We propose that Wnt5a, which is expressed along the midline in r3 and more anterior regions of the hindbrain, can act as a chemoattractive cue to facilitate the migration of FBM neurons located in anterior r4, adjacent to the r3/r4 boundary, rostrally into r3 and r2. A, In a wild type hindbrain, Celsr1 expression in the ventricular zone inhibits Wnt5a-dependent activation through an unknown mechanism (?), blocking the rostral migration of FBM neurons into r3. B, In a Celsr1-deficient hindbrain, the inhibition is relieved and FBM neurons migrate rostrally into r3 toward the Wnt5a source.