Matrix metalloproteinases mediate the dismantling of mesenchymal structures in the tadpole tail during thyroid hormone‐induced tail resorption

Abstract

It has been suggested that a family of tissue remodelling enzymes called matrix metalloproteinases (MMPs) play a causal role in the process of tail resorption during thyroid hormone-induced metamorphosis of the anuran tadpole; however, this hypothesis has never been directly substantiated. We cloned two new Xenopus MMPs, gelatinase A (MMP-2) and MT3-MMP (MMP-16), and the MMP inhibitor TIMP-2. These clones were used along with several others to perform a comprehensive expression study. We show that all MMPs and TIMP-2 are dramatically induced in the resorbing tail during spontaneous metamorphosis and are spatially coexpressed, primarily in the remodelling mesenchymal tissues. By Northern blotting, we show that all the examined MMPs/TIMP-2 are also induced by treatment of organ-cultured tails with thyroid hormone (T₃). Using the organ culture model, we provide the first direct evidence that MMPs are required for T₃-induced tail resorption by showing that a synthetic inhibitor of MMP activity/expression can specifically retard the resorption process. By gelatin zymography, we also show T₃ induction of a fifth MMP, preliminarily identified as gelatinase B (GelB; MMP-9). Moreover, T₃ not only induces MMP/TIMP expression but also MMP activation, and we provide evidence that TIMP-2 participates in the latter process. These findings suggest that MMPs and TIMPs act in concert to effect the dismantling of mesenchymal structures during T₃-induced metamorphic tadpole tail resorption.