Fig. 5. Differential effects of Notch on Hey1, Hey2 and Bmp2. Stage 12 hearts were electroporated to misexpress modulators of the Notch pathway signaling, cultured for 24 hours and analyzed for effects on endogenous gene expression, as described in Fig. 3. (A) Activation of the Notch pathway with Myc-tagged CSL-VP16 or Notch2_icd increased the number of cells that expressed endogenous Hey1, relative to neighboring cells, and attenuation of Notch with HA-tagged Mfng caused a decrease in Hey1-positive cells. By contrast, Notch pathway agonists and antagonists did not affect Hey2 expression. (B,C) Histological sections demonstrating that misactivation of the Notch pathway (B) or inhibition of endogenous Notch responsiveness by Mfng (C) elicited reciprocal and cell-autonomous effects on endogenous Hey1. Scale bar: 25 µm. (D) Attenuation of Notch signaling with Mfng did not cause a cell-autonomous effect on the expression of Bmp2, consistent with the observations that Hey2 is not regulated directly by Notch (A) yet suppresses Bmp2 (see Fig. 4). Asterisks in A,D indicate statistical significance of the difference between the Notch pathway modulators and the GFP control (P<0.05, ² test).