Sweet Taste Receptors Regulate Proteins in Developing Drosophila

 

Drosophila melanogaster relies on contact chemosensation to detect nutritious foods, avoid ingesting toxic chemicals and choose mates and safe places to deposit eggs. Flies sense tastants and scents through gustatory bristles and pegs distributed on multiple body parts, including wing margins and legs. The sensillum's gustatory receptor neurons express 68 gustatory receptors (GRs). Unlike mammalian chemosensation, functional Drosophila GRs may include three or more subunits. Many GRs seem to be expressed in multiple cell types that are not associated with contact chemosensation, raising the possibility that these proteins may have roles that extend beyond the detection of tastants and scents. 

Researchers have found that a cluster of genes encoding 6 receptors, known as gustatory receptors 64 (GR64s), was overexpressed in epithelial cells of mutant larvae, which experience cellular stress as a result of a buildup of dysfunctional proteins. To further investigate, the researchers rendered GR64 function in larval epithelial cells that contained stress-inducing mutations. Losing the taste receptors resulted in a large amount of death among the stressed cells. They found that the loss of GR64s prevented the cells from digesting accumulated proteins via autophagy compared to cells with functioning receptors, indicating that the receptor cluster may have something to do with cellular homeostasis. In their normal role as taste receptors, GR64s oversee calcium flow,  involved in protein regulation. Furthermore, the researchers found that calcium influxed into mutant cells has less activity in GR64-free cells compared to controls, making calcium signaling a common candidate for how receptors may maintain proteostasis. 

It was very intriguing how the researchers identified the nonconical role of gustatory receptors in proteostasis maintenance for their function in neuronal sensation. Although, the article did not fully connect calcium activity to protein regulation. Regardless, calcium activity is an important unknown for a proper understanding of how this receptor functions. 

Does obesity reshape our sense of taste?

 

 

 

 

Severely overweight mice had an impaired ability to detect sweets and fewer taste buds compared to slimmer mice.  Obesity can lead to alterations in the brain and also nerves that control peripheral taste.  This is an important find because taste buds play a vital role in regulating appetite, what and how much we eat.  It’s not clear exactly how an inability to detect sweetness might encourage weight gain but previous research showed obese people yearn for sweet and savory foods and might not taste these flavors as well as thinner people.  Determining the connection between taste and appetite with obesity may encourage more healthy eating and new treatments for obesity.   

http://www.sciencedaily.com/releases/2013/11/131121154944.htm
http://www.buffalo.edu/news/releases/2013/11/030.html

Some Carnivores have no Sweet Tooth

Sciencenews.org and MSNBC both recently reported on a new study which has found that some carnivores lack the ability to taste sweet things because of mutations to certain taste receptor genes such as Tas1r2. The researchers studied 12 animals, 7 of which eat only meat and had gene mutations to certain receptors that normally enable the ability to taste sweets. These 7 animals included bottle nosed dolphins, sea lions, spotted hyenas and fossas; all of these animals are predators and hunt for their food, suggesting that they do not need to taste sweet things. However, this was not enough evidence to claim that all carnivores are unable to sense sweetness because other results showed that some carnivorous animals can taste sweet, that not all or any of their sweet receptor genes were inhibited by mutations. Carnivorous animals which can taste sweetness include domestic cats, raccoons, spectacled bears, Canadian otters and red wolves, among many others documented in the past. These animals often eat a broader variety of foods and do not always hunt for their food (they may scavenge). Although it is interesting that this study was able to identify specific gene mutations associated with sweet taste receptor loss, it is not enough to prove that all carnivores lack the sweet sense. Instead, it is much more likely that the study found an example of how evolution has led to some species being able or not able to taste sweet based on their foraging habits.