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Figure 1. The Brown and Wolpert chiral molecule model. (A) In two dimensions, a biological molecule which occurs only as one enantiomer (schematized by the letter ‘F’) can be tethered with respect to one dimension (e.g., anterior-posterior). The chirality of the molecule then defines a left-right direction, which can provide asymmetrical information, such as the rightward transport of some determinant (schematized in red). (B,C) In three dimensions, the same mechanism can function in a cell that is molecularly polarized along, and can orient the chiral molecule with respect to, the anterior-posterior and dorso-ventral axes. This type of mechanism allows each cell to know which direction is Left and which is Right.
