Autophagy-related genesatg7andbeclin1are essential for energy metabolism and survival during the larval-to-juvenile transition stage of zebrafish

Abstract

High mortality is usually observed during the transition from larvae to juvenile in teleost which is related to the transition from endogenous to exogenous feeding. Autophagy is an evolutionary regulated cellular mechanism highly conserved in eukaryotic organisms to maintain energy homeostasis against stress including starvation. To investigate whether autophagy plays a role during the larval-juvenile transition, we generated atg7 and beclin1 zebrafish mutant lines using CRISPR/Cas9 technology. In this study, both atg7 and beclin1 null zebrafish exhibited a normal body confirmation; nevertheless, they completely died around 15 dpf and 9 dpf respectively. During larval-juvenile transition period, atg7 and beclin1 mutants were unable to cope with the metabolic stress after yolk absorption at 5 dpf and fail to activate autophagy in response to nutrient restriction, and without external feeding, all mutants died nearly at 8 dpf. Dramatic defects in the intestine architecture and metabolic functions in the liver were observed even though providing larvae with an external food supply, suggesting that autophagy isn’t only important during yolk depletion but also within food plenty. Treatment with rapamycin, an activator of autophagy, could effectively extend the survival time of both atg7 and beclin1 null zebrafish through lowering the metabolic rate while it couldn’t activate autophagy in mutants via the canonical pathway. Our findings provided a molecular evidence for the physiological, histological and metabolic changes that occur during the transition process from the larval to the juvenile stages and the chief role of autophagy on the body metabolism during these turning milestones.Author summaryZebrafish Danio rerio has emergrd one of the most powerful research models for studying genes expression during early embryogenesis and postnatal development. On the basis of the cell mechanisms, Macroautphagy, a natural regulated pathway disassembles unnecessary or dysfunctional components orchestrated by more than 36 autophagy related-genes conserved from yeast to mammals. Among those genes are atg7 and beclin1 which have been proved to play an important role in regulating post natal development in some mammals however their roles during zebrafish development still unedited. During this research, CRISPER/CAS9 were adopted to know atg7 and beclin1 knockout effects on the mutants’ metabolism during shifting from maternal yolk acquisition to exogenous feeding and the role of autophagy during the larvae to pre-juvenile development. Herein, we found out that larvae couldn’t abandon autophagy in both fasting and feeding conditions as larvae died earlier before pre-juvenile development despite feeding declaring the importance of autophagy not only to provide the cell with essential nutrients during starvation but also to get rid of cargos inside the eukaryotic cells. Briefly, if the larvae didn’t recycle those cargos due to autophagy perturbations, they will die despite providing suitable conditions including food and acclimatization.

atg7 -Based Autophagy Activation Reverses Doxorubicin-Induced Cardiotoxicity

“…To interrogate the functions of autophagy in aAIC, we obtained an atg7 sa10973 mutant (hereafter referred to as atg7). 22 Although homozygous atg7 −/− zebrafish die during the larva-juvenile transition period with severe cardiac pathology and gastrointestinal tract developmental defects, 23,24 heterozygous atg7 +/− zebrafish appear normal until at least 2 years of age. We noted reduced LC3-II expression in the atg7 +/− hearts and a reduced response to BafA1 treatment (Figure 1H, 1I, and 1J), suggesting attenuated basal autophagy and autophagic flux.…”

Zebrafish as a model to study autophagy and its role in skeletal development and disease

“…For example, the development of conditional knockout lines of autophagy related genes for skeletal cells would enable the role of autophagy in these cells to be explored more accurately. Moreover, the development of inducible knockout lines would be especially helpful as the loss of essential autophagy proteins has proved to be developmentally lethal in several models (Dong et al 2020 ; Mawed et al 2019 ).…”