Fig. 1. Internalization of the native and chimera syndecan-4 proteins. (A) RFPEC cells expressing the FcR-S4 construct were decorated with Cy3-labeled (red) human non-immune IgG (niIgG) and then clustered with AlexaFluor 647-labeled (green) FGF2. IgG decorated FcR-S4 chimeras are present on the surface of the cells and in the cytoplasm 20 minutes after FGF2 clustering (red). FGF2 is present both on the cell surface and in the cytoplasm. Note co-localization (yellow) of internalized FGF2 and FcR-S4 chimeras (merged image). This observation is consistent with FGF2-induced oligomerization of FcR-S4 native S4 heterodimers. (B) FcR-S4-expressing cells decorated with biotinylated niIgG followed by clustering with Cy3-labeled clustering antibodies (red). Biotinylated niIgG remaining on the cell surface was visualized by streptavidin-Cy5 (green). Dual stain on the merged image shows cell surface localized FcR-S4 whereas single red stain shows internalized FcR-S4. Right figure shows the merged color image overlaid with a DIC image. Lower figure shows Z-plane projection of the area in the white rectangle.