How eggs do it

Tiniest of errors in sex cell division can lead to abnormalities in offspring. Arshad Desai from Ludwig Institute for Cancer Research, San Diego, USA, filmed egg cell division for the first time. He explained to Manupriya the division mechanism and how it can lead to birth defects

 
By Manupriya
Last Updated: Saturday 04 July 2015

imageDescribe your findings.

When cells divide, they require specialised proteins called microtubules arranged in an American football-shaped spindle. Microtubules divide DNA in two equal parts by pulling them apart with the help of a special organelle, called centrosome. Egg cells lack this organelle.

We filmed egg cell divisions to understand how DNA gets divided in daughter cells. Movies were made of normal egg cells and of those tinkered by inhibiting proteins that aid in division. Prior to our study, it was thought that microtubules moved the divided cell chromosomes towards the spindle’s ends. In the study, published in Nature Cell Biology, we showed that chromosomes in egg cells move apart by being pushed in the middle—most likely caused by the growth of microtubules between the chromosome halves.

Why was this missed earlier?

In most organism it is difficult to do a live imaging of egg cell division because it is a lengthy process and occurs within complex ovarian tissue. In our experimental organism, a nematode—Ceanorhabditis elegans—the division happens in less than an hour.

Can this result be extrapolated to humans?

It remains to be seen. In the evolutionary tree, humans and nematodes shared a common ancestor one billion years ago. Our earlier work on cell division in vegetative cells showed that mechanisms in the nematode and humans are similar.

Do you think the different separation mechanism in egg cells is responsible for chromosomal abnormalities?

Possible. However, human egg cells are arrested before spindle formation for much of their lifespan in the ovary. It is likely that a problem created during this halt is revealed during division of egg cells. I suspect the mechanism could contribute but may not be the primary source of errors.

What are the finding’s implications on human biology?

Major Implications are on egg cell defects in chromosome segregation which lead to infertility and birth defects, like Down’s syndrome caused by incorrect number of chromosomes.

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