(A,B) BrdU labeling showed similar proliferation index between control and mutant. (C,D) TUNEL assay showed an increased apoptotic rate in PA mesenchyme in mutant compared to the control. (E,F) Immunofluoresence staining revealed the β-galactosidase positive cells (NCCs) in PA mesenchyme. (G) No difference (p=0.94) was detected in the proliferation rate of NCCs in the PA-OFT region in control (23±11%) and in mutant (23±7%); Values are means ± SEM, n = 6. (H–O) RNA whole-mount in situ hybridization indicated the expression of both Msx1 and Msx2 were downregulated in the PA-OFT area in the mutant. J, K, N and O are higher magnification views of the PA-OFT area in H, I, L and M respectively.