Three different turkey luteinizing hormone receptor (tLH-R) isoforms II: Characterization of differentially regulated tLH-R messenger ribonucleic acid isoforms in the ovary

We have recently characterized three different, alternatively spliced, part ial turkey LH receptor (tLH-R) cDNA isoforms by the combination of reverse transcription-polymerase chain reaction (RT-PCR) and 5'- and 3'-rapid ampli fication of cDNA ends. The first cDNA (intact form: tLH-R-intact) showed 98 % and 72-75% similarity with chicken and mammalian LH receptor sequences, r espectively. The other two cloned cDNA isoforms (insertion and truncated fo rms: tLH-R-insert and tLH-R-trunc) could encode truncated soluble protein i soforms that lack the transmembrane region. Northern blot analysis detected two transcripts of 3.0 kilobases (kb) (tLH- R-intact) and 1.5 kb (tLH-R-trunc) in the turkey ovary but could not discri minate a third alternatively spliced transcript (tLH-R-insert) due to the s mall 86-base pair difference in the size range of approximately 3.0-kb mRNA s. But with the combination of RNase protection assay, RT-PCR, and Northern blot analysis, three different alternatively spliced tLH-R mRNA isoforms w ere quantified. Differential expression of the tLH-R mRNA isoforms was demo nstrated in ovarian stromal tissue during various reproductive stages and i n the theca and granulosa layer through follicular development. To gain a b etter understanding of the physiological significance of the three differen t tLH-R isoforms, fetal RNA from the theca layer through follicular develop ment after prolactin (PRL) treatment was analyzed by RT-PCR. PRL treatment for 8-14 days significantly increased the steady-state levels of total tLH- R mRNAs, including tLH-R-insert and tLH-R-trunc mRNAs, compared to those in nontreated controls. In contrast, the steady-state levels of tLH-R-intact mRNA during the same period was not significantly changed when compared to that in nontreated controls. The present study shows that tLH-R transcripts are alternatively spliced in a tissue-specific manner in the turkey and that the mechanism may, in part , be controlled hormonally.