Biochemical chip solves cell-mating puzzle

A research team at The John Hopkins University, led by Andre Levchenko, have revealed in the journal Nature how they used their patented microfluidic chip to study yeast cells merging together.

The research has solved a long-standing mystery of how a specific kinase protein, Kss1, helps cells send and receive signals from one another and the environment.

When this process is impaired, it can lead to diseases such as cancer.

As cancer is characterised by the uncontrolled growth of cells, any research relating to this process could have important implications for anti-cancer drug development.

Yeast cells are often used to study cell behaviour.

"Yeast is a very simple single-celled organism, but in many respects it operates much like a human cell," said Andre Levchenko, an assistant professor in the Department of Biomedical Engineering.

"

That's why it's been studied for many years; what we find out in yeast often holds true for humans as well.

In this study, we looked at how yeast cells signal one another when they want to merge, engaging in a type of mating behaviour.

Human cells 'talk' to one another in a similar way, and it's important to understand this process."

During the mating process, yeast cells use pheromones to catch the attention of other cells.

When sensors on the surface of a nearby cell pick up this 'scent', mitogen-activated protein kinases (MAPKs) carry the message to the cell nucleus.

The proteins mediate the cellular response through activating multiple genes.

However, according to the John Hopkins team, biologists didn't know why the amount of two different forms of MAPKs increased during this event.

Only one of them, called Fus3, appeared to be in charge of the courtship process.

"The role of the second type of MAPK was unclear," said Saurabh Paliwal, lead author of the Nature article.

"Through experiments with a microfluidic chip and with mathematical modelling, we were able to learn that this second MAPK, called Kss1, does play a crucial role.

Without it, the mating process does not proceed as smoothly."

The researchers used cameras attached to a microscope to study how yeast cells responded to differing pheromone levels with and without Kss1 present.

They discovered that the protein helps yeast cells in two ways.

First, it helped cells diversify their responses at low pheromone concentrations, so that only a small fraction of cells might engage in 'expensive' mating behaviour, which consumes a lot of cellular resources.

Secondly, in the cells that were attempting to mate, Kss1 improved the precision of finding the partner.

The researchers said their findings show the importance of unravelling the role of multiple, apparently redundant proteins that are often activated by the same message passing through a cell.

They also address why cells do not get confused when they are activated by multiple signalling messengers.

The microfluidic chip resembles a computer chip only with a series of tiny channels and chambers - some 20 times smaller than the diameter of human hair - replacing electrical circuitry.

Within the chip, computer-controlled fluid pressure and microscopic valves allow the researchers to isolate and conduct experiments on extremely small clusters of cells.

"The level of control we can achieve on the conditions affecting just a few cells is unbelievable," said Levchenko.

"This is far beyond what you can do in a traditional biology lab dish that's filled with a large colony of cells."

The microfluidic chip was invented and patented by a team that included Levchenko and Paliwal, who teamed up with Alex Groisman, a physicist from the University of California, San Diego.