Fig. 4. Normal distribution of neural crest cells in Msx2 mutant mice. Mice carrying the R26R lacZ allele were crossed with mice bearing a Wnt1-Cre transgene, thus marking neural crest cells with lacZ. Embryos at the indicated developmental stages were stained for ß-galactosidase activity and the stain visualized in wholemount or cross section. (E,F) Frozen sections, (G-J,M,N) paraffin sections. Enlarged views of boxed areas in G and H are shown in I and J. Lines in K and L indicate the level of sections shown in M and N. No significant difference in neural crest distribution was evident at E9.5 (A,B). At both E11.5 and E12.5, there was no difference in the density or distribution of lacZ-positive cells the area of the frontal bone rudiment (C,D, arrowheads; E,F, arrows). In some E12.5 embryos there was a delay in the migration of neural crest dorsally (compare G and I with H and J). By E16.5, no difference was apparent (compare K and M with L and N). br1, first branchial arch; bv, blood vessel; ch, cerebral hemisphere; e, eye; ep, epithelium; fb, frontal bone; fn, fronto-nasal process; pb, parietal bone; sm, sutural mesenchyme. Scale bars: 200 µm in B,F,H,N; 1 mm in D,L; 50 µm in J.

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