Ontogeny of gene expression of group IB phospholipase A2 isoforms in the red sea bream, Pagrus (Chrysophrys) major

The red sea bream (Pagrus major) was previously found to express mRNAs for two group IB phospholipase A2 (PLA2) isoforms, DE-1 and DE-2, in the digestive organs, including the hepatopancreas, pyloric caeca, and intestine. To characterize the ontogeny of the digestive function of these PLA2s, the present study investigated the localization and expression of DE-1 and DE-2 PLA2 genes in red sea bream larvae/juveniles and immature adults, by in situ hybridization. In the adults, DE-1 PLA2 mRNA was expressed in pancreatic acinar cells. By contrast, DE-2 PLA2 mRNA was detected not only in digestive tissues, such as pancreatic acinar cells, gastric glands of the stomach, epithelial cells of the pyloric caeca, and intestinal epithelial cells, but also in non-digestive ones, including cardiac and lateral muscle fibers and the cytoplasm of the oocytes. In the larvae, both DE-1 and DE-2 PLA2 mRNAs first appeared in pancreatic tissues at 3 days post-hatching (dph) and in intestinal tissue at 1 dph, and expression levels for both gradually increased after this point. In the juvenile stage at 32 dph, DE-1 PLA2 mRNA was highly expressed in pancreatic tissue, and DE-2 PLA2 mRNA was detected in almost all digestive tissues, including pancreatic tissue, gastric glands, pyloric caeca, and intestine, including the myomere of the lateral muscles. In conclusion, both DE-1 and DE-2 PLA2 mRNAs are already expressed in the digestive organs of red sea bream larvae before first feeding, and larvae will synthesize both DE-1 and DE-2 PLA2 proteins.