A Sinister Twist

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Science  11 Aug 2000:
Vol. 289, Issue 5481, pp. 833
DOI: 10.1126/science.289.5481.833b

Despite outward appearances, humans are not bilaterally symmetric—our internal organs show pronounced left-right asymmetries in morphology and placement. How do these asymmetries arise during development?

The intestine of the nematode Caenorhabditis develops as a simple tube that eventually adopts a characteristic left-handed “twist” as a result of circumferential movements of cells at the anterior end. Hermann et al. find that induction of this twist requires the LIN-12/Notch signaling pathway. Initially all intestinal cells contain comparable levels of the Notch-related receptor LIN-12; however, contact with nonintestinal cells that express the Delta-related ligand LAG-2 and are present only on the left side of the intestine results in a selective reduction in LIN-12 levels on that side. This asymmetric pattern of LIN-12 is thought to underlie subsequent asymmetric cell-cell interactions involving a different LIN-12 ligand, APX-1, which in turn lead directly to the intestinal twist. — PAK

Development127, 3429 (2000).

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