atg7 and beclin1 are essential for energy metabolism and survival during the larval-to-juvenile transition stage of zebrafish

Abstract The high mortality in larval-to-juvenile transition is a big problem in aquaculture which is related to the shifting from endogenous to exogenous feeding. However, the underlying causes remain poorly understood. Autophagy, an evolutionary regulated cellular mechanism, is highly conserved in eukaryotic organisms to maintain energy homeostasis against stress including starvation. To investigate whether autophagy plays a role during larval-to-juvenile transition, we generated atg7 and beclin1 zebrafish mutant lines using CRISPR/Cas9 gene editing technology. In this study, both atg7 and beclin1 null zebrafish died during larval-to-juvenile transition because atg7 and beclin1 mutants were unable to cope with the metabolic stress after yolk absorption and fail to activate autophagy in response to nutrient restriction. Meanwhile, dramatic defects in the intestine architecture and metabolic functions in the liver of these mutants were observed even though refeeding them. Treatment with rapamycin, an activator of autophagy, could effectively extend the survival time of both atg7 and beclin1 null zebrafish through decreasing the metabolic rate while it couldn\u0027t activate autophagy in mutants via the canonical pathway. Thus, our results revealed that autophagy played a crucial role in zebrafish ontogeny during larval-to-juvenile transition, and it could be considered as one of the most important endogenous factors judging the survival rate of the developing embryos during this period.