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Fig. 6 The activation of Fgf signaling can restore the expression of mesodermal-specific genes that are down-regulated by cas misexpression. (A–L) Either cas mRNA, or a combination of cas with CA-mek mRNAs, were injected into a marginal blastomere of a 16-cell stage zebrafish embryo. Embryos injected with mRNA(s) were examined for ntl, spt or papc expression at the 50% epiboly stage (5. 3 hpf) and myoD expression at the 80% epiboly stage (8. 3 hpf). Nuclear lacZ (nlacZ) mRNA was used as a lineage tracer. Red staining by β-galactosidase activity indicates the progeny of injected cells. The progeny of marginal blastomeres gives rise to the marginal clones of the cells. (A–I) All images are of animal pole views. (J–L) Dorsal views with anterior to the top. (A, D, G, J) The nlacZ mRNA injections did not disrupt the ntl, spt, papc or myoD expression profile. (B, E, H, K) The expression of the mesodermal genes ntl, spt, papc or myoD was down-regulated by cas mRNA misexpression (arrows). (C, F, I, L) The down-regulation of the mesodermal genes ntl, spt, papc or myoD by cas mRNA misexpression was restored by co-injection with CA-mek mRNA (arrows).
Reprinted from Developmental Biology, 300(2), Mizoguchi, T., Izawa, T., Kuroiwa, A., and Kikuchi, Y., Fgf signaling negatively regulates Nodal-dependent endoderm induction in zebrafish, 612-622, Copyright (2006) with permission from Elsevier. Full text @ Dev. Biol.