Engrailed controls the dorsal-ventral choice of lateral LMC axons <i>in vivo</i>.

<p><b>(a)</b> An ectopic source of either En1, En2, or En1-SR was established by injecting the proteins into the dorsal mesenchyme of the developing chick wing. <b>(b)</b> Immunohistochemical detection of neurofilament (red) and EphA4 (green) visualizes the dorsal-ventral branching point and EphA4-positive LMCl axons. After injection of En1 into the dorsal wing bud more EphA4-positive axons are present in the ventral branch compared to mock (PBS) injection (arrows). <b>(c)</b> Quantification of axonal EphA4 signal results in a higher average EphA4 intensity in the ventral branch after En1 injection when compared to embryos where PBS was injected EphA4 signal was not altered significantly if En2 (28.75% ± 0.48 SEM, n = 4) or En1-SR (29.75% ± 1.25 SEM) were injected into the dorsal wing mesenchyme. <b>(d)</b> The expression patterns of the dorsal marker <i>Lmx1b</i> were not altered by injection of ectopic En1 into the dorsal wing. Scale bar in d equals 100μm for b and 250μm for d.