Fig. 1

Pax3- and Pax7-expressing cells contribute to mouse OSM. (A-I) Immunodetection of MyHC (A-C,F,H,I), smooth muscle myosin (I), EYFP (B,F,H) and βgal (G); nuclei staining (DAPI/Hoechst; B,F-I); and histochemistry for alkaline phosphatase (AP; A,C) or βgal (D,E) on transverse cryosections of murine oesophagus. (A) The sternohyoid muscle (sh) was AP⁺, whereas the adjacent sternomastoid muscle (sm) was unlabelled. (B) Pax3^Cre/+;R26R^EYFP mice show MyHC in some EYFP⁺ cells (arrows) at E15.5. (C) By P0, Pax3^Cre/+;Z/AP mice have OSM cells marked with AP (dots outline an area of staining over a fibre). Some OSM is unmarked (arrowheads), and neural cells between the longitudinal and circumferential OSM layers are marked (asterisks). (D) Tamoxifen treatment of Pax7^CE/+;R26R^lacZ mice at E11.5 marked cells at E16.5 in outer longitudinal muscle layer (lml, where OSM is present) but only rare cells in inner circumferential muscle layer [cml, lacking OSM at this stage (see A)]. (E) Wnt1^Cre;R26R^lacZ (right panel) mice had neural crest cells between the muscle layers (asterisk). (F) Tamoxifen treatment of Pax7^CE/+;R26R^EYFP mice at E12.5 marked OSM cells in lml at E16.5 with EYFP (arrow). Small rare Pax3⁺ cells are found adjacent to the OSM. (G) At E16.5, Wnt1^Cre;R26R^lacZ mice have βgal in a thin layer of neurofilament-containing cells between the muscle layers (asterisk). (H) Treatment of Pax7^CE/CE;R26R^EYFP mice with tamoxifen at P11 led to abundant EYFP-marked OSM cells at P14 (arrow) and smaller EYFP-marked cells lacking MyHC (arrowhead). (I) At E14.5, Pax3^Cre/Cre mice show slightly reduced and disorganised smooth muscle myosin (green), compared with Pax3^Cre/+ littermates. There is a lack of longus colli striated muscle (lc) in mutant. ca, carotid artery; t, trachea; oe, oesophagus. (J) Mouse OSM development (red, sarcomeric myosin) among smooth muscle (green, smooth myosin), drawn approximately to scale. Boxed areas in the left panels are magnified on the right. Boxed areas in J are shown in panels above. Scale bars: 50 μm in A; 20 μm in B-I.