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Humans and fruit flies have the same tastes. The substances that are identified are very different from insects. Except when it sours.
In a new study, Professor Craig Montell of UC Santa Barbara and his co-author, a fellow named Anindya Ganguly, identify and describe a taste receptor that is sensitive to acidity in fruit flies. The human sour receptors is in the same family of channels as the protein. The results were published in the National Academy of Sciences.
Montell said that the paper solved the longstanding question of what the sourreceptor is in an insect. This one has been conserved since flies and humans last shared a common ancestor 800 million years ago.
The finding shows that the taste of sour must be very important for survival. It's surprising that many other important taste pathways aren't conserved between flies and humans, since the unrelated receptors detect many of the same chemicals.
The identity of sour taste receptors has been a mystery. Montell said that no one knew the sour taste in animals until a few years ago. Otopetrins wouldn't have been obvious candidates. The recent discovery that they function in acid taste made by Professor Emily Liman at USC, is the reason why they weren't known to play any role in taste at all.
There are three fruit flies: OtopLA, OtopLB and OtopLC. The team found 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 888-353-1299 The flies couldn't tell the difference between acid and sugar solutions. When the mutants were presented with acidic sugar solutions, they showed less activity in their taste cells.
OtopLA has a dual role in flies' behavior. It is important for the insects to be attracted to slightly acidic foods. The brain interprets a stimuli through the connections between the neurons and the receptor. If you give the flies bitter compounds in a sweet neuron, they will eat it. "It's not the substance but the brain regions that are activated that matter," said the lead author. One chemical can cause a positive or negative response depending on its concentration.
The team looked at where OtopLA was expressed in the fly's taste system after knowing which Otop to focus on. Montell explained that flies have five gustatory response neurons.
GRNs are activated by sugars.
B GRNs are stimulated by bitter compounds.
C GRNs respond to water.
Positive ion like calcium can be detected by D GRNs.
Low salt is what E GRNs respond to.
OtopLA is expressed in the A, B, C and D GRNs.
The team found that the OtopLA receptor in B and D GRNs was responsible for the insects' aversion to acidic substances. A fly's attraction to weak acids was brought back when the A or C GRNs were restored. The fly's taste system has an acidity threshold. The attraction of the A and C GRNs wins out if levels are low. The repulsion of the B and D GRNs wins out when the acidity is high.
The function of the other two fly otopetrins is still a mystery, and the researchers are eager to begin tackling it.
It was a bit of a surprise that an otopetrin was a sour receptor. The vestibular systems of mice were the first to identify the proteins. Natural selection co-opting a different function in one organ for a completely different function in another is one example of their role in taste. Evolution is a tinkerer, not an inventor or engineer.
OtopLA is not the first taste receptor the team has linked to acids. The group discovered that the IR7a responds to acidity. acetic acid is the main component in vinegar. OtopLA responds to acidic conditions of all varieties.
The specificity of IR7a may allow flies to avoid potentially dangerous foods. "Flies feed on overripe food," he said. "Good food is good for the flies, and bad food is bad for them." Fruit flies can discriminate between different acids by using different chemical processes. Somebacteria produce acetic acid while others do not.
The three otopetrins in humans and mice are not related to the three in fruit flies. The mechanism for detecting acids developed early on and persisted for hundreds of millions of years, according to the use of otopetrins for acid taste. There could have been an ancestral otopetrin gene that was duplicated and evolved into today's varieties.
The question of whether otopetrin receptors are required for acid taste in animals is raised by the findings. Montell said that it would make the protein unique.
There is a requirement for an Otopetrin-like protein for acid taste. There is a book titled "211064118"
The National Academy of Sciences has a journal.
Researchers identify and characterize a sourreceptor from fruit flies to humans.
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