Molecular cloning and functional analysis of polymeric immunoglobulin receptor gene in orange-spotted grouper (Epinephelus coioides).

As one of the most important mucosal effectors, polymeric immunoglobulin receptor (pIgR) mediates the transcytosis of polymeric immunoglobulins (pIgs) to protect the organisms. In this study, a full-length cDNA of pIgR was isolated from orange-spotted grouper (Epinephelus coioides), and the sequence analysis of deduced protein revealed the presence of only two Ig-like domains (ILDs), and the absence of the conserved Ig-binding site and complementary determining region (CDR). The grouper pIgR mRNA was detected in almost all the peripheral tissues examined, especially the mucosal tissues by RT-PCR. Additionally, recombinant grouper pIgR was stably expressed in the COS-7 cell line and identified as a 40-kDa transmembrane receptor. Furthermore, the association of recombinant pIgR and purified grouper pIgM was demonstrated. Taken together, the present study provided strong evidence that grouper pIgR was produced as a transmembrane protein, and probably involved in the pIgM transport.