In a comparison of the marsupial genome to genomes of non-marsupials, including human, published in the May 10 issue of the journal Nature, the team found that most innovations leading to the human genome sequence lie not in protein-coding genes, but in areas that until recently were referred to as "junk" DNA.
The effort to generate the high-quality genome sequence of the gray short-tailed, South American opossum, Monodelphis domestica, began in 2003 and cost approximately $25 million. The sequencing work was funded by the National Human Genome Research Institute (NHGRI), part of the NIH, and carried out at the Broad Institute Sequencing Platform, which is a member of NHGRI's Large-Scale Sequencing Research Network.
"The opossum genome occupies a unique position on the tree of life. This analysis fills a crucial gap in our understanding of how mammalian genomes, including our own, have evolved over millions of years," said NHGRI Director Francis S. Collins, M.D., Ph.D. "These new findings illustrate how important it is to understand all of the human genome, not just the fraction that contains genes that code for proteins. We must identify all functional elements in the genome if we are to have the most complete toolbox possible to explore human biology and improve human health."
Marsupials are unique among mammals because their young are born at an extremely early stage of development, attach to their mother's teats and complete their subsequent development while in a protective pouch. This makes the young readily available for early developmental research.
There are many other areas of biomedical research for which Monodelphis serves as a model. For example, it is the only laboratory animal known in which ultraviolet radiation alone can cause melanoma, a type of skin cancer that also strikes humans exposed to too much of the sun's ultraviolet rays. Having the sequence of the opossum genome will give researchers the ability to learn more about the molecular basis of melanoma and its progression, as well as explore development of new therapies and preventive treatments.
The opossum genome sequence also provides researchers with a fresh perspective on the evolutionary origins of the human genome. It sheds light on the genetic differences between placental mammals, such as humans, mice and dogs, and marsupial mammals, such as opossums and kangaroos.
"Marsupials are the closest living relatives of placental mammals. Because of this relationship, the opossum genome offers a unique lens though which to view the evolution of our own genome," said Kirstin Lindblad-Toh, Ph.D., co-director of the Broad Institute's genome sequencing and analysis program and the study's senior author.
Marsupials and the ancestors of placental mammals diverged 180 million years ago. By comparing the opossum and human genomes, researchers were able to pinpoint genetic elements that are present in placental mammals, but missing from marsupials —that is, the genetic factors that may underlie many of the differences between the two types of mammals.
Interestingly, about one-fifth of the key functional elements in the human genome arose during this relatively recent evolutionary period. By focusing on the recent genetic innovations, the scientists made two major findings:
- First, the vast majority (about 95 percent) of recent genetic innovation lies not in protein-coding genes, but in regions of the genome that do not contain genes and that many had referred to as junk DNA until recently. Researchers now know that junk DNA may contain regulatory elements that influence the activity of nearby genes, but the full extent of the importance of these non-gene regions is still being revealed. The new results suggest that mammals evolved not so much by inventing new kinds of proteins, as by tweaking the molecular controls that dictate when and where proteins are made.
- Second, many of the new DNA instructions appear to be derived from transposons, or "jumping genes," which are also located in areas once thought to be junk DNA.
"Transposons have a restless lifestyle, often shuttling themselves from one chromosome to another," said the study's first author Tarjei Mikkelsen, a Broad Institute researcher. "It is now clear that in their travels, they are disseminating crucial genetic innovations around the genome."
Other important findings to emerge from the analysis of the opossum genome include:
- The opossum has many genes involved in immunity, challenging the notion that marsupials possess only primitive immune systems.
- The opossum genome has an unusual structure with fewer chromosomes than the human genome (9 pairs versus 23 pairs, respectively) but a longer total length (3.4 billion versus 3 billion bases, respectively).
Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute
Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy