Viscoelastic relaxation of collagen networks provides a self-generated directional cue during collective migration

There is growing evidence that the physical properties of the cellular environment can impact cell migration. However, it is not currently understood how active physical remodeling of the network by cells affects their migration dynamics. Here, we study collective migration of small clusters of cells on deformable collagen-1 networks. Combining theory and experiments, we find that cell clusters, despite displaying no apparent internal polarity, migrate persistently and generate asymmetric collagen gradients during migration. We find that persistent migration can arise from viscoelastic relaxation of collagen networks, and reducing the viscoelastic relaxation time by chemical crosslinking leads to a reduction in migration persistence. Single cells produce only short range network deformations that relax on shorter timescales, which leads to lower migration persistence. This physical model provides a mechanism for self-generated directional migration on viscoelastic substrates in the absence of internal biochemical cues.

Mitotic and pheromone-specific intrinsic polarization cues interfere with gradient sensing inSaccharomyces cerevisiae

Polarity decisions are central to many processes, including mitosis and chemotropism. InSaccharomyces cerevisiae, budding and mating projection (MP) formation use an overlapping system of cortical landmarks that converges on the small G protein Cdc42. However, pheromone-gradient sensing must override the Rsr1-dependent internal polarity cues used for budding. Using this model system, we asked what happens when intrinsic and extrinsic spatial cues are not aligned. Is there competition, or collaboration? By live-cell microscopy and microfluidics techniques, we uncovered three previously overlooked features of this signaling system. First, the cytokinesis-associated polarization patch serves as a polarity landmark independently of all known cues. Second, the Rax1-Rax2 complex functions as a pheromone-promoted polarity cue in the distal pole of the cells. Third, internal cues remain active during pheromone-gradient tracking and can interfere with this process, biasing the location of MPs. Yeast defective in internal-cue utilization align significantly better than wild type with artificially generated pheromone gradients.

Using pyrene to probe the effects of poloxamer stabilisers on internal lipid microenvironments in solid lipid nanoparticles

Pyrene can be used to investigate the internal polarity inside solid lipid nanoparticles; small changes in the structure of the poloxamer surfactants can influence the polarity inside the core.

Intrinsic polarization cues interfere with pheromone gradient sensing in S. cerevisiae

Polarity decisions are central to many processes, including mitosis and chemotropism. In S. cerevisiae, budding and mating projection (MP) formation use an overlapping system of cortical landmarks that converge on the small G-protein Cdc42. However, pheromone gradient sensing must override the Rsr1-dependent internal polarity cues used for budding. Using this model system, we asked what happens when intrinsic and extrinsic spatial cues are misaligned. Is there competition, or collaboration? By live cell microscopy and microfluidics technics we uncovered three previously overlooked features of this signaling system. First, the cytokinesis-associated polarization patch serves as a polarity landmark independently of all known cues. Second, the Rax1-Rax2 complex functions as novel pheromone promoted polarity cue in the distal pole of the cells. Finally, we showed that internal cues remain active during pheromone gradient tracking and that they interfere with this process biasing the location of MPs, since yeast defective in internal cue utilization align significantly better than wild- type with artificially generated pheromone gradients.

An Internal Polarity Landmark Is Important for Externally Induced Hyphal Behaviors in Candida albicans

ABSTRACT Directional growth is a function of polarized cells such as neurites, pollen tubes, and fungal hyphae. Correct orientation of the extending cell tip depends on signaling pathways and effectors that mediate asymmetric responses to specific environmental cues. In the hyphal form of the eukaryotic fungal pathogen Candida albicans, these responses include thigmotropism and galvanotropism (hyphal turning in response to changes in substrate topography and imposed electrical fields, respectively) and penetration into semisolid substrates. During vegetative growth in C. albicans, as in the model yeast Saccharomyces cerevisiae, the Ras-like GTPase Rsr1 mediates internal cellular cues to position new buds in a prespecified pattern on the mother cell cortex. Here, we demonstrate that Rsr1 is also important for hyphal tip orientation in response to the external environmental cues that induce thigmotropic and galvanotropic growth. In addition, Rsr1 is involved in hyphal interactions with epithelial cells in vitro and its deletion diminishes the hyphal invasion of kidney tissue during systemic infection. Thus, Rsr1, an internal polarity landmark in yeast, is also involved in polarized growth responses to asymmetric environmental signals, a paradigm that is different from that described for the homologous protein in S. cerevisiae. Rsr1 may thereby contribute to the pathogenesis of C. albicans infections by influencing hyphal tip responses triggered by interaction with host tissues.

On the Internal Polarity of the Golgi Apparatus with Special Regard to Its Relationship to GERL

The authors emphasized that from the cytochemical standpoint the Golgi apparatus has an internal polarity and that GERL is a part of this organelle.