Featured Research

from universities, journals, and other organizations

Fertility: Sacrificing eggs for the greater good

Date:
May 29, 2014
Source:
Carnegie Institution
Summary:
Part of a woman's egg production involves a winnowing of the egg supply during fetal development. As much as 80 percent of a baby girl's egg supply is lost even before she is born. New research has gained new insights into the earliest stages of egg selection, which may have broad implications for women's health and fertility.

This image shows mouse fetal ovary whose eggs (colored green) were protected from dying by AZT. Blue color identifies genomic DNA in all cells of the ovary.
Credit: Image courtesy of Safia Malki

A woman's supply of eggs is a precious commodity because only a few hundred mature eggs can be produced throughout her lifetime and each must be as free as possible from genetic damage. Part of egg production involves a winnowing of the egg supply during fetal development, childhood and into adulthood down from a large starting pool. New research by Carnegie's Alex Bortvin and postdoctoral fellow Safia Malki have gained new insights into the earliest stages of egg selection, which may have broad implications for women's health and fertility. The work is reported in the early on-line edition of Developmental Cell.

Related Articles


The most stringent egg selection takes place at the earliest stages. Even before a baby girl is born, she has already lost 80 percent of her initial pool of immature eggs during fetal development. This phenomenon has been observed in primates and rodents, as well as some invertebrates, which indicates that it has been around for a long time evolutionarily speaking. But despite its ancient origins, little is understood about how these decisions are being made.

Bortvin's team discovered that the fetal egg die-off is connected to segments of the egg's DNA known as transposable elements or "jumping genes." As developing eggs gain the ability to guide embryo development, transposons gain the ability to start moving. These ancient virus-like genes begin to leapfrog around the egg's DNA, thereby producing new mutations, just as transposon movement causes color mutations in ears of corn. A transposable element named LINE1 is the most likely to become activated in mammalian eggs.

Jumping genes can be particularly destructive in sperm and eggs, since much of their genetic material is an essential part of the recipe for developing a healthy baby. Think of the genome of an egg or sperm as a stack of papers being photocopied. In order to be read and understood, they have to come out of the copier in the same order they went into it. But jumping genes are like pages that insert themselves at random into the stack, making the reading process difficult or even impossible.

Prior studies by Bortvin and others showed that male germ cells quash the movement of transposons, minimizing mutations and ensuring high levels of sperm production. In contrast, Bortvin and Malki discovered that female mice allow transposon movement to take place, but then get rid off immature eggs harboring the highest number of mutations before the female mouse is even born. The team proposes that this purging process allows for the selective survival of immature eggs whose genetic material has acquired relatively few new mutations.

Bortvin's group also discovered that the process of immature egg purging must be finely balanced. Overly stringent surveillance could result in excessive egg purging, too few surviving eggs, and premature loss of fertility. Surveillance that is not stringent enough, on the other hand, would allow eggs with a lot of jumping gene-related errors to survive, and lead to a high level of birth defects, such as those caused by an incorrect number of chromosomes in the offspring.

"Our findings suggest that the ovary of a newborn girl already contains both 'good' eggs and those destined to give rise to Down syndrome or miscarriages," Bortvin said. "Further study may show that these 'good' cells are ovulated first and the abnormal ones usually come later."

Importantly, Bortvin and Malki discovered that a drug AZT, which inhibits multiplication of AIDS-causing HIV virus in humans, also alters jumping gene activity in immature eggs. In particular, it is effective against LINE1 transposons. This discovery raises the possibility that the number and quality of immature eggs might be enhanced by drug treatment.

Finally, Bortvin and Malki's work raises the question of whether this immature egg purge is actually a blessing in disguise. Despite their destructive power, jumping genes are also the source of serendipitous genetic novelty that can make species stronger and better suited for survival over time. By allowing just the right amount of beneficial transposon-generated genetic variation, female mammals are giving their offspring and species the best chance of thriving in an uncertain, dangerous world.


Story Source:

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


Journal Reference:

  1. Safia Malki, Godfried W. van der Heijden, Kathryn A. O’Donnell, Sandra L. Martin, Alex Bortvin. A Role for Retrotransposon LINE-1 in Fetal Oocyte Attrition in Mice. Developmental Cell, 2014; DOI: 10.1016/j.devcel.2014.04.027

Cite This Page:

Carnegie Institution. "Fertility: Sacrificing eggs for the greater good." ScienceDaily. ScienceDaily, 29 May 2014. <www.sciencedaily.com/releases/2014/05/140529142452.htm>.
Carnegie Institution. (2014, May 29). Fertility: Sacrificing eggs for the greater good. ScienceDaily. Retrieved October 25, 2014 from www.sciencedaily.com/releases/2014/05/140529142452.htm
Carnegie Institution. "Fertility: Sacrificing eggs for the greater good." ScienceDaily. www.sciencedaily.com/releases/2014/05/140529142452.htm (accessed October 25, 2014).

Share This



More Health & Medicine News

Saturday, October 25, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Texas Nurse Nina Pham Cured of Ebola

Texas Nurse Nina Pham Cured of Ebola

AFP (Oct. 25, 2014) — An American nurse who contracted Ebola while caring for a Liberian patient in Texas has been declared free of the virus and will leave the hospital. Duration: 01:01 Video provided by AFP
Powered by NewsLook.com
Toxin-Packed Stem Cells Used To Kill Cancer

Toxin-Packed Stem Cells Used To Kill Cancer

Newsy (Oct. 25, 2014) — A Harvard University Research Team created genetically engineered stem cells that are able to kill cancer cells, while leaving other cells unharmed. Video provided by Newsy
Powered by NewsLook.com
IKEA Desk Converts From Standing to Sitting With One Button

IKEA Desk Converts From Standing to Sitting With One Button

Buzz60 (Oct. 24, 2014) — IKEA is out with a new convertible desk that can convert from a sitting desk to a standing one with just the push of a button. Jen Markham explains. Video provided by Buzz60
Powered by NewsLook.com
Ebola Protective Suits Being Made in China

Ebola Protective Suits Being Made in China

AFP (Oct. 24, 2014) — A factory in China is busy making Ebola protective suits for healthcare workers and others fighting the spread of the virus. Duration: 00:38 Video provided by AFP
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

 

Health & Medicine

Mind & Brain

Living & Well

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