Lysyl oxidase (ras recision gene) expression in human amnion: ontogeny and cellular localization

The tensile strength of human fetal membranes is attributable to interstitial collagens of the zona compacta of the avascular amnion. Collagen fiber strength and proteolytic resistance is provided by inter and intramolecular cross-links of collagen fibrils, which are formed in a series of reactions initiated by lysyl oxidase. Lysyl oxidase activity in amnion tissues varied by more than 400-fold in a highly significant inverse manner as a function of gestational age (12-43 weeks). At 12-14 weeks gestation, the levels of lysyl oxidase messenger ribonucleic acid, protein, and activity in amnion are very high. During the second trimester of pregnancy, however, these decline abruptly, and a nadir is reached at about 20-24 weeks gestation, which persists to term. The level of lysyl oxidase messenger ribonucleic acid was greater in amnion mesenchymal cells than in amnion epithelial cells. The decline in lysyl oxidase in amnion may be attributable to a correspondent decline in the density of amnion mesenchymal cells with fetal development.