Does Human DNA Come From a Virus?
About eight percent of human genetic material comes from a virus
and not from our ancestors, according to researchers in Japan
and the U.S.
The study, and an accompanying News & Views article by University
of Texas at Arlington biology professor Cédric Feschotte,
is published in the journal Nature.
The research showed that the genomes of humans and other mammals
contain DNA derived from the insertion of bornaviruses, RNA viruses
whose replication and transcription takes place in the nucleus.
Feschotte wrote on recent research led by Professor Keizo Tomonaga
at Osaka University in Japan. Feschotte said this virally transmitted
DNA may be a cause of mutation and psychiatric disorders such
as schizophrenia and mood disorders.
In his article, Feschotte speculates about the role of such viral
insertions in causing mutations with evolutionary and medical
The assimilation of viral sequences into the host genome is a
process referred to as endogenization. This occurs when viral
DNA integrates into a chromosome of reproductive cells and is
subsequently passed from parent to offspring. Until now, retroviruses
were the only viruses known to generate such endogenous copies
in vertebrates. But Feschotte said that scientists have found
that non-retroviral viruses called bornaviruses have been endogenized
repeatedly in mammals throughout evolution.
Bornavirus (BDV) owes its name to the town of Borna, Germany,
where a virus epidemic in 1885 wiped out a regiment of cavalry
horses. BDV infects a range of birds and mammals, including humans.
It is unique because it infects only neurons, establishing a persistent
infection in its host's brain, and its entire life cycle takes
place in the nucleus of the infected cells. Feschotte said this
intimate association of BDV with the cell nucleus prompted researchers
to investigate whether bornaviruses may have left behind a record
of past infection in the form of endogenous elements. They searched
the 234 known eukaryotic genomes (those genomes that have been
fully sequenced) for sequences that are similar to that of BDV.
"The researchers unearthed a plethora of endogenous Borna-like
N (EBLN) elements in many diverse mammals, " Feschotte said.
The scientists also were able to recover spontaneous BDV insertions
in the chromosomes of human cultured cells persistently infected
by BVD.Based on these data, Feschotte proposes that BDV insertions
could be a source of mutations in the brain cells of infected
"These data yield a testable hypothesis for the alleged,
but still controversial, causative association of BDV infection
with schizophrenia and mood disorders," Feschotte said. The
research in Feschotte 's laboratory, which largely focuses on
transposable elements, the genetic elements that are able to move
and replicate within the genomes of virtually all living organisms,
is representative of the research under way at UT Arlington, an
institution of 28,000 students on its way to becoming a nationally
recognized, top-tier research university.
January 8, 2010