Fig. 8. Cell proliferation and survival are reduced in Nkx2.5^Cre/+; Fgf8^flox/- mutants. Cell proliferation rates at E9.0 were assessed in section by anti-phospho-histone H3 immunostaining (red) in normal (A) and mutant embryos (B). SYTO13 counterstain (green) marks nuclei. Marked reduction in proliferation was noted in the PE and SM of mutants compared with controls (n=3 and 4, respectively). Statistical analysis indicates that decreases in cell proliferation in the PE and SM were significant (P<0.05), while rates in the OT, RV, LV and atria were unaltered (G). LysoTracker Red staining at E9.0 in normal (C) and mutant (D) embryos in confocal optical sections (white signal indicates cell death). Increases in cell death are observed in the SM contiguous with the outflow tract (OT) of mutant embryos. Additionally, increases in cell death are observed in the PE at the level of the OT. LysoTracker Red staining at E9.5 (E,F; red signal indicates cell death) demonstrate that mutant embryos (F) have excess death of NCCs in the pharyngeal arches (1,2). Embryos were counterstained with anti-AP2 (green). OT, outflow tract; SM, splanchnic mesoderm; PE, pharyngeal endoderm; RV, right ventricle; LV, left ventricle; O, otocyst; E, eye.