Fig. 4. Loss of PDGFR-PI3kinase signaling results in defective migration. (A,A') PDGFR^GFP/+, (B,B') PDGFR^PI3K/GFP and (C,C') PDGFR^TKO/GFP. PDGFR-expressing cells (as detected by PDGFR^GFP) are present in the perichondrium and in the mesenchyme surrounding the vertebral arch. (A,A') Heterozygote control section is at the level of the perichondrium and therefore displays more PDGFR-positive chondrocytes. The PDGFR-positive mesenchyme adjacent to the vertebral arch extends just beyond the tip of the arch in the heterozygote control, but has failed to advance in the (B,C) mutants. Sections are representative of furthest advancement of the vertebral arch and adjacent mesenchyme population in two embryos of each genotype. (A'-C') DAPI fluorescence of the sections in A-C. Adjacent mesenchyme is outlined. Asterisks denote the tip of the vertebral arch. Arrow indicates mesenchyme. va, vertebral arch; nt, neural tube. Scale bar: 100 µm. (D) In vitro migration assay. Heterozygous cells (grey bars) migrated in a dose-dependent manner in response to PDGF-AA and PDGF-BB ligands, whereas mutant cells (striped bars) were unable to migrate in response to PDGF-AA and showed a decreased response to PDGF-BB. Both genotypes were able to migrate in response to 10% serum. This experiment is representative of three independent experiments.