In the ascidian embryo, a fibroblast growth factor (FGF)-like signal from presumptive endoderm blastomeres between the 32-cell and early 64-cell stages induces the formation of notochord and mesenchyme cells. However, it has not been known whether endogenous FGF signaling is involved in the process. Here it is shown that 64-cell embryos exhibit a marked increase in endogenous extracellular signal-regulated kinase ( @entity3963 /MAPK) activity. The increase in @entity3963 activity was reduced by treatment with an FGF receptor 1 inhibitor, @entity7795 , and a @entity8047 ( @entity3963 kinase/MAPKK) inhibitor, @entity5732 . Both drugs blocked the formation of notochord and mesenchyme when embryos were treated at the 32-cell stage, but not at the 2- or 110-cell stages. The dominant-negative form of Ras also suppressed notochord and mesenchyme formation. Both inhibitors suppressed induction by exogenous basic FGF. These results suggest that the FGF signaling cascade is indeed necessary for the formation of notochord and mesenchyme cells during ascidian embryogenesis. It is also shown that FGF signaling is required for formation of the secondary notochord, secondary muscle and neural tissues, and at least @entity3963 activity is necessary for the formation of trunk lateral cells and posterior endoderm. Therefore, FGF and @entity8047 signaling are required for the formation of various tissues in the ascidian embryo.

Role of the FGF and XXXX signaling pathway in the ascidian embryo.

@entity5732 :: ('MESH:C113580', 'Chemical') :: ['U0126'] @entity7795 :: ('MESH:C105686', 'Chemical') :: ['SU5402'] @entity3963 :: ('5594', 'Gene') :: ['ERK'] @entity8047 :: ('5609', 'Gene') :: ['MEK']
@entity8047 :: (5609,Gene) :: ['MEK']
