Biomedical Engineering Reference
In-Depth Information
was subsequently changed to
Vangl2
(Van Gogh-like 2) (
Kibar, Gauthier,
Lee, Vidal, & Gros, 2003; Kibar, Vogan, et al., 2001
).
Ltap/Vangl2
mRNA and protein are expressed throughout the neuroepithelium of the
forming NT prior to (E7.5), during (E7.5-8.5), and after (E9.5) NT
closure (
Kibar, Underhill, et al., 2001; Kibar, Vogan, et al., 2001
). Ltap/
Vangl2 protein is also developmentally expressed in additional tissues
(
Torban et al., 2007
), and indeed,
Lp/Lp
embryos display defects in the
inner ear (organization of hair cells of the cochlea), the heart (outflow
tract defects), and the musculoskeletal system (fused ribs) (see below).
This suggests that
Ltap/Vangl2
is not only required for successful NT
formation but is also instrumental for multiple additional aspects of
embryonic development (
Montcouquiol et al., 2003; Phillips, Murdoch,
Chaudhry, Copp, & Henderson, 2005; Torban et al., 2008
).
Ltap/Vangl2
gene encodes a 521-amino acid-residue highly hydropho-
bic integral membrane protein composed of four transmembrane domains
(
Kibar, Underhill, et al., 2001; Torban, Wang, Groulx, & Gros, 2004
),
two solvent accessible extracytoplasmic loops, and intracellular amino and
carboxy termini (
Iliescu, Gravel, Horth, Apuzzo, & Gros, 2011
). The
large carboxy-terminal cytoplasmic domain includes a PDZ-binding
motif (PBM) at its extremity (
Fig. 10.3
). We identified independent loss-
of-function
Ltap/Vangl2
mutations at the three known
Lp
alleles: the
original
Lp
(S464N) and the chemically induced
Lp
m1Jus
(D255E) and
Lp
m2Jus
(R259L) alleles (
Guyot et al., 2011; Kibar, Underhill, et al., 2001;
Kibar, Vogan, et al., 2001
). These mutations are specific for
Lp
mice and
affect amino acid residues that are highly conserved throughout evolution.
Subcellular localization experiments by immunofluorescence in transfected
MDCK cells indicate that while the wild-type protein is expressed at the
plasma membrane,
Lp
-associated variants are mistargeted and are retained
in the endoplasmic reticulum.
Lp
-associated mutations cause Vangl protein
instability, reduced half-life, and increased proteasome-dependent
degradation, all possibly secondary to a basic misfolding defect (
Gravel,
Iliescu, Horth, Apuzzo, & Gros, 2010; Iliescu, Gravel, Horth, Kibar, &
Gros, 2011; Torban, Wang, et al., 2004
).
Vertebrates have a second
Vangl
gene (
Vangl1
) that encodes a protein
sharing
75% similarity with Vangl2 (
Torban et al., 2008
). In the develop-
ing NT,
Vangl1
mRNA and protein are expressed in the most ventral part of
NT (floor plate) and notochord in a pattern complementary to that of
Vangl2 (
Torban et al., 2008
). Embryo homozygotes for a targeted deletion
of
Vangl1
(
Vangl1
gt/gt
)(
Antic et al., 2010
) display craniorachischisis at low
