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Fig. 5. Accumulation of ß-catenin in Foxf mutant intestinal epithelium.
ß-Catenin immunostaining (A-D,F-K) and TUNEL assay (E; red nuclei
indicate apoptotic cells) of E18.5 small intestine of wild type (A,F,H,J),
Foxf1-/+; Foxf2-/+ (B-E) and
Foxf2-/- (G,I,K). (A) In normal E18.5 small
intestine, ß-catenin is most abundant in the basal epithelial cells of
the intervillus pits and decreases along the villus axis (non-specific
staining in the gut lumen is due to the stickiness of the meconium).
(B-D) In Foxf mutants, ß-catenin concentration stays high all the
way to the villus tip. Foxf1-/+;
Foxf2-/+ differs from Foxf2-/- in
having a mosaic pattern with sharp boundaries between regions of the
epithelium with high and low ß-catenin (C,D; arrowheads in B). (E)
Patches of TUNEL-positive (apoptotic) cells match the low ß-catenin
mosaic pattern. (F,G) Higher magnifications show nuclear localization
of ß-catenin at base of villi in wild type (F), but ubiquitous nuclear
ß-catenin in Foxf mutants (G). (H) Only membrane-associated
ß-catenin is found only in cells from upper half of wild-type villus;
nuclei (white arrowhead) are negative. (I-K) Both nuclear (white
arrowheads) and membrane-associated ß-catenin are found in cells from the
upper half of Foxf2-/- villus (I; circular organelle in
adjacent cell is a goblet cell mucus vesicle) and from the base of wild-type
(J) and Foxf2-/- villus (K). Epithelial depolarization is
beginning in K, in spite of the seemingly intact contact with the mesenchyme:
the membrane associated ß-catenin has begun to expand from the lateral
and into the apical surface (black arrowhead) and nuclei are centrally located
in the cells. (L-Q). Normal or reduced amounts of the major
glycosaminoglycan proteoglycans in Foxf mutant intestine. Immunostaining with
antisera against nidogen (Entactin; L,O), perlecan (M,P) and syndecan 1 (N,Q)
on cryosections of E18.5 small intestine from wild type (L-N) and
Foxf2-/- (O-Q). Nidogen and perlecan are constituents of
the mesenchymal ECM and present in normal amounts in Foxf mutants. Syndecan 1
is membrane anchored, present on the basolateral face of epithelial cells and
reduced in Foxf mutant intestine.
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