Tissue-specific activities of the Fat1 cadherin cooperate to control neuromuscular morphogenesis
(A) Scheme representing the shape of the CM muscle seen from the side of an embryo, featuring the area covered by GdnfLacZ+ muscle progenitors in purple, MLC3F-2E+ muscle fibers represented in blue, and CM-innervating axons represented in green, indicating (vertical lines) the level corresponding to sections shown in (B) and (C). (B) Cross section of an E12.5 GdnfLacZ/+ embryo, at the middle CM level, immunostained with antibodies to Pax7 (red) and β-galactosidase (green), showing that GdnfLacZ is expressed in Pax7+ progenitors. (C) Cross sections of an E12.5 GdnfLacZ/+; Etv4-GFP+ embryo at the anterior CM (top pictures), middle CM (middle row), and posterior CM (bottom row) levels and immunostained with antibodies to Pax7 (red), β-galactosidase (red), Myh1 (green), and GFP (green) and with DAPI (blue). At each level, three neighboring sections of the same embryo were used with the indicated antibody combinations. In (C), inserts show high magnifications of the area highlighted with the yellow dotted square. Scale bars: low-magnification pictures in C: 200 μm; inserts in C: 40 μm; high-magnification (right) pictures in B: 40 μm; low-magnification pictures (left) in B: 200 μm. ant, anterior CM level; β-Gal, β-galactosidase; CM, cutaneous maximus; C5 to C8, Cervical levels 5 to 8; Etv4, Ets variant gene 4; Etv4-GFP, transgenic line in which expression of an Etv4-GFP fusion protein is driven by the Etv4 locus (S1 Table); GFP, green fluorescent protein; mid, middle CM level; Myh1, myosin heavy chain 1; Pax7, paired box 7; post, posterior CM level; T1 to T3, Thoracic levels 1 to 3.