Promoter function of different lengths of the murine luteinizing hormone receptor gene 5 '-flanking region in transfected gonadal cells and in transgenic mice

The purpose of these studies was to explore the sex- and tissue-specific ex pression of the LH receptor (LHR) gene. Fusion genes containing three diffe rent lengths of the 5 ' -flanking region of the mouse LHR gene (7.4 kb, 2.1 kb, and 173 bp), beta -globin intron, and the beta -galactosidase (beta -G AL) reporter gene were constructed. Function of these fusion genes [LHR (7. 4 kb)/beta -GAL, LHR (2.1 kb)/beta -GAL, and LHR (173 bp)/beta -GAL] was st udied in vitro and in vivo. beta -GAL expression was higher in transfected mouse Leydig (mLTC-1) than in granulosa (KK-1) tumor cells with all three c onstructs. The shortest LHR (173 bp)/beta -GAL construct showed the highest level of beta -GAL, expression in both cell types. beta -GAL expression wa s clearly suppressed with the 2.1-kb promoter and was nearly undetectable w ith the 7.4-kb construct. In transgenic mice, all three constructs directed beta -GAL expression to adult Leydig cells, displaying decreasing intensit y with increasing promoter length. Unexpectedly, beta -GAL expression was a lso found in elongating spermatids, but not in fetal Leydig cells. There wa s no expression in any ovarian cell type with the three constructs used, ex cept that one of five mouse lines with the LHR(7.4 kb)/beta -GAL construct expressed beta -GAL in their thecal cells. Two lines transgenic for the 7.4 - and 2.1-kb promoter constructs each directed high beta -GAL expression to the brain, with higher intensity in 7.4-kb lines. All promoters directed e xpression to the pituitary gland, some faintly to the adrenal gland. Northe rn hybridization analysis of the beta -GAL transcripts in Leydig cells reve aled that the 173-bp promoter mainly gave rise to the full-length beta -GAL messenger RNA, whereas the 2.1- and 7.4-kb promoters mainly induced transc ription of truncated beta -GAL messages. This suggests that the 5 ' -flanki ng region, upstream of -173, determines the formation of splice variants of the structural gene to be transcribed. The present findings in transgenic mice provide in vivo evidence for basal transcriptional activity of the fir st 173 bp upstream of the LHR translation initiation codon. In conclusion, the promoter function of the mouse LHR 5 ' -flanking region is tissue, age, and sex specific. The sequence upstream of the basal promoter determines e xtragonadal LHR expression as well as the alternate splicing of its message . The promoter sequences directing LHR expression to fetal Leydig cells and ovary reside outside the 7.4-kb 5 ' -flanking region and remain to be iden tified.