cDNA deduced procionin. Structure and expression in protochordates resemble that of procholecystokinin in mammals

Abstract

Using an improved 3' RACE (PCR) amplification system containing oligonucleotide primer with an inosine at ambiguous codon positions and inverse PCR to amplify the 5' ends, we have isolated and characterized cDNA clones which encode cionin, a protochordean homologue of the mammalian hormones, cholecystokinin (CCK) and gastrin. The full-length cloned cDNA of 510 bp encoded a 128 amino acid preprocionin. Reverse transcription-PCR and subsequent cDNA cloning revealed that cionin mRNA is expressed in both the neuronal ganglion and the gut of the protochordate Ciona intestinalis. The primary structure of procionin resembles that of proCCK more than that of progastrin. Sequence-specific immunochemical analysis showed that the cionin gene is expressed also at peptide level in both the gut and the neural ganglion. The neuronal processing of procionin is, however, more complete both with respect to carboxyamidation and tyrosine O-sulfation. Hence, the tissue-specific expression of the cionin gene in Ciona intestinalis resembles that of the CCK gene in mammals.