Fig. 1. Mouse OFT cushion morphogenesis is disrupted in Fgf8^c/-;Isl1Cre mutants. Fgf8^c/-;Isl1Cre mutants are labeled as Fgf8;Isl1Cre. (A) Transverse section across the proximal outflow tract (OFT) of a E10.5 control embryo shows many mesenchymal cells in a thick layer of cardiac jelly (bracket) lining the myocardium (My). The arrow points from proximal (close to right ventricle) to distal OFT. (B) Sagittal section spanning the OFT and atrioventricular canal (AVC) cushions of E10.5 control embryo. (C) Transverse section across the proximal OFT of an E10.5 Fgf8;Isl1Cre mutant embryo reveals hypoplastic cushions (arrowheads) with few mesenchymal cells in a thin layer of cardiac jelly (bracket). (D) Sagittal section of the OFT and AVC of an E10.5 Fgf8;Isl1Cre mutant with hypocellular OFT cushions (arrowhead) but normal AVC cushions. (E,F) Sagittal sections of an E11.5 control embryo shows mesenchymal cells throughout the OFT cushions. (G,H) Sagittal sections of E11.5 Fgf8;Isl1Cre mutants with hypoplastic proximal (black arrowhead) and distal (green arrowhead) OFT cushions. (I) Section through the heart (ht) of an X-Gal-stained 6-somite stage (6ss) Rosa26^lacZ;Tie2Cre embryo. (J) Section of proximal OFT cushion (arrowhead) of an E11.5 Rosa26^lacZ;Tie2Cre embryo. All of the cells in the proximal cushion are stained and the distal cushion contains unstained CNC. (K) Section of an E9.25 Rosa26^lacZ;Tie2Cre embryo. Box encloses proximal OFT cushion. (L) Mesenchymal cells that invaded a collagen gel from an E9.25 Rosa26^lacZ;Tie2Cre proximal OFT explant (box in K). For quantitated data, see Fig. S1 in the supplementary material.