Researchers press rewind on cell division
About three-quarters of household dust consists of dead skin cells that have been sloughed off the human body. These cells are replaced by cell division, a process which occurs millions of times every day in the human body.
Cell division – or mitosis – replaces dead or damaged cells and is, therefore, essential in maintaining the integrity of all multicellular organisms.
Structures called telomeres determine how many times an individual cell will divide before it dies. Telomeres are lengths of DNA attached to chromosomes; each time a cell divides, the telomeres shorten, and when they reach a certain length the cell is instructed to stop dividing and die. When this process does not function properly, cells divide uncontrollably, leading to cancer.
Now, researchers at the Oklahoma Medical Research Foundation report in this week's Nature that they have managed to reverse the cycle of cell division. This is a discovery which could lead to treatments for cancer.Before a human cell can divide, it must first duplicate its 23 pairs of chromosomes, so that each daughter cell receives a complete set of genes. Once this DNA replication is complete, the two sets of chromosomes line themselves up along the middle of the cell. Each set of then moves to opposite ends of the cell along structures called spindles, so that when the cell splits in two, the resulting daughter cells each contain a complete set of genes.
Micrograph showing chromosomes (labelled red) moving along mitotic spindles (green). The cell cycle is under the control of two proteins, cyclin B and cyclin-dependent kinase 1 (Cdk1). Cyclin B activates Cdk1, which is an enzyme. Once the two sets of duplicated chromosomes have moved to opposite poles of the cell and the cell begins to divide, levels of cyclin B decrease and, as a result, Cdk1 stops functioning.
Decreased cyclin B concentration is believed to act as a trigger which drives the cell into dividing, and this work confirms it. Team leader Gary Gorbsky and his colleagues used Cdk1-blocking compounds to make frog eggs divide even though cyclin B levels were high. This caused the eggs to start dividing in two. When the Cdk1-blocking compound was then washed away, the eggs stopped dividing mid-cycle, the duplicated chromosomes returned to their original positions, and a single cell was reformed.
Timing was crucial in these experiments. The chemicals had to be added at a specific stage of the cell cycle or they had no effect on cell division.
Cell division expert Professor Johnathan Pines, of the Gurdon Institute in Cambridge, said that the research is unlikely to lead directly to new treatments for cancer, although "it is useful for us to understand how the cell goes through the process of segregating the chromosomes".
