Amoeboid chemotaxis

Although there is evidence that both the actin and microtubule cytoskeletal systems contribute to amoeboid chemotaxis, the evidence is strongest for the importance of the actin cytoskeleton. Drugs that inhibit the actin cytoskeleton, such as cytochalasins, have dramatic effects on chemotaxis, at least in part due to an inhibition of cell motility [202]. Assays of actin localization and polymerization indicate that chemoattractant stimulation has strong effects on the actin cytoskeleton... 

Thus, for amoeboid chemotaxis, the spatial aspects of the signaling pathways need to be examined as well when considering excitation and adaptation pathways. These issues will be discussed in more detail in the section on signal transduction. 

SegaU, J.E. (1990). Mutational studies of amoeboid chemotaxis u ngDictyostelium discoideum. Armitage, J.P. and Lackie, J.M. Biology of the chemotactic response. 241-272. Cambridge, Cambridge University Press. 

Computer-based quantitative models that address the complexity of a signaling network with its many interacting components are valuable for studies of chemotaxis. Chapter 30 summarizes a computer program that quantifies movement of amoeboid cells. Chapter 31 introduces mathematical calculations on experimentally generated chemoattractant gradients. Finally, Chapters 32 and 33 introduce two computational models that are constructed to simulate spatial-temporal dynamics of signaling networks for eukaryotic chemosensing. 

Chemotaxis of cells with amoeboid movement (e.g., white blood cells) usually follows this mechanism (Chapters 5 and 6). 

As noted previously, the evidence for the contribution of microtubules to amoeboid cell motility and chemotaxis is mixed [242]. The microtubule organizing center has been reported to be localized to either the front or rear side of the nucleus, depending upon the cell type [167, 187, 188]. Alterations in microtubules can affect fibroblast lamellipod extension and motility [150], but in some assays, chemotactic responses may be unaffected [202]. Alterations in acetylation enhance chemotactic ability [98]. Microtubules have been proposed to alter the stability of adhesion sites, enhancing their disassembly [II9]. In sum, microtubules are likely to be permissive for amoeboid motility and chemotaxis, and respond to polarization of the cell generated by the actin system with polarization of the microtubule system. This may in turn stabilize cell polarity and enhance overall chemotactic efficiency. In the absence of a strong external stimulus, or in cases in which autocrine secretion influences cell polarization, the microtubule apparatus may provide critical signals for cell polarity [164]. 

A variety of assays are available to quantitate amoeboid motility and chemotaxis. More detailed discussions of the strategic and practical aspects of deciding on which chemotaxis assay to use are given in [257]. What follows is a brief overview. Because the assays are of varying... 

Gradient-stimulated modulation of the direction of movement (classical, narrow definition of chemotaxis) Amoebae (e.g., Dictyostdium discoideum), cells with amoeboid movement (e.g., tumor cells, white blood cells), spermatozoa (of, e.g., hydroids and tunicate) 5,6,7... 

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