Researchers work out the mechanics of asymmetric cell division

May 3, 2007

When a cell divides, normally the result is two identical daughter cells. In some cases however, cell division leads to two cells with different properties. This is called asymmetric cell division and plays an important role in embryonic development and the self-renewal of stem cells.

Researchers from the European Molecular Biology Laboratory (EMBL) have now worked out the mechanism underlying asymmetric cell division in nematode worms. The study, which is published in the current issue of Cell, reveals that interactions between the mitotic spindle and the cell cortex are crucial for asymmetric division.

Soon after the egg cell has been fertilized, the developing embryo of the nematode worm Caenorhabditis elegans undergoes its first cell division. The division gives rise to a bigger cell at the anterior end of the embryo, where the head will develop, and a smaller cell at the posterior end. For this asymmetric division to take place, the mitotic spindle, the apparatus that separates a cell's chromosomes, needs to be located not centrally but towards the posterior of the egg. The cellular structures that make sure the spindle gets to the right place are protein filaments called microtubules. They are dynamic structures that constantly grow and shrink by adding on or taking off individual building blocks.

"Just before cell division the mitotic spindle moves towards the posterior of the cell while oscillating up and down," says François Nédélec, group leader at EMBL. "We wanted to find out the mechanisms of this motion and explore its properties."

Nédélec and his group combined computer simulations with microscopy studies to test the predictions made about microtubule behaviour experimentally. This approach revealed that the interaction of the microtubules forming the mitotic spindle and the cell cortex, a structure lining the cell just beneath the plasma membrane, most likely brings about the correct positioning of the spindle towards the posterior of the cell. The microtubules grow until they reach the borders of the cell and touch the cortex. Upon contact with the cortex, the filaments immediately start to shrink.

"This shrinkage is then translated into a pulling force at the cortex," says Cleopatra Kozlowski from Nédélec's group, who carried out the research together with Martin Srayko from the Max Planck Institute of Molecular Cell Biology and Genetics. "How exactly this works we don't know yet. One possibility could be that part of the cortex holds on to the microtubule while it shortens, and so pulls on the whole spindle."

The nature of so-called force generators on the cortex is yet unclear, as is the question if more of them are active at the posterior to give more net force in that direction. But computer simulations show that the concept of force generators that translate the dynamic behaviour of microtubules into a pulling force can explain the specific movements of the mitotic spindle.

The same principle might apply also to asymmetric cell division in other organisms and contexts, such as stem cell renewal. The cellular components involved in such divisions have been conserved throughout evolution making it likely that different species might also share the mechanism of the process.

Source: European Molecular Biology Laboratory

Explore further: Researchers map out genetic 'switches' behind human brain evolution

Related Stories

How chromosomes 'cheat' for the chance to get into an egg

November 2, 2017

Each of your cells contains two copies of 23 chromosomes, one inherited from your father and one from your mother. Theoretically, when you create a gamete—a sperm or an egg—each copy has a 50-50 shot at being passed on. ...

A force-driven mechanism for establishing cell polarity

November 6, 2017

A team of researchers from the Mechanobiology Institute, Singapore (MBI) at the National University of Singapore, along with colleagues from Temasek Life Sciences Laboratory and A*STAR's Institute of Molecular and Cell Biology ...

A crucial enzyme unveiled at last

December 5, 2017

After 40 years of research, researchers at the CEA, CNRS, University Grenoble-Alps, University of Montpellier and Inserm have finally identified the enzyme responsible for the tubulin detyrosination. Surprisingly, it is not ...

Recommended for you

Quantum dot ring lasers emit colored light

January 22, 2018

Researchers have designed a new type of laser called a quantum dot ring laser that emits red, orange, and green light. The different colors are emitted from different parts of the quantum dot—red from the core, green from ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.