Читать книгу Principles of Virology, Volume 1 - Jane Flint, S. Jane Flint - Страница 26

Every cell in our body contains viral DNA. Human endogenous retroviruses, and elements thereof, make up about 8% of our genome. Most are inactive, fossil remnants from infections of germ cells that occurred over millions of years during our evolution. Some of them are suspected to be associated with specific diseases, but the regulatory sequences and protein products of other endogenous retroviruses have been coopted during our evolution for their unique functions. For example, retroviral gene products may play a role in the regulation of pluripotency in germ cells, in transmission of signals at neuronal synapses, and clearly in the way that we give birth. The development of the human placenta depends on cell fusion promoted by a retroviral protein. If not for these endogenous retroviruses, we might be producing our young in eggs, like birds and reptiles.

Recent genomic studies have revealed that our viral “heritage” is not limited to retroviruses. Human and other vertebrate genomes harbor sequences derived from several other RNA and DNA viruses. As many of these insertions are estimated to have occurred some 40 million to 90 million years ago, this knowledge has provided unique insight into the ages and evolution of their currently circulating relatives. The conservation of some of these viral sequences in vertebrate genomes suggests that they may have been selected for beneficial properties over evolutionary time.