Fig. 5: Expressing myosin-7a-M7BP complexes in cells produces substantial filamentous networks and filopodial protrusions.

A S2 cells transfected with M7BP-mCherry or GFP-myosin-7a alone show no discernable difference in cell morphology compared to that of GFP transfection. Scale bar = 5 μm. (representative of five independent experiments) B Co-transfection of GFP-myosin-7a (green) with M7BP-mCherry (red) results in the induction of an extensive filamentous structure throughout the cell body and the extension of filopodial protrusions. Scale bar = 5 μm. Images are representative of 12 independent transfection experiments. C Co-transfection a monomeric tailless myosin-7a (GFP-M7aS1SAH, green) with M7BP-mCherry (red) does not induce the filopodia or the filamentous network phenotypes observed in B. Scale bar = 5 μm. (representative of four independent experiments) D Magnified images of box 1 in B (top panel) and box 3 in C (bottom panel) show that full-length myosin-7a and M7BP are colocalized on the filamentous structures, whereas M7aS1SAH and M7BP are diffusive and non-colocalized within the cell. Scale bars = 2 μm. E Colocalization analysis of regions from box 1 and box 3 yielded high degree of colocalization correlation between full-length myosin-7a and M7BP in contrast to the low colocalization score between M7aS1SAH and M7BP. N = 9802 pixels from ROI 6 × 12 μm. F Movie frames taken from in vitro single-molecule motility assays (left) and in vivo live cell imaging of a filopodium (right) show that myosin-7a-M7BP complexes stay for long duration at the end of actin filaments. G Kymographs of box 4 and 5 in F show that myosin-7a-M7BP complexes (green) travel with comparable speed in vivo along filopodia as they do in vitro along fixed actin filaments.