Opposing Effects of Circadian Clock Genes Bmal1 and Period2 in Regulation of VEGF-Dependent Angiogenesis in Developing Zebrafish

Molecular mechanisms underlying circadian-regulated physiological processes remain largely unknown. Here, we show that disruption of the circadian clock by both constant exposure to light and genetic manipulation of key genes in zebrafish led to impaired developmental angiogenesis. A bmal1-specific morpholino inhibited developmental angiogenesis in zebrafish embryos without causing obvious nonvascular phenotypes. Conversely, a period2 morpholino accelerated angiogenic vessel growth, suggesting that Bmal1 and Period2 display opposing angiogenic effects. Using a promoter-reporter system consisting of various deleted vegf-promoter mutants, we show that Bmal1 directly binds to and activates the vegf promoter via E-boxes. Additionally, we provide evidence that knockdown of Bmal1 leads to impaired Notch-inhibition-induced vascular sprouting. These results shed mechanistic insight on the role of the circadian clock in regulation of developmental angiogenesis, and our findings may be reasonably extended to other types of physiological or pathological angiogenesis. [Display omitted] ► Circadian clock genes regulate developmental angiogenesis ► Bmal1 and Period2 display opposing angiogenic functions ► VEGF mediates Bmal1-induced angiogenesis ► Bmal1 binds to the VEGF promoter and controls its rhythmic expression Most vertebrates have clock genes to regulate the rhythmicity of various physiological processes. Blood vessels are essential for embryonic development and tissue repair. Cao and colleagues demonstrate that developmental angiogenesis is regulated by clock genes. As light-light and dark-dark cycles differentially regulate the expression levels of clock genes, these conditions may impair or enhance developmental angiogenesis. Their findings may be reasonably extended to pathological conditions and potentially be useful for selection of optimal drugs for treatment of various human diseases.