Fig. 4.

Generation of a robust difference between the left and right LPMs. Expression patterns of spaw (red), lefty1 (blue) or oep (green) at the 15- to 18-somite stages. We hypothesize that Spaw and Lefty1 can diffuse at a similar rate, as shown in the central graph. In the left LPM (L-LPM), Spaw binds to an Activin receptor (AcR) and Oep pair, and activates spaw expression even in the presence of Lefty1. In contrast, the small amounts of Spaw in the right LPM (R-LPM) cannot stimulate spaw expression due to the antagonistic effect of Lefty1