In summary, our observations reconcile the contrasting models of filovirus budding and allow us to describe the sequence of events taking place during budding and release of MARV virus. We propose that this represents a general sequence of events also followed by other filamentous and rod-shaped viruses. Furthermore, we demonstrate that virus shape is determined both by viral and cellular factors. The model for filamentous virus budding presented here raises a number of new questions. Do elements of the cytoskeleton or other cellular components play a specific role in mediating envelopment or budding of filamentous or spherical virus particles? Is one end of the PM-associated NC specifically able to initiate the extrusion of the filament, as in rhabdoviruses, or is the directionality of the extrusion process random? What is the organisation of the NC and VP40 matrix layers in the released Table 2 . 3D analysis of virus shape and NC length at different steps of filamentous MARV budding. 