Figure 1.

Elucidation of the Developmental Origin of PC Muscle and Satellite Cells

(A and B) Structure and localization of the PC. Histological sections of dorsal skin showing the presence of AP-Mrf4⁺ fibers (in B195APZ mice) (A) and striated MyHC⁺ fibers (in wild-type mice) (B).

(C) Schematic representation of embryonic muscle development from presomitic mesoderm to myotome formation (modified from Buckingham and Rigby, 2014). Sequential expression of Myf5 (at the PSM), Pax3, Pax7, and again Myf5 (at the somite) transcription factors is depicted at the top.

(D) Myf5⁺ lineage traced by immunofluorescence with anti-GFP antibody of Myf5Cre^SOR;R26YFP dorsal skin sections.

(E) Pax3⁺ lineage traced by fluorescence of GFP and Tomato in Pax3^Cre/+ dorsal skin sections.

(F) Pax7⁺ lineage traced by immunofluorescence with anti-GFP and anti-Laminin antibodies of Pax7^CE dorsal skin sections.

(G) TEM image of PC satellite cell ultrastructure from ultrathin skin sections. Asterisk indicates condensed chromatin patch.

(H) Histological section of dorsal skin showing the localization of nlacZ-Myf5⁺ cells (arrows) (in B195APZ mice).

(I) In Pax3nLacZ mice, no staining of the PC was observed indicating that PC satellites are nlacZ-Pax3-negative cells.

(J) Immunofluorescence with anti-PAX7 antibody demonstrates Pax7⁺ cells (arrows) in a satellite cell position underlying Laminin⁺ basement membrane. (J′) Higher-magnification inset.

(K) Satellite cell marked by anti-GFP antibody in Myf5Cre^SOR;R26YFP mice.

(L) Satellite cell marked by anti-GFP antibody in B195AP-Cre;R26YFP mice. Nuclei were counterstained with Hoechst 33258 (blue).

Scale bars represent 100 μm in all panels with the exception of (G) (2 mm) and (L) (10 μm). See also Figure S1.