Fig. 3: Scx and Osr1 lineages provide myogenic cells in foetal mouse limbs.
From: Unexpected contribution of fibroblasts to muscle lineage as a mechanism for limb muscle patterning
a–c Transverse forelimb sections of E14.5 ScxCre:Rosa26Tom:Scx(GFP) mice. a Tomato expression shows Scx lineage in tendons and limb CTs (red), while GFP shows Scx expression in tendons (green). b Focus on ventral muscles labelled with both MYOD and MYOG antibodies (green). c Focus on myogenic cells MYOD/MYOG+ cells that are Tomato+ (red, arrows), close to a tendon labelled with GFP(Scx) (white asterisks). d, e Longitudinal sections along a limb muscle of E14.5 ScxCre:Rosa26Tom:Scx(GFP) mice labelled with PAX7 (green) and Tomato (red) antibodies. Tendon is highlighted with a white asterisk. Panel e is a high magnification of muscle tips. Arrows point to PAX7+ cells (green) that are Tomato+ (red, Scx lineage), close to the tendon (white asterisk). f Percentage of PAX7+/Tomato+ cells versus PAX7+ cells and percentage of MYOD-MYOG+/Tomato+ cells versus MYOD/MYOG+ cells. Data are presented as mean values ± SD from 3 limbs. g–j Forelimb sections of E15.5 Osr1CreERT2:Pax7GPL mice (with tamoxifen injection at E11.5) immunostained with betaGal (Pax7 lineage in Osr1-lineage-derived cells, green) and PAX7 (red) antibodies, combined with DAPI (blue). g Global view of a forelimb transverse section. h Focus on ventral limb muscles. Tendons are highlighted with white asterisks. i Focus on a muscle region close to a tendon (asterisks). Arrows point to betaGal+ cells (green) that are PAX7+ (red), while arrowheads point to betaGal+ cells that are not PAX7+ anymore. j High magnification of betaGal+ cells (green), arrows point to the betaGal + /PAX7+ nuclei that are located in between myotubes (myosins, grey), while arrowheads point to the betaGal+ nuclei (green) in which PAX7 has been downregulated after cell incorporation into myotubes. k, l Forelimb sections of E15.5 Osr1CreERT2:Pax7GPL mice immunostained with betaGal (green) and MYOD-MYOG (red) antibodies, combined with DAPI (blue). l is a focus of ventral limb muscles of k. m Percentage of betaGal+ versus PAX7+ cells and versus MYOD-MYOG+ cells in limb muscles of E15.5 embryos. Data are presented as mean values ± SD from 3 limbs.
