Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why human egg cells don't age well

01.07.2015

When egg cells form with an incorrect number of chromosomes--a problem that increases with age--the result is usually a miscarriage or a genetic disease such as Down syndrome.

Now, researchers at the RIKEN Center for Developmental Biology in Japan have used a novel imaging technique to pinpoint a significant event that leads to these types of age-related chromosomal errors.


Chromosomes are seen as red, and kinetochores are green. (A-B) Bivalent appears normal (green arrows). (C) Bivalent begins to hyperstretch (orange arrows). (D-E) Single pairs begin to move independently (red and purple arrows). (E) Balanced predivision of sister chromatids (red and purple arrows).

Credit: RIKEN

Published in Nature Communications, the study shows that as egg cells mature in older women, paired copies of matching chromosomes often separate from each other at the wrong time, leading to early division of chromosomes and their incorrect segregation into mature egg cells.

Most cells have two copies of each chromosome--one from each parent. Immature egg cells begin this way, but are transformed through a process called meiosis into mature egg cells that only have one copy of each chromosome. At the beginning of meiosis each chromosome copies itself and joins with its matching pair to form a group of four chromosomes that swap genetic material.

These groups of four chromosomes--called bivalents--then split apart into single pairs, and the cell divides. One part continues as the egg cell and the other part degrades. In the second stage of meiosis, the single pairs of chromosomes--two sister chromatids joined in the middle--separate and the egg cell divides again in the same way, leaving a single mature egg cell with one copy of each chromosome.

"What we found," explains team leader Tomoya Kitajima, "is that in older cells, the bivalents sometimes separate early, and this leads to division of sister chromatids in the first stage of meiosis, rather than in the second stage."

To determine the most common type of age-related segregation errors, the researchers first used a novel high resolution imaging technique to visualize chromosomes in live mouse egg cells throughout the whole first stage of meiosis. They found that chromosomes were always distributed correctly in young egg cells, but that a little less than 10% of older cells suffered from segregation errors.

Closer examination of the chromosome-tracking data showed that the dominant type of error was predivision of sister chromatids, and not movement of intact chromosome pairs to only one of the new cells.

The tracking data also allowed researchers to go back in time and look at what was happening to chromosomes that eventually segregated incorrectly. They found that a large majority of them had been part of bivalents whose connection between paired chromosome copies had become hyperstretched and then snapped earlier in meiosis, leaving single pairs.

The researchers then confirmed that the number of singly paired chromosomes--also called univalents--was higher in older mouse and even human egg cells, indicating that age-related segregation errors could be tracked back to increased numbers of prematurely separated chromosome pairs.

"We were surprised and pleased that the vast majority of errors are preceded by a single common event--bivalent separation," says Kitajima. "Now we can focus our efforts on developing an artificial tie to suppress premature separation and on understanding the molecular mechanism underlying the age-related reduction in bivalent cohesion that appears to precede it."

Reference:

Sakakibara Y, Hashimoto S, Nakaoka Y, Kouznetsova A, Hoog C, and Kitajima TS (2015). Bivalent separation into univalents precedes age-related meiosis I errors in oocytes. Nature Communications. doi: 10.1038/ncomms8550.

Adam Phillips | EurekAlert!

More articles from Life Sciences:

nachricht New risk factors for anxiety disorders
24.02.2017 | Julius-Maximilians-Universität Würzburg

nachricht Stingless bees have their nests protected by soldiers
24.02.2017 | Johannes Gutenberg-Universität Mainz

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

Im Focus: Three Magnetic States for Each Hole

Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".

Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Stingless bees have their nests protected by soldiers

24.02.2017 | Life Sciences

New risk factors for anxiety disorders

24.02.2017 | Life Sciences

MWC 2017: 5G Capital Berlin

24.02.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>