Lysyl oxidases: Expression in the fetal membranes and placenta

The cross-linking of the connective tissues in the fetal membranes and plac enta is important for their tensile strength and elasticity. We have studie d the expression of lysyl oxidase (LOX) because it is the classical enzyme responsible for the cross-linking of collagen and elastin. We have also stu died the two recently described, genetically distinct lysyl oxidase-like ge nes and proteins, lysyl oxidase-like (LOSL) and lysyl oxidase-like 2 (LOXL2 ), of unknown functions. Specific antisera have been used for immunolocaliz ation in fetal membranes and placentae from early pregnancy terminations an d after caesarean section at both preterm and term, prior to labour. In add ition, the steady state mRNA levels of the three genes has been quantitated in separated amnion, chorion, decidua and placentae collected at term befo re labour. The immunocytochemistry shows that the spatial expression of the three lysyl oxidases is similar in early pregnancy in both the fetal membr anes and placentae. However, by preterm this pattern had diverged and becom es greatest at term. The expression of the genes found at term was similar to the results of protein expression obtained by immunocytochemistry, with the exception of LOXL which had high placental gene expression, but low lev els of immunolocalized protein. Thus by term, LOX was expressed predominant ly in the amniotic epithelium, with little espression in the placenta, whil e LOSL showed highest gene espression in the placenta and lowest expression in the amnion. LOXL2 expression was again different and was expressed pred ominantly in the chorionic cytotrophoblast of the membranes with low expres sion in both the amnion and placentae. These results suggest that these thr ee members of the lysyl oxidase family may hare similar roles in early preg nancy during the development of the placenta and fetal membranes, but their divergence as pregnancy advances to term, may reflect changes in substrate specificity and connective tissue composition. (C) 2001 Harcourt Publisher s Ltd.