Expression and localization study of pIgR in the late stage of embryo development in turbot (Scophthalmus maximus).

The receptor responsible for maternofetal transmission of immunoglobulin (Igs) in the teleosts is not clear. Polymeric immunoglobulin receptor (pIgR) specifically binds with IgA and IgM and mediates the transcytosis of intracellular polymeric immunoglobulins (pIgs) at the mucosal surface to protect against pathogens. Hence there is a possibility that it may be involved in the transmission of maternal Igs. The aim of the present study was to detect the expression and localization of pIgR during embryonal development in turbot (Scophthalmus maximus). pIgR gene was first cloned from eggs and embryos of turbot with or without parent immunization. The expression and distribution of pIgR in unfertilized egg and in embryos ranging from day 1 to day 5 after fertilization were analyzed using reverse transcriptase quantitative polymerase chain reaction and in situ hybridization. pIgR gene was detected in all eggs and embryos at different stages of development, with the highest level detected on the 5th day. pIgR mRNA was observed to be first located in the whole blastoderm and enveloped the yolk sac. Later, it was located around entoderm including primary digestive tract and pronephric tubule tract, and finally it was located at the joint of abdomen and vitelline membrane. Then, Eukaryotic expression plasmid carrying pIgR gene was constructed and transfected into HEK293T cells. Results showed mature pIgR protein located on the cellular membrane, and could bound IgM in vitro. Our findings provide information for studying the involvement of pIgR in maternal Igs transportation in turbot.