Proenkephalin A is expressed in mesodermal lineages during organogenesis

Proenkephalin A (PEA) encodes several neuropeptides with an opioid activity, as well as other peptides with as yet unknown functions. As an initial step toward finding possible roles for PEA gene products in non‐neuronal tissues, we have determined sites of PEA expression during mouse embryonic development, employing in situ hybridization. We report here the unexpected observation that in addition to its abundance in brain, PEA RNA is expressed in non‐differentiated mesodermal cells of diverse lineages in the process of their development into several adult tissues and organs; it drops to undetectable levels upon terminal differentiation of these tissues. In a particular example of differentiating mesoderm, the developing kidney, the transient expression of PEA mRNA and of its encoded peptide Met‐enkephalin was demonstrated by both in situ and Northern blot hybridizations, as well as by a radioimmunoassay. These findings suggest a novel role for PEA‐derived peptide(s) in mesoderm growth or differentiation during organogenesis.