6 research outputs found
Persistent Cellular Motion Control and Trapping Using Mechanotactic Signaling
Chemotactic signaling and the associated directed cell migration have been extensively studied owing to their importance in emergent processes of cellular aggregation. In contrast, mechanotactic signaling has been relatively overlooked despite its potential for unique ways to artificially signal cells with the aim to effectively gain control over their motile behavior. The possibility of mimicking cellular mechanotactic signals offers a fascinating novel strategy to achieve targeted cell delivery for in vitro tissue growth if proven to be effective with mammalian cells. Using (i) optimal level of extracellular calcium ([Ca2[superscript +] ][subscript ext] = 3 mM) we found, (ii) controllable fluid shear stress of low magnitude (Ï < 0.5 Pa), and (iii) the ability to swiftly reverse flow direction (within one second), we are able to successfully signal Dictyostelium discoideum amoebae and trigger migratory responses with heretofore unreported control and precision. Specifically, we are able to systematically determine the mechanical input signal required to achieve any predetermined sequences of steps including straightforward motion, reversal and trapping. The mechanotactic cellular trapping is achieved for the first time and is associated with a stalling frequency of 0.06 ~ 0.1 Hz for a reversing direction mechanostimulus, above which the cells are effectively trapped while maintaining a high level of directional sensing. The value of this frequency is very close to the stalling frequency recently reported for chemotactic cell trapping [Meier B, et al. (2011) Proc Natl Acad Sci USA 108:11417â11422], suggesting that the limiting factor may be the slowness of the internal chemically-based motility apparatus.SUTD-MIT International Design Centre (Grant IDG31400104
Peeling model for cell detachment
In many experimental situations, the adhesion of cells to solid
substrates is due to non-covalent chemical bonds. It is the
thesis of this paper that many phenomena occurring in cell
detachment experiments, such as in I (E. Decavé, G. Garriver, Y. Brechet,
B. Fourcade, F. Bruckert, Biophys. J. 82, 2383 (2002)),
result from the static and dynamic
properties of the adhesive bridges at the extreme margin of the
cell. This region defines the adhesive belt where the
distribution of connected bonds crosses over to zero where the
membrane leaves the substrate. The theoretical model we introduce
in this paper discusses the threshold force together with the
peeling velocity in the same theoretical framework. In this
one-dimensional model, the threshold force results from a
non-homogeneous distribution of anchor proteins along the membrane
so that the adhesive belt increases its capacity to resist motion
with increasing the external force. Analyzing the kinetics of the
the contact line motion, we derive the characteristic
relationship speed versus external force and we describe the
non-equilibrium state of the adhesive belt as a function of the
speed. We discuss our model in view of the experimental results
obtained with D. discoideum for hydrodynamic shear
experiments. Our results could be also confronted to single-cell
observations
Unraveling the role of surface mucus-binding protein and pili in muco-adhesion of lactococcus lactis
Adhesion of bacteria to mucus may favor their persistence within the gut and their beneficial effects to the host. Interactions between pig gastric mucin (PGM) and a natural isolate of Lactococcus lactis (TIL448) were measured at the single-cell scale and under static conditions, using atomic force microscopy (AFM). In parallel, these interactions were monitored at the bacterial population level and under shear flow. AFM experiments with a L. lactis cell-probe and a PGM-coated surface revealed a high proportion of specific adhesive events (60%) and a low level of non-adhesive ones (2%). The strain muco-adhesive properties were confirmed by the weak detachment of bacteria from the PGM-coated surface under shear flow. In AFM, rupture events were detected at short (1002200 nm) and long distances (up to 6002800 nm). AFM measurements on pili and mucus-binding protein defective mutants demonstrated the comparable role played by these two surface proteinaceous components in adhesion to PGM under static conditions. Under shear flow, a more important contribution of the mucus-binding protein than the pili one was observed. Both methods differ by the way of probing the adhesion force, i.e. negative force contact vs. sedimentation and normal-to-substratum retraction vs. tangential detachment conditions, using AFM and flow chamber, respectively. AFM blocking assays with free PGM or O-glycan fractions purified from PGM demonstrated that neutral oligosaccharides played a major role in adhesion of L. lactis TIL448 to PGM. This study dissects L. lactis muco-adhesive phenotype, in relation with the nature of the bacterial surface determinants