Characterization of the agr2 gene, a homologue of X. laevis anterior gradient 2, from the zebrafish, Danio rerio.

We characterized a zebrafish (Danio rerio) anterior gradient 2 homologue (agr2) gene. agr2 contains an open reading frame of 513bp encoding 171 amino acids. Deduced amino acid sequence comparison showed that the zebrafish agr2 protein shares high (80-89%) amino acid sequence similarity with those homologues of anterior gradient 2 (HAGR2, MAgr2, Tagr2, and Sagr2) from the human, mouse, pufferfish, and Atlantic salmon, while sharing less (67-71%) sequence similarity with those anterior gradient 2 genes (XAG-2, XAG-1, XAgr2, MAgr3, and HAGR3) from Xenopus laevis, mouse, and human. Both phylogenetic and syntenic analyses indicate that zebrafish agr2 is the orthologue of human AGR2 and mouse Agr2 genes. Whole-mount in situ hybridization indicated that zebrafish agr2 is expressed in most organs, such as epidermis, olfactory bulbs, otic vesicles, pharynx, esophagus, pneumatic duct, swim bladder, and intestine, which contain mucus-secreting cells. Moreover, semi-quantitative RT-PCR demonstrated agr2 is expressed in the gill, pharynx/esophagus, swim bladder/pneumatic duct, and intestine in the adult fish. In contrast, Xenopus anterior gradient 2 homologues are mainly expressed in ectoderm-derived organs including the cement gland and otic vesicles, while human and mouse anterior gradient 2 orthologues are mainly distributed in endoderm-derived organs including the trachea, lungs, stomach, intestines, and colon.