Bombesin Receptor Gene Expression in Rat Embryos: Transient GRP-R Gene Expression in the Posterior Pituitary

Bombesin-like peptides can stimulate growth of cultured cells derived from ectoderm, endoderm, or mesenchyme and act as autocrine growth factors in some lung carcinoma cell lines. Recently, cDNA clones for two mammalian bombesin receptors (BN-R), gastrin-releasing peptide receptor (GRP-R) and neuromedin B receptor (NMB-R), were characterized and shown to be present in distinct regions of the central nervous system at birth. To determine whether the spatial and/or temporal expression of BN-R genes correlated with tissue-specific or organ-specific developmental events, the prenatal distribution of GRP-R and NMB-R mRNAs were compared by in situ hybridization histochemistry. The differential expression of these two BN-R genes was striking. From early embryonic stages, GRP-R mRNA was expressed in various organs, including nervous, urogenital, respiratory, and digestive systems. In contrast, NMB-R gene expression was detected at later embryonic stages and the distribution of expression was much more limited. In most tissues, after onset of expression, both receptor mRNAs showed a steady increase in expression throughout development. However, transient expression of GRP-R mRNA was seen in the posterior pituitary. Intense GRP-R labeling of posterior pituitary cells was seen from E12 to E20, but at birth, GRP-R mRNA levels were undetectable. These results suggest that (a) two BN-R subtypes mediate independent functions during development, (b) ontogenesis of multiple organs may involve GRP-R mediated events, and (c) GRP-R gene expression is involved in differentiation/development of the pituitary gland.