Elucidation of the neural basis of instinctive behaviors in insects utilizing neural activity-dependent gene expression

Taketoshi Kiya (Kanazawa University)

It is a great honor and pleasure to be awarded for this prestigious award. Taking this precious opportunity, I would like to introduce my studies conducted so far and future direction.

Insects exhibit a variety of fascinating behaviors and many of these behaviors are hard-wired. From childhood, I have been strongly interested in instinctive behaviors of animals and wanted to figure out why animals can behave appropriately without being taught from others. Out of many animals, insects drew my interest most strongly, since they can perform highly ordered behaviors even with such tiny brains. Since I first had the opportunity to addressmy hard-wired questions as a graduate student, I am luckily pursuing my interest as a researcher.

Aiming at elucidating the neural basis of instinctive behaviors in insects, I focused on immediate early genes (IEGs), whose expressions increase in response to neural activity, asthe marker of neural activity. By now, I identified two novel IEGs from insect brains which can be reliably used as neural activity markers and comprehensively mapped active neurons in brains of insects showing instinctive behaviors, as below.

  1. Identification of a brain region related to foraging and dancing behavior in the honeybee, utilizing a novel IEG kakusei.
  2. Identification of a conserved IEGHr38 and visualization of neurons activated by sex pheromones and courtship behavior in fly and silkmoth.

Here, I briefly summarize each study.

1. Workers of honeybees (here I studied European honeybees) are able to transmit the location of rich food sources which they found during their foraging trips by exhibiting dance behavior. This behavior is well-known as “dance communication” of honeybees. In dance communication, foragers transmit information of ‘distance’ and ‘direction’ of food sources by ‘waggle duration’ and ‘angle’ of dances. Nestmates follow the dance in the dark hive, decode dance information, and reach the indicated food sources, which are sometimes several kilometers away from the hive. Although this highly sophisticated behavior long drew interest of researchers, the neural mechanism of dance communication was totally unknown. To understand the neural mechanism of dance communication, I thought that it is essential to know the active brain regions and neurons in dancers. To identify active brain regions in dancers, I came to the idea to use IEGs as a neural activity marker. Since no IEG was known in insects, I screened for genes upregulated upon neural activity and identified a novel IEG kakusei from honeybee brains. Establishing neural activity mapping methods utilizing kakusei, I discovered that a subtype of mushroom body neurons is preferentially active in dancers. Further examinations revealed that the activity is related to foraging experience and visual inputs during foraging. This study for the first time identified an IEG from insect brains and revealed a candidate brain region related to dance communication. What role do these mushroom body neurons play in dance communication? This question remains unsolved. In the future study, I would like to reveal the neural circuit and its working principal that govern dance communication ability of honeybees.

2. Instinctive behaviors of insects are so diverse and all species have their own unique behaviors. As an entomologist, it is a dream to establish a method that is useful to detect active neurons in any insect that one wants to investigate. From silkmoth brain, I identified a highly conserved IEG Hr38 and confirmed that Hr38 can reliably be used as a neural activity marker in silkmoth, fly, and honeybee. Using Hr38, I revealed comprehensive neural activity pattern of male silkmoth stimulated with sex pheromone and of male fly stimulated with females. Hr38 is the first conserved IEG in insects to be reported. Since Hr38 is conserved among metazoans and in situ hybridization is applicable to any animals, Hr38 can serve as a neural activity marker, when one wants to identify brain regions and neurons active during instinctive behaviors. Utilizing transgenic techniques of silkmoth and fly, I am currently establishing activity-dependent neural tracing methods, where neurons activated by certain behaviors can be visualized with GFP and artificially controlled by optogenetics. Utilizing these novel methods, I would like to identify and reveal functions of novel neural circuit of instinctive behaviorsin insects in future studies.

Finally, I would like to express my deepest gratitude to all of my advisors, collaborators, and family. These works were not at all possible without their help.