Cells like to move in crowds, it seems

Cells don’t move and interact with each other in the way scientists have always believed, according to Australian researchers.

Cells are simulated in a mathematical model to replicate the experiments and identify cell-to-cell interactions. Credit: ACEMS

Writing in the Journal of the Royal Society Interface, a team from the ARC Centre of Excellence for Mathematical and Statistical Frontiers (ACEMS) suggests that cell movement actually increases when there are more cells around.

“Scientists in the past have thought of cells like people. The more space you’ve got, the easier it is to move,” says co-author Matthew Simpson. “Turns out, it is more complicated than that. They need more cells before they move.”

The paper is currently available on the pre-print server bioRxiv.

Lead author Alex Browning says the team was surprised by the finding, in part, perhaps, because it wasn’t their aim. Their focus was on testing mathematical models they had developed, which happened to have applications in biology. 

They applied modelling and statistical analysis to a scratch assay: in this common process, cells are placed in a well, then a scratch is made to create a large vacant region that separates them. 

Scientists then observe how the cell population grows and cells move to fill up that space. In this particular research, the team used prostate cancer cells.

Browning and colleagues say they found that typical experimental protocols did not vary the initial cell density, or the initial number of cells used.

“We wanted to explore how cell density affected the dynamics of the experiment by quantifying this,” he says. “Our mathematical and statistical methods allowed us to identify the nature of cell to cell interactions in the experiments that might lead to density-dependent behaviour.”

Biologists and mathematicians alike have assumed that cell movement, or motility, is independent of density, and not affected by cell-to-cell interactions, Browning says, but “our results showed the opposite of what has always been assumed”.

“It turns out a higher density environment where there are more cell-to-cell interactions actually increased cell movement.”

Co-author Wang Jin, a mathematical biologist, says the results are significant because biologists regularly grow cells in the lab for experiments but there is no standard protocol that tells them how many cells they should put into the well each time. 

“Our results show that it matters how many cells they use,” he says.

Equally, says Simpson, there are implications for mathematicians.

“The simplest thing we have done here is to change the initial number of cells. By changing some of the most fundamental features of these experiments, which is so basic that no one ever questions, we actually learn an awful lot,” he says.

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