Flipping Switches
to Unlock the Genome
Alexander Deiters | North Carolina State University
An ordinary lamp shining
light on a gene in a cell in a lab in Raleigh, N.C., could become part of
a biomedical breakthrough. That is, if the light hits just the right kind
of cell, one engineered to respond to light by turning genes on or off.
Such a light-switch for genes is part of the future of Alex Deiters’ research linking biology and chemistry and could aid study in areas like birth defects and cancer.
It works when UV light causes a tiny organic molecule to open, and change its structure, and when ordinary sunlight causes the molecule to close. Such molecules have not previously been used in living organisms for biomedical applications.
Photochemical Genetics Traditional methods for studying gene functions in multicellular model organisms have several disadvantages, for example the potential of lethal phenotypes due to a lack of temporal control. We are developing novel tools based on the interplay of small organic molecules and proteins, DNA, or RNA, which enable temporal and spatial control of gene function using light. More specifically, we are working towards the photoregulation of transcription, translation, and the protein function itself. By using light as an input signal which can be controlled with high precision, these methods will be used to elucidate the function of genes in model organisms like zebrafish and C. elegans. These model organisms have the advantage of being completely transparent, allowing the laser irradition on a single cell level.
“This is one step in a new way to learn to study the gene to see how it behaves,” Deiters said. “This approach represents a fundamentally new way to actually turn a gene off using light.”
Current light-activation methods are not reversible. Since Nature regulates gene activity in a reversible fashion, this project will aim for Nature’s level of precision. It’s all part of the closer study of the estimated 20,000 to 25,000 human genes, whose sequencing was announced in May 2006. “We know the genes,” Deiters said. “We don’t know their functions. We need new tools to dissect the functions of genes.”
The genetic light switch, he said, is a good example of bringing various disciplines together, like biologists – who think on a macroscopic level, about cells and organisms – and chemists – who think about the smallest parts, about molecules.
“Now we can harness their synergistic effects,” he said, “and create precise tools to investigate biological functions.” An advantage of light-based switching is that light has few other effects, and flipping the switch does not disturb anything else in the organism under study. “Light is a great tool,” Deiters said.
For example, biologists studying a birth defect could use a tool that would switch the gene for the defect off or on at a precise moment in embryonic development. They could then reverse the step, by switching the gene back.
Research in several areas could benefit from such precision tools to reach inside the cell and make genetic alterations at a specific place and time.
The genetic light-switch will involve engineering an RNA component into the cells to provide the proposed switching capacity through an interaction with the small-molecule light receptor. The small molecule would simply be added to the engineered organism.
Take the example of a common lab model, the zebrafish. The light receptor molecule would be added to its water and taken up by the fish. Irradiation of the molecule would lead to an interaction with the engineered RNA, which in turn would switch the gene under study on or off. The researcher would watch for resulting changes, say, a shorter tail, as clues to a gene’s function.
In an advanced application, perhaps 10 years away, different molecules could be added to respond to light of various wave lengths. In one cell, genes could be switched independently by light irradiation at various wavelengths, leading to possible creation of light-regulated gene networks.
For now, tests will center on a simple bacteria, then move to a mammalian cell cultures. And well down the road, someone may be switching a human gene and watching to learn whether a form of cancer could be averted.
Nov. 1, 2007
