Just the right size - Cell counting in Dictyostelium

The regulation of tissue and organism size plays an essential, but poorly u nderstood, role in multicellular development. Genes have been identified th at affect body and organ size in a number of animals. Two recently identifi ed genes, smIA and countin, are required for the proper function of a cell- counting mechanism that regulates organism size in the eukaryotic microorga nism Dictyostelium discoideum. The discovery of this process now allows the study of size regulation in a simple multicellular system.