Distribution of fibrillin 1 in extracellular matrix and epithelia during early development of avian embryos

Fibrillin microfibrils are widely distributed components of extracellular m atrices that function in the formation of elastin, serve structural roles a nd provide substrates for cell adhesion. To determine when and how fibrilli n-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 aor ta cells or human MG-63 cells. Both antibodies recognize fibrillar material associated with the surfaces of cultured cells. The antibodies appear to b e specific for fib-1 as there was only weak cross reactivity to a bacterial ly expressed fragment from the corresponding region of fib-2 and the patter n of immunofluorescence in embryonic tissue is distinctly different from th at of JB-3. a fib-2 specific antibody (Rongish et al, 1998), In embryos, fi b-1 is first detected at stage 6 in the epiblast during gastrulation. In su bsequent stages fib-1 fibers appear in all tissues and are present througho ut the first 6 days of development. Immunoreactive fibers are present in ba sal 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 fi b-2 mRNA in early embryonic stages. This temporal and spatial distribution indicates fib-1 has functions in early development that are distinct from f ib-2.