Temporal changes in collagen composition and metabolism during rodent palatogenesis

Cleft lip and palate is a common craniofacial malformation in man. The aeti ology is multifactorial and not known. Since collagen is a major structural component of the developing palate, we studied its composition and metabol ism during palate shelf formation and elevation in the rat. Palatal shelves were harvested at embryonic days (E) 15, 16 and 17 as well as post-partum. Palatal collagen increased threefold from E15 to E17 and tenfold from E17 to 5-day-old pups. Palatal calcification was seen in the main, post-partum. Collagen cross-linking, which may be important in shelf elevation and unio n, varied. The concentration of hydroxylysyl-pyridinolone cross-links was g reatest prior to shelf elevation, declining thereafter. Similarly, the high est concentration of dihydroxylysinononorleucine was seen at E16 and this s upports the concept of a compliant mesenchymal shelf responding to an intri nsic elevating force. We then determined if enzymes responsible for matrix degradation, matrix metalloproteinases (MMP) and the tissue inhibitors of m etalloproteinases (TIMPs) altered over the same time periods. MMP-2, and TI MP-1 and TIMP-2 were identified by gelatin zymography and reverse zymograph y, respectively. MMP-3 activity was determined with a fluorogenic substrate assay. TIMP-1, TIMP-2 and MMP-3 levels remained constant from E15 to E17. The MMP-2 levels showed a significant elevation from E15 to E16 and E16 to E17. This suggests the regulation of extracellular matrix is likely to be o f importance in palate morphogenesis. (C) 2000 Elsevier Science Ireland Ltd . All rights reserved.