Expression of two proopiomelanocortin mRNAs in the islets of Langerhans of neonatal rats.

Proopiomelanocortin-(POMC) derived peptides have been found in pituitary and in nonpituitary tissues including the endocrine pancreas. However, only a truncated 800-base POMC-like mRNA is demonstrable in most nonpituitary tissues. The functional relevance of this RNA is doubtful, because it lacks the sequences of translation initiation and signal peptide (exon 1 and 2). Recently we have demonstrated the truncated POMC-like mRNA in pancreatic islets. Using PCR techniques in this paper we prove the existence of a full-length POMC mRNA in this tissue. This RNA contains the sequences of exon 1 and 2, as shown by Southern blot technique and by sequencing parts of the PCR products. We suppose that this RNA is the source of the POMC peptides in islets despite of its small amount.