“…Cell motility through complex 3D microenvironments also requires efficient probing of the cell surroundings via specialized sensory protrusions such as filopodia (Jacquemet et al, 2015). Filopodia are finger-like actin-rich protrusions widely used by cells in vivo during normal processes, such as development (Sato et al, 2017;Haas and Gilmour, 2006;Zhang et al, 2018), angiogenesis (Gerhardt et al, 2003), immune surveillance (Liu et al, 2018), and wound healing (Wood et al, 2002;Pickering et al, 2013), and also during tumourigenesis (Shibue et al, 2012(Shibue et al, , 2013 and cancer cell dissemination (Paul et al, 2015;Jacquemet et al, 2017;Follain et al, 2018;Liu et al, 2018). Filopodia have integrin-positive adhesive tips for ECM sensing and cells can employ filopodia to recognize ECM gradients (Johnson et al, 2015), ECM topography (Albuschies and Vogel, 2013) or ECM stiffness (Wong et al, 2014;Chan and Odde, 2008).…”