The coding sequence of chick Tal1 was cloned into an expression vector and electroporated into St.3 embryos. (A,C,E,G) Expression profile in WT control embryos. (B,D,F,H) Expression profile in Tal1 gain-of-function embryos. (B',D',F',H') GFP expression marks the cells where Tal1 is expressed. (B",D",F",H") Overlay of the GFP signal and the in-situ hybridization assay. The yellow dotted line represents the normal borders of the cardiac crescent.