Fig. 1. (A-F) Immunolocalization of SIRP in growth cones of cortical neurons cultured either on laminin (A-D) or poly-D-lysine (E,F). Bar, 10 µm. (G-I) Double-immunofluorescence of SIRP and CD81 in a growth cone on laminin. Bar, 5 µm. Growth cones were double-labeled with anti-SIRP antibody (Alexa Fluor® 594-conjugated secondary antibody; B,D,E,F,G,I) and FITC-phalloidin (C,D,F) or anti-CD81 (Alexa Fluor® 488-conjugated secondary antibody; H,I). D is the merged image of B and C (overlap appears yellow), and A is the corresponding phase-contrast image. F is the merged image of E with that of phalloidin labeling (not shown separately). I is the merged image of G and H and shows extensive co-localization (yellow) of SIRP and CD81. Images are 0.1 µm optical sections obtained by digital deconvolution. The arrows in D point to SIRP immunoreactivity in filopodial tips. The arrows in I indicate filopodial tips with prominent SIRP and CD81 overlap.