Molecular cloning of prolactin receptor of the Peking duck

Prolactin receptor (PRLR) cDNA of Peking duck was cloned using reverse transcription-PCR methodology (GenBank accession no. EF502054). The duck PRLR (dPRLR) cDNA contains 2,439 bp including the ATG start codon and TAA stop that encodes 832 amino acid residues. The putative receptor protein had 2 strong hydrophobic stretches: one was the signal sequence in N-terminal region and the other was the single transmembrane region of 24 amino acid residues in the central portion. Excluding the signal sequence, the mature dPRLR contained 808 amino acid residues with a theoretical molecular mass of 91.5 kDa. The mature protein could be divided into 3 domains, extracellular domain (ECD), transmembrane domain, and intracellular domain. The ECD contained 2 homologous repeat units with approximately 67% amino acid sequence identity to each other. The membrane distal unit and proximal unit consisted of 204 and 212 amino acids, respectively. Each unit was similar to the singular ECD of the mammalian PRLR. The characteristic extracellular cysteines and the WSXWS motif of the cytokine receptor were conserved in both repeat units. The intracellular domain of dPRLR consisted of 368 amino acids at the C-terminus and contained 2 conserved regions-box 1 and box 2. The aforementioned characters of duck were all similar to chicken and mammalians, which implied that the dPRLR had same mechanism with other species. Sequence similarity analysis shows that the dPRLR shares approximately 45 to 97% amino identity and approximately 30 to 96% nucleic acid identity as compared with other species. Overall, the greatest sequence identity was found with goose PRLR. In a phylogenetic analysis, the duck PRLR was found to cluster with the PRLR of goose, turkey, chicken, and pigeon. Semiquantitative reverse transcription-PCR indicated that dPRLR mRNA was expressed in all 8 tissues. Expression in the kidney was greatest in varietals tissues.