During development, facial branc
hiomotor (FBM) neurons, w
hic
h innervate muscles in t
he vertebrate
head, migrate caudally and radially wit
hin t
he brainstem to form a motor nucleus at t
he pial surface. Several components of t
he Wnt/planar cell polarity (PCP) pat
hway, including t
he transmembrane protein Vangl2, regulate caudal migration of FBM neurons in zebrafis
h, but t
heir roles in neuronal migration in mouse
have not been investigated in detail. T
herefore, we analyzed FBM neuron migration in mouse
looptail (
Lp) mutants, in w
hic
h Vangl2 is inactivated. In
Vangl2Lp/+ and
Vangl2 Lp/Lp embryos, FBM neurons failed to migrate caudally from r
hombomere (r) 4 into r6. Alt
houg
h caudal migration was largely blocked, many FBM neurons underwent normal radial migration to t
he pial surface of t
he neural tube. In addition,
hindbrain patterning and FBM progenitor specification were intact, and FBM neurons did not transfate into ot
her non-migratory neuron types, indicating a specific effect on caudal migration.
Since loss-of-function in some zebrafish Wnt/PCP genes does not affect caudal migration of FBM neurons, we tested whether this was also the case in mouse. Embryos null for Ptk7, a regulator of PCP signaling, had severe defects in caudal migration of FBM neurons. However, FBM neurons migrated normally in Dishevelled (Dvl) 1/2 double mutants, and in zebrafish embryos with disrupted Dvl signaling, suggesting that Dvl function is essentially dispensable for FBM neuron caudal migration. Consistent with this, loss of Dvl2 function in Vangl2Lp/+ embryos did not exacerbate the Vangl2Lp/+ neuronal migration phenotype. These data indicate that caudal migration of FBM neurons is regulated by multiple components of the Wnt/PCP pathway, but, importantly, may not require Dishevelled function. Interestingly, genetic-interaction experiments suggest that rostral FBM neuron migration, which is normally suppressed, depends upon Dvl function.