Fig. 3. pointed embryos exhibit a significant increase in Svp-positive cardioblasts. Dorsal views of stage 16 wild-type (A,B) and pnt (C,D) embryos labeled for Svp-lacZ (A,C), and Svp-lacZ and Mef-2 (B,D). (A,B) In wild-type embryos, 12 Svp-negative cardioblasts arise anterior to the first Svp-positive cardioblast (broken white line), seven of these cardioblasts are visible in A and B. Posterior to this location, there is a reiterative pattern of two Svp-lacZ positive cardioblasts (yellow/orange) and four Svp-lacZ negative cardioblasts (green) per hemisegment. (C,D) In pnt embryos, cardioblast development anterior to the first Svp-positive cardioblast (broken white line) appears normal. However, many ectopic cardioblasts are found posterior to this location and the majority of these cells express Svp-lacZ at high (arrow) or moderate levels (arrowhead). The broken white line separates the anterior heart domain from the posterior seven heart segments; anterior is towards the left.