Fusion of Sendai Viruses or Subviral Envelope Components with Chicken Erythrocytes Observed by Freeze‐Fracture Electron Microscopy

Abstract

Four different types of envelope of Sendai virus or subviral components, that is, infectious and non-infectious virions, reassembled envelope particles (REP), and Tween-ether-treated envelope fragments (TE), were studied comparatively for membrane interactions with chicken erythrocytes by freeze-fracture electron microscopy, specifically for membrane alteration by envelope fusion.The freeze-fracture replicas of the attachment of the four envelopes in the cold exhibited a common pattern of impressions with attached envelopes, although the fracture plane traversed from erythrocyte to envelope at the periphery of the contact areas of three of the envelopes but not of TE, where the fracture plane mostly cut only through erythrocyte membranes impressed with TE. The freeze-fracture replicas of the four envelopes reacting with erythrocytes after a short incubation period at 37 C exhibited distinctive features: infectious virions and REP displayed evidence of envelope fusion, but non-infectious virions and TE showed a particular pattern of envelope association without fusion. Our data demonstrate that the pattern specific for envelope fusion is the formation of a continuous membrane from envelope to cell membrane in a cross fracture of an erythrocyte.Although envelope fusion by Sendai virions has been extensively studied by electron microscopy (1, 3, 4, 18, 20-28, 31, 36), the morphology of membrane interactions of subviral envelope particles with cell membranes as well as those of non-infectious Sendai virions (9, 30) with host cells is not yet well elucidated. Using Sendai virions and subviral envelope components, which were different from each other in their ability to affect membranes, we wanted to observe membrane alterations during the interactions of these envelopes with cell membranes and to charaterize the membrane changes specific for envelope fusion. The envelopes we used were infectious and non-infectious virions, reassembled envelope particles (REP) from Nonidet P40 (NP40)-solubilized virus envelopes (16), and Tween-ether-treated envelope fragments (TE) (15). Non-infectious Sendai virions, which contain a precursor fusion protein (9, 30), do not have hemolytic or cell fusion activity (8, 11). REP has these activities (16), and although much evidence 25

Reconstitution of the fusogenic activity of vesicular stomatitis virus.

“…Typically the virosomes display an asymmetric distribution of the protein with most of the spikes on the external surface of the bilayer. They bind to cells, and in some cases they have been shown to fuse with red blood cells (Miller et al, 1980;Hosaka et al, 1983;Kawasaki et al, 1983;Marsh et al, 1983) or with liposomes (Eidelman et al, 1984;Scheule, 1986). In no case have such virosomes been shown to fuse into the plasma membrane of nucleated cells.…”