Making Dictyostelium stick

euronal growth cones have detergent-resistant membranes (DRMs), specialized cell membrane fractions enriched in GPI-anchored proteins and intracellular signaling molecules. But are the DRMs involved in regulating neurite outgrowth? Yes, say Nakai and Kamiguchi (page 1097), who developed a new technique for selectively disrupting DRMs, and used it to demonstrate the functional importance of these structures in neuronal growth cones for the first time. The authors modified a technique called micro-scale chromophore-assisted laser inactivation (micro-CALI) to specifically disrupt the integrity of DRMs in living cells. A ligand with attached dye was bound to GM1 ganglioside in the DRMs. N Making Dictyostelium stick sing a clever genetic screen, Fey et al., reporting on page 1109, have identified the first cell–substrate adhesion molecule in the social amoeba Dictyostelium discoideum. The protein shares some structural features with adhesion molecules in higher eukaryotes, suggesting that the relatively simple amoeba will be a useful model system for understanding the contributions of substrate adhesion to cell movement. The authors generated a panel of Dictyostelium insertional mutants, and then screened the transformants by repeatedly transferring them to new culture dishes. Only mutants that lacked the ability to attach to the dish were transferred. This screen identified nine independent substrate adhesion deficient (sad) mutants, one of which has now been characterized. sad A defines a novel gene encoding a molecule critical for cell–substrate adhesion in vegetative cells. GFP-tagged SadA protein localizes U to the plasma membrane. In addition to multiple membrane-Cells lacking SadA move faster but with less path persistence. spanning regions, the protein's predicted structure includes three EGF-like domains, suggesting that these domains may be an evolutionarily conserved feature of adhesion molecules. Mammalian cell–substrate adhesion is more complex than one molecule, but the identification of nine genes essential for adhesion in Dictyostelium is an encouraging start. The authors are now characterizing the other Sad genes in an effort to determine how their gene products interact. ᭿ Arp2/3 gets inhibited he Arp2/3 protein complex is a central regulator of actin assembly. Although a number of Arp2/3 activators have been identified in recent years, Humphries et al., on page 993, are the first to find a direct inhibitor of the complex: the highly conserved actin cytoskeleton component coronin. Using a combination of biochemical and genetic strategies, the authors found that the yeast coronin protein Crn1 physically and functionally interacts with the Arp2/3 complex in vivo via an evolutionarily conserved coiled-coil …