Chemotactic signals

Foxman EF, Kunkel EJ, Butcher EC. Integrating conflicting chemotactic signals. The role of memory in leukocyte navigation. J Cell Biol 1999 147(3) 577-588. 

Figure 17.3 (a) A neutrophil squeezing between endothelial cells to enter the interstitial fluid. This demonstrates the extreme plasticity of neutrophils (and other immune cells) which enables them to pass through spaces much smaller than their normal diameter. Such entry requires chemotactic signals, (b) Diapede-sis. A neutrophil enters the interstitial space, where it is activated and then phagocytoses bacteria. Finally the neutrophil suffers either necrosis or apoptosis and then phagocytosis. 

Amsler, C. D. and Matsumura, P, Chemotactic signal transduction in Escherichia coli and Salmonella typhimurium, in Two-Component Signal Transduction, Hoch, J.A. and Silhavy, T.J., Eds., ASM Press, 1995, 89. 

A particularly important connection between signalling pathways controlled by heterotrimeric and monomeric G proteins is chemotaxis. Chemotactic signals are received by G-protein-coupled receptors and transmitted by Py-subunits of heterotrimeric G proteins, notably to phosphoinositide 3-kinase (Ptdins 3-kinase) and phospholipase C. Finally, monomeric G proteins direct the signal to the cytoskeleton, promoting crawling and rolling of cells (see discussion of the role of phosphoinositides for the orientation of the cell towards stimuli in Chapter 4). 

A second CXCR3 variant has also been identified that is truncated at the C-terminus (CXCR3-alt, [6]). This altered receptor has a predicted four or five-transmembrane structure lacking the third and most of the second extracellular loop. In spite of the truncated form of CXCR3-alt, this variant was able to transduce a chemotactic signal by CXCL11 that was sensitive to inhibition by pertussis toxin. 

Die output of individual flagellai motors in E. coli was measured as a function of the intracellular concentration of the chemotactic signaling protein. The concentration of this molecule, fused to GFP, was monitored with fluorescence coiielation spectroscopy. Motors from different bacteria exhibited an identical steep input-output relation, suggesting that they actively contribute to signal amplification in chemotaxis. Uiese experimental studies can be extended to quantitative in vivo studies of other biochemical networks. ... 

The chemical analysis of the chemotactic signal utilized by D. discoideum amoebae in the course of aggregation showed (Konijn et al., 1967) it to be cyclic AMP (cAMP). This molecule (fig. 5.5) is known to play an important role in higher organisms, where stimulation by... 

Fig. 5.3. Waves observed during aggregation of D. discoideum amoebae on agar. Light bands represent amoebae moving chemotactically in response to signals emitted by aggregation centres. Dark bands correspond to amoebae that are immobile due either to refractoriness or to the absence of chemotactic signal (Alcantara Monk, 1974).

The initial study of Gerisch Hess (1974) did not propose any molecular basis for the oscillations in light scattering in suspensions of D. discoideum amoebae. However, in that same study, the authors showed that extracellular cAMP is capable of inducing an immediate phase shift of the oscillations (fig. 5.9). This observation suggests an important role for the chemotactic signal in the control of the oscillatory phenomenon. 

Darmon, M., P. Brachet L.H. Pereira da Silva. 1975. Chemotactic signals induce cell differentiation in Dictyostelium discoideum. Proc. Natl. Acad. Sci. USA 72 3163-6. 

The proposed model for the transduction of chemotactic signals via CheY, the tumble regulator, includes which of the folloveing ... 

P., and Yanagida, T. (2001) Stn e-molecule analysis of chemotactic signaling in Dictyostd-ium cells. Science 294, 864-867. 

Abe, T., Maeda, Y., and lijima, T. (1988) Transient increase or the intracellular Ca + concentration during chemotactic signal transduction in Dictyostelium discoideum cells. Differentiation 39, 90-96. 

Quantitative studies of chemotactic signaling require experimental techniques that can expose single cells to chemical stimuli with high resolution in both space and time. Recently, we have introduced the method of flow photolysis (Anal. Chem. 79 3940-3944, 2007), which combines microfluidic techniques with the photochemical release of caged compounds. This method allows us to tailor chemical stimuli on the length scale of individual cells with subsecond temporal resolution. In this chapter, we provide a detailed protocol for the setup of flow photolysis experiments and exemplify this versatile approach by initiating membrane translocation of fluorescent fusion proteins in chemotactic Dictyostdium discoideum cells. 

Single-Molecule Imaging Techniques to Visualize Chemotactic Signaling Events on the Membrane of Living DictyosteHum Cells... 

Keep the dish still for the first hour of incubation, and then move it to a shaker and add cAMP (100 nM final) every 6 min for the next few hours until the cells show polarized shapes, which is a hallmark of chemotactic competence. Proper development is critical to obtain reliable data of chemotactic signaling molecules in Dictyostdium cells see Note 4). Note that some mutant cell lines have a defect in developmental progress, which affects cARl mobility (rrr Note 5). 

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