Fig. 4. Effects of compromised PDGFA signaling on gastrula. Stage 10.5 gastrulae of uninjected controls (A,D,G) are compared with sibling embryos injected with inhibitory dnPDGFA mRNA (B,E,H) and wild-type lfPDGFA mRNA (C,F,I). (A-C) Gastrulae were fixed and fractured in the sagittal plane, dorsal is towards the right, animal towards the top; arrowheads, dorsal blastopore; small arrows, ventral blastopore; large arrows, pointed leading edges in controls, and corresponding positions in treated embryos. (D-F) In parallel, gastrulae were prepared for scanning electron microscopy. The BCR was removed to expose the surface of the leading edge mesoderm that had been in contact with the BCR substratum. Animal is towards the top. Arrow, cells with laterally or vegetally oriented protrusions. Scale bar: 50 µm. (G-I) BCRs of gastrulae were stained for the presence of a FN fibril matrix.