Atf4b Regulates Tricarboxylic Acid Cycle and Early Embryonic Development in Zebrafish

Activating transcription factor 4 (ATF4) is a critical transcription factor involved in stress response. It exerts essential regulatory effects on cellular metabolism. Zebrafish genome contains two ATF4 paralogs, atf4a and atf4b. The function of Atf4a has been documented previously while that of Atf4b remains elusive. To investigate the impact of Atf4b on zebrafish development and metabolism, we generated an atf4b knockout zebrafish using CRISPR/Cas9. Sequence alignment revealed that zebrafish Atf4b shares conserved domains only in the leucine zipper and DNA-binding regions with mammalian ATF4. Morphological examination showed no apparent deformities in atf4b^-/- embryos while body length was significantly reduced. Metabolomic profiling demonstrated the elevated citrate level accompanied by reduced downstream metabolites like oxoglutarate, malate and succinate in the tricarboxylic acid (TCA) cycle with a marked decrease in ATP production. Atf4b deficiency induced mitochondrial damage and significantly compromised survival under acidic stress conditions. These findings evidenced the crucial role of Atf4b in zebrafish growth, energy metabolism and stress adaptation, and provided novel insights into the integrated mechanism coupling developmental processes, metabolic homeostasis and stress response.