Tiny fruit flies may hold the key to unlocking the mysteries behind certain diseases. University researchers, in collaboration with researchers at the University of California at Irvine, used a technique known as homologous recombination to model temperature-dependent seizures - known as febrile seizures - in fruit flies, thereby enabling them to study the mechanisms behind epilepsy. In a study published in the Journal of Neuroscience Oct. 10, the scientists developed a method to transpose a region of the human epileptic seizure-causing mutation directly into the analogous region of a fruit fly's gene, transferring the human disease into the flies.
This work represents the first time scientists have "put a human disease-causing mutation into a fly gene" using homologous recombination, said Robert Reenan, professor of biology. "If we do it as carefully as we possibly can to make it as close as possible to the human condition, we have a better chance of using the model to search for cures," he said.
The researchers observed that when they increased the temperature, the fruit flies began exhibiting signs of neural overactivity before becoming paralyzed. When the temperature was then decreased back to normal, the fruit flies continued seizing, some for as long as 20 minutes.
Flies that had only one copy of the mutated gene did not seize as much as those with two copies of the mutation did. Diane O'Dowd, professor of developmental and cell biology at UC Irvine and a co-author on the study, said that children under the age of five typically do not regulate internal temperatures very well and frequently have temperature-dependent seizures. Individuals with the mutation continue to have these seizures as adults.
O'Dowd's group recorded neurons in fruit fly brains and discovered that certain inhibitory neurons, called GABA-ergic neurons, do not function properly when the temperature increases. Thus, excitatory neurons essentially work overtime, which the researchers hypothesize could potentially be related to the resulting seizures.
To test this hypothesis, the researchers gave the mutant flies a toxin that blocks GABA receptors and saw a resulting increase in seizing. As a follow-up, O'Dowd plans to grow neurons from tissues of humans with the disease to see if the pattern from the fruit flies still holds.
John Manak, an assistant professor of biology at the University of Iowa who was not associated with the study, said he is "a big fan of using Drosophila models" and believes this research could be useful for genetic screening. Manak suggested a follow-up study to identify which specific GABA-ergic neurons are associated with the physical characteristics of the disease.
The researchers now have the option of exploring other mutations in the fruit fly. They hope to find other genes that, when mutated, could essentially cancel out the effect of the disease-causing mutation. This could lead to potential new avenues to therapy, Reenan said. This type of approach could lead to major advances in studying other diseases, such as genetically inherited diabetes and Lou Gehrig's disease.
Another possible route is to "humanize" the fly genes by sneaking in the human amino acid sequence. If the flies remain normal, scientists can then introduce the human mutation into these genes and observe whether defects develop.
Reenan said initially he wasn't sure whether this technique would work but decided to go ahead and explore it. The day before the adult flies hatched, Jeff Gilligan '12, a student in his lab, came in "and looked kind of sick," Reenan said. "The next day, he came in, and he said, 'The flies are out! The flies are out!' and we put the flies into the vial, and we watched, and we were like, 'Oh, my God, they're seizing!'"
"It was worth it," he added.