Egg cells use unusual method of division

Aug 27, 2010

(PhysOrg.com) -- In a study of egg cells using time-lapse microscopy, researchers at the University of California, San Diego School of Medicine and the Ludwig Institute for Cancer Research have discovered an unusual property of meiosis — cell division that produces reproductive cells in sexually reproducing organisms.

The discovery of an “inside out” mechanism by which egg cell chromosomes separate from each other may shed light on mistakes made in chromosome distribution that can lead to Down syndrome, high miscarriage rates in humans and the age-related decrease in fertility in human females. Their findings are reported in the September issue of .

relies on the merger of chromosomes present in the sperm and egg at fertilization. Formation of sperm and requires the process of meiosis, which halves the chromosome number of each parent, so that the sperm-egg merger regenerates a cell with two copies of each chromosome. The reduction of chromosome number in meiosis is accomplished through two divisions without an intervening duplication of the genome.

Both meiotic and mitotic divisions require specialized protein polymers called microtubules. These polymers are organized into a football-shaped spindle with the polymer ends embedded in a special organelle — called the centrosome — at each end of the football. Egg cells, however, are unusual in that they lack centrosomes, and instead use a spindle that is self-organized from microtubules. Egg cells, especially in humans, are prone to mistakes in dividing the chromosomes during meiosis — mistakes which result in reproductive problems in humans such as Down syndrome, infertility and miscarriages.

Researchers led by Arshad Desai, professor of cellular and molecular medicine and investigator with the Ludwig Institute at UC San Diego, used the roundworm C. elegans as a model to study egg cell division. Julien Dumont, a postdoctoral fellow in the Desai lab, developed time lapse microscopy methods to observe egg cell meiosis with high precision.

Prior to this study, dividing cell were thought to move apart by pulling on the microtubule polymers and moving into the ends of the spindle, like a person pulling himself up on a rope. But the UC San Diego researchers discovered that, in C. elegans egg cells, chromosome move apart by being pushed in the middle — most likely caused by the growth of microtubule polymers between the chromosome halves.

“This finding suggests that egg cells use a special mechanism for meiotic chromosome separation,” said Desai. “Since defects in egg cell underlie infertility in humans, it will be important for future research to address whether such a mechanism is also operating in human females.”

Explore further: Molecular gate that could keep cancer cells locked up

Related Stories

A unique arrangement for egg cell division

Aug 09, 2007

Which genes are passed on from mother to child is decided very early on during the maturation of the egg cell in the ovary. In a cell division process that is unique to egg cells, half of the chromosomes are eliminated from ...

Matrimony inhibits Polo kinase

Dec 04, 2007

Suspended animation is something we only associate with Sci Fi programs, but something remarkably similar actually occurs in unfertilized egg cells, in the ovaries of animals as different as humans and fruit flies. In an ...

Protein role in meiosis re-evaluated by researchers

Apr 17, 2008

Proteins that control cell division play a far more nuanced role than researchers previously thought in the process that gives rise to reproductive cells, according to new findings by MIT biologists.

Recommended for you

Molecular gate that could keep cancer cells locked up

Jul 31, 2014

In a study published today in Genes & Development, Dr Christian Speck from the MRC Clinical Sciences Centre's DNA Replication group, in collaboration with Brookhaven National Laboratory (BNL), New York, ...

The 'memory' of starvation is in your genes

Jul 31, 2014

During the winter of 1944, the Nazis blocked food supplies to the western Netherlands, creating a period of widespread famine and devastation. The impact of starvation on expectant mothers produced one of the first known ...

Sugar mimics guide stem cells toward neural fate

Jul 30, 2014

Embryonic stem cells can develop into a multitude of cells types. Researchers would like to understand how to channel that development into the specific types of mature cells that make up the organs and other structures of ...

User comments : 0