Figure 3.

Proposed morphogenic mechanisms mediated by matrix metalloproteinases (MMPs) and MMP inhibitors. At sites of invasion and migration (TEBs [terminal end buds], lateral side branches, invasive end buds), MMP activity may induce a transient epithelial-to-mesenchymal transition (EMT), thereby allowing the tip to move forward. Alternatively, high levels of MMP inhibitors may force an 'ameboid-like' movement, independent of MMP activity, through the meshwork of the extracellular matrix [96].