Fig. 2

Early overexpression of nkx2.5 rescues late morphological defects in nkx2.5^-/- embryos. (A–D) Lateral views of live embryos, anterior to the left, at 52 hpf. All embryos were heat-shocked at 21 somites. Aside from cardiac defects and pericardial edema, the non- transgenic nkx2.5^-/- embryos appear morphologically normal (C). While heat shock of wild-type embryos yields no evidence of toxicity (B), the cardiac defects and pericardial edema in the nkx2.5^-/-;Tg(hsp70l:nkx2.5-EGFP) embryos are dramatically improved (D). (E–H) Lateral views of live embryos, anterior to the right, at 52 hpf. Compared to non-transgenic (E) and transgenic (G) wild-type hearts, the non-transgenic nkx2.5^-/- heart (F) is unlooped and has striking defects in both ventricular and atrial morphologies. In contrast, the transgenic nkx2.5^-/- heart (H) resembles its wild-type sibling (G) indicating a rescue of chamber proportions. (I,J) Bar graphs illustrate the percentage of phenotypically wild-type (gray) and nkx2.5^-/- (black) embryos in multiple clutches of non-transgenic (I) and transgenic (J) siblings following heat shock at specific developmental stages. Gross phenotypic assessment was performed assaying for morphological features noted in (A-H) at 52 hpf. The total number of embryos screened at each time point is noted. Fisher exact tests (one-sided; p<0.01) were performed; asterisks indicate statistically significant differences between proportions of non-transgenic (I) and transgenic (J) wild-type and phenotypically nkx2.5^-/- embryos. A notable decrement in the percentage of transgenic nkx2.5^-/- embryos between 7 somites and 26 hpf denotes rescue of morphological ventricular and atrial defects.