TBX1 and Micrognathia: At the same time, in some tissues that are outside of the Tie2Cre recombination domain, VEGF may also regulate or intersect with Tbx1. This may for example explain the reported decrease in Tbx1 expression in the pharyngeal arch region of Vegfa mutants, and the higher incidence and severity of mandible hypoplasia in Vegfa mutants compared to Tie2Cre/Nrp1 mutants.