Suppression of positional errors in biological development

Description

Cells in developing embryos behave according to their positions in the organism, and therefore seem to be receiving `positional information'. A widespread view of the mechanism for this is that each cell responds locally to the concentration level of some extracellular chemical which is distributed in a spatial gradient. For molecules conveying and receiving the positional signal, concentrations are likely to be low enough that, per individual cell, only a few thousand molecules may be involved. Fluctuations to be expected in these numbers (Poisson distribution) could readily lead to errors up to a few percent of embryo length in the reading of position. This is an intolerable level of error for some developmental pattern-forming events. Embryos must have means of suppressing such errors. We maintain that this requires communication between cells, and illustrate this by using the reaction part of two well-known Turing-type reaction–diffusion models as the local gradient reader. We show that switching on diffusion in these models leads to adequate suppression of positional errors., Peer-reviewed article, Published. Received 31 December 1997, Revised 20 July 1998, Accepted 21 July 1998, Available online 24 March 1999.