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Left-Right Patterning

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Human anatomy is asymmetric with the heart located on the left side and the liver on the right. Asymmetry is a feature common to all vertebrates and even paired-symmetric organs such as lungs display asymmetries in the number of lobes. Evidence that nodal signaling is responsible for left-right specification comes from genetic analysis of organisms deficient in left-right specification. These genetic studies led to identification of mutations in components in the nodal signaling pathway such as ActRIIB, Criptic, and FoxH1 in mouse.[1] These studies found that the left-right symmetry is created as a result of nodal antagonist expression on the right side of the embryo which is balanced by nodal upregulating itself on the other half of the embryo. The result is a nodal gradient that is high on the ventral side of the embryo and, through antagonist action, declines as a gradient to the midline. Studies on the nodal signaling pathway and its downstream targets such as PITX2 in other animals have shown it may also control left-right asymmetric patterning in sea squirt, amphioxus, sea urchin and [mollusc]] lineages. [2]

  1. ^ Burdine RD, Schier AF (April 2000). "Conserved and divergent mechanisms in left-right axis formation". Genes Dev. 14 (7): 763–76. PMID 10766733.
  2. ^ Namigai, E; Kenny NJ; Shimeld SM (2014). "Right across the tree of life: the evolution of left–right asymmetry in the Bilateria". Genesis. 52 (6): 458–470. doi:10.1002/dvg.22748. {{cite journal}}: Cite has empty unknown parameter: |1= (help)