Fig. 3. Caveolae interact with intermediate filaments in the notochord. (A) Thin sections of 3-day post fertilisation embryos showing caveolae within the cell-cell contact regions of the notochord. Caveolae (c) at the plasma membrane contact a distinct layer of filaments on the cytoplasmic side (f indicates layer of filaments). Frequent connections (arrowheads) between caveolae and filaments are apparent (boxed areas in A shown in lower panels). (B) Images from a tomogram of the notochord (see supplementary material Movie 1). (C) Images of same areas boxed in B with arrowheads indicating the same areas in different sections. Connections between caveolae and filaments are apparent. (D) Paraffin embedded 72-hour zebrafish sections labelled with a pan-cytokeratin antibody indicating expression in the notochord. Boxed regions demonstrate regions of interest in panel E and F with panel E showing cells in the periphery of the notochord, and panel F showing a central region. (E) In the peripheral regions, caveolin is associated with the plasma membrane between cells (arrows) and keratin is associated with bundles of fibres (arrowhead). (F) In the central strut-like regions of intercellular contact, cytokeratin fibres are found on either side of caveolin-labelled caveolae. Immunogold labelling of 3-day zebrafish sections show caveolin (small gold, arrows) in close proximity to cytokeratin (large gold, arrowheads). Note that the notochord is particularly hard to preserve in frozen sections owing to the large `empty' vacuoles and extremely thin bridges of cytoplasm in between. S, sheath; PM, plasma membrane. Bars, 200 nm (A,B); 100 nm (inset A,C); 100 µm (D); 100 nm (E,F).