ER-mitochondria contacts and mitochondrial fusion correlate with increased mitochondrial activity during vertebrate embryogenesis

Increased mitochondrial activity is essential for embryo development. Although conserved across organisms, the molecular basis of this increase is unknown, as detailed biochemical analysis in vertebrates is hampered by the limited availability of material. Using zebrafish as a model for vertebrate development, we comprehensively profile mitochondrial activity, morphology, metabolome, proteome, and phospho-proteome, as well as respiratory chain activity. Our data show that the mitochondrial proteome undergoes major changes during embryogenesis. While respiratory chain complex levels remain largely constant, we identify a marked increase in mitochondrial-ER association during early embryogenesis. Moreover, time-lapse imaging of mitochondrial dynamics reveals a transition from fragmented to elongated mitochondria starting during somitogenesis. Overall, our systematic profiling of the molecular and morphological changes of mitochondria during embryogenesis provides a valuable resource for further investigation of mitochondrial function. Our study reveals that increased mitochondrial-ER interaction and changes in mitochondrial morphology may contribute to its regulation during vertebrate development.