Welcome to the Roth Lab Home Page

You have found the laboratory of Mark Roth in the Division of Basic Sciences at the Fred Hutchinson Cancer Research Center in Seattle, Washington. My lab is currently interested in metabolic flexibility and suspended animation, chromosome segregation, and diagnostics.

   

Metabolic Flexibility and Suspended Animation

Our work in suspended animation derives from the fact that many animals exhibit what we call "metabolic flexibility," the ability to dial down their respiration and heartbeat and, in effect, "turn themselves off" in response to physical or environmental stress. Mammalian examples include hibernation from ground squirrels to bears as well as estivation (quiescence in response to heat) and embryonic diapause, a pause in embryonic development found in about 70 species of mammals. Meanwhile, many invertebrates can go dormant for days, months, and even years before reanimating. Finally, germ and somatic stem cells are well known to exit the cell cycle for extended periods of time and to re-enter only when it is favorable for the organism.

Our approach to understanding this flexibility has been to develop the means to stop animals for given periods of time and then reanimate them to normal function. We use the term suspended animation to refer to a state where all observable life processes (using high resolution light microscopy) are stopped: the animals do not move nor breathe and the heart does not beat. We have found that we are able to put a number of animals (yeast, nematodes, drosophila, frogs, and zebrafish) into a state of suspended animation for up to 24 hours through one basic technique: reducing the concentration of oxygen.

By examining the precise oxygen tensions needed to induce suspended animation, we also found discrete and lethal oxygen tensions exist just above the oxygen level that enables suspended animation. In other words, there is a range of oxygen levels that is too low to support life, but going below that causes the animals to suspend. We hypothesized that perhaps we could prevent death in low oxygen situations by adding agents that effectively inhibit oxygen utilization and induce suspended animation.

Carbon monoxide, a well-known gas, is extremely toxic because it does exactly that: binds to sites where oxygen binds in the body. We found that we can successfully put nematodes into a state of suspended animation using carbon monoxide, and these results with invertebrate systems encouraged us to explore other systems and agents.

Using another highly toxic gas, hydrogen sulfide, we found we can reversibly reduce the metabolic rate of mice: exposed to 80 ppm of hydrogen sulfide, mice enter into what we call a "hibernation-like" state, where their core temperature can be reduced as much as 11 degrees and their metabolic rate as judged by carbon dioxide production and oxygen consumption drops 10-fold. We've kept the animals in this state for 6 hours and they recover completely.

Our success in altering the metabolic rate of these mammals has given us the tools to pursue several promising lines of research, including whether it might be possible to 'suspend' human organs (for transplant) or to 'buy time' for human patients in trauma.

   

Chromosome Segregation

My lab for many years has focused on the cell biology of the kinetochore in C. elegans. Our work on this dynamic structure required for accurate chromosome segregation during mitosis has provided detailed metrics for our work on suspended animation.

We have defined a number of genes that encode proteins required for the assembly of the kinetochore and studied the roles they play in mitosis. Using antibodies specific for these kinetochore components we have found that several of the proteins become reorganized and separate from the kinetochore when the chromosomes move toward the center of the cell at metaphase. Surprisingly, these proteins still associate with the chromosomes but now form a network on the poleward faces of the chromosomes. Using loss of function mutants we found that this network is required to enable adjacent chromosomes on the metaphase plate to interact with one another. In the absence of these reorganized kinetochore proteins the chromosomes fail to move as a unit to the poles and instead move individually leading to multiple nuclei reforming around the chromosomes as they exit mitosis.

   

Diagnostics

Our work in human diagnostics has focused on the development of a test for autoimmune disease.

Anti-SR Systemic Lupus Erythematosus (SLE) Test

The SLE test grew out of our previous work on the biochemistry of SR proteins, a family of conserved phosphoproteins proteins we identified twelve years ago. We found SR proteins are required for the regulation of alternative pre-mRNA splicing, but also found that they are autoantigens in patients suffering from SLE. Using this information we developed a new diagnostic test for lupus and met the criteria established by the Food and Drug Administration to manufacture and distribute this test in the United States and the test is currently being prepared for market distribution. This test improves the ability for physicians to accurately diagnose patients with SLE, a disease that is notoriously difficult to diagnose. Without an accurate diagnosis many patients suffer the symptoms for years unable to access appropriate care or therapies.

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