Dr. Johné Liu is unlocking the secrets of egg cell maturation to gain insights into infertility and cancer.

February 1, 2006

Picture a cell dividing, and you usually picture it squeezing apart into two equal-sized daughter cells. But when some cells divide, the division isn't equal at all. Immature egg cells, for example, divide to produce one huge mature egg along with a tiny "polar body". The polar body has the genetic material (DNA) equal to that in the egg but it is destined for a very different fate - destruction.

Dr. Liu is exploring frog eggs as a model to investigate the molecular mechanisms that control this kind of unequal (or "asymmetric") cell division. Frog eggs are giant cells; each is equivalent in volume to more than 1 million average human cells. Their size, combined with their ease of culture, has made frog eggs a popular experimental model and frog egg research has contributed to many fundamental discoveries in modern biology. Dr. Liu recently showed that a protein called Cdc42 plays a crucial role in controlling polar body formation in frog egg cells. Dr. Liu's recent work is published this week in the prestigious international journal Current Biology.

As all vertebrates including humans have the Cdc42 protein, Dr. Liu wonders if Cdc42 has a universal role in controlling asymmetric cell division. He is particularly intrigued by the possibility that Cdc42 may play a vital role in stem cell division. Stem cells also divide asymmetrically, albeit not necessarily in size, with one daughter remaining a stem cell and the other going on to differentiate into a mature skin, liver, blood or other cell. Recent research suggests that stem cells may also be the ultimate source of immortality in cancer, with cancer stem cells slowly dividing asymmetrically to renew themselves while also producing the rapidly dividing aggressive cancer cells that form most of a tumour. If Cdc42 is proven to be a vital part of cancer stem cells, scientists may one day develop specific drugs that target Cdc42 as cancer therapeutics.

Dr. Liu is a Senior Scientist in the OHRI's Hormones, Growth & Development program and a Professor at the University of Ottawa (Faculty of Medicine, Departments of Obstetrics and Gynaecology and Biochemistry, Microbiology and Immunology). For more information, see Dr. Liu's online profile, the Hormones, Growth and Development website, the Oocyte Health Program website, or Dr. Liu's new book.

Making a movie of polar body formation during frog egg maturation:
A frog egg is shown on top with a box surrounding the polar body (light microscope image). The bottom panel shows enlarged fluorescent confocal microscope images of the polar body. The polar body appears green and the spindle (the structure that organizes and separates chromosomes during cell division) appears red. Images are collected in a time sequence from left to right, with different angles shown in each row. Note that the polar body is extremely small compared with the egg.