Celsr1–3 Cadherins in PCP and Brain Development - Current Topics in Developmental Biology - page 170

A B

nV

VII

nVI

nVII

Celsr1 ko/ko WT

C D

Celsr2 Dgen/Dgen & Celsr2 Dgen/Dgen ; Celsr1 ko/ko Celsr2 Dgen/Dgen ; Celsr3 ko/ko & Fzd3 ko/ko

Figure 7.4 Migration of facial branchiomotor (FBM) neurons in normal and Celsr1 - 3
knockout mice. Drawings summarize the phenotype at P0. In wild-type animals (A),
FBM neurons form a single nucleus (nVII) in a region that derives from r6. Their axons
loop around the abducens nucleus (nVI) before exiting the rhombencephalon dorsally,
caudal to the trigeminal nucleus (nV). In Celsr1 ko/ko mutants (B), in addition to the normal
nVII, FBM neurons form another ectopic nucleus at the level of nV, but their axons leave
the rhombencephalon at the right position. This is due to aberrant migration of FBM
neurons in lateral r2 during embryogenesis. In Celsr2 Dgen/Dgen and Celsr2 Dgen/Dgen ;
Celsr1 ko/ko (C), the facial nerve genu is completely abnormal and axons do not loop
around nVI because FBM neurons migrate prematurely in lateral r4-r5, forming lateral
heterotopias. In Celsr2 Dgen/Dgen ; Celsr3 ko/ko and in Fzd3 ko/ko , in addition to the absence of
the genu of the facial nerve, the size of nVII is reduced because of embryonic cell death
(D). “r,” rhombomere; nV, motor trigeminal nucleus; nVI, abducens nucleus; nVII, facial
nerve nucleus.

even rostral to the trigeminal (nV) nucleus but send their axons normally in
the facial nerve ( Fig. 7.4B ). In the hindbrain, Celsr1 is expressed in
progenitors and in the floor plate, but not in postmitotic FBM neurons.
Consistent with this, conditional inactivation of Celsr1 in progenitors
under Nk6.2-Cre recombination induces abnormal rostral migration,
whereas its deletion in FBM neurons using Isl1-Cre does not.