Sequence analysis of cDNA and genomic DNA, and mRNA expression of the medaka fish homolog of mammalian guanylyl cyclase C

We isolated the cDNA and genomic DNA encoding a membrane guanylyl cyclase o f medaka fish (designated as OlGC6), and determined their complete nucleoti de sequences. The open reading frame for OlGC6 cDNA predicted a protein of 1,075 amino acids. Phylogenetic analysis indicated that OlGC6 is a member o f the enterotoxin/guanylin receptor family, We also determined the partial genomic structure of the gene of another membrane guanylyl cyclase of medak a fish, OlGC2, which is a member of the natriuretic peptide receptor family . The intron positions relative to the protein-coding sequence are highly c onserved in the intracellular domains of OlGC6, OlGC2, mammalian GC-A, and GC-E. Despite their divergent primary structures, some intron positions als o seem to be conserved in the extracellular domains of different membrane g uanylyl cyclase genes. Northern blot analysis demonstrated that an OlGC6 tr anscript of 3.9 kb is only present in the intestine, while reverse transcri ption (RT)-PCR analysis demonstrated that the OlGC6 transcript is present i n the kidney, spleen, liver, pancreas, gallbladder, ovary, testis, brain, a nd eye. RT-PCR also demonstrated that OlGC6 is only expressed zygotically a nd that transcripts are present from 1 day after fertilization, i.e. long b efore the intestinal tissues begin to develop.