Hem-1 and actin generate self-sustaining waves through a cycle of propulsion and annihilation.

University of California, San Francisco scientists discovered that torrents of microscopic waves composed of signaling protein Hem-1 propel white blood cells toward a chemical signal made by invading microbes. The discovery was recorded on videotape using a high-resolution light microscope.

This protein and a second key player, actin, were already known to trigger cells to move. Their interaction to generate the self-sustaining waves was previously unknown, report the researchers. This wave action is generated by the same kind of three-part circuit that fires electrical signals along a neuron, the researchers observe.

By videotaping fluorescently tagged Hem-1 proteins, the scientists found that self-generating waves of Hem-1 control the pattern of assembly of building blocks of actin, which physically contacts the cell membrane and prods it forward. However, actin is not only an output of Hem-1 action, it also appears to eliminate the Hem-1 that has assembled it, the new research shows. The scientists think that this cycle of Hem-1 propulsion and annihilation is likely to produce the series of waves seen under the microscope.

The cell-propelling circuit contains a third component that makes it self-sustaining. The researchers found evidence that before each Hem-1 protein is eliminated, it recruits an additional Hem-1 right next door. As each Hem-1 succumbs, a new one appears but only on one side. The team thinks the structure of actin physically blocks Hem-1 from recruiting its daughter Hem-1 on one side so that it is sequentially added only in one direction, which determines the direction of cell movement.

The scientists observed the Hem-1 activation of actin assembly and actin’s inhibition of Hem-1 accumulation. The recruitment component was not directly observed, but is consistent with their observations and experiments.

The research findings were reported in the August 13 online edition of Public Library of Science Biology.

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