A frequency difference in optical-density oscillations of early Dictyostelium discoideum density classes and its implications for development

Abstract. This paper describes the separation of preaggregation-stage Dictyostelium discoideum cells into various density classes on preformed, linear Percoll density gradients and reports the finding of frequency differences in the cyclic-AMP (cAMP) oscillatory signalling system of different density classes. The cAMP oscillations were measured via their associated optical-density oscillations using a device constructed to measure cell agglutination via light-scattering changes and capable of handling 24 samples simultaneously. We found that the least dense cells oscillated at a higher frequency than the most dense cells. Mixtures of fast- and slow-oscillating cell populations synchronized at an intermediate frequency. We propose that the 'tip' is a high-frequency pacemaker which persists throughout development and use these findings to explain how the 'tip', i.e. the anterior end of all multicellular structures, can function as an organizer.