Extended Data Figure 1: Somitic mesoderm-derived cells migrate into the AER before AF formation and occupy a position distal to the AER basement membrane.
From: A somitic contribution to the apical ectodermal ridge is essential for fin formation
a–h, Somite-derived cells are positioned distally to the basement membrane of the AER. Pectoral fin of Tg(pax3a:GFP) transgenic embryos at 36 hpf (a–d, lateral view) and 48 hpf (e–h, transverse view), stained for pan-laminin (red), which marks the basement membrane of the AER (a, e), GFP (green) (b, f), DAPI (blue) (c, g), and a merged view (d, h). Arrowheads mark the somite-derived cells that invade the AER, and occupy a position distal to the basement membrane. i–l, Somite-derived cells are positioned within the AER and adopt expression of an epithelial marker. Dorsal view of a pectoral fin of a Tg(pax3a:GFP) embryo at 48 hpf, stained with an antibody against We3 (red), which is an epithelial marker for the AER and wound epithelium in salamander limbs (i), GFP (j), a merged view (k), and a merged differential contrast (DIC) image (l). Somite-derived cells (arrows) not only reside in the epithelial AER, but also co-express the epithelial marker. m–p, Histological analysis of the positioning of somite-derived cells within the AER and AF. Haematoxylin and eosin (H&E) staining (m, o) and periodic acid-Schiff (PAS) staining (n, p) on sagittal sections of Tg(pax3a:GFP) pectoral fins at 44 hpf (m, n) and 48 hpf (o, p). PAS specifically stains the basement membranes of tissues owing to the presence of Schiff-reactive glycoproteins within these structures. Arrows mark somitic mesoderm-derived cells in the AER (m, n) and AF (o, p), respectively. Both these histological analyses reveal that somite-derived cells are positioned distally to a continuous basement membrane. Scale bars, 20 μm.
