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A novel membrane guanylyl cyclase (membrane GC), OIGC8, was identified in the medaka fish Oryzias latipes by the isolation of full-length cDNA (4958 bp) and genomic DNA (14.3 kbp) clones. Phylegenetic analysis indicated that OIGC8 does not belong in any known vertebrate membrane GC subfamily. OIGC8 consists of an extracellular domain (214 residues), a transmembrane segment (19 residues), and an intracellular protein kinase-like domain (284 residues) and a cyclase catalytic domain (228 residues), although the extracellular domain is about half the length (around 450 residues) of other known vertebrate membrane GCs, OIGC8 transiently expressed in COS-7 cells exhibited only basal guanylyl cyclase activity. None of the known ligands (rat ANP, BNP CNP, and C-ANF) and various medaka fish tissue extracts, which activated OIGC1, OIGC2, and OIGC7 differentially, stimulated basal activity, suggesting that OIGC8 is an orphan receptor. The OIGC8 gene consists of 24 exons and exists as a single copy on the medaka fish genome. Northern blot hybridization showed that a 5 kb-OIGC8 mRNA was expressed in the kidney and the testis at a high level and a 3.3 kb-OIGC8 mRNA was expressed only in the brain. The RNase protection, RNA Ligase-Mediated Rapid Amplification of cDNA Ends (RLM-RACE), and reverse transcription-polymerase chain reaction (RT-PCR) analyses demonstrated that the 3.3 kb-OIGC8 mRNA detected in the brain is transcribed from the second transcription initiation site, and contains an intron at the position prior to the catalytic domain, the translation product of which appears to be a protein lacking the cyclase catalytic domain. [ABSTRACT FROM AUTHOR]

Presents information on a study which reported the complete nucleotide sequence and the expression of a complementary DNA clone in the egg jelly of the sea urchin Diadema setosum. Materials and methods of the study; Structural characterization of Diadema setosum membrane guanylyl cyclase; Immunological characterization.

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