Creb function is critical for hypoxia/reoxygenation-induced catch-up growth and the associated maintenance of neural crest cells in zebrafish embryos.

Animal growth progresses under favorable conditions; however, it slows when environmental conditions deteriorate. Conversely, when unfavorable conditions are removed, growth accelerates, and underdeveloped animals rapidly catch up to age-equivalent body size. This process is known as "catch-up growth", yet its molecular mechanisms are not fully understood. Zebrafish embryos temporarily exposed to hypoxia followed by reoxygenation exhibit catch-up growth, and mitogen-activated protein kinase (Mapk) signaling plays essential roles in this growth spurt. Here, we show that a Mapk-target transcription factor, cAMP response element-binding protein (Creb), is indispensable for catch-up growth. Pharmacological inhibition of Creb significantly slowed the reoxygenation-induced catch-up growth but had a limited effect on normal growth in embryos that had never experienced hypoxia/reoxygenation. Although Creb had only a minor effect on cell proliferation, it significantly affected the expression of genes involved in the maintenance and differentiation of neural crest cells (NCCs) and their derivatives in the reoxygenated embryos. In addition, continued Creb blockade clearly affected the growth of pharyngeal and mandibular skeletons, which are largely derived from cranial NCCs. The effect of Creb inhibition on skeletal formation in reoxygenated fish was greater than that observed in normally developed fish. Furthermore, RNA-seq analysis of isolated NCCs, followed by pathway analysis and gene set enrichment analysis, predicted Creb as an indispensable molecule contributing to reoxygenation-specific gene expression in NCCs of the catching-up embryos. These results reveal a previously unknown role for Creb in NCCs and suggest that this role is critical for embryonic catch-up growth in response to environmental oxygen fluctuations.