CHARACTERIZATION AND RELATIVE ABUNDANCE OF ALTERNATIVELY SPLICED LUTEINIZING-HORMONE RECEPTOR MESSENGER-RIBONUCLEIC-ACID IN THE OVINE OVARY

Complementary DNA (cDNA) clones encoding the LH receptor (LHR) were recently isolated from pig, rat, mouse, and human testes or ovaries. Many of the LHR cDNAs isolated from these species encoded incomplete and, therefore, possibly inactive forms of the LHR. The four major incomplete cDNAs, designated B, C, D, and E, were due to alternative splicing of the full-length cDNA, designated the A form. Northern analyses of messenger RNA (mRNA) encoding LHR in these species and in sheep revealed multiple mRNA species in ovarian tissue, but were unable to distinguish between the full-length (functional) form and the splice variants. We have used reverse transcription of mRNA, amplification via the polymerase chain reaction, and cDNA sequencing to determine which alternatively spliced mRNA species were present in ovine ovarian follicles and corpora lutes, and ribonuclease protection assays to confirm these results and determine the relative abundance of these splice variants. Ovine LHR cDNAs of the full-length A form, B form, and two novel splice forms, designated F and G, were isolated and sequenced. By using LHR cDNAs that spanned the regions of the gene in which the majority of splicing variation occurred, ribonuclease-protected fragments of different sizes were generated depending on which mRNA species (A-G) were present. It is estimated that the ratios of the steady state mRNA levels of the splice variant B form/full-length A form/G form/F form were 5-3.5:1:1:0.3. The E, C, and D forms were not detected, even when using the sensitive method of reverse transcription-polymerase chain reaction for the latter two forms. The overall level of expression of LHR mRNA was greater in corpora lutea than follicles, but the relative abundance of the splice variants was similar in follicles and corpora lutea.