The role of FGF signaling in the establishment and maintenance of mesodermal gene expression in Xenopus

Abstract

FGF signaling is important for the formation of mesoderm in vertebrates, and when it is perturbed in Xenopus, most trunk and tail mesoderm fails to form. Here we have further dissected the activities of FGF in patterning the embryo by addressing its inductive and maintenance roles. We show that FGF signaling is necessary for the establishment of xbra expression in addition to its well-characterized role in maintaining xbra expression. The role of FGF signaling in organizer formation is not clear in Xenopus. We find that FGF signaling is essential for the initial specification of paraxial mesoderm but not for activation of several pan-mesodermal and most organizer genes; however, early FGF signaling is necessary for the maintenance of organizer gene expression into the neurula stage. Inhibition of FGF signaling prevents VegT activation of specific mesodermal transcripts. These findings illuminate how FGF signaling contributes to the establishment of distinct types of mesoderm.

Zygotic VegT is required for Xenopus paraxial mesoderm formation and is regulated by Nodal signaling and Eomesodermin

“…4M). These results are consistent with previous reports that showed FGF signaling is required for the gene expression of Xbra and Tbx6, and has no effect on the expression of Eomes (Fang et al, 2004;Fletcher and Harland, 2008;Isaacs et al, 1994;Schulte-Merker and Smith, 1995). These results suggest that FGF signaling is not necessary for induction of zVegT and Eomes, but is required for the expression of Xbra and Tbx6.…”

“…The effect of inhibition of FGF signaling on VegT expression has been reported previously (Fletcher and Harland, 2008;Lustig et al, 1996;Stennard et al, 1996). However, mVegT and zVegT were not distinguished in these experiments.…”

Role of Signaling Pathways and Epigenetic Factors in Lineage Determination During Human Embryonic Stem Cell Differentiation

“…FGF4 secreted by ICM also causes primitive endoderm differentiation [43]. Further along the developmental timeline, FGF signaling is required for the induction of paraxial mesoderm and for maintenance (but not induction) of axial mesoderm [44][45][46]. FGF is required for primitive streak formation and cell migration during gastrulation [45,47].…”

“…Activin/Nodal [23][24] FGF [24,[38][39][54][55] Block Activin/Nodal [12,14] Low Activin/Nodal [13,[18][19] Short-term BMP [18][19]27] FGF [44][45][46][47], Wnt [66,[68][69]73] High Activin/Nodal [13,17,[20][21] Wnt [66, 68-69, 71, 73] Low PI3K [21,85] Block Activin/Nodal [12,14] High BMP [15] Block Activin/Nodal [12,14,22] Block BMP [15,22] FGF [51,53,57,60] Block Activin/Nodal [12,14] Low BMP [16], FGF [51,57] Hippo [101] (? )…”

Forming and Interpreting Gradients in the Early Xenopus Embryo

“…The second included members of the fibroblast growth factor family, such as FGF2 (Kimelman and Kirschner 1987;Slack et al 1987) and FGF4 (Isaacs et al 1992). In this article, we consider only members of the TGF-b family: Although distinctions of this sort may be a little simplistic (Fletcher and Harland 2008), TGF-bs appear to play the major role in initiating mesoderm formation, whereas FGF family members may be more involved in maintaining mesodermal identity (Kroll and Amaya 1996;Heasman 2006).…”