Temporospatial distribution of matrix metalloproteinase and tissue inhibitors of matrix metalloproteinases during murine secondary palate morphogenesis

Extracellular matrix (ECM) molecules are known to play a pivotal role in th e morphogenesis of the secondary palate. The maintenance and degradation of the ECM is mediated in part by the matrix metalloproteinases (MMPs) and th eir endogenous inhibitors TIMPs. MMPs and TIMPs have previously been shown to be developmentally regulated within the palatal shelf during secondary p alate morphogenesis. This study was conducted to examine the temporospatial distribution of these enzymes and their inhibitors within the palatal shel ves using immunofluorescent localization to determine if specific changes o ccur in their distribution concomitant with events in palatal shelf formati on and reorientation. Frontal sections through the posterior palatal shelve s at gestational day (gd) 12, 13 and 14 were immunofluorescently stained fo r MMPs 2, 3, 9, and 13 and TIMPs 1, 2, and 3 using standard protocols and c ommercially available antibodies. The results demonstrated that MMPs and TI MPs were already present within the palatal shelf mesenchyme 30 h prior to reorientation and closure and that their expression within the shelf mesenc hyme increased as the shelves remodeled, then decreased with closure and fu sion. Increased distribution of MMPs and TIMPs within specific regions of t he palatal mesenchyme and palatal epithelial basement membrane preceded dec reases previously observed within these areas for their substrates, fibrone ctin, collagen III and collagen I. In addition, MMP-3 and TIMP-3 were immun olocalized to regions of the palatal epithelium that undergo reorganization concomitant with reorientation. The results of this study indicate that MM Ps and TIMPs are developmentally regulated during palatal shelf morphogenes is and that their distribution correlates with the distribution of the ECM components of the palatal shelf they regulate. These results provide suppor t for the idea that temporospatially controlled interactions between MMPs a nd their substrates may be pivotal in modulating events in palatal morphoge nesis.