Matrix metalloproteinase function in non-mammalian model organisms.

Matrix metalloproteinases (MMPs), adamalysins, astacins, and serralysins are members of the metzincin superfamily of proteases. MMPs constitute a large protein family of both secreted and membrane-tethered enzymes that are synthesized as zymogens (proMMP) and activated by a cysteine-switch mechanism. First described over 50 years ago by Gross and Lapiere as a collagenolytic activity in amphibian tissues, the human MMP family now encompasses 23 different genes whose encoded proteins are capable of cleaving a variety of extracellular matrix protein substrates. Since their expression is upregulated in many cancer cell types, MMPs have received much attention particularly in the areas of tumor progression and metastasis. However, in terms of normal developmental processes, much less is known regarding MMP function and substrate identity. Data from knockout mouse studies support the notion that MMPs are not essential regulators of embryonic development, suggesting redundancy between MMPs or the presence of subtle phenotypes. However, studies on MMP function in other model systems indicate a larger role for MMP-dependent proteolysis during embryonic processes. Here, we review the current knowledge of MMPs from diverse model systems ranging from flowering plants and invertebrates to non-mammalian vertebrates.