Proopiomelanocortin gene expression during pig pituitary and brain development

The expression of proopiomelanocortin (POMC) mRNA, which plays an important role in neural, endocrine, neuroendocrine and immune systems, was studied by in situ hybridization during the development of pituitary in the domestic pig. The POMC gene was activated as early as fetal day 30 (E30). The signal for POMC mRNA in the anterior lobe progressively increased from E30 to E80 and then remained at relatively constant level. In contrast, POMC transcripts in the intermediate lobe first appeared at E40 and steadily increased during development. POMC transcripts in the brain were first found at E40 and were scattered in the arcuate nucleus (AN) and nucleus medialis thalami (NMT). At E50 the extra-pituitary POMC mRNA was located not only in the AN and NMT but also in the fasciculus tegmenti and entorhinal cortex. In the posterior lobe, no signal was detected. The specific pattern of expression of the pig POMC gene in the pituitary and in specific regions of the central nervous system suggests important roles for POMC in fetal development. These results also suggest that POMC is excellent for studying the expression and regulation of pituitary hormone genes because of its tissue-specific regulation and developmental pattern.