Novel evolutionary lineages of the invertebrate oxytocin/vasopressin superfamily peptides and their receptors in the common octopus (Octopus vulgaris).
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CTR2 and OPR cloned from O. vulgaris as additional OT/VP superfamily receptors
"In the present study, we have identified an additional CTR, CTR2, and a novel OP receptor, OPR."
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CTR2 specifically activated by cephalotocin in Xenopus oocyte assay
"CTR2 and OPR expressed in Xenopus oocytes induced calcium-mediated inward chloride current in a CT- and OP-specific manner respectively."
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CTR2 mRNA mainly in peripheral tissues (branchia, vas deferens, testis)
"CTR2 mRNA was mainly distributed in peripheral tissues, although CT did not induce contractile activities on the smooth muscles of several Octopus tissues."
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CTR2 proposed to mediate ammonia excretion via branchia
"Arg-vasotocin caused prominent transient increases in urea excretion from branchia of toadfish, and Arg-vasotocin receptor mRNA was expressed in the branchia. Furthermore, ammonia is excreted from the branchia of octopus. Consequently, it can be presumed that CT is involved in the control of ammonia excretion via CTR2 expressed in the branchia."
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CTR2 proposed to mediate steroid hormone production/secretion via vas deferens and testis
"These findings, combined with the abundant expression of CTR2 in the vas deferens and testis, support a notion that CT participates in production and/or secretion of the steroid hormones via CTR2."
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Invertebrate OT/VP receptors not activated by vertebrate OT/VP peptides
"These invertebrate receptors are not activated by vertebrate OT/VP family peptides."
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Ligand-receptor selectivity depends on peptide residues at positions 2-5
"The amino acid residues of OP and CT at positions 2-5 were presumed to play crucial roles in the binding selectivity to their receptors."
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Key vertebrate OT/VP binding residues are conserved in CTRs but not in OPR
"Several regions and residues, which are requisite for binding of the vertebrate OT/VP receptor family with their ligands, are highly conserved in CTRs, but not in OPR."
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Ligand-receptor selectivity in octopus evolved through a different mechanism than vertebrates; vertebrate selectivity depends on polarity of residue 8, while octopus OP and CT share isoleucine at position 8 and selectivity depends on residues 2-5
"the ligand-receptor selectivity were established through different evolutionary lineages from those of their vertebrate counterparts"
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CTR2, CTR1, and OPR genes all have a conserved intron between TM6 and TM7 domains, consistent with common ancestry with vertebrate OT/VP receptor genes
"OPR, CTR1, and CTR2 genes, similar to all the vertebrate receptors, have an intron between the sixth and seventh TM domains"
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CT and OP genes evolved through gene duplication from a common ancestral gene, mirroring the OT/VP duplication in vertebrates
"the CT and OP genes, similar to the OT/VP family, evolved through duplication"