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Fig. 3. Loss of Wnt9a leads to defects in joints, and ectopic Wnt9a can
transform chondrocytes in fibroblast-like cells. (A) P0 forelimbs
stained with Alcian Blue/Alizarin Red. (a) Wild-type elbow region; (a')
Wnt9a-/- elbow, in which an ectopic Alcian Blue-stained
nodule is present in the humeral-radial joint (HRJ) (arrow). Serial sections
of wild-type (b,c) and Wnt9a-/- (b',c') P0
forelimbs, showing Alcian Blue (arrow in b') and
Col2a1-positive (arrow in c') chondrocytes instead of synovial
cells within the HRJ fold. Serial sections of wild-type (d,e) and
Wnt9a-/- (d',e') at E15.5, showing that in the
mutant cells in the HRJ region express Sox9 (d'), and that a
small cluster of cells expresses Col2a1 (arrow in e'). (f)
Schematic diagram of the carpal elements, metacarpal elements of digits I-V
and distal row of carpal elements 1-5 in wild type. c, central carpal element;
r and u, radial and ulnar element; R and U, radius and ulna. (f')
Partial fusion between carpal elements c and 3 (arrow) in
Wnt9a-/-. (g) Schematic diagram of the tarsal elements in
wild type; Cal, calcaneus; cub, cuboid; l.c., lateral cuneiform; i.c.,
intermediate cuneiform; nc, navicular; t, tarsal; metatarsal elements of
digits II-V. (g') Partial joint fusion between the intermediate
cuneiform and navicular tarsal elements (arrow) in the mutant. (B)
Immunohistochemical staining for collagen type II and collagen type III on
chicken sternal chondrocytes infected with RCAS-AP, RCAS-Wnt5a, RCAS-Wnt9a and
RCAS-caß-cat, showing that Wnt9a and caß-cat-infected chondrocytes
change their morphology, and that instead of producing collagen type II they
synthesize collagen type III. (C) Western blot for ß-catenin using
protein extracts from infected chondrocytes, showing that cells infected with
a RCAS virus expressing Wnt9a or Wnt3a have increased ß-catenin
levels.
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