Biomedical Engineering Reference
In-Depth Information
8. COORDINATION OF ASYMMETRIC CELL DIVISIONS
DURING POSTEMBRYONIC DEVELOPMENT
Similar to embryonic cell polarity, polarity orientations are coordi-
nated with high/low POP-1 asymmetry after most postembryonic cell
divisions through the functions of multiple Wnt genes (
Yamamoto et al.,
2011
). Six seam cells (V1-V6) on the lateral side of animals undergo self-
renewing asymmetric division. Even though these cells are aligned along
the anterior-posterior axis and contact with each other, their polarity does
not appear to depend on communication between neighboring cells as in the
PCP regulation in
Drosophila
wing, as reversal of polarity in one of the seam
cells does not affect that of its neighbors (
Whangbo, Harris, & Kenyon,
2000; Yamamoto et al., 2011
). Instead, the analyses of Wnt compound
mutants showed that their polarity orientation is independently controlled
by redundant functions of multiple Wnt genes (
Fig. 3.6
). Polarity of the
V1-V4 seam cells is affected in triple Wnt mutants (
cwn-1
,
cwn-2 egl-20
)
but not in the double mutants among them (minor defects were observed
LIN-44
EGL-20
CWN-2
CWN-1
Wild type—normal polarity
Quadruple Wnt mutants—abnormal orientation
LIN-44
EGL-20
CWN-1
CWN-2
Triple mutants of Wnt receptors—loss of polarity
CWN-2
Posterior expression of CWN-2—normal polarity
Figure 3.6 Regulation of polarity orientation in seam cells by multiple Wnts. In wild
type, Wnts are expressed anteriorly (CWN-2) or posteriorly (CWN-1, EGL-20, LIN-44) to
seam cells. In quadruple Wnt mutants as in quintuple ones, polarity orientations were
randomized. In contrast, after knock down of three Wnt receptors, cells were not polar-
ized. Posterior expression of CWN-2 rescued polarity defects in a compound Wnt
mutant.
