Immunofluorescence and immunohistochemical techniques were used to define the distribution of cytoskeletal (cytokeratin 8, vimentin) and extracellular matrix components (collagen type I, collagen type II, hyaluronic acid, and aggrecan) and bone morphogenetic proteins 4 and 7 (BMP4 and BMP7) in the notochord of the lesser spotted dogfish Scyliorhinus canicula L. Immunolocalization of hyaluronic acid was observed in the notochord, vertebral centrum, and neural and hemal arches, while positive labeling to aggrecan was observed in the ossified centrum, notochord, and the perichondrium of the hyaline cartilage. Type I collagen was observed in the mineralized cartilage of the vertebral bodies, the notochord, the fibrocartilage of intervertebral disc, and the perichondrium. A positive labeling to type II collagen was observed in the inner part of the cartilaginous vertebral centrum and the notochord, as well as in the neural arch and muscle tissue, but there was no appreciable labeling of the hyaline cartilage. The presence of both BMP4 and BMP7 was seen in the mineralized vertebral centrum, notochordal cells, and neural arch. The notochordal cells expressed both cytokeratin 8 and vimentin, but predominantly vimentin. Hyaluronic acid, collagen type I, and collagen type II expression confirmed the presence of a mixture of notochordal and fibrocartilaginous tissue in the intervertebral disc, while BMPs confirmed the presence of an ossification in the cartilaginous skeleton of the spotted dogfish.
Keywords: BMPs; aggrecan; collagen type I; collagen type II; dogfish; hyaluronic acid; intermediate filaments; notochordal cells.
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