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Expression of the full-length and alternatively spliced equine luteinizing hormone/chorionic gonadotropin receptor mRNAs in the primary corpus luteum and fetal gonads during pregnancy

Unité de Physiologie de la Reproduction et des Comportements, UMR 6175 INRA-CNRS-Université F. Rabelais de Tours-Haras Nationaux, 37 380 Nouzilly, France

Correspondence should be addressed to Marie Saint-Dizier, Equipe Hypophyse, Station Physiologie de la Reproduction et du Comportement, Institut National de la Recherche Agronomique (INRA), 37 380 Nouzilly, France; Email: dizier{at}tours.inra.fr

The full-length equine luteinizing hormone/chorionic gonadotropin (LH/CG) receptor (eLH/CG-R_A) cDNA and two alternatively spliced isoforms (eLH/CG-R_B,C) were isolated from luteal tissue and characterized using a combination of reverse transcription-polymerase chain reaction (RT-PCR) and 5'-rapid amplification of cDNA ends. The 680-amino acid full sequence of eLH/CG-R_A displayed 87–92% homology with other mammalian LH/CG-Rs. The eLH/CG-R_B and eLH/CG-R_C cDNA isoforms were truncated from the 3'-end of exon X: eLH/CG-R_B spliced out of frame into the last exon whereas eLH/CG-R_C contained an in-frame stop codon within a divergent sequence. Consequently, both eLH/CG-R_B and eLH/CG-R_C cDNA isoforms encoded putative proteins without transmembrane and intracellular domains.

In order to study the responsiveness of the primary corpus luteum (CL) and fetal gonads to eCG, the expression of eLH/CG-R mRNAs was examined by RT-PCR and Northern blot analysis during early and mid-pregnancy. All three eLH/CG-R cDNA isoforms (eLH/CG-R_A,B,C) were expressed from day 14 to day 83 of pregnancy in the primary CL and from day 44 to day 222 in fetal gonads. Interestingly, the primary CL at days 89 and 151 expressed only truncated eLH/CG-R cDNA isoforms. The relative values of Northern hybridized major 7, 5.7, 3.9 and 1.8 kb eLH/CG-R mRNA transcripts tended to decrease in the primary CL whereas the unique major 1.8 kb eLH/CG-R mRNA was steadily expressed in fetal gonads during pregnancy. These results show that the expression of eLH/CG-R mRNAs occurs in the fetal gonads before ceasing in the primary CL and suggest that eCG may be involved in the gradual transition from a luteal to a feto-placental output of steroids during equine pregnancy.

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				M. Saint-Dizier, F. Foulon-Gauze, F. Lecompte, Y. Combarnous, and M. Chopineau Cloning and functional expression of the equine luteinizing hormone/chorionic gonadotrophin receptor J. Endocrinol., December 1, 2004; 183(3): 551 - 559. [Abstract] [Full Text] [PDF]