Researchers discover a new mechanism that regulates stem cell division

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Researchers discover a new mechanism that regulates stem cell

division

http://www.news-medical.net/?id=22447

Errors in stem cell division can give rise to tumours. By studying

stem cells in the fruit fly, scientists at the Institute for

Research in Biomedicine (IRB Barcelona) have identified one of the

mechanisms that govern how these cells divide. The study appears

this week in the scientific journal Developmental Cell.

Stem cells have the extraordinary capacity to divide producing two

very distinct cells: one retains stem cell identity and continues to

undergo asymmetric division, while the other specializes for a

specific function and shows limited capacity to divide. This

strategy allows a single stem cell to generate great amounts of

tissue during a lifetime.

To ensure the correct differential identity of the resulting cells,

the complex apparatus that divides that stem cell in two must form

along a pre-established axis. If this does not occur, the division

may be symmetric, which will generate two identical stem cells. That

is to say, instead of producing tissue, the stem cells with

a " disoriented " division axis may give rise to more stem cells; this

is potentially dangerous for the organism as it would lead to

uncontrolled proliferation of this type of cell.

How is this danger avoided? Researchers headed by Cayetano González,

ICREA Research Professor at IRB Barcelona, have studied stem cell

division and discovered that one of the key factors lies in the

behaviour of the intracellular structure known as the centrosome.

Most animal cells have two centrosomes before division takes place

and their position governs the direction of the division. In cells

that divide symmetrically (giving rise to two identical cells), the

two centrosomes of cell are practically identical. Surprisingly,

and his team found striking differences in the two

centrosomes of the stem cells they were studying. One is located in

a fixed position and is very active during the entire cell cycle,

while the other moves around the cell before coming to a standstill,

becoming activated only seconds before division.

The most surprising aspect of this complex behaviour is its precise

regulation. The imaginary line that passes through the centrosomes

once they are both in position, coincides perfectly with the

orientation in which the stem cell must divide to guarantee the

asymmetry of daughter cells. The intracellular asymmetry of two

functionally distinct centrosomes is a decisive factor in the

regulation of asymmetric stem cell division and prevents the

proliferation of these cells.

These studies have been possible thanks to sophisticated technology

that combines the generation of genetically modified flies in which

normally colourless cell components are stained, with advanced high

resolution microscopy techniques, thereby allowing in vivo

observations.

Elena Rebollo, member of the research team and first author of the

study, explains that " thanks to these techniques and to hundreds of

hours of filming, we have been able to observe the step-by-step

process of stem cell division. We've even been able to identify one

of the proteins that differentiates the centrosomes of the stem

cell " . " This protein " , explains González, " is one of the tumour

suppressors that we described in 2005, which suggests that the

centrosome plays a key role in preventing these stem cells from

becoming malignant; a question to which we are currently devoting

considerable research effort " . These studies form part of a research

line on the relation between stem cells and cancer followed by this

laboratory.