Nanoscale Forces during Confined Cell Migration

In vivo, immune cells migrate through a wide variety of tissues, including confined and constricting environments. Deciphering how cells apply forces when infiltrating narrow areas is a critical issue that requires innovative experimental procedures. To reveal the distribution and dynamics of the forces of cells migrating in confined environments, we designed a device combining microchannels of controlled dimensions with integrated deformable micropillars serving as sensors of nanoscale subcellular forces. First, a specific process composed of two steps of photolithography and dry etching was tuned to obtain micrometric pillars of controlled stiffness and dimensions inside microchannels. Second, an image-analysis workflow was developed to automatically evaluate the amplitude and direction of the forces applied on the micropillars by migrating cells. Using this workflow, we show that this microdevice is a sensor of forces with a limit of detection down to 64 pN. Third, by recording pillar movements during the migration of macrophages inside the confining microchannels, we reveal that macrophages bent the pillars with typical forces of 0.3 nN and applied higher forces at the cell edges than around their nuclei. When the degree of confinement was increased, we found that forces were redirected from inward to outward. By providing a microdevice that allows the analysis of force direction and force magnitude developed by confined cells, our work paves the way for investigating the mechanical behavior of cells migrating though 3D constricted environments.

Phenological synchrony between Scaphoideus titanus (Hemiptera: Cicadellidae) hatchings and grapevine bud break: could this explain the insect's expansion?

Scaphoideus titanus is the invasive vector of the phytoplasma causing the Flavescence dorée in European vineyards. This epidemic is a serious threat to viticulture that has been increasing for more than 60 years in Europe. We studied the effect of synchrony with the plant phenology and the effect of plant-sap quality on the individual fitness. Thus, we conducted laboratory experiments to determine if insect hatchings were synchronized with grapevine bud break. We used two natural populations: one from a cold winter vineyard and one from a mild winter vineyard. In both cases, egg hatching was synchronized with bud break and leaf appearance. The phloem quality of the young and old leaves as a food source was analysed by high-performance liquid chromatography, and the effects on S. titanus growth were evaluated. Phloem composition varied with the grapevine cutting's age but also varied between leaves of different ages from the same plant. The older leaves were less nutritious because they had the highest carbon-to-nitrogen ratio and the lowest content of essential amino acids. Despite diverse phloem qualities, no fitness difference was observed. We found that the synchronization of egg hatchings with bud break is well regulated. However, the nymphs are not affected by the phloem-sap quality, suggesting that S. titanus may accept different food qualities and that egg hatching synchrony could contribute to population expansion in vineyards.