Figure 3.
Transplanted ES cell-derived motoneurons project axons to axial muscles. A, D, Cross sections through st. 31 chick embryos showed that the majority of the transplanted eGFP+ cells translocated to the medial/ventral aspect of the neural tube. B, ES cell-derived motoneurons extended axons out of the neural tube through the ventral root (B, arrow) and projected dorsally around the DRG as part of the dorsal ramus (A, B, arrowheads). C, Dorsal projecting eGFP+ axons formed part of the dorsal ramus (C, arrow) and innervated the longissimus muscle (C, arrowheads; muscle delineated by dotted line). The endogenous cutaneous nerve is indicated with an open arrowhead. A–C, β-III tubulin immunohistochemistry was used to visualize both the endogenous chick and transplanted mouse neurons. D, Neurolucida reconstruction shows that all of the eGFP+ axons in a representative st. 31 chick embryo (green tracings) projected dorsally and either formed part of the longissimus muscle nerve (D, arrow) or incorrectly targeted the skin (D, arrowhead). Each green dot in the neural tube represents one eGFP+ neuron. For comparison, the projection patterns of the endogenous β-III tubulin+ chick neurons are shown in red on the contralateral side. The longissimus muscles are indicated with dotted lines. In all sections, dorsal is up. NC, Notochord. Scale bars: A, D, 100 μm; B, C, 200 μm.