Yeast-GAP studies the effects of genetic changes of yeast cells exposed to the space environment. The results will help scientists to understand how cells respond to radiation and microgravity, will impact the determination of health remedies and will increase the basic understanding of cell biology.Principal Investigator(s)
University of Colorado at Boulder, BioServe Space Technologies, Boulder, CO, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)Research Benefits
Information PendingISS Expedition Duration:
October 2003 - September 2006Expeditions Assigned
8,13Previous ISS Missions
Experiments focusing on how microorganisms react to microgravity began with NASA's Biosatellite program in the 1960s and have continued to play an integral part in NASA's research program.
This experiment was designed to study how individual genes respond to microgravity conditions. To achieve this, scientists studied yeast cells, eukaryotic cells, or cells that contain a distinct nucleus bound by a cell membrane. Mammalian cells have a similar eukaryotic structure, and the results of this experiment could aid in understanding more complex mammalian cell response to microgravity. Yeast cells are far simpler than mammalian cells because they have a well-characterized, much smaller genome. This makes it easier for scientists to study how microgravity alters the makeup of the cells and their potential function.
Yeast is an ideal candidate for such a study because it is hardy enough to resist the rigors of flight, requires no refrigeration, and poses little risk to ISS crewmembers. The experiment used genetically engineered cells of brewer's yeast (Saccharomyces cerevisiae) and a special cell growth chamber called a group activation pack (GAP) developed by BioServe Space Technologies. The goal is to identify the precise genes of yeast that are affected by growth in microgravity to understand differences in the growth of yeast cells in space and on Earth.
Due to upmass limitations following the Columbia accident in 2003, Yeast-GAP was separated into two phases. Two GAPs were flown to ISS on 13 Progress and operated during ISS Expedition 8. The remaining two GAPs, Yeast-GAP-2, are identical to the first Yeast-GAP investigation were flown as a Sortie investigation on STS-115/12A during ISS Expedition 13.
Understanding how microbes reproduce and mutate in space may lead to the development of additional countermeasures to protect crewmembers on future long duration missions.Earth Applications
Any insight into the genetic controls of a single-celled organism like yeast or certain bacteria can yield tremendous benefits on Earth, including increased antibiotic production as well as further insight into general cell biology. Research, such as Yeast-GAP, can lead to further developments in cancer research.
Crewmembers activated the yeast samples by inserting a crank into the GAP and turning the handle then deactivating after 30 minutes. There were a total of thirty-two FPAs contained with in four GAPs. The yeast samples were returned to scientists on Earth for detailed analysis.Operational Protocols
Crewmembers activated Yeast-GAP by inserting a crank into each of the GAPs. Once the crank was turned, this allowed the nutritious medium to be introduced to the dominant yeast. Once activated the yeast was allowed to reproduce for 30 minutes or 5 generations. After the 30 minutes, the experiment was deactivated by crewmembers using the crank. Once the handle of cranked, a fixative solution was introduced to the yeast and they were held in stasis for the return to Earth.
Yeast-GAP was sent to space in October 2002 and September 2006 to determine the effects microgravity has on S. cerevisiae. More specifically, this experiment was conducted to determine which genes impart a survival advantage and which a disadvantage under the unique environmental conditions associated with microgravity. To accomplish this, a gene deletion series of yeast strains were combined and grown in the same media and identical growth conditions both in flight and on the ground.
It was found that indeed select key genes are necessary for robust growth during space flight (deletion leads to poor growth) while others appear to inhibit growth in microgravity (deletion leads to enhanced growth). Space flight cultures exhibited survival advantages in strains with deletions in their catalytic active genes. In comparison to ground controls, flight cultures held were disadvantaged with deletions dealing with strains lacking transporter, antioxidant and catalytic activity. Yeast-GAP further identified specific genes critical for survival in space (Johanson et al 2007).
Yeast-GAP was able to identify Stress Response Element (STRE) genes associated with microgravity. STRE genes are activated in response to specific stresses, including osmotic stress, heat shock, and environmental stresses such as microgravity. This experiment investigated the gene expression changes of the STRE genes SSA4, YIL052C, and YST2, with transcription regulation involving Sfp1 and Msn4. Results show that space flight significantly decreased expression of most genes, with only one left unaffected. Next, transcriptional regulation of YIL052C and SSA4 were explored. Genes were striped of one of their transcriptional factors and evaluated to determine each gene?s dependence on the corresponding factor. Both genes lacking Msn4 decreased expression while genes lacking Sfp1 did not experience any change. This suggests that the cellular effects of the space environment are at least in part mediated by the transcription factor Sfp1. This is significant because it demonstrates the importance of true microgravity experimentation (in contrast to ground simulations of microgravity) which can lead to a better understanding of the mechanisms behind cellular responses to this unique environment (Coleman et al 2008).
Finally, phenotypic variations were observed as assessed by scanning electron microscopy (SEM). Yeast cells grown under ground-based conditions revealed a normal budding pattern with buds developing adjacent to previous bud scars. Yeast cells exposed to microgravity exhibited random and more numerous budding patterns. (Johanson et al 2007).
These early investigations were designed to be launched on an unmanned spacecraft (Progress) well in advance of processing on board the ISS and remain stable for months before return to Earth and analysis. The results obtained demonstrate the robustness of studies utilizing S. cerevisiae as a model for eukaryotic cell studies. These studies demonstrate that the yeast gene deletion series is a powerful tool to assess the effects of microgravity and other environmental factors on cellular level responses, which is likely to be relevant to more complex organisms including humans.
Johanson K, Wilson JW, Honer zu Bentrup K, Nickerson CA, Gonzalez-Villaobos RA, Stodieck LS, Freeman J, Ramamurthy R, Nesbit J, D'Elia R, Muse KE, Hammond J, Allen PL, Hammond TG. Haploid deletion strains of Saccharomyces cerevisiae that determine survival during space flight. Acta Astronautica. 2007; 60(4-7): 460-471. DOI: 10.1016/j.actaastro.2006.09.011.
Goulart C, Coleman CB, Rupert M, Stodieck LS, Hoehn A, Allen PL, Hammond TG. Novel Sfp1 Transcriptional Regulation of Saccharomyces cerevisiae Gene Expression Changes During Spaceflight. Astrobiology. 2008; 8(6): 1071 - 1078. DOI: 10.1089/ast.2007.0211.
Johanson K, Lewis FC, Cubano LA, Hyman LE, Hyman LE, Allen PL, Hammond TG. Saccharomyces cerevisiae gene expression changes during rotating wall vessel suspension culture. Journal of Applied Physiology. 2002; 93: 2171-2180.
Wilson JW, Pierson DL, Nickerson CA, Ramamurthy R, Porwollik S, Ott CM, McClelland M. Low-Shear modeled microgravity alters the Salmonella enterica serovar typhimurium stress response in an RpoS-independent manner. Applied and Environmental Microbiology. 2002; 68(11): 5408-5416. DOI: 10.1128/AEM.68.11.5408-5416.2002.
Wilson JW, Pierson DL, Nickerson CA, Ramamurthy R, Porwollik S, Ott CM, McClelland M, Allen PL, Hammond TG. Microarray Analysis Identifies Salmonella Genes Belonging to Low-Shear Modeled Microgravity Regulon. Proceedings of the National Academy of Sciences of the United States of America. 2002; 99(21): 13807-11382. DOI: 10.1073/pnas.212387899.