Final Report Summary - DRYLIFE (Surviving the dry state: engineering a desiccation-tolerant mammalian cell)
Some organisms can survive almost complete desiccation for indefinite periods during which they enter a state of suspended animation. This remarkable ability, called anhydrobiosis (“life without water”), is found in most biological kingdoms, including bacteria, fungi, animals and plants. How anhydrobiosis works is unclear, although it was first described by Antony van Leeuwenhoek in bdelloid rotifers over 300 years ago, and one of the main aims of this project was to improve understanding of this remarkable phenomenon at the molecular and cellular levels. A subsidiary goal was to use our knowledge of anhydrobiosis to improve the stability of mammalian cells, which are not normally able to survive drying. One reason for attempting this is that once anhydrobiotic organisms have viably entered the dry state, they are able to withstand extreme temperature and pressure without harm, a property of particular interest for biomedical and environmental applications. A second reason for wanting to create a desiccation-tolerant mammalian cell is that this would allow us to claim a clear understanding of the phenomenon of anhydrobiosis: as Richard Feynman said, “What I cannot create, I cannot understand.” We call this approach “anhydrobiotic engineering”.
We have studied three types of organism to gain insight into anhydrobiosis: the bdelloid rotifers of van Leeuwenhoek, bakers’ yeast and anhydrobiotic nematodes, all of which are able to survive desiccation. For the first two organisms, we have studied their genetics to provide clues. The rotifer is not well characterised genetically, so in collaboration with colleagues in the Department of Genetics, University of Cambridge, we have determined its whole DNA sequence, and have focused initially on active genes. One major surprise in these tiny animals is that perhaps 10% of its genes seem to have been captured from other organisms, mostly microbes, over the course of evolution. Many of these “foreign” genes have been put to use by the rotifer and at least some of them participate in the way the animal reacts to drying. So one remarkable possibility is that bdelloid rotifers use genes obtained from other creatures to help them survive. Yeast are much better characterised than the rotifer, and we have been able to screen yeast mutants for their ability to cope with desiccation. We find that genes involved in removing damaged proteins in the cell are vital for survival of drying, suggesting that maintaining cell proteins in a healthy state is particularly important.
This last conclusion fits well with other achievements of the project, where we have investigated the function of a special category of proteins implicated in anhydrobiosis. These are unstructured proteins that, counterintuitively, nevertheless have functions within the cell. One function seems to be help reduce the damaging effects of desiccation on other proteins: loss of water can cause most proteins with a defined three-dimensional structure to lose that structure and become “sticky”, such that they form aggregates with detrimental consequences for their function. Some unstructured proteins can reduce this aggregation and thereby mitigate the effects of water loss in anhydrobiotic organisms. We have been able to define this novel function in some detail, particularly for proteins obtained from nematodes and rotifers, and have called the proteins responsible “molecular shields”.
We have found it more difficult to use what we have learned about anhydrobiosis to increase the desiccation tolerance of mammalian cells growing in the laboratory – there are many technical challenges involved, including the apparently simple task of determining just how dry a dried cell is. Our experiments to date suggest that multiple changes will need to be made to mammalian cells to allow them to survive the dry state.
We have studied three types of organism to gain insight into anhydrobiosis: the bdelloid rotifers of van Leeuwenhoek, bakers’ yeast and anhydrobiotic nematodes, all of which are able to survive desiccation. For the first two organisms, we have studied their genetics to provide clues. The rotifer is not well characterised genetically, so in collaboration with colleagues in the Department of Genetics, University of Cambridge, we have determined its whole DNA sequence, and have focused initially on active genes. One major surprise in these tiny animals is that perhaps 10% of its genes seem to have been captured from other organisms, mostly microbes, over the course of evolution. Many of these “foreign” genes have been put to use by the rotifer and at least some of them participate in the way the animal reacts to drying. So one remarkable possibility is that bdelloid rotifers use genes obtained from other creatures to help them survive. Yeast are much better characterised than the rotifer, and we have been able to screen yeast mutants for their ability to cope with desiccation. We find that genes involved in removing damaged proteins in the cell are vital for survival of drying, suggesting that maintaining cell proteins in a healthy state is particularly important.
This last conclusion fits well with other achievements of the project, where we have investigated the function of a special category of proteins implicated in anhydrobiosis. These are unstructured proteins that, counterintuitively, nevertheless have functions within the cell. One function seems to be help reduce the damaging effects of desiccation on other proteins: loss of water can cause most proteins with a defined three-dimensional structure to lose that structure and become “sticky”, such that they form aggregates with detrimental consequences for their function. Some unstructured proteins can reduce this aggregation and thereby mitigate the effects of water loss in anhydrobiotic organisms. We have been able to define this novel function in some detail, particularly for proteins obtained from nematodes and rotifers, and have called the proteins responsible “molecular shields”.
We have found it more difficult to use what we have learned about anhydrobiosis to increase the desiccation tolerance of mammalian cells growing in the laboratory – there are many technical challenges involved, including the apparently simple task of determining just how dry a dried cell is. Our experiments to date suggest that multiple changes will need to be made to mammalian cells to allow them to survive the dry state.