dbx1a expression is absent in tcf3 morphants. (A,A′) Whole-mount lateral and cross-section views of 18 hpf wild-type embryos hybridized for dbx1a mRNA. (B,B′) tcf3 morphant embryos hybridized for dbx1a, showing loss of expression throughout intermediate spinal progenitors. Residual expression is likely to be in postmitotic neurons. (C,D) Double in situ hybridization for dbx1a (red) and tcf3 (blue), showing overlap between the two genes. (E,F) Both wild-type (E) and tcf3 morphants (F) have a similar gap (red lines) between the pax3 (dorsal) and nkx6.1 (ventral) expression domains, suggesting that a general dorsoventral shift in patterning has not occurred.