Evaluating Amino Acid Detection in Drosophila

Overview

Amino acids are essential to the human diet. However, little is known about how the body senses and perceives amino acids. To study chemosensory and gustatory systems on a smaller, simpler scale, Drosophila melanogaster (fruit fly) is used as a model. It has been previously noted that mated females have a higher preference for amino acids than males and virgin females because they need protein to produce eggs. Additionally amino acid deprived flies have a high preference for amino acids because they are known to ingest amino acids based on their internal amino acid levels. In terms of chemosensation, Ir genes (ionotropic receptor genes) are hypothesized to respond to amino acids. The role of these Ir genes can be studied by mutating flies using CRISPR genome engineering to delete individual genes from the fly genome. These flies are then tested against wild-type flies in various assays. If the deleted gene is responsible for the hypothesized function, the assay should have lower responses than that of the wild-type. The objective of this experiment is to determine whether or not certain amino acids enhance perception of sucrose, whether or not amino acids are recognized and ingested in flies raised on standard (i.e. amino acid containing) food, and if the perception of amino acids is decreased in the Ir25a and Ir76b mutants, indicating that those genes are involved in amino acid detection. A two-choice feeding assay was used to perform this experiment. In this assay, a large number of flies are placed in an arena and given the choice to feed on two different substrates for a short period of time. Importantly, two dyes (red and blue) are mixed in with each of the two substrates. After the feeding period, the flies are examined under a microscope to determine which substrate they ingested according to the color of their abdomens. The preference index is calculated with the following formula: PI=N(blue)+0.5(purple)/(N(blue)+N(pink)+N(purple)),each trial was repeated with switched dyes to avoid bias. Throughout the two choice assays, three amino acids, serine, threonine, and alanine, were tested. In the first set of trials, the two choices included 5mM Sucrose vs. 5mM Sucrose + 100mM Amino Acid to see if the amino acid enhanced perception of sucrose. In the second set of trials, 5mM Sucrose vs. 100mM Amino Acid was tested to see if the flies were attracted to amino acids without sucrose. Each trial was tested with wild-type flies, Ir25a flies, and Ir76b flies. According to the results, certain amino acids enhance perception of sucrose, and surprisingly, males can perceive amino acids just as well as females, if not better. However, when given a choice between sucrose and an amino acid, males prefer sucrose more than females. Additionally, data supports that Ir25 and Ir76b both play a role in amino acid perception as flies lacking either gene had lower preference for amino acid containing sugar substrate, compared to wild-type flies. Therefore, Ir genes (ionotropic genes) are likely involved in amino acid perception.

Competition history

• AJAS 2018 Category not listed

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