GJA5 and cancer: Prior studies show that Cx40-deficiency leads to reduced microvascular complexity in Cx40−/− mice during development and in cancer,15,16,18 but knockout of both Cx40 orthologs in zebrafish embryos significantly enhances intersegmental vessel growth, a process that occurs primarily through sprouting angiogenesis.6 In this study, we corroborate the phenotype of Cx40−/− mice using an in vitro microvessel-on-a-chip (VMO) model, in which we show that siRNA-based Cx40 knockdown leads to modest reductions in microvessel network complexity.