Figure 1. A,B: Whole-mount in situ hybridisation analysis of Sox10 expression in embryonic day (E) 9.5 wild-type (+/+) (A) and Twist-/- (-/-) embryos (B). Black arrowheads indicate the separation of the trigeminal and facioacoustic ganglia in the wild-type embryo (A) and the absence of this separation in the mutant embryo (B) due to the intermingling of the two streams of Sox10-expressing cells extending from the hindbrain to the first and second branchial arches. In the trunk, Sox10-expressing cells are organized in segmental clusters heralding the formation of the dorsal root ganglia and the spinal nerves (asterisks). C–E: Histological sections of the head at the plane of the upper (preotic) hindbrain to forebrain of a E10 wild-type embryo showing the Sox10-expressing cells (presumptive glial cells) in the trigeminal ganglia (C), and the extended distribution of Sox10-expressing cells from the neural folds to the branchial arch in the Twist-/- embryo (D,E) and the persistent expression of Sox10 in the postmigratory cells in the first (D) and the second (E) branchial arch. Asterisks marks closure defect of the neural tube. F,G: The segmental regionalization of Sox10-expressing cells in the trunk of an E9.5 wild-type embryo (F) and the diffused distribution of Sox10-expressing cells in the upper trunk and localisation of Sox10-expressing cells (white arrow in G) at the dorsal aspect of the paraxial mesoderm of the lower trunk of a E9.5 Twist-/- embryo (G). H,I: Histological section of E9.5 embryos through the thoracic region showing Sox10-expressing cells in the dorsal root ganglia and the spinal nerve of wild-type embryo (H) and more dispersed in the paraxial mesoderm of Twist-/- embryo (I). The arrow in I points to the Sox10-expressing cells that spread dorsoventrally from the dorsal border of the paraxial mesoderm to the perinotochordal and periaortic mesenchyme. J–S: The pattern of the cranial ganglia and peripheral nerves of E11 wild-type (J,L,P,R) and Twist-/- embryos (K,M,N,O,Q,S) revealed by neurofilament staining. Examples of abnormal cranial nerve patterns are as follows. K: Fusion of gV and gVII/VIII and the more dorsal location of the ganglia to the edge of the open neural tube (asterisk), merger of glossopharyngeal and vagus nerve (black arrow), and expanded nodose ganglion (white arrow); M: dorsally displaced gV, mixing of nerves of trigeminal and facial ganglia (asterisks) that project to the second branchial arch, disorganized pattern of the ophthalmic and maxillary branches (bracket), and the ectopic projection of the ophthalmic branch of the trigeminal nerves (arrows); N: complete loss of ophthalmic and maxillary branches of the trigeminal nerves (bracket) and the small size of gV, which becomes similar to that of GVII/VIII; O: small gV and loss of ophthalmic and maxillary branches, and truncated and mandibular branch of trigeminal nerve (bracket) and diversion of facial nerve to join the vagus nerve (asterisk). P: Postotic region of the wild-type embryo showing the organization of the glossopharyngeal, vagus, and hypoglossal nerves. Q: Postotic region of Twist-/- embryo showing the foreshortened vagus nerves, the merging of glossopharyngeal and vagus nerves, and the abnormal proximal branches and the short occipital roots of the truncated hypoglossal nerve (asterisk) that failed to reach the ventral pharynx. R,S: The segmental organization of the spinal ganglia and nerves in the trunk of wild-type (R) and Twist-/- embryo (S). +/+, wild-type; -/-, Twist-/- ; ba1, first branchial arch; ba2, second branchial arch; drg, dorsal root ganglion; hb, hindbrain; ht, heart; fb, forebrain; fg, fore-gut; nt, neural tube; ov, otic vesicle. Ganglia and nerves: gV, trigeminal ganglion and V1 ophthalmic; V2 maxillary; V3 ; mandibular branches; gVII/VIII, facioacoustic ganglion, nVII, facial nerve; gIX, glossopharyngeal ganglion, nIX, glossopharyngeal nerve; gX, vagal nerve; Xj, jugular branch of vagus nerve; Xn, nodose branch and nodose ganglion of the vagus nerve; nXII, hypoglossal nerve; cv, cervical nerve, oc, occipital nerve; sn, spinal nerve; sym, sympathetic ganglia and nerves; th, thoracic nerves.
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