Featured Research

from universities, journals, and other organizations

New insights into biology of germ cells: Machinery for recombination is part of chromosome structure

Date:
August 9, 2011
Source:
University of Vienna
Summary:
During the development of gametes, such as egg and sperm cells in humans, chromosomes are broken and rearranged at many positions. Using state of the art technology, researchers in Austria have analyzed this process at high resolution. The surprising observations regarding the mechanism of meiosis are now published in a new article.

This is a section of a chromosome with "DNA-break machines." Loops of sister chromatids (blue and turquoise) are linked and held in shape by ring-shaped molecules. The machines are anchored between the DNA-loops at the axis of the chromosome. One of the two machines holds on to a piece of DNA it just has broken. This model only illustrates the principles described in the text above; other details (such as the form of the machines, colors etc.) are symbolic and not to be taken literally.
Credit: Illustration courtesy of Franz Klein

During the development of gametes, such as egg and sperm cells in humans, chromosomes are broken and rearranged at many positions. Using state of the art technology, the research group of Franz Klein, professor for genetics at the Max F. Perutz Laboratories of the University of Vienna, has analyzed this process at high resolution. The surprising observations regarding the mechanism of meiosis are now published in the journal Cell.

Without meiosis there would be no sexual reproduction, as germ cells have to be generated in this specialized cell division. Meiosis results in daughter cells containing a single, complete set of chromosomes, while body cells contain two sets. During fertilization, when sperm and egg fuse, their sets of chromosomes are combined to form a diploid embryo to close the cycle.

Enigmatic meiosis

There are 46 chromosomes in every human cell, 23 maternal and 23 paternal ones. When germ cells are produced, one aspect of the reduction in chromosome numbers comes from merging maternal and paternal chromosomes to form a single daughter chromosome -- a mechanisms called recombination. "The more we learn about meiosis, the more mysterious it becomes," says Franz Klein from the Department for Chromosome Biology of the University of Vienna. "It is surprising that maternal and paternal chromosomes find each other at all. Because at the time of interaction all chromosomes have generated a sister and are tightly connected with her like a Siamese twin. Normally, in non-meiotic cells, chromosomes only interact and exchange with the sister chromosome. However, during the development of germ cells, only the exchange between parental chromosomes can guarantee the production of daughter cells with the right number of chromosomes," explains Klein.

Nano-view of the chromosome

Franz Klein and his research team have analyzed components of the protein machinery, which initiates recombination by DNA-breakage. They created a high resolution map of the chromosomes and marked the interaction sites with those proteins. "Thanks to DNA microarray-technology, we get a resolution in the nanometer range, with insights unimaginable before," says Klein. The researchers were surprised to find the DNA-breaking machine tightly associated with chromosomal axis regions, instead of being soluble -- an observation with far reaching consequences.

Disposable machines

One of the many riddles in meiosis was how breaks on chromosomes impede the occurrence of other breaks in their vicinity. Earlier research had shown that each individual DNA-breakage complex only works a single time. "As we now know that these machines are anchored, we understand why there is preferentially a single break per region. The locally bound machine has fired and other machines can't get there as they are anchored to other chromosomal regions," explains Klein.

When chromosomes are out of shape

Healthy chromosomes can form DNA loops, which are, in meiosis, connected by a protein axis. Defective genes can cause chromosomes to lose this shape. "No one could understand why the shape of chromosomes influences the function of the DNA-break machines. Now we know that these machines have to anchor between loops on the chromosome axis. If their loop-environment changes they anchor in different regions or lose functionality altogether," says Klein.

Hyperactive sister

Sister chromosomes are connected like Siamese twins along the chromosome axis, where the DNA-break machines are anchored. It was very mysterious, how the sister chromosome is prevented to take part in the repair of DNA breaks during meiosis, despite being so close to the damage. A special feature of meiosis is the formation of a zone along the chromosome axis that inhibits recombination.

Franz Klein concludes: "We think that the DNA-break machines are anchored at the axis to position the breaks right within the recombination inhibiting zone. This may attract the sister chromosome loop, which remains trapped in the recombination inhibiting zone by one of the two ends flanking the break, while the second end docks off to form a search tentacle for finding the paternal chromosome. We have evidence for many details of this scenario -- but most importantly, the inhibition of the involvement of the sister breaks down, if the anchoring of the DNA-break machines is defective. This indicates that anchoring may be indeed a key mechanism to control the sister. The result of a sister, hyperactive for DNA-break repair in meiosis is the death or severe impairment of the developing embryo."

Funding

The published work was conducted within the framework of the Special Research Program F34-"Dynamic Chromosomes" of the FWF. Seven research groups of the Max F. Perutz Laboratories (MFPL) and the Institute of Molecular Pathology (IMP) collaborate in this research program to unravel questions of chromosome biology. Coordination: Franz Klein and Jan Michael Peters, this year's Wittgenstein awardee.


Story Source:

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


Journal Reference:

  1. Silvia Panizza, Marco A. Mendoza, Marc Berlinger, Lingzhi Huang, Alain Nicolas, Katsuhiko Shirahige, Franz Klein. Spo11-Accessory Proteins Link Double-Strand Break Sites to the Chromosome Axis in Early Meiotic Recombination. Cell, 2011; 146 (3): 372-383 DOI: 10.1016/j.cell.2011.07.003

Cite This Page:

University of Vienna. "New insights into biology of germ cells: Machinery for recombination is part of chromosome structure." ScienceDaily. ScienceDaily, 9 August 2011. <www.sciencedaily.com/releases/2011/08/110809104254.htm>.
University of Vienna. (2011, August 9). New insights into biology of germ cells: Machinery for recombination is part of chromosome structure. ScienceDaily. Retrieved April 20, 2014 from www.sciencedaily.com/releases/2011/08/110809104254.htm
University of Vienna. "New insights into biology of germ cells: Machinery for recombination is part of chromosome structure." ScienceDaily. www.sciencedaily.com/releases/2011/08/110809104254.htm (accessed April 20, 2014).

Share This



More Plants & Animals News

Sunday, April 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Mich. Boy Unearths 10,000-Year-Old Mastodon Tooth

Mich. Boy Unearths 10,000-Year-Old Mastodon Tooth

Newsy (Apr. 20, 2014) A 9-year-old Michigan boy was exploring a creek when he came across a 10,000-year-old tooth from a prehistoric mastodon. Video provided by Newsy
Powered by NewsLook.com
Vermont Goat Meat Gives Refugees Taste of Home

Vermont Goat Meat Gives Refugees Taste of Home

AP (Apr. 18, 2014) Dairy farmers and ethnic groups in Vermont are both benefiting from a unique collaborative effort that's feeding a growing need for fresh and affordable goat meat. (April 18) Video provided by AP
Powered by NewsLook.com
Man Claims He Found Loch Ness Monster With... Apple Maps?

Man Claims He Found Loch Ness Monster With... Apple Maps?

Newsy (Apr. 18, 2014) Andy Dixon showed the Daily Mail a screenshot of what he believes to be the mythical beast swimming just below the lake's surface. Video provided by Newsy
Powered by NewsLook.com
First Ever 'Female Penis' Discovered In Animal Kingdom

First Ever 'Female Penis' Discovered In Animal Kingdom

Newsy (Apr. 18, 2014) Not only are these newly discovered bugs' sex organs reversed, but they also mate for up to 70 hours. 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