Dictyostelium as model system for studies of the actin cytoskeleton by molecular genetics

The actin cytoskeleton is an essential structure for most movements at the cellular and intracellular level. Whereas for contraction a muscle cell req uires a rather static organisation of cytoskeletal proteins, cell motility of amoeboid cells relies on a tremendously dynamic turnover of filamentous networks in a matter of seconds and at distinct regions inside the cell. Th e best model system for studying cell motility is Dictyostelium discoideum. The cells live as single amoebae but can also start a developmental progra m that leads to multicellular stages and differentiation into simple types of tissues. Thus, cell motility can be studied on single cells and on cells in a tissue-like aggregate. The ability to combine protein purification an d biochemistry with fairly easy molecular genetics is a unique feature for investigation of the cytoskeleton and cell motility. The actin cytoskeleton in Dictyostelium harbours essentially all classes of actin-binding protein s that have been found throughout eukaryotes. By conventional mutagenesis, gene disruption, antisense approaches, or gene replacements many genes that code for cytoskeletal proteins have been disrupted, and altered phenotypes in transformants that lacked one: or more of those cytoskeletal proteins a llowed solid conclusions about their in vivo function. In addition, tagging the proteins or selected domains with green fluorescent protein allows the monitoring of protein redistribution during cell movement. Gene tagging by restriction enzyme mediated integration of vectors and the ongoing interna tional genome and cDNA sequencing projects offer the chance to understand t he dynamics of the cytoskeleton by identification and functional characteri sation of all proteins involved. (C) 1999 Wiley-Liss, Inc.