Fig. 4. Cranial nerves and epibranchial placode formation in mice. (A-C) Anti-neurofilament immunochemistry at 10.5 dpc. Wild-type embryo (A). (B) Sox3 null embryo with a fusion of the IX and X cranial nerves. (C) Sox3 null embryo, in which nerves from the distal VII and IX ganglia do not reach PA2 and PA3, respectively (inset corresponding to the boxed region). (D,E) Phox2a in situ hybridisation at 9.5 dpc, showing the epibranchial placodes. (D) Wild type. (E) Sox3 null embryo with a reduced geniculate placode and a fusion of the petrosal and nodose placodes. (F,G) Ngn2 in situ hybridisation at 10.5 dpc. (F) Wild-type embryo (magnification of petrosal/nodose placodes, inset). (G) Sox3 null embryo, in which petrosal and nodose placodes are connected (magnification, inset). (H) Statistical analysis of the placodal and cranial nerves defects in Sox3 null embryos.