Fine structure and morphogenesis of Borna disease virus

Abstract

Borna disease virus (BDV), a negative nonsegmented single-stranded RNA virus, has not been fully characterized morphologically. Here we present what is to our knowledge the first data on the fine ultrastructure and morphogenesis of BDV. The supernatant of MDCK cells persistently infected with BDV treated with n-butyrate contained many virus-like particles and more BDV-specific RNA than that of untreated samples. The particles were spherical, enveloped, and approximately 130 nm in diameter; had spikes 7 nm in length; and reacted with BDV p40 antibody. A thin nucleocapsid, 4 nm in width, was present peripherally in contrast to the thick nucleocapsid of hemagglutinating virus of Japan. The BDV particles reproduced by budding on the cell surface.

FIG. 1

Distribution of the diameters of virus-like particles observed by negative staining and ultrathin sectioning.

FIG. 2

Ultrathin section of induced MDCK/BDV cells embedded in epoxy resin. (a) Extracellular virus-like particles. (Inset) Extracellular virus-like particles at a high magnification. (b) Virus-like particles in cytoplasmic vacuoles. Bars, 100 nm.

FIG. 3

Antibody reactivity of BDV-, HVJ-, and HIV-infected cells as detected by immunoelectron microscopy. (a) Induced MDCK/BDV cells reacted with anti-BDV p40 antiserum. The arrow shows the budding of BDV, and the arrowheads show particles that have reacted with the antiserum. (b) Induced MDCK/BDV cells did not react with normal rabbit serum. (c) MDCK/HVJ cells did not react with anti-BDV p40 antiserum. (d) Molt-4/HIV-1 cells reacted with anti-HIV-1 RT rabbit serum. (e) Molt-4/HIV-1 cells did not react with normal rabbit serum. Bars, 100 nm.

FIG. 4

Inner structures of BDV and HVJ. Stereoscopic observation of electron micrographs of virus-like particles observed in ultrathin sections of induced MDCK/BDV cells embedded in epoxy resin. The ultrathin sections were observed at tilts of +5° (a) and −5° (b). (c) Ultrathin section of BDV particles, with an arrow showing the thin nucleocapsid. (d) Ultrathin section of HVJ particles, with an arrow showing the thick nucleocapsid. (e and f) Schematic diagrams of BDV and HVJ, respectively.

FIG. 5

Sequential images of the budding process in induced MDCK/BDV cells. The spiked membrane area (arrow in panel a) becomes an extracellular particle (d). (b and c) Intermediate stages of the budding. Bar, 100 nm.