Transposons, or "jumping genes," make up roughly half of the human genome. Geneticists previously estimated that they replicate and insert themselves into new locations roughly one in every 20 live births.
New results, published in the June 25, 2010 issue of Cell, suggest that every newborn is likely to have a new transposon somewhere in his or her genome.
"Now it looks like every person might have a new insertion somewhere," says senior author Scott Devine, PhD, associate professor of medicine at the University of Maryland School of Medicine's Institute for Genome Sciences. "This is an under-appreciated mechanism for continuing mutation of the human genome."
The research was initiated at Emory University School of Medicine, where Devine was in the Department of Biochemistry. First author Rebecca Iskow, PhD (now a postdoctoral fellow at Brigham & Women's Hospital in Boston) was a graduate student at Emory. Two other papers on human transposons appear in the same issue of Cell.
Transposons resemble e-mail spam: short repeated sequences that have no obvious function other than making more of themselves. The full name for the type of transposon that is most abundant in the human genome is retrotransposon. The "retro" term comes from how they replicate: first, the DNA is transcribed (copied) into RNA, and the RNA is reverse-transcribed into DNA again. This process normally only happens during very early in development, when the cells that will become eggs and sperm have not turned down a separate path of differentiation.
"Transposons are the original selfish genes, and this strategy makes sense for them, because it makes sure new copies will get carried into the next generation," Devine says.
While working in Devine's lab as a graduate student, Iskow devised a technique for "amplifying" the stretches of individual genomes that border transposons and reading thousands of the junctions with advanced sequencing techniques, then comparing them to the reference human genome.
"The basic problem was that a new insertion can be anywhere within three billion base pairs – how do you find it compared to all the other ones?" Devine says.
Ninety-seven percent of genomes the team surveyed had at least one rare insertion of the L1 variety of transposon that was present in only a single human in the study, and some genomes had several. Since the study surveyed 76 genomes, "rare" insertions could still be shared by large groups consisting of thousands of people. Rare insertions corresponded to the most recent transposons, which are less likely to have their jumping abilities impaired by other types of mutations.
Devine's team also showed that transposons frequently jump to new locations during the process of tumor formation. Surveying 20 lung tumors and comparing their genomes against the normal tissues they came from, the team found that six tumors had new transposon insertions that were not present in the normal adjacent tissues.
"This indicates that transposons are jumping in tumors and are generating a new kind of genomic instability," Devine says.
Transposons can inactivate tumor suppressor genes and can facilitate rearrangements that involve large stretches of chromosomes. Geneticists have already identified many transposons that interrupt genes and cause human diseases, including neurofibromatosis, hemophilia and breast cancer.
Scientists believe a process called methylation, which silences genes during differentiationalso shuts off transposons' ability to jump. Analyzing the patterns of mutations in the lung tumors suggested that during tumor formation, modified methylation patterns may be allowing transposons to re-awaken, Devine says.
Several scientists from the Biomolecular Computing core facility and the Winship Cancer Institute of Emory University were involved in the research.
The research was supported by grants from the National Human Genome Research Institute, the American Cancer Society and Sun Microsystems.Reference:
Writer: Quinn Eastman
The Robert W. Woodruff Health Sciences Center of Emory University is an academic health science and service center focused on missions of teaching, research, health care and public service. Its components include the Emory University School of Medicine, Nell Hodgson Woodruff School of Nursing, and Rollins School of Public Health; Yerkes National Primate Research Center; Winship Cancer Institute of Emory University; and Emory Healthcare, the largest, most comprehensive health system in Georgia. Emory Healthcare includes: The Emory Clinic, Emory-Children's Center, Emory University Hospital, Emory University Hospital Midtown, Wesley Woods Center, and Emory University Orthopaedics & Spine Hospital. The Woodruff Health Sciences Center has a $2.5 billion budget, 17,600 employees, 2,500 full-time and 1,500 affiliated faculty, 4,700 students and trainees, and a $5.7 billion economic impact on metro Atlanta.
Learn more about Emory's health sciences: http://emoryhealthblog.com - @emoryhealthsci (Twitter) - http://emoryhealthsciences.org
Vince Dollard | EurekAlert!
A Map of the Cell’s Power Station
18.08.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau
On the way to developing a new active ingredient against chronic infections
18.08.2017 | Deutsches Zentrum für Infektionsforschung
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Materials Sciences