(A–H) Transverse sections through E5 (A–D) or E6 (E-H) chick heads infected with control (A,B,E,F) or DNErbB4 (C,D,G,H) virus. The lateral pouch is outlined in A. The extent of infection was assayed by 3C2-gag immunostaining for control virus (A,C) or by in situ hybridization for DNErbB4 (C,G). Adjacent sections were probed for cNetrin1 (B,D) or cNetrin2 (F,H). At both E5 and E6, cNetrin1 and cNetrin2 are expressed normally in the fusion plate epithelium (arrowheads, brackets) despite abundant expression of DNErbB4 here. (I–L) Lateral (I,K) and top-down (J,L) views of E7 paintfilled inner ears of control (I,J) and experimental (K,L) embryos. No change in the size or shape of the overall inner ear (I,L) or lateral canal (J,L) is evident.