Figure 5. Wnt1-Cre-medidated conditional deletion of Pax3 within the NC lineage does not affect OFT septation but does perturb NC-derived Schwann cell morphogenesis.

(A–F) Wnt1-Cre;R26R lacZ lineage mapping of wildtype (A–C) and Pax3^Δ5/Wnt1Δ5 conditional mutant NC cells (D–F). CNC colonization of E10.5 mutant 4/6^th PAAs and OFT is equivalent to wildtype, but E11.5 mutants exhibit disorganized Schwann cell morphogenesis and clump on neurons (arrows in E). Conditional mutants also exhibit exencephaly (D, F), but are otherwise identical to wildtype littermates. (G&H) In situ hybridization with Pax3 full length probe (G) and Pax3 exon5-specific probe (H) on adjacent conditional mutant E10 sections. Note Δ5 transcripts are missing in uppermost dorsal NT (arrow in H). Phase contrast images are inset to verify tissue integrity. Both exon5-specific and full length probes are identically expressed in somites (som). (I&J) Consistent with in situ data, Pax3 protein is absent in mutant uppermost dorsal NT (arrows in J), but in region below Wnt1-Cre expression, Pax3 immunohistochemistry signal intensity is similar to control littermates. (K&L) Gross view of P10 pups showing generalized pigmentation defects in mutants (inset in L). LacZ staining- revealed melanocytes (arrow in K) in control epidermal basal layer (*) that are positive for melanin (brown), a marker for mature melanocytes. Mutants exhibit lacZ-positive melanocytes at similar densities but are all negative for melanin synthesis.