etv2 expression analysis in wild‐type, etv2 ci32G + −/− and etv2 ci32Gt−/− embryos at the 20‐somite, A‐C, and 24 hpf stages, D‐F. Embryos were obtained from an incross of etv2 ci32Gt+/−; UAS:GFP +/+ parents and sorted based on their GFP fluorescence pattern. Antisense etv2 RNA probe which corresponds to the C‐terminal portion of the etv2 coding sequence and 3′UTR downstream of the Gal4 insertion side was used for in situ hybridization (see Experimental Procedures). A‐C, In non‐fluorescent wild‐type siblings (wt), strong etv2 expression is apparent in vascular progenitors in the anterior lateral plate mesoderm, presumptive progenitors of the anterior and common cardinal veins, and in vascular progenitors next to the tailbud (arrows). Weaker expression in the dorsal aorta (DA) is also apparent. Note the reduced etv2 expression in etv2 ci32Gt+/− embryos and nearly absent expression in etv2 ci32Gt−/− embryos. D‐F, In wild‐type siblings, strong etv2 expression is apparent in the cranial venous vasculature, including the primordial midbrain channel (PMBC) and the middle cerebral vein (MCEV), as well as the tail plexus region (arrow). Weaker expression in the DA is also apparent. Note the reduced etv2 expression in etv2 ci32Gt+/− embryos and nearly absent expression in etv2 ci32Gt−/− embryos
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