SFU News - February 23, 2006

Worms on front line of in study of space radiation = study

A round trip to Mars could expose travellers = to more=20 than one-quarter the LD50 dose which means that one person = in eight=20 could die from radiation poisoning while the rest would be = very=20 sick.

The United States, and perhaps other = countries, are=20 planning a manned mission to Mars. Unfortunately, it=92s not = known if=20 humans can survive the 35-60 days=92 trip across 100-million = kilometres of space to the rocky red planet.

Nor do we know what effects radiation = will have on=20 the travellers. We don=92t even know how much radiation they = will be=20 exposed to.

The Brookhaven National Laboratory in New = York used=20 its particle accelerator to attempt to simulate the = radiation=20 exposure of a round trip to Mars. The results showed an = expected=20 exposure of approximately 130,000 millirem =96 more than 370 = times the=20 annual average dose for North Americans (350 millirem). = Scary stuff=20 for the people going to Mars.

It gets worse. According to the = University of=20 California Davis=92 environmental health and safety website, = the human=20 LD50 is about 500,000 millirem. LD50 means a dose lethal = enough to=20 kill 50 per cent of the people exposed. So a round trip to = Mars=20 could expose the travellers to more than one-quarter the = LD50 dose,=20 which means that one person in eight could die from = radiation=20 poisoning while the rest would probably be very sick. This = does not=20 even take into account unpredictable solar flares which = could=20 increase the dose several fold.

The Brookhaven results may or may not be = true.=20 Little is known about the effects of long exposure to space=20 radiation either aboard the International Space Station = (ISS) =96=20 where there has been continual habitation for a few years = =96 or for=20 long-duration spaceflights such as the planned Mars mission. = While=20 manned spacecraft have been equipped with excellent = radiation=20 detection devices, they don=92t measure the harm that space = radiation=20 does to people.

What we need is a good system to collect = data on=20 the biological effects of radiation in space. That=92s where = Worms=20 in Space comes in =96 a set of projects involving SFU = researchers=20 that will hopefully lead to the development of radiation=20 countermeasures enabling long-duration manned spaceflight = and=20 continual habitation aboard the ISS.

What are these worms? They are tiny = nematodes=20 called Caenorhabditis elegans. An adult is about 1 = millimetre=20 long =96 about as long as a grain of salt is wide. C. = elegans=20 has many advantages as a model system for studying the = effects of=20 radiation in space. One advantage is its small size. A C. = elegans experiment doesn=92t need much room. This is = important=20 because it=92s expensive to launch weight into orbit and = spacecraft,=20 even the ISS, are very cramped. In addition, C. = elegans has a=20 generation time of just a few days; a two-week lifespan in = which a=20 single hermaphrodite produces about 300 offspring; a limited = number=20 of cells (less than 1,000); and it=92s easy to maintain in a = laboratory. These advantages mean that experimental = procedures can=20 be short, flexible and cost effective. The worms can be kept = in=20 little bags so that the astronauts can just inject liquid = food into=20 the bags every few weeks.

Another advantage is that C. = elegans is the=20 simplest multi-cellular organism with a completely known = genomic DNA=20 sequence. Like humans, C. elegans has about 20,000 = genes.=20 About 4,500 of these genes are effectively doing the same = jobs in=20 worms as in humans. These similar genes include a large set = whose=20 job is to repair DNA damage. Not only does C. elegans = have a=20 similar number of genes to us, they have a lot of = effectively the=20 same genes and similar DNA repair systems, making C. = elegans=20 an excellent model for learning about potential biological = damage to=20 humans in the space environment.

C. elegans has already been to space = on several=20 missions. These include the 1993 and 1996 flights that = carried=20 experiments for Greg Nelson of the Jet Propulsion Laboratory = (JPL);=20 the 2003 Columbia flight, which crashed in Texas and carried = experiments for Nate Szewczyk of the University of Pittsburg = and=20 Catharine Conley of NASA=92s Ames laboratory; and the 2004 = First=20 International C. elegans experiment (ICE-first) on = the Delta=20 mission in which Ann Rose, an SFU alumna, headed the = Canadian Space=20 Agency(CSA)-funded part of the four-country collaboration = (Canada,=20 France, Japan and the U.S.).

Believe it or not, live worms were = recovered from=20 the disaster of the Columbia. They survived an impact 2,295 = times=20 the force of Earth=92s gravity. "This is a very exciting = result," said=20 Catharine Conley of NASA (Astrobiology Article 1921). = "It=92s=20 the first demonstration that animals can survive a re-entry = event=20 similar to what would be experienced inside a meteorite. It = shows=20 directly that even complex small creatures originating on = one planet=20 could survive landing on another without the protection of a = spacecraft."

The two JPL experiments and ICE-first = used a C.=20 elegans mutagen testing system developed in SFU = professor David=20 Baillie=92s NSERC-funded SFU laboratory by research = associate Raja=20 Rosenbluth and grad student Bob Johnsen, now a research = associate.=20 Called the eT1-system (named before the movie ET came out), = the=20 system can capture mutations in C. elegans=92 genome = for=20 analysis on the ground after a completed spaceflight.

Like us, C. elegans has two sets = of=20 chromosomes, so even if there is a mutant gene on one = chromosome the=20 normally functioning gene on the other is usually sufficient = to=20 perform that gene=92s function. The offspring of a worm with = a mutant=20 gene will get either the mutant or the normal gene. Because = the=20 normal gene does an important job while the mutant = doesn=92t, over the=20 generations worms with the normal gene will out-compete = mutant worms=20 and the mutation is eventually lost. This loss is not good = if you=20 want to analyse space radiation-induced genetic damage. The = eT1=20 system maintains mutations so they won=92t be lost.

While the first worms-in-space = experiments were for=20 short-time (about one generation) exposure to space = radiation during=20 the JPL flight, the ICE-first experiment was for a little = longer -=20 11 days in space. These short experiments yielded only a few = mutations, not much above the number of spontaneous = mutations we=20 would expect on Earth.

This is likely because satellites in low = Earth=20 orbit, including the ISS, are protected by the Earth=92s=20 magnetosphere. Trips to the Moon or Mars will last a lot = longer and=20 will not be protected by the magnetosphere. Nobody knows = what=20 biological effects these long trips will have on humans. =

Here at SFU, we have a CSA grant to look = into this=20 problem. We will use the eT1 system to get an accurate = assessment of=20 the biological effects of long exposure to radiation on the = ISS and=20 from this we=92ll develop a biological accumulating = dosimeter for=20 longer trips.

Two of our research questions: How do = biological=20 systems respond to fluctuating dosages of different types of = radiation in space? Do DNA repair systems work differently = in space=20 than on Earth? We will look at multi-generational effects = (which=20 can=92t be done with humans) by placing C. elegans on = the ISS=20 for several months. Our current plan is to fly the worms to = the ISS=20 in 2007-08. We are also having discussions with TRIUMF, = located at=20 UBC, to expose eT1-system worms to radiation in its particle = accelerator, simulating the ISS environment.

Once we have radiation-exposed worms back at SFU we=92ll = use newly=20 developed Nimblegen DNA-array chip technology to analyse the = worms.=20 These chips contain bits of DNA from C. elegans=92 = 20,000=20 genes, so by comparing the exposed worms with the chips = we=92ll be=20 able to rapidly identify any mutations.