Distribution of fibrillin I in extracellular matrix and epithelia during early development of avian embryos.

Fibrillin microfibrils are widely distributed components of extracellular matrices that function in the formation of elastin, serve structural roles and provide substrates for cell adhesion. To determine when and how fibrillin-1 (fib-1) may function in early development we have examined the temporal and spatial distribution of fib-1 in chicken embryos. Using homologous PCR we amplified and cloned a 407 nt fragment of chicken cDNA that appears to code for an orthologue of FBN-1. Bacterially expressed protein was used to prepare two monoclonal antibodies, both of which recognize a 350 kD band in immunoblots or immunoprecipitates in supernatants of chicken embryonic aorta cells or human MG-63 cells. Both antibodies recognize fibrillar material associated with the surfaces of cultured cells. The antibodies appear to be specific for fib- as there was only weak cross reactivity to a bacterially expressed fragment from the corresponding region of fib-2 and the pattern of immunofluorescence in embryonic tissue is distinctly different from that of JB-3, a fib-2 specific antibody (Rongish et al. 1998). In embryos, fib-1 is first detected at stage 6 in the epiblast during gastrulation. In subsequent stages fib-1 fibers appear in all tissues and are present throughout the first 6 days of development. Immunoreactive fibers are present in basal laminae and mesenchyme filled spaces, but they also form random arrays with an apical-basal polarity within epithelia. Using primers specific for FBN-1 and FBN-2 in RT-PCR reactions we confirm the presence of fib- 1 and fib-2 mRNA in early embryonic stages. This temporal and spatial distribution indicates fib-1 has functions in early development that are distinct from fib-2.