Fig. 2. pointed represses cardioblast development. (Top) The pointed locus, highlighting the intron-exon structure of pntP1 and pntP2. (Bottom) High-magnification dorsal views of stage 16 wild-type (A), l(3)012309 (B), pnt⁸⁸ (C) and pnt^RR112 (D) embryos labeled for Mef2. (A) In wild-type embryos, the heart is formed by two single rows of cardioblasts that meet at the dorsal midline (white arrow). In embryos that contain a P element insert in pnt (B), a deletion of the pntP1 locus and the shared exons of pntP2 (C) or a mutation in the splice donor site of a pntP2-specific exon (D), ectopic cardioblasts develop and form enlarged hearts comprising disorganized rows of cardioblasts (arrows, B-D). Anterior is towards the left; white arrow indicates the dorsal midline.