Date of this Version
To examine the relationship between the molecular mechanisms underlying ovulation rate and transcriptional regulation of the porcine GnRHR gene, our laboratory has isolated the GnRHR gene promoter from the Control, Index and Meishan lines (McDonald, 2005). Previous work in our laboratory has indicated divergent luciferase activity among reporter vectors containing 5000 bp of 5’ flanking region for the porcine GnRHR gene from all three genetic lines transiently transfected into gonadotrope-derived αT3-1 cells (Fig 1.1; McDonald, 2005). This suggests differential mechanisms involved in the transcriptional regulation of the GnRHR gene among pig strains.
Additionally, our laboratory identified a single base alteration between the Meishan and homologous Control/Index promoters located at -1235 bp of 5’ flanking region. This single bp substitution allows for the binding of the p65 and p52 subunits of NF-κB and an Sp1-like protein in the Meishan promoter, events that are absent in the Control/Index promoters (McDonald, 2005). Transient transfections with vectors containing block replacement mutations of these binding sites, either singly or in combination, decreased luciferase activity by approximately 25%. Despite a significant reduction in promoter activity, however, luciferase values were not reduced to levels exhibited by reporter constructs containing the full-length Control promoter. This suggests that other unidentified element(s) within the Meishan proximal promoter contribute to its enhanced activity. Therefore, we need to identify additional elements and transcription factors that contribute to the line-specific activity of the porcine GnRHR gene.