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. 2011 Feb 1;138(3):475–485. doi: 10.1242/dev.056010

Fig. 7.

Fig. 7.

Model for effect of sulfated glycosaminoglycans (sGAGs) during asymmetric gene expression. (A) Asymmetrically-produced Xnr1 in the left LPM beginning at stage 18/19 begins to move anteriorwards, concentrated over ECM of left LPM/periaxial tissue surfaces, and begins to induce Lefty. Lefty travels anteriorly along left LPM/periaxial ECM more rapidly than does Xnr1, and into endoderm. Lefty catches up to Xnr1, shutting down Xnr1 autoregulation. Lefty stability may prevent a second Xnr1 wave from initiating. (B) sGAGs (stippling) within LPM and periaxial ECM (yellow line) help retain a significant fraction of Xnr1 in proximity to left LPM, while Lefty (not shown) moves more freely to right LPM either directly through endoderm or `up-and-over' the dorsal axial midline. sGAG removal allows lateral travel of Xnr1 into endoderm, reducing LPM signal and planar movement. This orthogonal transfer reduces the strength of Xnr1 autoregulation within the LPM.