response to short-term incubation with ovine LH, in vitro, and that gr anulosa cells acquire LH responsiveness only subsequent to follicle se lection into the rapid growth phase.