Wnt1 is selectively down-regulated in the cerebellum of arl13b mutants. wnt1 is transiently expressed in the cerebellum of WT embryos (A, A’) (arrows) while it is dramatically reduced in arl13b mutants (B, B’). A and B, dorsal view; A’ and B’, lateral view. Note that the expression of wnt1 is selectively decreased in the cerebellum while its expression at the midbrain–hindbrain boundary is intact. A–B’, Scale bar 100 μm.