|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
|
Fig. 5. Skeletal and molecular analyses of Tcf4-/-;
Lef1-/- compound mutants. Histological staining on
transverse sections through E15.5 wild-type
(Tcf4+/+/Lef1+/+) mouse embryos shows
(A) the normal length of the cartilaginous nasal septum (ns) and
(B) the curvature of the nasal cartilage (nc) and condensations of the
whisker buds (black arrows). The nasal epithelium (ne) is correctly organized.
(C) In compound null-mutant embryos nasal cartilage (nc) growth is
truncated and whisker buds are absent (black asterisks). Despite this dramatic
alteration in shape, the cartilage is still well developed and the nasal
epithelium (ne) is organized. (D) In contrast to the wild-type nasal
septum shown in A, the mutant nasal septum is dramatically foreshortened.
(E,F) Ventral view of Alcian Blue/Alizarin Red skeletal
preparation (mandibles removed) shows that in wild-type embryos (E), the
basisphenoid (bs), premaxillae (pmx, white dotted line), maxillae (mx),
palatine bones (pal) and the nasal septum have formed normally and have their
proper orientation relative to one another. (F) Tcf4-/-;
Lef1-/- mutants exhibit grossly underdeveloped premaxillae
(pmx, dotted white line), which fail to make contact and fuse across the
midline. The major skeletal elements of the posterior palate appear normal.
(G) Pentachrome staining of transverse sections through E15.5 jaws
reveal tooth primordia at the bell stage, where the dental epithelium (de) has
invaginated and dental mesenchyme (dm) has condensed in response to signals
from the ectoderm. (H) Tcf4-/-; Lef1-/-
dental epithelium (de) fails to invaginate properly. Note, however, that
maturation of Meckel's cartilage (mk) and the bone of the mandible (mn) are
unaffected by the loss of Tcf4 and Lef1. (I,J) Pentachrome
staining of transverse sections through E15.5 wild-type embryos reveals the
characteristic `Y' shape (yellow dotted line) of the anterior nasal septum,
which correlates to the location of the infranasal depression (ind). In an
adjacent tissue section, the osteogenic condensation of the maxillae is
evident (dotted white line), as well as the tooth (t) and epithelial seam
(dotted white box) of the palatal shelves, which is dissolving on an
appropriate time scale. (K,L) In E15.5 Tcf4-/-;
Lef1-/- littermates, the osteogenic condensation of the
maxillae is reduced (dotted white line), the tooth (t) is developmentally
delayed and the epithelial seam (dotted white box) of the palatal shelves
remains evident. The anterior nasal septum exhibits a dysmorphic `T' shape
(yellow dotted line), corresponding to the malformed midface seen earlier
(Fig. 4). (M,N)
In situ hybridization on transverse sections of E15.5 wild-type embryos shows
that collagen II (Col II) is expressed throughout the cartilaginous
nasal septum (ns) and Msx1 transcripts are detected in surface
ectoderm (se, dotted red line), nasal epithelium (ne) and undifferentiated
mesenchyme. (O,P) In E15.5 Tcf4-/-;
Lef1-/- littermates, Msx1 expression is specifically
lost in surface ectoderm (dotted red line) but maintained in nasal epithelium
and underlying mesenchyme. Collagen II transcripts persist in the dysmorphic
nasal septum (ns), indicating normal chondrocyte differentiation. Scale bars:
white, 1 mm; black, 100 µm.
|
