USU, NIH study maps hotspots of genetic rearrangement

Findings in mice could aid in understanding how mammals genetically adapt

Researchers at the Uniformed Services University of Health Sciences (USU) and the National Institutes of Health (NIH) are concentrating focus on mouse chromosomes to map hotspots of genetic recombination – sites where DNA breaks and reforms to shuffle genes. Their findings have the potential to improve the detection of genes linked to disease and to help understand the root causes of genetic abnormalities. The research, published online April 3 in Nature, moves scientists one step closer to understanding how mammals evolve and respond to their environments.

Genetic recombination occurs at hotspots in cells that form sperm and eggs. At these sites, rearrangements ensure that the combination of genes passed on to every sperm and egg cell is unique. By studying precursors of mouse sperm cells during the early stages of genetic recombination, the scientists have created a precise, first-of-its-kind map of recombination hotspots in a multi-celled organism.

With this map, researchers also hope to pinpoint where, how and why abnormalities in the number of chromosomes can occur. Such abnormalities – for instance, the extra copy of chromosome 21 that gives rise to Down syndrome – are the leading known cause of miscarriages, congenital birth defects, and mental retardation in the United States.

“We wanted to figure out how recombination varied across the genome,” said R. Daniel Camerini-Otero, M.D., Ph.D., one of the senior authors on the paper and a researcher at the NIH’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). “Hotspots are the starting point for the process that ensures that every person is unique. These hotspots facilitate the adaptation of populations to environmental influences through evolution. Our findings will allow us to explore things like how environment and genetic background affect the recombination landscape.”

“Now that we have mapped recombination hotspots genome-wide, we can actually carry out studies on the whole mouse genome,” said Galina Petukhova, Ph.D., assistant professor in the USU Department of Biology and one of the paper’s senior authors. “This will be very beneficial in extending our knowledge to organisms as complex as humans, as faulty recombination can lead to infertility or birth defects. We continue to move closer to our ultimate goal of helping to prevent these health issues.” "This work is a powerful illustration of the utility of model organisms in the quest to understand fundamental biological processes and their role in human health," said George Santangelo, Ph.D., who oversees Dr. Petukhova's and other genetic recombination grants at the NIH’s National Institute of General Medical Sciences, which helped fund this research.

Camerini-Otero compared the map’s new level of precision to the difference between being able to zoom in to see a city block – all that was available until now – to being able to zoom in to see each and every building on that block. “What we were looking for was resolution that was much higher than ever seen before,” said Camerini-Otero. “Now that we can actually see these individual events, we can begin to understand their molecular structure.”

The researchers – including lead authors Fatima Smagulova, Ph.D., of USU, and Ivan V. Gregoretti, Ph.D., of NIDDK– used cutting-edge DNA sequencing technology and lots of computational power to take a snapshot of all the individual pieces of DNA that were taking part in recombination at a given moment in living cells. They then used this snapshot of short DNA pieces to draw a map of where chromosomes have an increased potential to be broken and to come back together in new ways.

Mice were used as subjects for this study because the researchers needed a population that could be created with a specific and identical genetic background. With this initial study a success, they hope to apply the same techniques to study recombination in people in the near future.

The end result is a catalog of about 10,000 hotspots and resembles a detailed map of where diversity can arise in the genome and of sites where such processes may go awry. The researchers next plan to apply what they’ve seen and learned with this new map to further understand chromosomal abnormalities, genetic recombination, genome stability and evolution.  The study is available at http://www.nature.com/nature/journal/vaop/ncurrent/full/nature09869.html.

The Uniformed Services University of the Health Sciences, or USU, is the nation’s federal health sciences university. USU students are primarily active-duty uniformed officers in the Army, Navy, Air Force and Public Health Service who are being educated to deal with wartime casualties, emerging infectious diseases and other public health emergencies. Of the university’s more than 4,500 physician alumni, the vast majority are supporting operations in Iraq, Afghanistan and elsewhere, offering their leadership and expertise. For more information, visit www.usuhs.mil.

The NIDDK conducts and supports research in diabetes and other endocrine and metabolic diseases; digestive diseases, nutrition, and obesity; and kidney, urologic, and hematologic diseases. Spanning the full spectrum of medicine and afflicting people of all ages and ethnic groups, these diseases encompass some of the most common, severe, and disabling conditions affecting Americans. For more information about NIDDK and its programs, see www.niddk.nih.gov.

The National Institutes of Health (NIH) — The Nation's Medical Research Agency — includes 27 Institutes and Centers and is a component of the U. S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical, and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.

This research also was funded in-part by the National March of Dimes Foundation.