Chromosomes play an active role in animal cell division, reports a study published in the journal Nature.

Cell division is fundamental to all life forms. Human body develops from a single cell that divides billions of times to generate all tissue types, and some of these cells continue to divide billions of times every day throughout life.

For the moment, however, the molecular mechanisms involved are incompletely understood, and it was unknown until now that chromosomes could play an active role in cell division.

In animal cells, division involves mitosis, the separation of chromosomes followed by splitting of the cell into two new daughter cells by cytokinesis.

“Division is a complex and robust process that is generally performed flawlessly, but when an error occurs in DNA separation or during cytokinesis, it can be a source for triggering cancer, for example,” said study co-author Dr Gilles Hickson from the University of Montreal, Canada.

Working with fruit fly cells, Dr Hickson and co-authors discovered that chromosomes emit signals that influence the cortex of the cell to reinforce microtubule action.

One of the key signals involved that they identified acts via an enzyme complex – a phosphatase known as Sds22-PP1 – which is found at the kinetochores.

The scientists also demonstrated that this signaling pathway acts in human cells.

“Such evolutionary conservation from flies to humans is expected for processes as fundamental as cell division. This is what makes fruit flies such a powerful system for helping us to understand human biology,” Dr Hickson said.

“When chromosomes are segregated, they approach the membrane at the poles of the cell, and thanks to this enzyme’s actions, this contributes to the softening of the polar membrane, facilitating the elongation of the cell and the ensuing division that occurs at the equator.”

The discovery of this mechanism is a significant breakthrough in advancing knowledge about the cell division process.

“We have been watching cells divide for more than 100 years, but we continue to seek to understand the molecular mechanisms involved. This is important because cell division is so central to life, and to certain diseases,” Dr Hickson said.

In fact, all cancers are characterized by unchecked cell division, and the underpinning processes are potential targets for therapeutic interventions that prevent cancer onset and spread.

“But before we get there, we must continue to expand our knowledge about the basic processes and signals involved in normal cell division to understand how they can go awry, or how they can be exploited. Also different cell types in the body, and even in the same tissue, do not always divide in exactly the same way.”

“For example, stem cells divide asymmetrically, while most other cells divide symmetrically, and we still do not understand these differences in molecular terms. With the help of robust and well-characterized genetic models, such as the fruit fly, we will get there.”

“Ultimately, this could help the rational design of more specific therapies to inhibit the division of cancer cells, ideally without affecting the healthy cells that are dividing at the same time,” Dr Hickson concluded.

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Nelio T.L. Rodrigues et al. Kinetochore-localized PP1-Sds22 couples chromosome segregation to polar relaxation. Nature, published online July 13, 2015; doi: 10.1038/nature14496