Analysis of multi-parameter video measurements of human neutrophil movement and its relation to cell shape and cytosolic calcium

Capping protein levels influence actin assembly and cell motility in dictyostelium

Actin assembly is important for cell motility, but the mechanism of assembly and how it relates to motility in vivo is largely unknown. In vitro, actin assembly can be controlled by proteins, such as capping protein, that bind filament ends. To investigate the function of actin assembly in vivo, we altered the levels of capping protein in Dictyostelium cells and found changes in resting and chemoattractant-induced actin assembly that were consistent with the in vitro properties of capping protein in capping but not nucleation. Significantly, overexpressers moved faster and underexpressers moved slower than control cells. Mutants also exhibited changes in cytoskeleton architecture. These results provide insights into in vivo actin assembly and the role of the actin cytoskeleton in motility.

The fundamental motor of the human neutrophil is not random: evidence for local non-Markov movement in neutrophils

The search for a fundamental mechano-chemical process that results in net cell motion has led investigators to fit neutrophil tracking data to well described physical models in hopes of understanding the functional form of the driving force. The Ornstein-Uhlenbeck (OU) equation for mean square displacement describes a locally persistent and globally random process and is often used as a starting point for analysis of neutrophil displacements. Based upon the apparently close fit of neutrophil tracking data to this equation and the nature of its derivation, biologists have inferred that the motor of the neutrophil is best represented as a random process. However, 24 of 37 neutrophil paths that we investigated preferentially display programmatic rather than Markov short term correlations between displacements or turn angles. These correlations reflect a bimodal rather than a uniform distribution of subpath correlations in the two variables, and are strongly sampling rate-dependent. Significant periodic components of neutrophil shape change are also detected at the same time scale using either Fourier or elliptical Fourier transform-based descriptors of the neutrophil perimeter. Oscillations in neutrophil velocity have the same period. Taken together, these data suggest a nonstochastic, and perhaps periodic, component to the process driving neutrophil movement.

Transport of cytoplasmic particles catalysed by an unconventional myosin in living Drosophila embryos

Myosins are actin-activated ATPases that are able to translocate along actin filaments using energy derived from ATP hydrolysis. Non-muscle cells contain conventional myosins, which are similar in sequence and structure to muscle myosin, and a number of unconventional myosins whose head sequences are similar but tail sequences are unrelated to conventional myosins. The myosin superfamily currently consists of nine classes; Drosophila 95F is an unconventional myosin and the original member of class VI, which includes a homologue found in pig kidney. Some unconventional myosins have been suggested as mediators of some types of intracellular transport, but there is little direct evidence for this function (but see ref. 6). We have observed transport of cytoplasmic particles in live Drosophila embryos in three dimensions using computational optical sectioning microscopy. We present here evidence that this transport is actin-based, ATP-dependent and catalysed by one such unconventional myosin, the 95F myosin. This is, to our knowledge, the first direct observation of transport catalysed by an unconventional myosin in living cells.

Development of a shape vector that identifies critical forms assumed by human polymorphonuclear neutrophils during chemotaxis

Human polymorphonuclear neutrophils undergo characteristic shape changes that are critical to their ability to move and ingest their targets. We present here the construction of a simple shape vector, calculated from the coordinates of the cell perimeter, that can identify critical forms that a neutrophil assumes during the course of ameboid movement. The vector can be used to find neutrophils of a specific shape from the image analyzer data produced during a typical neutrophil tracking experiment.