Induction of matrix metalloproteinases and collagenolysis in chick embryonic membranes before hatching.

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Abstract
The membranes surrounding the chick embryo undergo striking morphological changes before hatching, which include structural degradation of the allantoic membrane. The fibrillar collagen content of the membranes declined by embryonic day (ED) 20 (the day of hatching). By ED 19, a 55-kDa matrix metalloproteinase (MMP) activity appeared in the extraembryonic fluid, and by ED 20 there was substantial 55-kDa MMP activity in embryonic membrane extracts. Reverse transcription-polymerase chain reaction was employed to clone a partial cDNA representing the chicken homologue of MMP-13, a 55- to 57-kDa enzyme. MMP-13 mRNA dramatically increased in abundance in embryonic membranes by ED 19, reaching a peak on ED 20. Introduction of the MMP inhibitor batimastat into the extraembryonic fluid prevented the structural changes in the embryonic membranes before hatching. We conclude that, like mammalian fetal membranes, chick embryonic membranes undergo terminal remodeling before hatching, in part as a result of increased MMP activity. The chicken egg system represents a novel in vivo model for exploring biochemical events leading to embryonic membrane remodeling prior to birth and to test inhibitors of MMPs for their ability to prevent collagenolysis and fetal membrane rupture.