Positional information and whorl morphogenesis in Polysphondylium.

Cellular slime molds of the genus Polysphondylium periodically release cell masses from the base of culminating fruiting bodies. These masses quickly undergo a change in symmetry from spherical to radial as they differentiate into distinctive arrays of secondary fruiting bodies arranged about a primary axis of stalk cells. Here we show that a major event in whorl morphogenesis is the activation of a prestalk-specific promoter early and globally in newly forming whorls. With time, transcript synthesis and amplification become restricted to the equator of the whorl and then to patches which define where secondary tip morphogenesis will occur. The localization of early prestalk message synthesis depends on positional information, in contrast to the establishment of early prestalk/prespore patterns in both Polysphondylium and Dictyostelium.