Monday, December 20, 2010

Stem Cells in Microgravity

One interesting and recent study on human embryonic stem cells experiencing net microgravity sheds some insight into what may be causing long lasting health problems for astronauts. Researchers at the University of New South Wales in Australia placed stem cells in a rotating machine developed by NASA that introduces a net gravity close to 0g. The stem cells were in the machine for 28 days, while the control group of stem cells was maintained in the exact same nourishing conditions while experiencing normal Earth gravity conditions. After the experiment, the cells showed several differences at the molecular layer. Nearly 64% of proteins in the microgravity group differed from those grown under normal gravity. In the microgravity treated stem cells, there was more expression of proteins that degrade bone and there was less expression of proteins with antioxidant effects. Additionally, proteins involved in cell division, the immune system, the muscle and skeletal systems, calcium levels within cells, and cell motility were also affected in this group.

These results suggest that microgravity conditions directly impact the development of stem cells in the human body. Human embryonic stem cells can develop into any cell type, and they play a role in repair of damaged tissue and in the maintenance of the normal regeneration of organs with the potential to regenerate. With this importance, if experiencing microgravity hinders their development, then long-term space travel poses serious threats to the health of astronauts. Research is currently being done on several differentiated cell types to determine if the molecular changes are more widespread, and these experiments will also take place on future missions into space in order to verify that these results are also seen in true microgravity, as opposed to net microgravity. Another implication of these results is that future research should be directed towards biomedical interventions that prevent these changes in protein expression.

Yet another implication of this study that concerns long-term survival during space travel is the complications that might arise during procreation. If cells do rely on gravity for some sort of mechanical feedback, then the development of an embryo in microgravity could prove to be impossible. Thus, if humans plan to make long distance trips to other planets in our solar system, the issue of genetically engineering human bodies for them to survive procreation in space might be a necessary step in future.

Wednesday, December 15, 2010

Microbialites (One more blog that I forgot to publish...)

A couple weeks ago, I gave a presentation on microbialites for our lesson on extremophiles. I chose to talk about microbialites because I’d never heard of them before, and because there’s been a lot of exciting research going on over the past few years regarding the potential for microbialites to serve as potential biosignatures for life on Mars.

Basically, microbialites are nothing more than organic sedimentary mineral deposits that are covered by a thin layer of microbes that become entombed in the mounds as they grow outwards. The difference between stromatolites and microbialites is that stromatolites are the Earth’s oldest known structure and show no direct evidence of life, whereas microbialites are relatively young in geological terms, as they are only about 12,000 years old. The reason that scientists are getting so excited about them is because they serve as macroscopic evidence of microscopic life. Chris McKay, a scientist with the NASA Astrobiology Institute, regarded microbialites as:

“They are helping us understand one of the big astrobiology questions how early life took hold and began to flourish on Earth, These fossils are like seeing a billion-year-old footprint in the sand and comparing it to a modern foot.”

NASA scientists realized the importance of microbialites over a decade ago, and began studying the ones that are growing in Pavillion Lake in British Columbia in 1998. The microbialites were formed layer after layer with the oldest lying on the bottom, thus the structure provides a record of growth and also yields important clues about the organisms that once lived there. In 2008, NASA researchers reported that the microbialites in Pavillion Lake were composed of calcium carbonate, ranging in size from small bumps just a few centimeters across to enormous structures as large as 12 feet high. Additionally, they came in a variety of vegetable-shapes: some were described as resembling cauliflower, other like broccoli, other like asparagus, and some like carrots.

How these "veggie"-microbialites came to be placed in this lake isn’t completely known. As of last year, scientists are sticking with the hypothesis that bacteria were involved in some way in creating the large structures. However, it's possible that the only role bacteria had was in the formation of the crusts on the surfaces of the structures, but the structures themselves are the products of a purely chemical, rather than biological, process.

Some cyanobacteria excrete calcium carbonate, so one possibility is that the crusts are composed of this bacterial waste. Another is that the bacteria built up an electric charge along their cell walls, which attracted the calcium carbonate in the lake water. Or maybe the cyanobacteria secreted slime that the carbonates bound to.

In other places around the world, Cyanobacteria are famous for building a variety of structures, from thick rubbery mats to the layered dome-like structures we know as stromatolites.Today, though, they are rare, existing only in extreme environments.
The shallow waters of Shark’s Bay, in Western Australia, for example, are home to large fields of dome-shaped stromatolites. But Shark’s Bay is too salty for the tiny worms that like to snack on the bacteria. That’s why the stromatolites can thrive: there’s nothing around to eat them.

Pavilion Lake, however, is “normal.” It has all kinds of larger organisms living in it. It’s even stocked with fish. This is what creates the mystery.

So, researchers are approaching this topic from a variety of different angles. Some of them are looking at the chemistry of the lake water to understand it's topography and underground water sources; and others are doing DNA analysis of the slime that coats the microbialites to figure out which organisms are living there, what they're eating, and what they're excreting. Still other researchers are comparing the carbon in calcium-carbonate samples from the slime layer to carbon from the core of the structures to see if there is a clear biological mark in the core. The basis behind performing this investigation is that living organisms generally use the lighter C-12 isotope, leaving behind the heavier C-13 isotope.

So far the research has been largely inconclusive. The carbonate in the surface communities have a signature of biological activity, however deeper down, the signature doesn't appear to be preserved. This is contradictory to what you would expect since if the structures were built by microorganisms, there should at least be some isotopic evidence of their biological origin. Though, there is a possibility that over time, the structures have dissolved and re-crystallized, and in the process of doing this, changed from one form of calcium carbonate to another, thus losing their biological carbon-isotope signature.

If this avenue of research turns up supportive findings, the results could provide new insight into how biosignatures are modified and preserved over time, which could aid in future efforts to for biosignatures on Mars.

Monday, December 13, 2010

How science fiction can inform Astrobiology: The recap of a discussion with Jeffrey A. Carver

Yesterday we met with science fiction writer, Jeffrey A. Carver. He was extremely welcoming and helpful in explaining to us much about science fiction, writing, and the intersections of these topics with astrobiology. The reason that we felt science fiction would be an interesting topic to discuss in astrobiology is that science fiction deals with the imaginative, which astrobiology lacks. Astrobiology seeks to understand where life could live, what it could look like, and how we could find it, however, this is intentionally limited by our current technology and scientific knowledge. Astrobiologists use science to try to figure out the same things that science fiction writers imagine. While fantasy imagines the impossible, science fiction narrates the possible.

Astrobiologists may say that much of science fiction is unfeasible, however, science fiction does function within the loose (or even strict) boundaries of science. For instance, NASA scientist Geoffrey A Landis, writes with a very strong science background and even works in the cutting edge of space research. There are other authors that are biologists, physicists, etc. and authors who merely have an interest in science and not a degree, that meld their imaginative stories with science.

Science fiction writers focus on the imaginative aspect of extraterrestrial life and space travel down and this perspective is interesting for astrobiology to take into account. There are new technologies and discoveries that have first been described by science fiction writers. A great example is Arthur C Clarke who imagined geostationary satellites, a global library and light rails well before they were developed. In fact, scientists have gone so far as to test the plausibility of space stations and artificial worlds described in science fiction. Clearly there is some overlap in our imagination and the expansion of the limits of science.

The existence of SETI provides evidence of the overlap between science fiction and astrobiology because the use of SETI to ‘find intelligent life’ suggests that there are sentient beings elsewhere in the universe that will be able to communicate in a manner that we understand and whom would want to communicate with us. This is not much more ‘realistic’ than what we find in science fiction. Indeed, some other ideas in science fiction like cloning, cryogenic suspension, and living on the moon are active areas of research (well, living on the moon was at least at some point an active scientific interest). Clearly, science fiction is not totally unfeasible—animals have been cloned and human bodies frozen after death. Science has just not been able to keep up with the imagination and these technologies are not as practical or useful as they appear in science fiction. New areas of research can even be described as ‘science-fiction-y’ such as the creation of a microbe using artificially produced DNA in the spring of 2010.

Scientists in general, are very skeptical and it is not within the discipline of science to imagine things that are far beyond what we already regard as fact or which are beyond what we can understand using current technology. Thus, astrobiologists do not need to believe that the worlds that appear in science fiction are possible, they just need to understand that science is a human endeavor, and because of this, science may be held back by our imagination. There are many topics in astrobiology that would have seemed far-fetched just a couple decades ago, like the idea of a biocentric universe-- that our cosmology and metaphysics cannot ignore the important interplay between conscious observers and quantum effects—and the two-slit experiment. Though science fiction writers may push the boundaries of the feasible at times, the feasible is a human-centric notion bounded by science. We don’t know what is feasible or not and taking a hint from science fiction writers and expanding our imagination of what life could look like and where it could live is an interesting thought experiment for astrobiology.