Characterization of the chicken follicle-stimulating hormone receptor (cFSH-R) complementary deoxyribonucleic acid, and expression of cFSH-R messenger ribonucleic acid in the ovary

Studies were conducted to characterize the chicken (c) FSH receptor (R) cDNA, and to evaluate expression of cFSH-R mRNA in the hen ovary at known stages during follicle development. A total of 2.5 kb of nucleic acid sequence including the complete cFSH-R coding region was isolated by a combination of the reverse-transcription polymerase chain reaction and 5'- and 3'-rapid amplification of cDNA ends techniques. Overall, the nucleic acid sequence homology of the cFSH-R cDNA coding region is 71.8% and 72.2% compared to the rat and bovine FSH-R, respectively, while the deduced amino acid sequence identity for the receptor protein (693 amino acids) is 71.9% and 72.4%, respectively. By comparison, the cFSH-R nucleic acid and amino acid sequences are 60.1% and 49.4% identical to the respective cLH-R sequences. Northern blot analysis detected a single 4.3-kb cFSH-R mRNA transcript, which was selectively expressed in ovarian (granulosa, theca, and stromal) tissues, but not the oviduct, adrenal, liver, muscle, or brain. As the follicle developed from the prehierarchical (6- to 8-mm diameter) to the largest preovulatory (F1 follicle) stage, cFSH-R mRNA levels progressively declined within both the granulosa and theca layers (p < 0.05). Moreover, cFSH-R mRNA levels were lower in whole atretic than in morphologically normal 3- to 5-mm follicles (p = 0.0015). The pattern of cFSH-R mRNA expression within the granulosa layer during follicle development was notably different from that of the recently reported cLH-R, in that cLH-R mRNA levels increase to become readily detectable coincident with dramatically increased steroidogenic capacity during the last few days before ovulation of the follicle. On the other hand, highest levels of cFSH-R mRNA in 6- to 8-mm (prehierarchical) follicles were consistent with a role for the cFSH-R in maintaining the viability of prehierarchical follicles and in initiating granulosa cell differentiation at the time when follicles are selected into the preovulatory hierarchy.