Genome complexity: retroviruses conrol immunity (Introduction)

by David Turell , Friday, March 04, 2016, 15:22 (3187 days ago) @ David Turell

DNA has about 8% retrovirus remnants which can control interferon usage, a basic defense mechanism:-http://www.the-scientist.com/?articles.view/articleNo/45503/title/Viral-Remnants-Help-Regulate-Human-Immunity/&utm_campaign=NEWSLETTER_TS_The-Scientist-Daily_2016&utm_source=hs_email&utm_medium=email&utm_content=26940621&_hsenc=p2ANqtz-8rYpCVdLFk4R8-_AQET5OIVkXV8aZrDQuXcjyglie1-tV0N4hqyvSpbRjJ9mvMsT8b8hYTG1C785ZM_AFIkmeAdrWvPg&_hsmi=26940621/-"Remnants of retroviruses that entered the human genome millions of years ago can regulate some innate immune responses. These viral sequences have previously been linked to controlling early mammalian development and formation of the placenta, among other things. A study published today (March 3) in Science establishes that one such endogenous retrovirus in human cells can also regulate the interferon response, which helps organisms quickly respond to infections. The work is one of the first reports to show that human cells could have adopted retroviral sequences to regulate their genes.-***-"Chuong and his University of Utah mentors Nels Elde and Cédric Feschotte began by scanning the sequences around interferon-induced genes, finding at least 27 transposable elements that likely originated from the long repeats at the ends of retroviral sequences. One such element, known as MER41, comes from a virus that invaded the genome approximately 45 million to 60 million years ago; the team found that its sequence in present-day human cells contained interferon-inducible binding sites.-"The group then focused on a MER41 sequence that occurs 220 base pairs upstream of an interferon-induced gene called AIM2, which activates an inflammatory response in cells. When the researchers deleted this MER41 element in a cell line using CRISPR/Cas9 gene editing, interferon treatment could not trigger the AIM2 gene. Without the interferon-mediated response, these cells were more susceptible to viral infections, the team found.-***-"In addition to AIM2, the group found MER41 elements helped regulate at least three other interferon-inducible genes involved in human immunity. Looking across the genomes of other mammals, the researchers also found MER41-like regulatory elements in lemurs, bats, and other species.-***-"Whether host cells coopted the viral sequences for their regulatory needs or if ancient viruses used their regulatory abilities to control host immunity during invasion is still unknown, according to Feschotte. “We can only speculate why ancient viruses might have carried these regulatory switches to begin with, but data suggest they had these systems built into their sequence already,” he told The Scientist. (my bold)-"Endogenous retroviral elements make up about 8 percent of the human genome, and similar regulatory effects might be found on other mammalian gene functions, said Mager. “What's cool about endogenous retroviruses is that their ends, known as LTRs, are optimized to have all these regulatory sequences in just 300 to 400 base pairs of DNA,” she said. “These units are powerhouses of regulatory potential.'”-Comment: Note my bold. Is this pre-planning using viruses to build effective DNA defenses?