Fig. 5. Expression of murine Sema6A mRNA in early development (E12–E13). Radiolabeled in situhybridization shows sites of Sema6A mRNA expression in horizontal sections of mouse embryos at E12 (A, B) and E13 (C–G). Sections through E12 embryos at midthoracic (A) and upper abdominal (B) levels show Sema6A mRNA expression in the somites (dotted outline), limb buds, ventral portions of the spinal cord (SC), dorsal root ganglia (asterisks), and the gastrointestinal tract and its mesenteries (GI). Sema6A is not expressed in the heart or liver, as shown. At both E12 (A,B) and E13 (C–G), Sema6A mRNA is excluded from the sites of the sympathetic chains (small arrowheads in A–G) but is consistently expressed in dorsal root ganglia (asterisks,A–G) and the ventral portions of the spinal cord (SC, A–G). At E13, Sema6A expression is shown at the following levels: lower cervical (C), midthoracic (D, including forelimb, and high power of sympathetic ganglia in G), upper abdominal (E), and lower abdominal (F, including hindlimb). Sema6A mRNA is not expressed in the heart (D) or liver (E). It is strongly expressed in the skeletal muscles, including diaphragm (E, Dia) and psoas (F, Ps). It is also expressed in the gastrointestinal tract, including duodenum (E,Duod), stomach (F, Sto), and intestinal loops including herniations present at this age (GI in E, F). Expression is also observed in the inferior poles of the lungs (E, arrows) and the kidneys (K in F). G is a high-power view of D showing Sema6A mRNA excluded from the sympathetic ganglia but present in the surrounding sheath (arrowheads) and in dorsal root ganglia (asterisks). Scale bars, 0.5 mm.