Molecular cloning and functional characterization of a vasotocin receptor subtype that is expressed in the shell gland and brain of the domestic chicken

In chickens, oviposition is correlated with increased plasma levels of the neurohypophysial hormone vasotocin, and vasotocin stimulates contraction of uterine strips in vitro. A gene encoding a vasotocin receptor subtype that we have designated the VT1 receptor was cloned from the domestic chicken. The open reading frame encodes a 370-amino acid polypeptide that displays s even segments of hydrophobic amino acids, typical of guanine nucleotide-pro tein-coupled receptors. Other structural features of the VT1 receptor inclu de two potential N-linked glycosylation sites in the extracellular N-termin al region, a conserved aspartic acid in transmembrane domain 2 that is foun d in nearly all guanine nucleotide-protein-coupled receptors, and two poten tial protein kinase C phosphorylation sites in the third intracellular loop and C-terminal tail. Expressed VT1 receptors in COS7 cells bind neurohypop hysial hormones with the following rank order of potency: vasotocin congrue nt to vasopressin > oxytocin congruent to mesotocin > isotocin. In addition , the expressed VT1 receptor mediates vasotocin-induced phosphatidylinosito l turnover and Ca2+ mobilization. In the chicken, expression of VT1 recepto r gene transcripts is limited to the shell gland (uterus) and the brain. Th us, the VT1 receptor that we have cloned may mediate contractions of the sh ell gland during oviposition and activate reproductive behaviors known to b e stimulated by vasotocin in lower vertebrates.