Osmotic regulation and tissue localization of the myo‐inositol biosynthesis pathway in tilapia (Oreochromis mossambicus) larvae (1182.6)

Abstract

The myo‐inositol biosynthesis (MIB) pathway converts glucose‐6‐phosphate to the compatible osmolyte myo‐inositol (MI), which protects cells from osmotic stress. We exposed tilapia larvae just after yolk sac resorption to various hypersaline environments and recorded robust induction of the enzymes that constitute the MIB pathway, myo‐inositol‐phosphate synthase (MIPS) and inositol monophosphatase 1 (IMPA1). Strong up‐regulation of these enzymes is evident at both mRNA (quantitative real‐time PCR) and protein (densitometric analysis of Western Blots) levels. The highest level of induction of MIB enzymes occurs at the highest salinity that larvae were exposed to (90ppt). Less severe osmotic stress causes proportionally lesser induction of the MIB pathway. Two distinct MIPS mRNA variants are present in tilapia larvae and both are induced at comparable levels for all the salinity challenges (34, 70 and 90ppt). Immunohistochemical localization of IMPA1 protein in sagittal sections of salinity stressed and control larvae identified tissues that are particularly potent in inducing the MIB pathway. These tissues include the skin, gills, eye (retina) and heart. We conclude that the MIB pathway plays an important role in protecting larval stages of tilapia from hyperosmotic stress. Therefore, tilapia larvae represent excellent in vivo models for studying physiological mechanisms by which the MIB pathway is regulated. Supported by NSF grant IOS‐1049780.Grant Funding Source: NSF IOS‐1049780