Karl Hasenstein is internationally recognized for his work on cell biology and on the response of plants to gravity. One of his experiments was aboard the Columbia Space Shuttle, destroyed in the disaster along with the ship and crew. He spoke with ultoday.com recently.

Tell us about yourself.

I'm from Germany, all of my degrees are from Germany. My doctorate is from the University of the Saarland, my dissertation was on auxin [plant growth hormone] transport in experimental and mathematical analysis. I did two post docs, one at San Diego State, one at Ohio State.

In came here in 1988, and I've worked on everything under the sun. My focus has been mechano-sensitivity in plants, mostly gravitropism [gravity response]. We've looked at all parts of the plant, but now we use roots because they grow fastest. We particularly analyzed the sensitivity of the molecular skeleton that supports and defines the cell.

You look at growth in weightless environments. How do you do that on the surface of the planet?

One of the things we use to neutralize the effect of gravity on plants is a clinostat, a rotating device that confuses the heck out of whatever it is we're trying to grow. At least, we think gravity is neutralized; we assume that it is, because the roots grow slowly and because they are also responding slowly.

The clinostats we use are nearly unique.

Nearly unique?

One of them is in fact unique. There was a researcher at UCLA, Jane Shen-Miller. For her own research she had collaborated with someone to build a machine in the '60's, using the technology of that time. When she retired, the machine was still there, but the controls and electronics filled two cabinets, and no one could get it to work. She offered it to me, and I got it working again. So this is truly a one-of-a-kind mechanism.

You have done some ground-breaking work on viscosity inside of cells.

This was work I did with my post-doc. We showed that there were regions of different viscosity within a single cell. This had been suspected, but we proved it.

In our last paper, we looked at the differential viscosity in the cytoplasm, the contents inside of the cell. It was the first paper that ever measured viscous behavior in different directions. The differences in intracellular viscosity are tremendous, and it leads to mechano-transduction. Think of it like this: if you stir your coffee, it will all stir pretty rapidly. But if you try to stir honey, it won't stir, or it won't stir as well.

Say you mix honey with your coffee, but the honey doesn't dissolve. When you stir it, the coffee and the honey will swirl past each other, but each will have a different viscosity. When you have mixed viscosity in one system, differences in viscosity can function as mechano-transducers. If you move one part of the honey, the signal can be mechanically transmitted to another area of the honey.

It's like struts connecting parts of the cell, only it's a thick fluid, not pieces of metal?

You could use that analogy.  That leads to the function of the cytoskeleton. The cell has a skeleton of actin filaments holding it together, and microtubles supporting it.

Like rods ands cables?

There you go.  On one hand the cytoskeleton cages the zones of viscosity, on the other hand, the viscosity defines the cytoskeleton but constantly repolymerizes the whole system. The filaments and microtubules are constantly breaking down and reassembling.

When we look at the structure of the cytoskeleton in a fixed [dead] cell, the proteins irreversibly link up in their natural state. You can look at that under the microscope. But in a living system they're dynamic.

The cytoskeleton is stress-defined, it gets stronger with stress. The same applies to bones; under stress, the shape and internal structure of bone changes. This is one of the reasons that this research is interesting to NASA, because the same things that happen in cells and in plants, happen to bone. In microgravity or zero gravity, there is an absence of stress. The cells that build up bone will stop working, and the cells that break down bone take over. So the bones begin breaking down.

In plants, you can see the response to stress in the growth patterns. When you look at the tree behind Billeaud hall, or the limbs of the Cathedral Oak, the cross section of the branches is a reversed teardrop, an egg shape, because that's the strongest design. Cells and plants and bone respond to stresses, and design themselves into the strongest, most efficient arrangements. All of this is mechanical engineering, only done by nature.

And without any calculus.

Anyway, in the cell this structural approach is what Donald Ingber at Harvard calls "tensegrity," a blend of "tension" and "integrity." The concept is very controversial. What I have worked on fits this model nicely. You get differential transduction in the cell based on the tensegrity. If you knock out the tensile strength, you get something different, if you knock out the microtubles, you get something different from that.

And all of this, of course, deeply alters the underlying chemical transactions throughout the cell.

What else are you working on?

Something else that is interesting is what I call solid-phase gene extraction. Actually, we're extracting mRNA, but the point is that this technology allows us to sample different regions inside the egg of the fruit fly, a single cell only 300 micrometers is diameter, without killing the egg. To do this, we used a solid tool, as opposed to what is typically done, which is liquid extraction. The patent is pending for this process.

Your experiments on the Space Shuttle Columbia were destroyed, and you lost friends in the disaster.

I knew the crew. We had two planning sessions over three years. You get to know everyone, not just the crew. I'm a little bitter over it. These guys were scientists as well as astronauts, and after the disaster NASA basically shut down the experimental part of the Space Shuttle program.

Recently they put out their first request for proposals since them. I'm applying for a new project.

Do you miss Germany?

This is home now. I'm half Cajun now. I can dance a two step.

At least I think I can.