Biomedical Engineering Reference
In-Depth Information
PCP signaling, please consult other articles in the same issue. So far, only the
“core” PCP components have been analyzed in axon guidance. Therefore,
this review focuses on the “core” components.
Planar polarity has mostly been studied in stationary cells that form
two-dimensional tissue sheets. Therefore, it is surprising that PCP signaling
components are involved in directional control of the motile axonal growth
cones. In addition to axon guidance, the same conserved genes that control
the “classic” PCP events are also important in many types of moving cells or
cellular structures, such as in convergent extension and neuronal migration
( Fenstermaker et al., 2010; Mrkusich et al., 2011; Shafer et al., 2011;
Shimizu et al., 2011; Wada & Okamoto, 2009 ). The function of PCP
components is required for the precise anterior turning of commissural
axon growth cones after midline crossing in the spinal cord and proper
anterior-posterior guidance of dopaminergic and serotonergic axons in the
midbrain and hindbrain. The anterior-posterior guidance of the spinal cord
and brainstem neurons, as well as the anterior-posterior migration of
zebrafish facial motor neurons and mouse branchinomotor neurons,
coincides with the anterior-posterior polarity observed in the intercalating
cells in zebrafish convergent extension ( Lyuksyutova et al., 2003; Qu et al.,
2010; Shafer et al., 2011; Wada & Okamoto, 2009 ). In addition to axon
guidance, there has been an explosion of papers demonstrating the function
of PCP genes in various developmental and disease processes in different
tissues ( Barrow, 2011; Carroll & Das, 2011; Happe, de Heer, & Peters,
2011; Heinonen, Vanegas, Lew, Krosl, & Perreault, 2011; Ng, 2012;
Sugiyama, Lovicu, & McAvoy, 2011; Sundberg et al., 2011; Wu, Ge,
Huang, Hua, & Mu, 2011; Yates & Dean, 2011; Zou, 2011 ).
The rapid expansion of the roles of these PCP genes automatically invites
the following questions: Is the term “planar cell polarity” being used too
loosely? Are some of the functions separate from the real PCP signaling?
Alternatively, this may suggest that a common signaling mechanism which
can impart polarity drives many morphogenesis processes, some of which are
obviously analogous to the classic PCP described in Drosophila and others are
not immediately similar at least on the surface. Given the broad nature of
planar polarity in tissues from all germ layers ( Zou, 2011 ), it is a formal pos-
sibility that the core PCP signaling system, being first characterized in fly
wing and eye, may be a widely used signaling module conveying direction-
ality in many cell types during various events of morphogenesis. “PCP
signaling” or “PCP-like signaling” or “PCP signaling module” refers to this
Search WWH ::




Custom Search