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Current descriptions of eukaryotic chemotaxis and cell movement focus on how extracellular signals (chemoattractants) cause new pseudopods to form. This 'signal-centred' approach is widely accepted but is derived mostly from special cases, particularly steep chemoattractant gradients. I propose a 'pseudopod-centred' explanation, whereby most pseudopods form themselves, without needing exogenous signals, and chemoattractants only bias internal pseudopod dynamics. This reinterpretation of recent data suggests that future research should focus on pseudopod mechanics, not signal processing. [ABSTRACT FROM AUTHOR]

Current models of eukaryotic chemotaxis propose that directional sensing causes localized generation of new pseudopods. However, quantitative analysis of pseudopod generation suggests a fundamentally different mechanism for chemotaxis in shallow gradients: first, pseudopods in multiple cell types are usually generated when existing ones bifurcate and are rarely made de novo; second, in Dictyostelium cells in shallow chemoattractant gradients, pseudopods are made at the same rate whether cells are moving up or down gradients. The location and direction of new pseudopods are random within the range allowed by bifurcation and are not oriented by chemoattractants. Thus, pseudopod generation is controlled independently of chemotactic signalling. Third, directional sensing is mediated by maintaining the most accurate existing pseudopod, rather than through the generation of new ones. Finally, the phosphatidylinositol 3-kinase (PI(3)K) inhibitor LY294002 affects the frequency of pseudopod generation, but not the accuracy of selection, suggesting that PI(3)K regulates the underlying mechanism of cell movement, rather than control of direction. [ABSTRACT FROM AUTHOR]

The EMBO workshop on Cell Migration, held in Heidelberg this May, highlighted new trends in cell migration research, as well as the need to reassess current dogma. Key insights included altered ideas for the roles of Rac and inositol lipids, for the ways that groups of cells coordinate their migration and for the importance of considering movement from both a cell biological and mechanical perspective. [ABSTRACT FROM AUTHOR]

SCAR/WAVE proteins are central regulators of cell motility that coordinate actin reorganization through activation of the Arp2/3 complex. Their activity is controlled by a large complex with four other members. A new study contradicts earlier work by suggesting that the entire complex is required for SCAR/WAVE activity at the leading edge. [ABSTRACT FROM AUTHOR]

Stereotyped behaviors are series of postures that show very little variability between repeats. They have been used to classify the dynamics of individuals, groups and species without reference to the lower-level mechanisms that drive them. Stereotypes are easily identified in animals due to strong constraints on the number, shape, and relative positions of anatomical features, such as limbs, that may be used as landmarks for posture identification. In contrast, the identification of stereotypes in single cells poses a significant challenge as the cell lacks these landmark features, and finding constraints on cell shape is a non-trivial task. Here, we use the maximum caliber variational method to build a minimal model of cell behavior during migration. Without reference to biochemical details, we are able to make behavioral predictions over timescales of minutes using only changes in cell shape over timescales of seconds. We use drug treatment and genetics to demonstrate that maximum caliber descriptors can discriminate between healthy and aberrant migration, thereby showing potential applications for maximum caliber methods in automated disease screening, for example in the identification of behaviors associated with cancer metastasis. [ABSTRACT FROM AUTHOR]

Focuses on cell biology. Use of the soil amoeba, Dictyostelium discoideum to understand the cellular mechanics; Technological innovations in the field of the Dictyostelium study; Characteristics of Dictyostelium, which are common to animals and plants; Significance of the study in the medical field. INSET: Box 1: The Dictyostelium genome project.