Dicty News Electronic Edition Volume 20, number 9 May 23, 2003 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at DictyBase--http://dictybase.org. ============= Abstracts ============= Formation of Hirano Bodies Induced by Expression of an Actin Cross-linking Protein With a Gain of Function Mutation Andrew Maselli, Ruth Furukawa, Susanne A. M. Thomson, Richard C. Davis, and Marcus Fechheimer Department of Cellular Biology, University of Georgia, Athens, Georgia 30602 Eucaryotic Cell, in press Hirano bodies are paracrystalline actin filament containing structures reported in association with a variety of neurodegenerative diseases. Yet, the biological function of Hirano bodies remains poorly understood, since nearly all prior studies of these structures employed post-mortem samples of tissue. In the present study, we have generated a full length form of a Dictyostelium 34 kDa actin cross-linking protein with point mutations in the first putative EF hand termed 34 kDa _EF1. The 34 kDa _EF1 protein binds calcium normally, but has activated actin binding that is unregulated by calcium. Expression of the 34 kDa _EF1 protein in Dictyostelium induced the formation of Hirano bodies as assessed both by fluorescence microscopy and transmission electron microscopy. Dictyostelium cells bearing Hirano bodies grow normally, indicating that Hirano bodies are not associated with cell death and are not deleterious to cell growth. Moreover, expression of the 34 kDa ĈEF1 protein rescues the phenotypes of 34 kDa null and 34 kDa/_-actinin double null cells. Finally, expression of the 34 kDa _EF1 protein also initiates formation of Hirano bodies in cultured mouse fibroblasts. These results show that failure to regulate the activity and/or affinity of an actin cross-linking protein can provide a signal for formation of Hirano bodies. More generally, formation of Hirano bodies is a cellular response to or a consequence of aberrant function of the actin cytoskeleton. Submitted by: Andrew Maselli [amaselli@uconnvm.uconn.edu] ----------------------------------------------------------------------------- Shared, Unique and Redundant Functions of Three Myosin Is (MyoA, MyoB and MyoF) in Motility and Chemotaxis in Dictyostelium David L. Falk*, Deborah Wessels*, Leslie Jenkins*, Tien Pham1, Spencer Kuhl*, Margaret A. Titus^ and David R. Soll* *WM Keck Dynamic Image Analysis Facility, Dept. Biological Sciences, University of Iowa, Iowa City, IA 52242, ^Dept. Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN J. Cell Science, in press Most cell types express two distinct forms of myosin I, amoeboid and short, distinguished by differences in their tail domains. Both types of myosin I have been implicated in the regulation of pseudopod formation in Dictyostelium discoideum. Computer-assisted methods for reconstructing and motion analyzing cells, and experimental protocols for assessing the basic motile behavior of mutant cells in buffer and the responses of these cells to the individual spatial, temporal and concentration components of a natural wave of the chemoattractant cAMP were used to assess shared, unique or redundant roles of three class I myosins, one amoeboid, myoB, and two short, myoA and myoF, in motility. Analysis of both single and double mutants revealed that all three myosins play independent roles in suppressing lateral pseudopod formation in buffer and during chemotaxis. One, myoB, also plays a unique role in priming cells to respond to the increasing temporal gradient in the front of cAMP waves, while myoF plays a unique role in maintaining the elongate, polarized shape of a cell in buffer, during chemotaxis in a spatial gradient of chemoattractant and in the front of a cAMP wave. Finally, myoA and myoF play redundant roles in the velocity response to the increasing temporal gradient in the front of a cAMP wave. These results, therefore, reveal an unexpected variety of shared, unique and redundant functions of the three myosin Is in motility and chemotaxis. Interestingly, the combined defects of the myosin I mutants are similar to those of a single mutant with constitutive PKA activity, suggesting that PKA plays a role in the regulation of all three myosin Is. Submitted by: Deborah Wessels [deborah-wessels@uiowa.edu] ----------------------------------------------------------------------------- Human Polymorphonuclear Leukocytes Respond To Waves Of Chemoattractant Like Dictyostelium Jeremy Geiger, Deborah Wessels and David R. Soll W. M. Keck Dynamic Image Analysis Facility, Department of Biological Sciences, The University of Iowa, Iowa City, IA 52242 Cell Motility and the Cytoskeleton, in press It has been assumed that the natural chemotactic signal that attracts human polymorphonuclear leukocytes (PMNs) over long distances to sites of infection is in the form of a standing spatial gradient of chemoattractant. We have questioned this assumption on the grounds first that standing spatial gradients may not be stable over long distances for long periods of time and second that in the one animal cell chemotaxis system in which the natural chemotactic signal has been described in space and time, aggregation of Dicytostelium discoideum, the signal is in the form of an outwardly relayed, nondissipating wave of attractant. Here, it is demonstrated that PMNs alter their behavior in each of the four phases of a wave of PMN chemoattractant, fashioned after the Dictyostelium wave, in a manner similar to Dictyostelium. These results demonstrate that PMNs have all of the machinery to respond to a natural wave of attractant, providing support to the hypothesis that the natural signal that attracts PMNs over large distances to sites of infection in the human body may also be in the form of a wave. Submitted by: Deborah Wessels [deborah-wessels@uiowa.edu] ============================================================ [End Dicty News, volume 20, number 9]