It was found that indeed select key genes are necessary for robust growth during spaceflight
(deletion leads to poor growth) while others appear to inhibit growth in microgravity (deletion
leads to enhanced growth). Spaceflight 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 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 spaceflight significantly decreased
expression of most genes, with only one left unaffected. Next, transcriptional regulation of
YIL052C and SSA4 were explored. Genes were stripped 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 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 2007).
Scanning electrograph image of Saccharomyces
cerevisiae cells grown on Earth.Scanning electrograph image of Saccharomyces
cerevisiae cells grown on the International Space
Station.