April 02, 2012
Watching a yeast cell age can be a real pain. In budding yeast like Saccharomyces cerevisiae, the buds quickly outnumber the mom. Which means scientists need to remove the buds as they appear.
Up until now, scientists have had to use a 50-year-old method that involves removing the buds by hand. Not only is this labor intensive, but the field is held back by the inability to use high resolution microscopy to investigate the aging process.
These technical limitations may soon be swept aside with a new microfluidic dissection technique described by Lee and coworkers in a recent study out in PNAS. These researchers were able to monitor 50 aging yeast at once with a variety of microscopic techniques without having to remove the buds by hand. And unlike the older technique, they were able to keep a constant environment for the yeast cells (i.e. no decrease in nutrients and/or build up in wastes).
Basically Lee and coworkers tucked the yeast mother cells under a micropad which they then washed with a constant flow of nutrients. Because the daughter cells are smaller than the mother, they are washed away as they emerge. So no manual bud removal is required.
Sounds convenient but the researchers needed to show that this new technique gave similar results as compared to the old one. And they did.
They showed that mutant strains behaved similarly with both techniques. So a SIR2 deletion mutant still had a shorter lifespan and a FOB1 deletion mutant still lived longer with microfluidic dissection. Not only that, but the number of divisions in an average yeast’s lifetime was comparable with both techniques. At first blush the techniques do seem comparable.
Now they were ready to take their new technique out for a spin to see what it could do. First they were able to show heterogeneity in how yeast cells age. Some cells died as spheres around their 12th division while others died as ellipsoids after their 25th division. The shape of the yeast later in life correlated with how long that yeast lived.
The researchers were also able to use GFP to explore the vacuoles of aging yeast. They found three classes of vacuoles: tubular, fused, and fragmented. The tubular vacuoles were only found in the longer-lived ellipsoid yeast.
Researchers could not have discovered these properties of aging yeast without the new microfluidic dissection technique. And these findings are really just the tip of the iceberg of what can now be learned about aging by studying yeast. It will be exciting to see what else scientists will be able to learn about the twilight of a yeast cell’s life.
Life and Death of a Single Yeast
by D. Barry Starr, Ph.D., Director of Outreach Activities, Stanford Genetics
Categories: Research Spotlight