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. Author manuscript; available in PMC: 2018 May 11.
Published in final edited form as: J Cardiovasc Dev Dis. 2014 Apr 8;1(1):52–72. doi: 10.3390/jcdd1010052

Figure 2.

Figure 2

Evolution of left-right specification. The fluid flow mechanism of symmetry breaking is seen in many vertebrates (red lines) while cell movement based mechanisms have been described in the chick and pig (blue lines). To the right are shown the distribution of key left-right patterning genes across the animal kingdom. Pitx2 is present in all animals shown but is not believed to play a role in left-right patterning in the Ecdysozoa which also lack Nodal. Pitx2 and Nodal are expressed on the right side of the body in Lophotrochozoa and Echinoderms and left in all others. The expression of these genes has not been described in the pig, the * indicates assumed expression. A function in left-right specification for the H+/K+ ATPase has been described in Echinoderms, Tunicates and all vertebrates except mammals.