Featured Research

from universities, journals, and other organizations

Genomic architecture presages genomic instability

Date:
October 3, 2011
Source:
Baylor College of Medicine
Summary:
When cells divide, DNA is copied perfectly and distributed among daughter cells evenly. Occasionally, DNA breaks during division and is rearranged, resulting in duplications or deletions. Now researchers who study families with such genomic disorders have found a shared architecture resulting from this jumble that is associated with very severe forms of disease.

When cells divide normally, DNA gets copied perfectly and distributed among the daughter cells with an even hand. Occasionally though, DNA breaks during division and is rearranged, resulting in duplications or deletions of important parts of the blueprint.

Now researchers at Baylor College of Medicine who study families with such genomic disorders have found a shared, yet unusual, architecture resulting from this jumble that is associated with very severe forms of disease. They also identified the genomic elements that produce such architecture, a finding that will help predict other unstable regions in the human genome.

The unusual architecture left a footprint, and a search for similar footprints in other regions of the genome may identify regions that underwent the same alteration during the evolutionary past. This event might occur more often than previously expected. A report on their work appears online in the current issue of Nature Genetics.

The rearrangement structure -- triplicated genetic material inverted and embedded within duplications of genetic material -- appeared in 20 percent of patients who had been diagnosed with MECP2 duplication syndrome, said first author Dr. Claudia Carvalho, a postdoctoral associate in the laboratory of Dr. James Lupski, vice chair of the department of molecular and human genetics at BCM and corresponding author of the report.

A mutation in MECP2 was first identified in association with Rett syndrome by the laboratory of Dr. Huda Zoghbi at BCM. In Rett syndrome, the protein associated with the gene has minimal or no activity and the disorder mainly affects girls. Later studies showed that too much MeCP2 protein because of increased MECP2 gene dosage could cause another serious disorder -- this time in boys and called MECP2 duplication syndrome.

In this new discovery, patients with the unusual complex triplication -- called in shorthand, DUP (duplication)-TRP (triplication)/INV (inverted)-DUP -- had a more severe constellation of symptoms associated with the genomic disorder. The patients required oxygen or a ventilator and had hearing loss, heart defects and difficulty swallowing that necessitated a feeding tube. In most patients with the syndrome, developmental delays in motor skills, limited or absent speech, autistic behavior, intellectual disability and recurrent infections are also typical symptoms.

"Dr. Melissa Ramocki (another of the paper's first authors and an assistant professor of pediatrics -- neurology at BCM) started to be able to predict which patients would have the DUP-TRP/INV-DUP," said Lupski. This means that the increased amount of genetic material increased the dosage of MeCP2 protein and made the disorder worse.

Carvalho proposes that the rearrangement may have occurred during the sperm cell generation. During meiosis (sexual cell division), a cell divides and produces four haploid cells containing one copy of each chromosome. The resulting chromosome set in each gamete (sperm or egg) cell is a unique mixture of paternal and maternal DNA, ensuring that offspring are genetically distinct from either parent. The process involves copying DNA and producing new strands for which special cellular machinery exists.

Sometimes, this process goes wrong. At one point, a piece of DNA replication machinery called the replication fork may collapse, forcing the cell to trigger its repair process. When the cell tries to make a new fork, the DNA can line up improperly and pair with a piece of seemingly compatible DNA oriented in the opposite direction. These elements called "inverted repeats" are ubiquitous in the human genome. This first event causes replication of the DNA in the wrong direction -- opposite to the way that it was going when the fork collapsed, which will lead to a segmental inverted duplication. A second event, believed to be obligatory to the viability of the cell, will bring the replication fork back into the correct direction and resume the replication process. This second event may now produce a triplication if the new replication fork is re-established within the region that was just copied twice.

This jumble of machinery, mismatched DNA ends and aberrant reproduction of the genetic material can cause the strange complex triplication rearrangement that results in disease, and it appears to occur in more than just MECP2 duplication syndrome.

Studying patients with another genomic disorder associated with the PLP1 gene, the researchers were able to find the same unusual genomic architecture (The PLP1 gene is associated with Pelizaeus-Merzbacher Disease, Spastic Paraplegia 2). In each case, inverted repeats of genomic DNA sequence appear to help mediate the complex inverted triplication.

"These inversions are important," said Carvalho. "There is no easy way to assay them, and we don't know how common they are in the genome."

"It may be possible that there are a lot of disease genes there and we don't see them," said Lupski. "The same mechanism that causes disease might also be involved in evolutionary change. In fact, this mechanism may have created new genes that might have made us more fit for our environment."

Dr. Philip J. Hastings, professor of molecular and human genetics at BCM who has studied mutational events resulting in rearrangements of different genomes for many decades, helped work out how the rearrangements might happen and is an author on the report as well.

Other authors include: Davut Pehlivan, Luis Franco, Claudia Gonzaga-Jauregui, Ping Fang, Alanna McCall, Daniela del Gaudio, Marjorie Withers, Pengfei Liu, Sau Wai Cheung, John Belmont and Huda Zoghbi, all of BCM; Eniko Karman Pivnick of the University of Tennessee; Stacy Hines-Dowell of LeBonheur Children's Hospital in Memphis, Tennessee; Laurie Seaver and Sansan Lee of Kapiolani Medical Specialists in Honolulu, Hawaii; Linda Friehling of Children's Medical Associates in Alexandria, Virginia; and Rosemarie Smith of Maine Medical Center in Portland.

Funding for this work came from the National Institute of Neurological Disorders and Stroke, the National Institute of General Medical Sciences, the Baylor College of Medicine Intellectual and Developmental Disabilities Research Center and the Eunice Kennedy Shriver National Institute of Child Health and Human Development.


Story Source:

The above story is based on materials provided by Baylor College of Medicine. Note: Materials may be edited for content and length.


Journal Reference:

  1. Claudia M B Carvalho, Melissa B Ramocki, Davut Pehlivan, Luis M Franco, Claudia Gonzaga-Jauregui, Ping Fang, Alanna McCall, Eniko Karman Pivnick, Stacy Hines-Dowell, Laurie H Seaver, Linda Friehling, Sansan Lee, Rosemarie Smith, Daniela del Gaudio, Marjorie Withers, Pengfei Liu, Sau Wai Cheung, John W Belmont, Huda Y Zoghbi, P J Hastings, James R Lupski. Inverted genomic segments and complex triplication rearrangements are mediated by inverted repeats in the human genome. Nature Genetics, 2011; DOI: 10.1038/ng.944

Cite This Page:

Baylor College of Medicine. "Genomic architecture presages genomic instability." ScienceDaily. ScienceDaily, 3 October 2011. <www.sciencedaily.com/releases/2011/10/111002190007.htm>.
Baylor College of Medicine. (2011, October 3). Genomic architecture presages genomic instability. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2011/10/111002190007.htm
Baylor College of Medicine. "Genomic architecture presages genomic instability." ScienceDaily. www.sciencedaily.com/releases/2011/10/111002190007.htm (accessed July 31, 2014).

Share This




More Health & Medicine News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Health Insurers' Profits Slide

Health Insurers' Profits Slide

Reuters - Business Video Online (July 30, 2014) Obamacare-related costs were said to be behind the profit plunge at Wellpoint and Humana, but Wellpoint sees the new exchanges boosting its earnings for the full year. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com
Concern Grows Over Worsening Ebola Crisis

Concern Grows Over Worsening Ebola Crisis

AFP (July 30, 2014) Pan-African airline ASKY has suspended all flights to and from the capitals of Liberia and Sierra Leone amid the worsening Ebola health crisis, which has so far caused 672 deaths in Guinea, Liberia and Sierra Leone. Duration: 00:43 Video provided by AFP
Powered by NewsLook.com
At Least 20 Chikungunya Cases in New Jersey

At Least 20 Chikungunya Cases in New Jersey

AP (July 30, 2014) At least 20 New Jersey residents have tested positive for chikungunya, a mosquito-borne virus that has spread through the Caribbean. (July 30) Video provided by AP
Powered by NewsLook.com
Xtreme Eating: Your Daily Caloric Intake All On One Plate

Xtreme Eating: Your Daily Caloric Intake All On One Plate

Newsy (July 30, 2014) The Center for Science in the Public Interest released its 2014 list of single meals with whopping calorie counts. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

    Environment News

    Technology News



    Save/Print:
    Share:

    Free Subscriptions


    Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

    Get Social & Mobile


    Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

    Have Feedback?


    Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
    Mobile: iPhone Android Web
    Follow: Facebook Twitter Google+
    Subscribe: RSS Feeds Email Newsletters
    Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins