כימוטקסיס וכיוון נדידת תאים

Chemotaxis is the movement of cells in response to a chemical stimulus.

While chemoattractants direct cell movement along their concentration gradient, chemorepellents signal the cell to move away from the stimulus.

These chemical cues are usually small molecules such as peptides, sugars, and lipids, which can bind specific cell-surface receptors.

For example, the tripeptides  released by bacteria, such as E.coli can bind and activate the G-protein coupled receptors or GPCRs on the surface of neutrophils.

The activated GPCRs polarize the cell by locally amplifying the signal via different signaling cascades — the Rac pathway at the cell front, and the Rho pathway at the cell rear.

This leads to cytoskeletal reorganization within the neutrophil that orients and directs its movement towards the pathogen.

In addition to diffusible chemicals, substrate-bound molecules, such as laminin glycoproteins, also induce chemotaxis.

These stimulants promote the adhesion of membrane protrusions to the substrate, thus directing cell migration along the chemical gradient.