Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
???displayArticle.abstract???
Catenins (alpha-, beta- and gamma- or plakoglobin) are cytoplasmic cadherin-associated proteins. Studies on cultured cells have suggested that both alpha-catenin and plakoglobin are important for the adhesive function of cadherins. alpha-catenin binds to both beta-catenin and plakoglobin and may link the cadherin/catenin complex to actin filaments. Separate domains of plakoglobin bind to cadherin and alpha-catenin, suggesting it may act as a bridge between these molecules. However, plakoglobin may have other activities: it is expressed in both desmosomal junctions in association with desmogleins and the cytoplasm in conjunction with APC, and previous work suggests it may act in a dorsal signalling pathway when overexpressed in Xenopus embryos. Here, we have studied the roles of alpha-catenin and plakoglobin directly, by depleting the maternal mRNAs coding for each of them in developing Xenopus embryos. We find that depletion of maternal alpha-catenin causes the loss of intercellular adhesion at the blastula stage, similar to that reported previously for EP cadherin. Depletion of plakoglobin results in a partial loss of adhesion, and a loss of embryonic shape, but does not affect dorsal signalling.
Fig. 1. Injection of antisense oligos complementary to a-catenin (A,C,E) or plakoglobin (B,D,E) mRNA depletes the endogenous maternal
mRNAs and proteins. (A) Northern blot, probed for a-catenin, of RNA (2 oocytes or embryos equivalent per lane) from cleavage stage (stage 4),
mid-blastula stage (stage 8), gastrula stage (stage 10.5) and late neurula stage (stage 18), either uninjected (U) or injected as oocytes with 4 ng
oligo A3 (A), and with 4 ng of oligo A3 plus 1.2 ng of mouse a-catenin mRNA (A+M). The exogenous mRNA is smaller because it contains
only the mouse a-catenin coding sequence. (B) Northern blot, probed for plakoglobin, of RNA from oocytes, midblastula stage (stage 8),
gastrula stage (stage 10.5), late neurula stage (stage 18), either uninjected (U) or injected as oocytes with 2 ng of oligo M7 (A), and with 2 ng of
oligo M7 plus 2 ng of plakoglobin mRNA. Both blots were stripped and reprobed for EF1aRNA, to indicate RNA loading. (C,D) Western blots
of proteins from stage 6 oocytes (C) and blastula-stage embryos (D), either uninjected or injected as oocytes with 4 ng of oligo A3 (C) or with
2.5 and 3 ng of oligo M7 (D). The blots were probed with a-catenin (C) and plakoglobin (D) antibodies (see Materials and Methods). (E,F)
Western blots of supernatant (S) or insoluble (P) fractions of proteins from blastula (stage 8) embryos (5 embryos per fractionation). (E) Lefthand
four lanes, embryos injected with 2.5 ng of oligo M7 and probed with plakoglobin antibody, compared to uninjected controls; right-hand
four lanes uninjected embryos compared to embryos injected with 5 ng of oligo A3 and probed with a-catenin antibody. (F) Left-hand six lanes,
control embryos compared to those injected with 1 or 1.2 ng of oligo 303 (Heasman et al., 1994b) and probed with b-catenin antibody; righthand
two lanes, control embryos probed for b-1 integrin.
Fig. 2. Depletion of maternal a-catenin mRNA and protein causes a disaggregated phenotype, which can be rescued using mouse a-catenin
mRNA. (A) A control embryo (left) together with an a-catenin-depleted sibling embryo (right) dissected at the blastula stage to show the loss of
interblastomere adhesion. (B) Midblastulae disaggregated and allowed to aggregate for 45 minutes. Blastomeres from a-catenin-deficient
embryos (right) failed to aggregate in comparison to wild-type blastomeres (left). (C) Blastulae derived from uninjected (middle) or injected as
oocytes with 4 ng oligo A3 (right), and 4 ng oligo A3 plus 1 ng mouse a-catenin mRNA (left) to show that mouse a-catenin mRNA was able to
restore a normal blastula morphology into a-catenin-depleted embryos.
Fig. 3. Depletion of maternal plakoglobin
mRNA and protein causes a phenotype marked
by a specific affect on cytoarchitecture, a mild
adhesion defect most evident in the vegetal
blastomeres and a delay of gastrulation. All
aspects of this phenotype are at least partially
rescued with Xenopus plakoglobin mRNA.
(A) A control embryo (top left, brown), a
plakoglobin mRNA-treated embryo (bottom left,
red) and two oligo doses of plakoglobin-depleted
embryos, 2.0 ng (top right, blue) and 2.5 ng
(bottom right, mauve). (B) Midblastulae
disaggregated and allowed to aggregate for 45
minutes. Blastomeres from plakoglobin-depleted
embryos (right) aggregate less well than control
blastomeres (left). (C) Comparison of
devitellined plakoglobin-depleted (left, mauve)
embryos to a-catenin-depleted embryos (right,
red). Plakoglobin-depleted embryos show a
flattened morphology that is not evident in the a-
catenin-depleted embryos. (D) Plakoglobindepleted
embryos are delayed in gastrulation. A
control embryo (top left, brown), a plakoglobin
mRNA-treated embryo (top right, red), and three
doses of plakoglobin oligo M7 (bottom left to
right) 2.5 ng (mauve), 2.0 ng (blue), 1.75 ng
(green). (E) Control and plakoglobin-depleted
embryos form normal neural structures. Starting
from left to right, plakoglobin-depleted embryos
2.5 ng (mauve), 2.0 ng (blue), 1.75 ng (green),
control embryo (brown) and plakoglobin
mRNA-treated embryo (red). (F) Partial rescue of oligo-mediated adhesion and cytoarchitectural defects at blastula stage with plakoglobin
mRNA. Control embryos (top), plakoglobin-depleted embryos (middle) and plakoglobin-depleted embryos injected with Xenopus plakoglobin
mRNA (bottom). (G) Plakoglobin mRNA can rescue the gastrulation delay of plakoglobin-depleted embryos. Plakoglobin-depleted embryos
(left),depleted embryos injected with Xenopus plakoglobin mRNA (middle) and control embryos (right).
Fig. 4. Northern blot probed for MyoD, a marker of dorsal
mesoderm. One embryo equivalent was loaded per lane at the
gastrula or neurula stage. Experimental embryos were derived from
oocytes injected with 1.75 ng, 2.0 ng or 2.5 ng of plakoglobin oligo
M7. The blot was stripped and reprobed with Ef1-ato control for
loading.
