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. 2016 Jul 15;7(35):57430–57441. doi: 10.18632/oncotarget.10619

Figure 1. The three main pathways with related genes and effectors in the somitogenesis.

Figure 1

The clock (red frame)-wavefront (blue frame) model and components are shown. The clock is mainly consisted of Notch pathway and series of genes and effectors. Dll1 and its downstream NICD and Lfng expressed periodically through a feed-back loop to form the “clock” model. FGF and WNT signal gradients constitute the wavefront. In the Wnt pathway, Wnt3a induces the expression of downstream β-cat and the Axin2. The AXIN2 and DKK1 proteins are both negative-feedback inhibitors of β-cat, thereby forming a cyclical change. Wnt3a induces the expression of Tbx6, which further activates the expression of Dll1 and connects with NICD through Hes7, thus establishing communication rapport of Notch and WNT pathway. In the FGF pathway, Fgf4 and Ff8 genes induce the expression of pERK, which further prompts the expression of downstream Dusp4 and Dusp6. The FGF signal oscillation is also based on a feed-back mechanism.