Evaluation of Individual-Cell Motility
Peter S. WalmodRasmus Hartmann‐PetersenAnton BerezinSøren PragVladislav V. KiselyovVladimir BerezinElisabeth Bock
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AbstractThe coordinated displacement of a cell is a highly complex process which relies on the integration of a series of signaling pathways and on the function of a large number of molecular components including all main structures of the cytoskeleton (1,2). Thus, a detailed knowledge of the regulation and function of the cytoskeleton is of central importance for the understanding of cell motility, and conversely, investigations of cell motility may shed light on the function of cytoskeletal components.KeywordsPersistence TimeNonlinear CurveCell SpeedChemotactic GradientChemotactic IndexThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.Keywords:
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Formation of spatial patterns of cells is a recurring theme in biology and often depends on regulated cell motility. Motility of the rod-shaped cells of the bacterium Myxococcus xanthus depends on two motility machineries, type IV pili (giving rise to S-motility) and the gliding motility apparatus (giving rise to A-motility). Cell motility is regulated by occasional reversals. Moving M. xanthus cells can organize into spreading colonies or spore-filled fruiting bodies, depending on their nutritional status. To ultimately understand these two pattern-formation processes and the contributions by the two motility machineries, as well as the cell reversal machinery, we analyse spatial self-organization in three M. xanthus strains: (i) a mutant that moves unidirectionally without reversing by the A-motility system only, (ii) a unidirectional mutant that is also equipped with the S-motility system, and (iii) the wild-type that, in addition to the two motility systems, occasionally reverses its direction of movement. The mutant moving by means of the A-engine illustrates that collective motion in the form of large moving clusters can arise in gliding bacteria owing to steric interactions of the rod-shaped cells, without the need of invoking any biochemical signal regulation. The two-engine strain mutant reveals that the same phenomenon emerges when both motility systems are present, and as long as cells exhibit unidirectional motion only. From the study of these two strains, we conclude that unidirectional cell motion induces the formation of large moving clusters at low and intermediate densities, while it results in vortex formation at very high densities. These findings are consistent with what is known from self-propelled rod models, which strongly suggests that the combined effect of self-propulsion and volume exclusion interactions is the pattern-formation mechanism leading to the observed phenomena. On the other hand, we learn that when cells occasionally reverse their moving direction, as observed in the wild-type, cells form small but strongly elongated clusters and self-organize into a mesh-like structure at high enough densities. These results have been obtained from a careful analysis of the cluster statistics of ensembles of cells, and analysed in the light of a coagulation Smoluchowski equation with fragmentation.
Myxococcus xanthus
Gliding motility
Collective motion
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Summary. Spermatozoa were collected from the rat caput epididymidis by micropuncture and their motility assessed after dilution in physiological saline containing carnitine or related compounds. l(+)-Carnitine caused, 2 min after dilution, a transient stimulation of the motility of spermatozoa with low initial motility. No stimulatory effects were seen on spermatozoa which had high initial motility. The d-isomer inhibited the motility of spermatozoa with high initial motility after 2 min and all compounds tested appeared to inhibit, at 20 min after dilution, the motility of spermatozoa with high initial motility. Acetyl-l-carnitine and acetyl-d-carnitine stimulated the motility of spermatozoa with low initial motility. This study suggests that carnitine may be important in the development by spermatozoa of the potential for motility and also to maintain mature spermatozoa in a quiescent state.
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AbstractThe coordinated displacement of a cell is a highly complex process which relies on the integration of a series of signaling pathways and on the function of a large number of molecular components including all main structures of the cytoskeleton (1,2). Thus, a detailed knowledge of the regulation and function of the cytoskeleton is of central importance for the understanding of cell motility, and conversely, investigations of cell motility may shed light on the function of cytoskeletal components.KeywordsPersistence TimeNonlinear CurveCell SpeedChemotactic GradientChemotactic IndexThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
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The bacterium Myxococcus xanthus has two motility systems: S motility, which is powered by type IV pilus retraction, and A motility, which is powered by unknown mechanism(s). We found that A motility involved transient adhesion complexes that remained at fixed positions relative to the substratum as cells moved forward. Complexes assembled at leading cell poles and dispersed at the rear of the cells. When cells reversed direction, the A-motility clusters relocalized to the new leading poles together with S-motility proteins. The Frz chemosensory system coordinated the two motility systems. The dynamics of protein cluster localization suggest that intracellular motors and force transmission by dynamic focal adhesions can power bacterial motility.
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Changes in cell-cell and cell-substrate adhesion markers are increasingly used to characterize disease onset and progression. However, these relationships depend on both the biochemical and molecular association between cells and between cells and their extracellular matrix, as well as the biophysical and mechanical properties orchestrated by cytoskeletal, membrane and matrix components. To fully appreciate the role of cell adhesion when determining normal physiology and the impact of disease on cellular function, it is important to consider both biochemical and biophysical attributes of the system being investigated. In this short viewpoint we reflect on our experiences assessing cell-cell and/or cell-matrix interactions in renal tubular epithelial cells.
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During the last two decades many structural studies have focused on cell-to-cell contacts and intercellular communication. These studies have been complemented in some cases with functional studies. The rationale behind these inquiries is obvious since cell-to-cell communication may have a profound influence on cell and tissue function.
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