Following the death of the polar bear Knut at Berlin Zoo, examinations carried out at the Leibniz Institute for Zoo and Wildlife Research in Berlin showed that Knut was suffering from virus-induced encephalitis (acute inflammation of the brain).
Researchers at Saarland University and IZW have now analyzed his genetic material and discovered and characterized new sequences of endogenous retroviruses. The retroviruses were also found in another former resident of Berlin Zoo: the giant panda Bao Bao.
The work of the research team indicates that these viruses were inserted into the genome of an ancestor of both bear species some 45 million years ago. These newly discovered viruses are very similar to those found in the genetic material of bats, cattle and even humans. Some of these viruses are suspected of being involved in triggering some diseases in humans. The study has now been published in a recent edition of the journal Virology.
Endogenous retroviruses (ERVs) are viruses that at some point in the past inserted themselves into the nuclear genome of a host's germ cell. Once integrated in a germ cell the virus would be passed on from one generation to the next and the endogenous retroviral genome would therefore be inherited to new species that evolve from the original host. 'ERV sequences and fragments make up about eight per cent of the human genome,' explains Professor Jens Mayer from the Department of Human Genetics at Saarland University. Endogenous retroviruses are found not only in humans, but also in other mammals such as horses, cattle, apes, koalas and, as has now been shown, in polar bears and giant pandas.
Working in collaboration with Professor Alex D Greenwood and Kyriakos Tsangaras from the Leibniz Institute for Zoo and Wildlife Research in Berlin, Jens Mayer has been taking a closer look at the DNA sequences from polar bears and great pandas. 'We have characterised endogenous retroviral sequences in both bear species and found a strong similarity between the two, which indicates that these two virus species are closely related,' says human geneticist Mayer. The researchers also identified ERV sequences in other bear species such as the brown bear, the black bear and the spectacled bear. 'Using molecular dating methods we have now been able to show that the retrovirus became integrated into the genetic material of an ancestor of today's bear species around 45 million years ago,' explains Greenwood. The research team also showed that the original retrovirus was closely related to those found in the genomes of bats and cattle. Interestingly, the viruses found in bears exhibit strong similarity with several endogenous retroviruses found in the human genome. 'Some of these sequences are suspected of playing a role in the occurrence of cancer, neurodegenerative or autoimmune diseases,' says Mayer.
The sort of extensive genome analysis of different species of wildlife carried out in this study helps scientists gain a better insight into the evolution of retroviruses by learning which retroviruses infected which groups of animals millions of years ago. The data can also provide valuable information on the evolutionary development of mammals. The researchers make use of a variety of techniques to analyse DNA sequences, including very recent high-throughput ('next generation') sequencing methods that facilitate highly efficient DNA sequencing.
Source: Saarland University