cDNAs CLONING AND mRNA EXPRESSION OF TWO PROLACTIN RECEPTORS IN ORANGE-SPOTTED GROUPER EPINEPHELUS COIOIDES

Prolactin (PRL) has many important physiological roles in the control of growth, osmoregulation and reproduction, which is mediated by prolactin receptor (PRLR). In this study, two cDNAs encoding PRLR were isolated from the gill of orange-spotted grouper Epinephelus coioides. The two cDNAs, one consisting of 1947bp and the other of 1749bp, encoding for putative 649- and 487-amino acid PRLR (designated PRLR1 and PRLR2, respectively), shared 40.4% identity in deduced amino acid sequence. PRLR1 and PRLR2 showed the conserved structural characteristics of PRLR family, including the WS motif, the box1 region, extracellular cysteine residues and intracellular tyrosine residues. However, there were differences of structural features between the two receptors as well. PRLR1 has 13 intracellular tyrosine residues while PRLR2 only has 8. The structural discrepancies thus undoubtedly indicated the distinct biological functions of PRLR1 and PRLR2. Real-time RT-PCR analysis showed that both PRLR1 and PRLR2 mRNAs were presented in all tissues tested and expressed extremely highly in gill, kidney and intestine, lowly in pituitary and hypothalamus. The expressions of PRLR1 and PRLR2 in different embryo developmental stages were also detected by real-time PCR. The strongest signal was detected in the fertilized egg stage for PRLR1, while in the stage of optic vesicle and smoite formation for PRLR2. The expression level of PRLR2 is much higher than PRLR1 in all stages examined except in the fertilized egg stage. The expression distinction of PRLR1 and PRLR2 suggested that they may play different roles during early development of orange-spotted grouper.