Expression of matrix metalloproteinase genes in regressing or remodeling organs during the amphibian metamorphosis

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Several matrix metalloproteinases (MMP) are induced by thyroid hormone (TH) during the climax of amphibian metamorphosis, and play a pivotal role in the remodeling intestine and the regressing tail and gills by degrading the extracellular matrix (ECM). We compared MMP gene expression levels precisely by the quantitative real time reverse transcription-polymerase chain reaction. The expression of MMP genes increases prominently at NF stages 60, 60-61, and 62 in the intestine, gills, and tail, respectively, when the drastic morphological change starts in each organ. The gene expression analysis in the TH-treated tadpoles and cell line revealed that MMP mRNAs are up-regulated in response to TH quickly within several hours to low levels and then increase in a day to high levels. All TH-induced MMP genes have thyroid hormone response elements (TREs). The presence of high affinity TREs in MMP genes correlates with the early TH-induction. Based on these results, we propose that TH stimulates the transcription of MMP genes through TREs within several hours to low levels, and then bring about the main increase of mRNAs by TH-induced transcriptional factors including TH receptor β in cell type-specific transcriptional environment.
2007-03-01