Life science
Biodiversity conservation, Medical & healthcare

Analysis of the neural mechanism in the brain that senses
the season based on the circadian clock
Department of Biological Sciences, Graduate School of Science
Assistant Professor Masaharu Hasebe
Researchmap https://researchmap.jp/masaharuhasebeLife science

Abstract
Many animals sense the season based on photoperiods, andadequately modulate physiological functions and behaviors. The
circadian clock, which forms about 24-hour rhythms, is suggested
to be important for the photoperiodic responses. However, cellular
photoperiodic responses in the brain that controls physiology andinvolvement of clock genes in the cellular responses have been
elusive. Here, we demonstrated that oviposition-promoting neurons
in the brain drastically changed their neuronal activity according to
day-length conditions by using the bean bug Riptortus pedestris.
Additionally, we also found that the photoperiodic neuronal response was attenuated by gene knockdown of the clock gene.

we succeeded in demonstrating that the circadian clock gene isimportant for the photoperiodic responses at the cellular level. By
applying the present combination-analysis, it is expected that thephotoperiodic response mechanism based on the circadian clockin various species will be clarified.

▍ Background & Results
Organisms living in temperate regions adapt to seasonal environmental changes by modulations of physiological functions,such as reproductive functions, nutrient accumulation, temperature
tolerance. Many organisms sense the season from changes in theday length. It is suggested that the circadian clock, which is a biological clock that forms about 24-hour rhythms, plays an importantrole in measuring the day length. Since the proposal of a model for
circadian rhythm-based photoperiodic time measurement by plant
physiologist Erwin Bünning in 1936, analysis of the central mechanism has been underway for many years.
Recent studies using genetic engineering techniques haveshown that circadian clock genes are important for the photoperiodic responses in some physiological functions, such as the reproductive function. However, it was unclear whether the circadianclock genes contribute to the photoperiodic responses at the cellular level in the brain that controls physiological functions.
Here, we analyzed the cellular photoperiodic response basedon the clock genes by using the bean bug Riptortus pedestris,
which shows clear photoperiodic responses in the reproduction.
Electrophysiological analyses revealed that large neurons in thepars intercerebralis drastically change their neuronal activity according to day-length conditions. Additionally, by applying the RNAinterference-mediated gene knockdown, we also demonstrated
that the knockdown of the clock gene abolished the photoperiodic
neuronal response. Finally, we analyzed the physiological role ofpars intercerebralis neurons using molecular genetic techniques,
and found that pars intercerebralis neurons express multiple neuropeptides which contribute to promoting oviposition.
The present results suggest that the clock gene plays an essential role in the cellular photoperiodic response in the oviposition-promoting neurons.

▍ Significance of the research and Future perspective
Photoperiodic responses based on the circadian clock are important for seasonal adaptation in various organisms. In the present study, by combining cellular analysis and gene manipulation,

P a t e n t
Hasebe, Masaharu; Shiga, Sakiko. Oviposition-promoting pars intercerebralis neurons show period-dependent photoperiodic changes in their firing
T r e a t i s e activity in the bean bug. Proceedings of the National Academy of Sciences of the United States of America. 2021; 118(9): e2018823118. doi: 10.1073/
pnas.2018823118
UR
L https://resou.osaka-u.ac.jp/ja/research/2021/20210224_1
K e y w o r d seasonal response, biological clock, brain, neuronal activity, gene manipulation