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as a receptor ligand pair and that Fj modulates their activity by
phosphorylation ( Brittle, Repiso, Casal, Lawrence, & Strutt, 2011;
Matakatsu & Blair, 2004; Simon, 2004; Simon et al., 2010; Sopko et al.,
2009 ). One observation that does not fit this model is the observation
that transgene-supplied Ft that lacks the extracellular domain provides
rescue of the ft PCP phenotype over most of the wing ( Matakatsu &
Blair, 2006 ). How to reconcile these observations is not clear. The Ft and
Ds proteins do not appear to accumulate asymmetrically as do fz/stan
pathway proteins; however, they are able to polarize cells. This is seen
both by their effect on hair polarity and by their activity leading to the
asymmetric accumulation of the atypical myosin Dachs ( Mao et al., 2006,
2011 ). Early studies found that the fz/stan pathway was functional in ds
and ft mutants but that it signaled in an anatomically abnormal way
( Adler et al., 1998 ), and subsequently, it was proposed that the ds/ft
pathway functioned as a global signal that oriented the activity of the
fz/stan pathway with respect to the body as a whole in the wing and eye
( Ma et al., 2003; Simon, 2004; Yang et al., 2002 ). However, studies by
Casal et al. (2006) provided compelling data that in the abdomen that the
ds/ft and fz/stan pathways functioned in parallel. For example, double
mutants of one ds/ft and one fz/stan pathway gene had a more severe
phenotype than any single mutant or double mutant where only one of
the pathways was affected. They also showed that ds/ft could repolarize
cells that were mutant for the fz/stan pathway. One interpretation of
these observations is that the relationship between the two pathways is
different in different tissues. This is not a satisfying explanation; however,
it may be correct. More recent experiments suggest that ds/ft may alter
fz/stan signaling in indirect ways by affecting the axis of cell division, cell
rearrangements, and the polarization of microtubules that are involved in
the transport of Fz-containing vesicles ( Harumoto et al., 2010; Mao
et al., 2011 ). There is increasing evidence that ds/ft also function in
vertebrate PCP ( Goodrich & Strutt, 2011 ).
3.3. Septate junction proteins
A third set of genes essential for the morphogenesis of normal wing PCP are
genes such as Gliotactin , Neuroglian , Coracle , and varicose ( Moyer & Jacobs,
2008; Venema, Zeev-Ben-Mordehai, & Auld, 2004 ). These genes
encode proteins that are associated with the septate junction, and they are
required for the alignment of neighboring hairs ( Fig. 1.5H and I ). The
septate junction is the invertebrate equivalent of
the vertebrate tight
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