analysis (fig. S6, B and C) confirmed that these
protrusions were front-back polarized, analogous
to the front-back polarity described in migrating
cells (Fig. 3, D to F, and fig. S6C). As actin-based
protrusions typically require the actin-related pro-
tein 2/3 (Arp2/3) complex ( 27 , 28 ), we tested
whether a specific Arp2/3 inhibitor, CK-666 ( 29 ),
disrupted basal protrusions and migration in vivo.
Integrity of cell-cell adhesions, crypt cellularity,
and mitosis were not affected during this short-term
CK-666 treatment, excluding potential confounding
effects on cell migration (fig. S7, B to D). In CK-666 – treated mice, apicobasal polarity and the
total protrusion area were not affected, but basal
front-back polarity was lost (Fig. 3, D to G, and
fig. S6D). Accordingly, CK-666 treatment inhibited
cell migration along the villi (Fig. 4, A and B). Next,
we generated an inducible, gut epithelium–specificKrndijaet al.,Science 365 , 705–710 (2019) 16 August 2019 4of6
Fig. 3. Epithelial cells display actin-rich basal
protrusions oriented in the direction of
migration.(A) Mosaic expression of LifeAct-
mCherry (red) in the intestinal epithelium.
Maximum intensity projection (Z range, 30mm).
Scale bars, 50mm. (B) Super-resolution 3D image
(Z range, 2.4mm) of a LifeAct-mCherry-expressing
enterocyte. Scale bar, 4mm. (C) Magnified 2D image
of the boxed region shown in (B). Scale bar, 2mm.
(D) Maximum Z projections of basal part of enter-
ocytes (Z range, 2.6mm) expressing LifeAct-mCherry,
control [dimethyl sulfoxide (DMSO)] or CK-666–
treated. Scale bars, 2mm. (E) Rose plots with average
normalized radial distances for protrusions. n, number
of cells analyzed. (F) Bar chart showing protrusion
length with respect to front-back orientation. ****P<
0.0001. (G) Super-resolution images; apical marker
ZO-1 (left) and basolateral markersa6integrin
(middle) and Na/K-ATPase (right). Boxed regions are
shown in high magnification. Scale bars, 5mm.
RESEARCH | REPORT