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Fig. 2. Mapping the spatiotemporal pattern of ß-gal activity in
TOPgal Wnt reporter embryos. (A,B) At E8.5, reporter
activity is restricted to the lateral (L) neural folds and is absent from the
medial (M) midline region near the anterior neural ridge (anr). (C)
X-Gal staining of a transverse section reveals reporter activity is confined
to lateral neuroectoderm of the neural fold (nf). (D) Frontal and
(E) lateral views at E9.5 illustrate reporter activity in cranial
neural crest cells migrating into the first pharyngeal arch (p1) and the
prosencephalon (pros). Cranial neural crest cells covering the midbrain (mb)
are also ß-gal-positive. (F) A transverse section through p1 show
that at this stage, X-Gal staining is found in neural crest (nc) cells but not
surface ectoderm (se) or neuroectoderm (ne). (G) Frontal and (H)
lateral views at E10.5 indicate a distinct boundary between reporter-positive
and reporter-negative cells. The frontonasal prominence (f) is devoid of
staining, whereas some staining is evident in the median nasal prominence (m).
The lateral nasal (l) and maxillary (mx) prominences show strong X-Gal
staining. (I) Transverse sections reveal that surface ectoderm and
mesenchyme of the median (m) and lateral nasal (l) prominences are sites of
X-Gal staining, but neither surface ectoderm or mesenchyme in the frontonasal
(f) prominence is positive for the reporter. (J) Frontal and (K)
lateral views at E11.5 show an increase in X-Gal staining in the median nasal
(m) prominence, whereas the frontonasal (f) prominence remains devoid of
staining. At this stage, the median nasal prominence and maxillary prominence
have fused (red asterisk). (L) Transverse sections show X-Gal staining
disappears from surface ectoderm, but persists in maxillary mesenchyme as the
prominences fuse (red asterisk). (M) Although reduced in size, the
median nasal prominence remains free of X-Gal staining. (N) Transverse
sections show a boundary between ß-gal-positive and ß-gal-negative
regions in the frontonasal mesenchyme (red arrows). At this stage, X-Gal
staining is restricted to mesenchyme (inset, red arrow). (O) At E12.5,
the frontonasal (f) prominence is compressed by the growth of the maxillary
(mx) prominences and (P) transverse sections show that the frontonasal
region lacks reporter activity. The median nasal (m) prominence exhibits
reporter activity. (Q) At E13.5, the mouse muzzle is fully formed and
ß-gal activity is evident in the whisker primordia. The continued growth
of the maxillae (mx) relative to the compressed frontonasal (f) prominence
produces the infranasal depression (ind, red arrow). (R,S)
Transverse sections show the general lack of X-Gal staining in the frontonasal
prominence relative to strong X-Gal staining in the maxillary prominences (mx,
red dotted line). (T,U) Low- and high-power magnifications at
E14.5 reveal frontonasal (f) prominence-derived tissues are reduced to a thin
stripe of midline tissue (dotted red line) that generally maintains its
ß-gal-negative status. The maxillary prominences (mx) remain
ß-gal-positive. (V) A ventral view reveals the general lack of
X-Gal staining in frontonasal prominence-derived primary (1o)
palate. The boundary of X-Gal staining follows the demarcation between
structures derived from the maxillary and frontonasal prominences (dotted red
lines). White dotted circle, incisive foramen. Scale bars: white, 250 µm;
black, 100 µm.
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