Fig. 5. PDGFA signaling and protrusive activity. (A) Protrusions in the mesoderm of normal and of PDGFA signaling-compromised gastrulae, as determined from scanning electron microscope pictures. Percentage of cells with no underlapping protrusions, with protrusions pointing animally, or vegetally, were assessed in uninjected embryos (n=157 cells), and in embryos injected with dnPDGFA (n=155) or lfPDGFA mRNA (n=158), respectively. Cells were scored as animally oriented if the vector, cell center-protrusion, pointed upwards at any angle in carefully oriented SEM pictures, and vegetally oriented if otherwise. The lower percentage of protrusion-bearing cells in dnPDGFA and lfPDGFA embryos, when compared with controls, is highly significant (significance level =0.001, ²-test), the difference between dnPDGFA and lfPDGFA embryos is not significant. (B,C) Protrusions of single mesodermal cells on substratum conditioned with control BCR, with BCR overexpressing lfPDGFA or dnPDGFA. (B) The percentage of cells extending cytoplasmic protrusions (lamellipodia or pseudopodial blebs) was determined. The fraction of cells with no processes is significantly higher on dnPDGFA conditioned substratum (n=317 cells) when compared with control (n=323) or lfPDGFA (n=467) substratum (significance level =0.01, ²-test). (C) Examples of typical cell morphologies (rhodamine-phalloidin staining of the actin cytoskeleton) are shown.