Faculty Spotlight: How UCR’s Adams lab is studying the effects of ETH on drosophila physiology

Courtesy of Augustine Cheng/HIGHLANDER
Courtesy of Augustine Cheng/HIGHLANDER

UCR Professor of Entomology and Neuroscience Michael Adams, along with members from his lab, recently sat down to discuss their ongoing research involving the process of ecdysis in fruit flies, and the overall impact of this research in understanding drosophila physiology, as well as possible ways to control the spread of diseases.

Arthropods, a group of species that includes organisms like spiders, crickets, flies and lobsters, all undergo the process of ecdysis, which is simply the shedding of the exoskeleton. As Adams explained, the exoskeleton is the outside covering of the organism that provides structural stability and protection to the organism. However, he added that having an exoskeleton “is somewhat limiting in terms of growth. So in order for the animal to grow, it has to go through multiple stages after cuticle shedding just so that they can get bigger. The exoskeleton places a constraint on how big the insect can get.” Ecdysis usually occurs throughout the lifespan and development of the organism, where, “insects typically have multiple larval stages (during their development), and so with each stage they grow,” according to Adams. And eventually, the organism reaches the maximum extensibility of their cuticle, or exoskeleton, which causes the release of hormones that eventually trigger the shedding of cuticle.

Sang Soo Lee, a fifth-year doctoral candidate working in Adams’ lab, explained that the lab utilizes drosophila, or the common fruit fly, in order to study the overall process of ecdysis. “Drosophila is a good genetic model, and is a much simpler animal model,” said Lee. It is estimated that fruit flies have around 125,000 to 250,000 neurons depending on their development compared to a human’s 100 billion neurons.

With respect to these fruit flies, Adams explained that these specific organisms have three distinct larval phases, where the transitions from the first to the second stage and from the second to the third stage involve ecdysis. “After the third stage, the flies pupate, and that’s the stage where the body plan really changes from a worm shape to a wing hexapod adult,” explained Adams. The wing hexapod adult is the appearance of the stereotypical fly that we all know and recognize.

Furthermore, during the process of ecdysis, the flies display stereotypical behaviors, called fixed action patterns, that, “once triggered, the behavior runs to completion without any sensory input,” said Adams. He elucidated that flies exhibit repeatable, invariant muscle contractions before, during and after the shedding of the exoskeleton that occur after a specific stimulus. This stimulus, or signal, ultimately causes the repeated muscle contractions and behavior of ecdysis. Adams, Lee and the other lab members have been investigating the source of this fixed action pattern, or more simply put, the signal that causes this shedding of the exoskeleton, or ecdysis, in fruit flies.

In a paper published in 2015, Adams and Lee proposed a mechanism by which the signaling of ecdysis occurs. Termed ecdysis triggering hormone (ETH), this peptide activates cells through the use of secondary messengers, or molecules within the cells that produce a cascade of products within the cell. In the case of fruit flies, ETH acts on the surface of neurons, and produces a rise in intracellular calcium, which in turn, excites the neuron and causes the fixed action patterns, or muscles movements that are seen in ecdysis. “This is what we call chemically-induced fixed action patterns,” said Adams, where the hormone is released into the bloodstream and acts on the neurons. Lee explained how he was able to visualize this rise in intracellular calcium through the use of GCaMP, or green fluorescent protein tagged calmodulin protein, which is a calcium indicator that lights up green under a fluorescent microscope to “indicate increasing levels of calcium, and therefore, a cell’s activation.” Furthermore, Lee found that depending on the stage of ecdysis, different neurons are activated, which give rise to the behavior of shedding the exoskeleton. “Using different genetic techniques, we can activate the neurons involved, or suppress and block the neurons involved and study the resulting behavior,” said Lee. These alterations to the ETH pathway confirmed the hormone’s involvement in the fixed action pattern of ecdysis, where artificially activating the ETH receptor causes an acceleration of muscle contractions in the shedding of the cuticle, and conversely blocks the receptor, delaying the shedding.

“The beautiful thing is that … all of these maneuvers can be done on an intact behaving animal … so we can see how their behavior changes,” said Adams. “In vivo,” added Lee.

Courtesy of Augustine Cheng/HIGHLANDER
Courtesy of Augustine Cheng/HIGHLANDER

Now that Adams and Lee have gained insight into how the ETH pathway contributes to the fixed action pattern of ecdysis, they are now looking into the role of this developmental hormone, ETH, in the adult stage of drosophila. As Lee explained, these adult flies “don’t need ecdysis behavior anymore, so we hypothesize that there might be something regulated by this hormone in the adult stage.” Adams quickly added, saying, “The hormone has been repurposed — it does one function during development, and now it is regulating completely different functions.” Other lab members are looking into ETH’s role reproductive processes in male and female flies, such as egg production, while Lee is currently working the hormone’s role in memory and emotions in the drosophila. Fruit flies have a specific courtship behavior where once a female fly has mated, she will reject the other males and will lay her eggs. In an experiment with a male fly being rejected by mated female flies, Lee explained how over time, the constant rejection from the female flies will actually change the male fly’s physiology. Specifically, when exposed to virgin females, the courtship activity will be “totally suppressed” in the male fly “because he remembered that he was rejected by another girl,” said Lee. Both Lee and Adams are still “speculating” on the possibility of these flies having emotions.

The Highlander also spoke to Tedrick Mangasarian, a fourth-year neuroscience major, who has been working in Adams’ lab for the past two years. Mangasarian, who aids Lee in preparing the drosophila for analysis, said working on the research that the lab conducts “has to be one of the best things I have done at UCR.” He explained how the work has expanded his perspective of the field of neuroscience and his future career paths, and later added that scientific research is “what science is, and what science will be in the future.”

“We always want to understand human behavior, human emotion, human cognition … I believe that understanding this hormonal circuit is quite important to understand hormonal signaling in much more complex animals,” said Lee. Blocking the creation of ETH was lethal to flies, a consequence that “could possibly be a way to control insects in the future,” explained Adams, to protect crops and prevent the spread of diseases through mosquitoes. Ultimately, for Lee, “By studying this, we can understand nature.”