Cloning, characterization and expression of the pepsinogen C from the golden mandarin fish Siniperca scherzeri (Teleostei: Perciformes)

Abstract

Pepsinogens are precursors of pepsins, which are gastric digestive proteinases that degrade food proteins into peptides. In the study reported here, the cDNA and its corresponding genomic DNA of the golden mandarin fish (Siniperca scherzeri, Perciformes) pepsinogen C (PGC) were cloned and sequenced. The golden mandarin fish PGC gene was deduced to have nine exons and eight introns, a structure similar to the PGCs of other vertebrates. The full-length cDNA was found to contain a 37-bp 5′-untranslated region, a 1,164-bp open reading frame, and a 304-bp 3′-untranslated region and the PGC protein to consist of a signal peptide, an activation segment, and a pepsin moiety. A sequence analysis revealed that pairwise sequence similarities of PGC proteins are around 70% between golden mandarin fish and other vertebrate groups, and around 90% within the fish group. A comparison of vertebrate PGC protein sequences revealed two motifs. One was in the activation segment that occurred only in the mammal and avian PGCs, suggesting that PGCs active in homeotherms (mammal and avian) have different activation mechanisms than those in poikilotherms (amphibian and fish). The second was in the pepsin moiety that occurred only in fish, suggesting the primitive position of fish among vertebrates. PGC mRNA is mainly expressed in the stomach and esophagus and at much lower levels in the skin and muscle. Taken together with results reported from other studies, the results reported here will lead to a better understanding of the molecular mechanisms of fish digestive physiology and the evolution of fish pepsinogen genes.