ABSTRACT
We showed previously that if Dictyostelium discoideum cells are sucked up into a small glass capillary with air at one end and plugged with mineral oil at the other, a sharp band of fast moving cells with pres talk characteristics formed within a minute at the air end of the cell mass. We now demonstrate that oxygen inside the capillary is responsible for the initiation and positioning of the sharp division line between prestalk-like and pres pore-like cells, and that the length of the prestalk zone is regulated by the oxygen concentration. Our results are compared to a quantitative theory, showing good agreement with the experiments. We also discuss the relevance of these observations to the differentiation of pres talk and prespore zones in normal slugs and the origins of polarity in this organism.