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Fig. 1. Shroom2 induces apical pigment accumulation but not apical constriction
in epithelial cells. (A) Shroom2 shares three regions of protein
similarity with Shroom3, an N-terminal PDZ domain and two ASD domains.
(B) The blastula assay. Xenopus blastomeres at the cleavage
stages undergo cell division without transcription
(Newport and Kirschner, 1982),
and through asymmetric divisions, give rise to both outer, polarized
epithelial cells and inner, non-polarized cells
(Chalmers et al., 2003). mRNA
(red) injected in individual blastomeres at the four-cell stage is distributed
to polarized (grey) and non-polarized (white) cells. (C,c')
Control Xenopus embryos with normal levels of apical pigment.
(D,d') Embryos injected at the four-cell with 1 ng of Shroom3 or
Shroom2. (E,e') Dramatic apical pigment accumulation. (F)
Shroom3 expression results in apical constriction and a reduction of surface
area, while Shroom2 expression had no effect on cell surface area.
(G-I) Actin localization is limited to cell junctions in control (G)
cells, while Shroom3-injected embryos (H) had high levels of ectopic actin
accumulation at their apical surfaces. Shroom3-injected cells accumulate only
modest amounts of apical actin (I). Actin accumulation is indicated by red
arrows.
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