Fig. 6.

Preferential activity of −7-kb enhancer transgene in corticotropes compared with promoter bias toward melanotropes. A, The different LacZ transgene reporters used to assess activities of POMC promoter, enhancer, or both together, are represented schematically at the top together with the number of transgenic e17.5 pups that express the transgene over the total number of transgenic pups analyzed. Coimmunofluorescence for Tpit (green) and βGal transgene (red) is shown for three different pituitaries harboring each of the three transgenes analyzed. Insets show magnifications of colocalization in anterior lobe. B, Quantitation of βGal transgene reporter expression in AL corticotropes relative to IL melanotropes. The expression of βGal transgenes was scored over the total number of Tpit-positive cells in AL and IL separately, and their ratio is presented for each transgene. For each expressing transgenic embryo, at least four pituitary sections were scored. Pairwise P values were calculated using t test for the enhancer constructs relative to the −480-bp promoter construct. Whereas the −480-bp promoter exhibits a preference for IL melanotrope expression, both reporters containing the enhancer exhibit preference for AL corticotropes.