Figure 5.

β-Catenin is required early in Pax3-derived somitic cells for generation of limb myogenic cells, but is not required in Pax3-derived migrating progenitors for specification of embryonic myoblasts. Loss of β-catenin in Pax7-derived cells does not affect myoblast specification. During embryonic myogenesis at E12.5 mutant Pax3^Cre/+;β-catenin^Δ/fl2–6;R26R^YFP/+ hindlimbs (E–H) contain many fewer YFP⁺ cells in the limb and none give rise to MyoD⁺ myoblasts as compared with heterozygous control Pax3^Cre/+;β-catenin^fl2−6/+;R26R^YFP/+ hindlimbs in which many YFP⁺ cells are present that give rise to YFP⁺MyoD⁺ myoblasts (A–D). In E12.5 mutant MCre^Tg/+;β-catenin^Δ/fl2–6;R26R^YFP/+ hindlimbs (M–P) in which β-catenin is inactivated in Pax3-derived cells after delamination from the somite, YFP⁺ MyoD⁺ myoblasts are present similar to the heterozygous control MCre^Tg/+;β-catenin^fl2–6/+;R26R^YFP/+ hindlimbs (I–L). In E12.5 mutant Pax7^iCre/+;β-catenin^Δ/fl2–-6;R26R^YFP/+ hindlimbs (U–X) YFP⁺MyoD⁺ myoblasts are present in similar numbers as found in heterozygous Pax7^iCre/+;β-catenin^fl2–6/+;R26R^YFP/+ hindlimbs (Q–T).