Figure 7: Spreading behaviour and distribution of ARPC5 and actin in normal and ARPC1B-deficient platelets.

Platelets in platelet-rich plasma were allowed to spread on fibrinogen for 30 min before fixation, staining and imaging by laser fluorescence structured illumination microscopy. (a) Each set of panels shows a wide field image (bars=5 μm) and (b) higher magnification images of representative spread platelets stained for CD61/fibrinogen receptor (red), ARPC5 (green) and F-actin (magenta; bars=2 μm). Most normal platelets show circular lamellipodia, peripheral ARPC5 and F-actin present at the lamellipodial edge and in stress fibres and nodules (see also Fig. 6). In contrast, at his time point many ARPC1B-null platelets (from Patient 1) have not spread, or show abnormal shapes and subcellular distributions of ARPC5 and F-actin (note: close up panels are collages necessitated by the sparse distribution of spread platelets; all others are cropped fields). ARPC1B-deficient platelets (from Patient 2) also show limited spreading and unusual spread morphologies, including extremely long filopodia containing long unbranched actin fibres.