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Figure 4. Altering Noggin levels in single B-tier or D-tier blastomeres alters the size of the neural plate progenitor pool, indicated by sox2 expression (A-F), and the numbers of nascent primary neurons, indicated by n-tubulin expression (G-T). A: A beta gal mRNA-injected (B-tier) embryo demonstrating that the width of the neural plate (purple) on the injected side (white line) is indistinguishable from the width of the neural plate on the uninjected control side (black line). B: A noggin mRNA-injected (B-tier) embryo has an expanded neural plate on the injected side (white line). C: A bmp4 mRNA-injected (D-tier) embryo has a reduced neural plate on the injected side (white line). D: Injection of the control MO (B-tier) on one side does not alter the width of the neural plate (white line). E: Injection of Noggin MO (B-tier) reduces the width of the neural plate (white line) on the side of injection. F: The entire neural plate is grossly reduced when bmp4 mRNA is injected into a B-tier blastomere. G: Control embryo demonstrating the three stripes of nascent primary neurons on each side of the neural plate. Asterisk indicates side injected with control ( beta -gal) mRNA. H: A noggin mRNA-injected (B-tier) embryo has expanded numbers of cells in the PMN (large arrow) and RBN (small arrow) stripes. I: D-tier expression of BMP4 represses the size of the RBN (small arrow) and interneuron (large arrow) progenitor stripes on the injected side. The PMN stripe is not visible in this neural groove stage embryo. J: Lineage labeling of an A-tier blastomere (red cells) after D-tier bmp4 mRNA injection demonstrates that many A-tier cells continue to express n-tubulin (arrows). J': beta gal mRNA-injected A-tier control. In contrast, many fewer B-tier-derived cells (arrows in K) and no C-tier-derived cells (red in L) express n-tubulin following bmp4 mRNA injection of the D-tier neighbor. K': Many beta Gal-labeled cells (between arrows) in B-tier control; L': Several n-tubulin expressing C-tier cells (arrows) in beta gal mRNA-injected control. M: Injection of a control MO on one side (asterisk) does not alter the three primary neuron progenitor stripes in the neural plate. N: Injection of Noggin MO into a dorsal B-tier blastomere reduces the PMN stripe (large arrow) on the side of the injection. O: Injection of Noggin MO into a ventral B-tier blastomere reduces the RBN stripe (small arrow) on the side of the injection. P,Q: Lineage labeling shows that after nMO injection of a B-tier blastomere, many B-tier-derived cells (between arrows) continue to express n-tubulin (P); in contrast, very few C-tier-derived cells (arrows) express n-tubulin after nMO injection of the B-tier neighbor (Q). R-T: Lineage labeling shows that after nMO injection of a C-tier blastomere, many A-tier-derived cells (R, between arrows) and B-tier-derived cells (S, between arrows) continue to express n-tubulin; in contrast, very few C-tier-derived cells (arrows) express n-tubulin (T). All examples are dorsal views. A-F are stage 14/15 (neural plate); G,H, J-N, P-T are stage 16/17 (neural fold); I, O are stage 19/20 (neural groove/tube). |