Phoenix from the ashes: The 5 million year old virus
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Around half of the human genome consists of repetitive DNA sequences. When these are studied in detail, more than 10% of our genome is found to be made up of retrotransposons, mobile genetic elements in which movement through the genome (transposition) involves reverse transcription with an RNA intermediate similar to that of a retrovirus. A major type of repetitive DNA element consists of retrovirus-like elements. Their structure closely resembles that of modern retroviruses, carrying internal sequences with homology to gag, pol, and sometimes env open reading frames flanked by long terminal repeats. Similar sequences occur in all higher organisms, from yeast to vertebrates. Human endogenous retroviruses (or HERVs), comprise of remnants of ancient exogenous retroviruses that have gained access to the human germ line. In this safe harbour, they have been vertically transmitted for generation after generation. Although most of these proviruses have suffered extensive deletions and mutations, HERV-derived transcripts and proteins have been detected in both healthy and diseased human tissues.
These genetic passengers we carry inside us are not entirely neutral. In rare circumstances, the integration of retroelements can cause significant harm by disrupting or disregulating essential genes. Fukuyama-type muscular dystrophy, one of the commonest autosomal recessive disorders in Japan, is caused by an ancient retrotransposon insertion (Kobayashi, K. et al. An ancient retrotransposal insertion causes Fukuyama-type congenital muscular dystrophy. 1998 Nature 394: 388-392). On the other hand, the protein syncytin, which is responsible for formation of the human placenta, is a captive retroviral envelope protein (Mi, S. et al. Syncytin is a captive retroviral envelope protein involved in human placental morphogenesis. 2000 Nature 403: 785-9).
HERV-K, is the youngest and most conserved family of endogenous retrovirus, but the role of HERV expression in disease remains unclear. After millions of years as our nearest neighbours, we still don’t know much about these things inside us! A team of French scientists has reconstructed the DNA sequence of a 5-million-year-old retrovirus and shown that it is able to produce infectious particles. The resulting retrovirus, which they named Phoenix, is the ancestor of the HERV-K line. This study is the first to generate an infectious retrovirus from a mobile element in the human genome, and so provides definitive proof of replication capabilities locked up in seemingly dead fossil genetic elements (Dewannieux M, et al. Identification of an infectious progenitor for the multiple-copy HERV-K human endogenous retroelements. Genome Res. 2006).
Phoenix became frozen in time after it integrated into the human genome about 5 million years ago, but still retains the potential for infectivity. However, although the resulting virus particles were capable of infecting mammalian cells in culture, infectivity was very low, presumably because the host cells have evolved mechanisms to resist uncontrolled virus propagation. So while it’s unlikely that this work will result in some sort of biblical plague, it is possible that a better understanding of the potential of HERV-K and its little friends may lead us towards the retrovirus particles that can be observed in some human cancers such as germline tumours and melanomas, and help to elucidate their significance in these diseases.
[...] Phoenix from the ashes: The 5 million year old virus French researchers have revived one of the silent passengers in our genome. There can be found quite some HERVs (human endogenous retroviruses), remnants of retroviruses, integrated in our genome. The youngest of these is HERV-K family. Now Phoenix, a purported ancestor of the HERV-K line has risen from the ashes, and the revived virus is indeed infect mammalian cells, although at a very low infectivity. Finding Gives Boost To Bioinformatics Use in Fighting Disease The use of computers to advance human disease research – known as bioinformatics – has received a major boost from researchers at the La Jolla Institute for Allergy & Immunology (LIAI), who have used it to successfully predict immune response to one of the most complex viruses known to man – the vaccinia virus, which is used in the smallpox vaccine. Immune responses, which are essentially how the body fights a disease-causing agent, are a crucial element of vaccine development. Filed under: Remaindered Links | [...]
good study thanks for this.but i have a question about that virus “can that virus still be active?” also “how did you notice that virus?”
As the paper says, the virus clearly is active.
Do you have any idea about how did they find or notice this virus? There is no knowledge on this.
[...] Med det samme vi snakker om blindpassasjerer i genomet kan det jo nevnes at franske forskere nylig har gjenopplivet en av dem vi har hatt med oss i 5 millioner år. Phoenix, som de har kalt viruset, er forfaren til HERV-K, en familie med humane endogene retrovirus som er integrert i det humane genom. Phoenix som reiste seg av asken var istand til å infisere mammalske celler (celler fra pattedyr), men hadde svært lav infektivitet, sannsynligvis fordi vertscellene har utviklet mekanismer for å motstå ukontrollert virusreplikasjon. [...]
[...] Phoenix from the ashes: The 5 million year old virus [...]
This is a truly profound result, because it raises the possibilty that – as happens in cats with feline leukaemia virus – recombination between dormant endogenous retroviruses and superinfecting viruses could give rise to new viruses with unexpected tropism / virulence characteristics. Which makes the question of whether or not we should use xenotransplants – pig heart valves, etc – even more interesting….
[...] example – that of the re-awakening of a “fossil” endogenous human retrovirus – was covered on this site recently. This has all sorts of interesting implications for the evolution of new retroviruses by [...]
This also seems to raise some questions regarding evolution. How much of an effect could DNA altering virii have played in the course of evolution? The sequencing of the genome is like reading the most interesting historical book ever written, but which has not yet been fully translated.
[...] Phoenix from the ashes: The 5 million year old virus [...]
[...] endogenous retroviruses: from ancestral pathogens to bona fide genes « MicrobiologyBytes on Phoenix from the ashes: The 5 million year old virusHuman endogenous retroviruses: from ancestral pathogens to bona fide genes « MicrobiologyBytes [...]
[...] Phoenix from the ashes: The 5 million year old virus [...]