Featured Research

from universities, journals, and other organizations

How yeast chromosomes avoid the bad breaks

Date:
August 8, 2011
Source:
Whitehead Institute for Biomedical Research
Summary:
Researchers have discovered how yeast cells protect themselves against a novel type of chromosome fragility that occurs in repeated DNA during meiosis -- the cell division that produces spores in fungi or eggs and sperm in plants and animals.

The human genome is peppered with repeated DNA elements that can vary from a few to thousands of consecutive copies of the same sequence. During meiosis -- the cell division that produces sperm and eggs -- repetitive elements place the genome at risk for dangerous rearrangements from genome reshuffling. This recombination typically does not occur in repetitive DNA, in part because much of it is assembled into specialized heterochromatin. Other mechanisms that restrain recombination in repetitive DNA have remained elusive, until now.

In a paper published online August 7 in the journal Nature, researchers in the lab of Whitehead Institute Fellow Andreas Hochwagen describe a defense mechanism in yeast that shields repetitive DNA from meiotic DNA recombination. According to the work of Hochwagen and his colleagues, the protective repeat-associated heterochromatin makes the DNA segments near the boundary of the heterochromatin particularly vulnerable to inappropriate meiotic recombination. DNA elements surrounding these at-risk border regions are protected from meiotic recombination by a novel system involving the concerted action of two proteins, pachytene checkpoint protein 2 (Pch2) and origin recognition complex subunit 1 (Orc1), which are present in organisms ranging from yeast to humans.

During meiosis an organism's chromosomes pair up, with every pair containing a copy inherited from each of the organism's parents. To match up the chromosomes, the cell breaks both strands of the chromosomes' DNA in multiple locations, and the chromosomes swap DNA sections that have the same sequence. Later, when the paired chromosomes are pulled apart, each resulting chromosome is a patchwork of maternal and paternal genes. The creation of reshuffled chromosomes assists chromosome assortment into spore, sperm, and egg cells, but it also has a profound effect on evolution, because it produces new genetic variants.

"To me it's always been very confusing why you would break your genome. It's your blueprint," says Hochwagen. "Obviously, it helps you make new variations and combinations of genes, but it's incredibly dangerous and you really need to make sure that it happens the right way."

In repetitive DNA, this system of breaking and swapping is particularly hazardous, as there are many options that a section of repeat DNA could be swapped with. If the wrong repeat is chosen, a chromosome can gain or lose a large chunk of DNA. In humans, such mistakes have been linked to genetic neurological and developmental disorders, including autism spectrum disorders and schizophrenia.

By studying the highly repetitive DNA that makes up yeast's ribosomal DNA (rDNA), Gerben Vader and Hannah Blitzblau, first authors of the Nature paper and postdoctoral researchers in Hochwagen's lab, have determined that yeast's rDNA is protected from inappropriate recombination by two mechanisms. It was previously shown that heterochromatin prevents chromosome breakage in repetitive DNA. But in their paper, Vader and Blitzblau demonstrate that, ironically, the protective heterochromatin renders the transition zone between the repetitive and non-repetitive DNA particularly fragile. The yeast cell buttresses these borders with Pch2 and Orc1, which prevent chromosome breakage across the entire transition zone. In their absence, rDNA frequently gains or loses repeats.

"We had previously seen very little chromosome breakage in large regions close to repetitive DNA," says Blitzblau. "The finding that the borders of heterochromatin are particularly fragile helps us to understand why the cell invests in specifically protecting these regions."

Although the modes of heterochromatin formation vary between organisms, similar strategies may be at work in higher organisms, too.

"In mice and flies repetitive DNA is also packaged into heterochromatin, and there is evidence that very few breaks happen in these regions during meiosis," says Vader. "So it is possible that this type of protection is a general phenomenon."

This research was supported by the National Institutes of Health (NIH), the Netherlands Organization for Scientific Research, and Howard Hughes Medical Institute (HHMI).

Andreas Hochwagen's primary affiliation is with Whitehead Institute for Biomedical Research, where his laboratory is located and all his research is conducted.


Story Source:

The above story is based on materials provided by Whitehead Institute for Biomedical Research. Note: Materials may be edited for content and length.


Journal Reference:

  1. Gerben Vader, Hannah G. Blitzblau, Mihoko A. Tame, Jill E. Falk, Lisa Curtin, Andreas Hochwagen. Protection of repetitive DNA borders from self-induced meiotic instability. Nature, 2011; DOI: 10.1038/nature10331

Cite This Page:

Whitehead Institute for Biomedical Research. "How yeast chromosomes avoid the bad breaks." ScienceDaily. ScienceDaily, 8 August 2011. <www.sciencedaily.com/releases/2011/08/110807143907.htm>.
Whitehead Institute for Biomedical Research. (2011, August 8). How yeast chromosomes avoid the bad breaks. ScienceDaily. Retrieved October 21, 2014 from www.sciencedaily.com/releases/2011/08/110807143907.htm
Whitehead Institute for Biomedical Research. "How yeast chromosomes avoid the bad breaks." ScienceDaily. www.sciencedaily.com/releases/2011/08/110807143907.htm (accessed October 21, 2014).

Share This



More Plants & Animals News

Tuesday, October 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

'Cadaver Dog' Sniffs out Human Remains

'Cadaver Dog' Sniffs out Human Remains

AP (Oct. 21, 2014) Where's a body buried? Buster's nose can often tell you. He's a cadaver dog, specially trained to find human remains and increasingly being used by law enforcement and accepted in courts. These dogs are helping solve even decades-old mysteries. (Oct. 21) Video provided by AP
Powered by NewsLook.com
White Lion Cubs Born in Belgrade Zoo

White Lion Cubs Born in Belgrade Zoo

AFP (Oct. 20, 2014) Two white lion cubs, an extremely rare subspecies of the African lion, were recently born at Belgrade Zoo. They are being bottle fed by zoo keepers after they were rejected by their mother after birth. Duration: 00:42 Video provided by AFP
Powered by NewsLook.com
Traditional Farming Methods Gaining Ground in Mali

Traditional Farming Methods Gaining Ground in Mali

AFP (Oct. 20, 2014) He is leading a one man agricultural revolution in Mali - Oumar Diatabe uses traditional farming methods to get the most out of his land and is teaching others across the country how to do the same. Duration: 01:44 Video provided by AFP
Powered by NewsLook.com
Goliath Spider Will Give You Nightmares

Goliath Spider Will Give You Nightmares

Buzz60 (Oct. 20, 2014) An entomologist stumbled upon a South American Goliath Birdeater. With a name like that, you know it's a terrifying creepy crawler. Sean Dowling (@SeanDowlingTV) has the details. Video provided by Buzz60
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:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

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