Cell Biology

Cells generate mechanical forces to shape tissues during morphogenesis. These forces can activate several biochemical pathways and trigger diverse cellular responses by mechano-sensation, such as differentiation, division, migration and apoptosis. Assessing the mechano-responses of cells in living organisms requires tools to apply controlled local forces within biological tissues. For this, we have set up a method to generate controlled forces on a magnetic particle embedded within a chosen tissue of Drosophila embryos. We designed a protocol to inject an individual particle in early embryos and to position it, using a permanent magnet, within the tissue of our choice. Controlled forces in the range of pico to nanonewtons can be applied on the particle with the use of an electromagnet that has been previously calibrated. The bead displacement and the epithelial deformation upon force application can be followed with live imaging and further analyzed using simple analysis tools. This method has been successfully used to identify changes in mechanics in the blastoderm before gastrulation. This protocol provides the details, (i) for injecting a magnetic particle in Drosophila embryos, (ii) for calibrating an electromagnet and (iii) to apply controlled forces in living tissues.

The microenvironment of solid tumours is a critical contributor to the progression of tumours and offers a promising target for therapeutic intervention (Cox and Erler, 2011; Barker et al., 2012; Cox et al., 2016; Cox and Erler, 2016). The properties of the tumour microenvironment vary significantly from that of the original tissue in both biochemistry and biomechanics. At present, the complex interplay between the biomechanical properties of the microenvironment and tumour cell phenotype is under intense investigation. The ability to measure the biomechanical properties of tumour samples from cancer models will increase our understanding of their importance in solid tumour biology. Here we report a simple method to measure the viscoelastic properties of tumour specimens using a controlled strain rotational rheometer.