LATERAL INHIBITION AND PATTERN-FORMATION IN DICTYOSTELIUM

This chapter discusses lateral inhibition and pattern formation in Dictyostelium amoebas that start to differentiate into either prespore cells or prestalk cells about 8 hrs after the initiation of development. The pattern of differentiation in Dictyostelium discoideum presents direct evidence that the initial proportioning of cell types occurs in a spatially independent manner. Localization of prespore cells to the posterior of slugs is a subsequent event that results from the prespore-specific differentiations themselves. The initial differentiation of the amoebas into prespore cells appears to depend only on temporal progression along the developmental pathway to the proper stage. It is the laggards that are kept from prespore differentiations and induced to follow the prestalk pathway. Pattern formation has often been analyzed in terms of long-range positional information, provided by the gradients of morphogens. The “French flag” model suggests that cells respond to different thresholds of a morphogen, by following different developmental pathways. Despite the considerable efforts to define molecular mechanisms that might mediate responses to graded positional information, convincing support for the model has been found only during the early development of Drosophila, in which a gradient of bicoid protein sets the polarity of the embryo. Short-range interactions, rather than field-wide positional signals, appear to regulate divergent patterns of differentiation in many developing systems, including Dictyostelium. © 1993, Academic Press Inc.