Biomedical Engineering Reference
In-Depth Information
The negative protein interactions between cytoplasmic proteins noted above
could also serve to remove mislocalized proteins and hence to increase the
asymmetry.
Taken together with earlier observations, one is lead to a model where
directed transport leads to a modest bias in the localization of the three trans-
membrane proteins. Direct protein interactions across the juxtaposed distal
and proximal membrane domains would stabilize proximally localized Vang
and distally localized Fz and hence increase the bias in protein localization.
The binding of the cytoplasmic proteins would further stabilize and increase
the size of the protein complexes. Thus, the formation of the asymmetric
protein complexes would involve several layers of mechanisms.
5. DIRECTIONAL CELL NONAUTONOMY
One striking property of
fz
and
Vang
mutant cells is the directional
domineering nonautonomy displayed by clones (
Taylor et al., 1998;
Vinson & Adler, 1987
)(
Fig. 1.1D and F
). This differs from the essentially
cell autonomous activity of other
fz
pathway genes (
Fig. 1.1E
) (these
other genes show very limited cell nonautonomy that is rare or limited to
neighboring cells) (
Chae et al., 1999; Collier & Gubb, 1997; Collier
et al., 2005; Gubb & Garcia-Bellido, 1982; Lee & Adler, 2002; Park
et al., 1996
). The polarity of wild-type cells distal to
fz
clones and
proximal to
Vang
clones is affected. This is due to hairs pointing toward
cells of lower Fz activity and toward higher Vang activity (
Adler,
Krasnow, & Liu, 1997; Adler, Taylor, & Charlton, 2000; Casal et al.,
2006; Strutt & Strutt, 2007
). Complementary effects are seen when cells
are manipulated to express higher Fz or Vang levels (
Adler et al., 1997;
Adler, Taylor, et al., 2000
).
5.1. The basis for directional cell nonautonomy
Early evidence suggested that
fz
had both cell autonomous and cell non-
autonomous functions (
Vinson & Adler, 1987
). Several
fz
alleles behaved
cell autonomously (
Vinson & Adler, 1987
) and that the cell nonautonomous
function of
fz
was independent of
dsh
and preceded and was temporally
separate from the cell autonomous function (
Lee & Adler, 2002; Strutt &
Strutt, 2002
). It is worth noting that the PCP system does not require
patterned expression of any of the
fz
pathways genes as even expression
of these genes provides complete rescue of null alleles (
Axelrod, 2001;
