Figure 1. Stages of invadopodium maturation.

Stage 1 (early precursor stage): invadopodia initially form as non-degradative precursors that consist of a core structure containing actin, cortactin, cofilin, N-WASp, Tks5 and other proteins. Stage 2 (late precursor stage): kinases are activated, β1 integrin and talin are recruited and Tks5 anchors the precursor to PI(3,4)P₂. Stages 3-4 (mature invadopodium stage): in stage 3, actin polymerization is activated by stimulation of the NHE-1-cofilin pathway, and continued actin polymerization drives invadopodial elongation and stabilization. In stage 4, microtubule and intermediate filament recruitment facilitates further elongation of the protrusion, and matrix proteases are recruited to degrade the ECM (modified from Artym et al., 2006; Oser et al., 2009; Schoumacher et al., 2010; Sharma et al., 2013).