Ontogeny of pro-opiomelanocortin (POMC) gene expression and translated products adrenocorticotrophin (ACTH) and alpha-melanocyte stimulating hormone (alpha-MSH) in the ovine fetal pituitary gland.

Abstract

This study sought to determine the ontogeny of pro-opiomelanocortin (POMC) mRNA by in situ hybridization, and the expression of alpha-melanocyte stimulating hormone (α-MSH) and adrenocorticotrophin (ACTH) by immunohistochemistry,in the ovine fetal pituitary gland. Detection of POMCmRNA, and of ACTH and α-MSH immunoreactivity was first noted at Day 40of gestation in the pars intermedia (PI) and the pars distalis (PD). After Day70, α-MSH immunoreactivity was confined to the PI whereasPOMC mRNA and ACTH immunostaining remained in both thePI and the PD. Increases (P < 0.05) ofPOMC mRNA expression were observed in the PI betweenDays 50-70 and levels then remained constant to Day 141 (term, 145days). In the basal region of the PD, POMC mRNAexpression was high at Day 40, declined (P < 0.01) byDay 50 and then increased progressively to Day 141 of gestation. Theproportion of ACTH-immunopositive cells in the PD also fell from 14% atDay 40 to 11.4% at Day 70 and then increased to 15.3% by Day141. In contrast, neither the level of POMC mRNAexpression nor the percentage of corticotrophs changed in the region of the PDimmediately adjacent to the PI. These data provide evidence for differentialprocessing of POMC in a tissue-specific manner duringearly fetal pituitary development.