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Figure 8 | EvoDevo

Figure 8

From: The Nodal signaling pathway controls left-right asymmetric development in amphioxus

Figure 8

Model of the Nodal signaling pathway during establishment of the LR asymmetry in amphioxus. Dashed lines mark proposed interactions based on the data from other chordates. Gray text denotes inhibition of expression of the respective factors. During neurulation, Nodal and its co-ligand Gdf1/3 are expressed symmetrically. However, right-sided inhibition of Nodal by Cerberus results in propagation of the pathway on the left side, where Nodal activates expression of Nodal, Gdf1/3, Lefty, and Pitx and inhibits expression of Cerberus. We propose that during the course of later development, Pitx interacts with organ-specific factors and promotes left-side specific morphogenesis. Anteriorly, Pitx is proposed to interact with Pit1 and to activate expression of Lhx3 to promote differentiation of cell types within the preoral pit. Slightly more posterior, Pitx is proposed to regulate expression of Dkk1/2/4, which inhibits Wnt/β-catenin signaling, and thus promotes fusion of ectoderm and endoderm epithelia during morphogenesis of the mouth opening. The mechanism underlying activation of expression of factors responsible for right-sided morphogenesis is currently unknown. csg, club-shaped gland; en, endostyle; fgs, first gill slit; m, mouth; pp, preoral pit.

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