Fig. 7. There is increased apoptosis in the pharyngeal arches of Fgf8^H/– mutants in domains adjacent and remote to Fgf8 expression. Whole mount TUNEL analysis was performed on 25 somite, stage-matched control. (A) and mutant (B,C) embryos. Pharyngeal arches are numbered and the otocyst is labeled (O); note the increased number of apoptotic cells in normal domains in the rostral arches (white arrowheads in B) and abnormal domains of apoptosis in the postotic region of the developing fourth and sixth arches (yellow arrowheads) in the mutants. Fgf8 expression by in situ hybridization on E9.5 control and mutant embryos. (D,E) Pharyngeal region of control embryo and (E) mutant embryo; note severely decreased quantity of Fgf8 message in the mutant (red arrowheads, consistent with results in Fig. 1B). Domains of apoptosis in B and C are seen both adjacent, and relatively distant, to normal regions of Fgf8 expression.