Virology Division News
Virology Division News
Arch Virol 144/4 (1999)
Progress and controversy in Bornavirus research: a meeting report
Institut für Medizinische Mikrobiologie und Hygiene, Freiburg, Federal Republic of Germany
Borna disease virus (BDV) is the type species of a new family, Bornaviridae, within the
nonsegmented negative-strand RNA viruses (Mononegavirales). Unlike other members of
the order Mononegavirales BDV replicates and transcribes in the nucleus and uses the
splicing machinery for modification of subgenomic RNAs. The host range includes a broad
variety of warmblooded animals and most likely humans. BDV is neurotropic and infection
of immunocompetent animals can result in Borna disease (BD), an immune-mediated brain
disorder, characterised by prominent disturbances of movement and behaviour. First hints
that BDV could also be associated with certain human diseases emerged from serological
studies beginning in the 80’s when psychiatric patients were found to be seropositive in an
indirect immunfluorescence assay (IFA). Ever since then, the question of whether BDV
infections cause psychiatric disorders in humans has remained a controversial issue.
An international meeting was held in Freiburg* to discuss progress and controversial
topics in Bornavirus research. Among the highlights were aspects of the molecular biology
of BDV, the neuropathology of BDV-infected animals and first reports on the multicenter
studies in Germany and Japan that evaluated the methods for detection of BDV in humans.
Molecular biology of BDV
BDV encodes at least six proteins including the nucleoprotein (N), the phosphoprotein (P),
a putative matrixprotein (gp18), the glycoprotein (G), the polymerase (pol) and the just
recently identified X-protein. Very little is known about the function of these proteins.
Colocalization studies indicated that P, N and X are part of the ribonucleoprotein particles.
Binding studies with individual proteins indicated that P might bind X and N at nonoverlap-
ping binding sites. Using various experimental approaches two groups from Giessen/
Marburg and Freiburg/Irvine [16, 18] presented data that the X-protein is a nuclear export
protein containing leucine-rich nuclear export sequences (NESs). Yeast two hybrid experi-
ments revealed a specific binding of X to the cellular NES-binding protein CRM1 (Expor-
tin). Intriguingly, mutation of the critical leucine residues within the NES did not only
* Bornavirus Meeting, 27–29 September 1998, Freiburg, Germany.