Ability to taste RNA speeds growth and increases fruit fly survival

Fruit fly larvae can taste ribonucleosides, the building blocks of RNA, according to a new study published in the journal PLOS Biology by Texas A&M College of Medicine researchers. Hubert Amrein, PhD, and Dushyant Mishra, PhD, the lead authors of the study, hypothesize that the ability to detect ribonucleosides in the environment helps promote the rapid growth needed by developing larvae and dramatically increases their survival.

Fats, proteins and carbohydrates make up the bulk of calorically rich macronutrients sought out by animals of all kinds. Taste receptors are generally thought to be attuned to identifying these compounds in the environment, allowing organisms to distinguish them from unpalatable and harmful compounds, which are usually bitter. Animals also need a fourth major macronutrient class, the ribonucleosides and deoxyribonucleosides, which are used to make RNA and DNA respectively. However, because animals can build their own ribonucleosides from carbohydrates and proteins, scientists had not previously known that taste receptors could sense them.

While testing the ability of fruit fly larvae to detect a variety of sugars, Amrein and his team discovered the larvae’s strong interest in consuming ribose, a sugar component of RNA, as well as RNA itself. The larvae seek to detect these compounds with a type of gustatory receptor proteins called Gr28. Taste neurons expressing subtypes of Gr28 were activated by ribose and RNA (but not deoxyribose), and when Gr28 genes were transferred to sugar-sensing taste neurons that don’t normally express them, these neurons were also activated by ribose and RNA.

This taste for RNA is not just a luxury; Amrein and his team found that larvae given food from which ribonucleosides were excluded fared worse than those grown on whole medium, and larvae lacking Gr28 receptors grew slower and had poorer survival rates than those with them.

Therefore, even though the body can synthesize them, the ability to detect these compounds in the environment provides an advantage to a rapidly growing organism such as the fruit fly larva, the authors argue, since the larva must increase its body weight by 200-fold in only a few days. “We hypothesize that the ability to taste RNA evolved because ingestion, rather than de novo synthesis, provides a survival advantage during this period of extreme growth,” said Amrein, who is professor and associate department head at the College of Medicine. “We now have evidence that the ability to sense RNA is fairly widespread among larvae of many other types of insects, including mosquitoes, which are major carriers of pathogens that cause dengue, zika and yellow fewer as well as well as malaria and other deadly diseases.”

This work was funded by the National Institutes of Health (grant numbers NIH-1R21 DC015327 and NIH-1RO1GMDC05606).