Extracellular matrix protein fibulin-2 is expressed in the embryonic endocardial cushion tissue and is a prominent component of valves in adult heart

Abstract

Fibulins-1 and -2 are two recently characterized extracellular matrix proteins of a novelprotein family. They are found in many tissues inthe adult stage, but several differences in theirexpression patterns were noted in cultured cells and adult tissues. Fibulin-1 is particularly wellexpressed in the endocardial cushion tissue (ECT)during embryogenesis and we therefore compared the expression patterns of fibulin-1 and -2 in the developing mouse heart. Antibodies against mouse fibulin-1 and -2 were used in immunofluorescence, and the expression of mRNAs were studied with synthetic oligonucleotides by in situ hybridization. A striking codistribution of fibulin-1 and -2 was seen at all stages of the development of the endocardial cushion tissue. Fibulin-2 was found tobe a more specific marker for the embryonic ECT than fibulin-1, which was also transiently expressed in cardiac muscle. Immunofluorescence showed that the fibulins remained expressed in valves of the heart in the adult stage. The results suggesta role of the two fibulins in the development of the ECT and in the maintenance of the tensile strength of the cardiac valves. © 1995 by Academic Press, Inc.