Laboratory of Comparative Neurobiology
Graduate School of ScienceProfessor

Sakiko SHIGA

shiga.sakiko.sci

Associate Professor
Assistant Professor

Yoshitaka HAMANAKA
Masaharu HASEBE

hamanaka

Assistant Professor

Aisa SAKAGUCHISpecially Appointed Assistant Professor
Xi Jilih.masaharu
sakaguchi.aisa.celas
xijier.pb4

URL: https://www.bio.sci.osaka-u.ac.jp/bio̲web/lab̲page/shiga/
Our research aims to elucidate theBrain neurons involved inbehavior and physiology of animals,
photoperiodic and diapause
which have been refined through natural regulation
selection, from the perspective ofneurobiology. In particular, we areinterested in how the brain and nervous
system process information with a timeaxis. We are trying to understand how
invertebrates such as insects and mollusks
use circadian clocks to know the seasons
based on environmental photoperiodic
information (combination of light and
The circadian clock neurons in thedark period), and how circadian clocks
brain are required for photoperiodic
produce rhythms that are multiples of 24
response in P. terraenovae. It is now
hours. By comparing the behavior andknown that circadian clock genes arephysiology of various animals andinvolved in the photoperiodic mechanism
understanding their similarities andin a variety of insects. However, it is notdiversities, we believe that we can also
known how the circadian clock reads day
explore the evolutionary paths oflength and switches between diapause
individual animals.
and non-diapause programs after acertain period of days. We have shown
Photoperiodism and diapause inthat circadian clock neurons haveinsects
contacts with pars laterals neurons(neurons required for diapause) and pars
Animals adapt their behavior andintercerebralis neurons (neurons required
physiology to the seasons, such as birdsong
for reproduction), and that the electricaland migration in birds and hibernation in
activity of the pars intercerebralis
mammals. Insects also develop andreproduce during the appropriate season for neurons exhibits photoperiodic response,depending on circadian clock gene
their survival, and go into diapause during
expression. We study how information
the harsh season, temporarily arrestingprocessing occurs in these neuraldevelopment and reproduction. In order tonetworks.
adapt to the seasons, animals need toaccurately predict and prepare for theTwo-day Behavioral Rhythm
coming seasons. The brain uses a circadian(Circaʼbiʼdian Rhythm)
clock to measure the length of the day,The black chafer Holotrichia parallela has
which provides a clue to the season, andthen counts the number of days to determine a unique behavioral rhythm in which it
emerges from the ground once every twothe season. Subsequently a developmental
program is determined for each season, and days at dusk to forage and mate, and thenrests in the ground for the remaining daygrowth, reproduction, and diapause are
and a half. This is called a circabidian
regulated through endocrine mechanisms.
rhythm, since the rhythm continues evenunder constant temperature and constant
We use field collected insects
darkness. The circabidian rhythm disappears
We study the neural mechanisms ofwhen the brain regions at which thephotoperiodism and diapause regulation bycircadian clock resides in many insects arerearing field-collected blow flies and beanremoved. Based on this, we believe that thebugs in the laboratory. Adults ofbrain has a mechanism that uses the 24-hour
Protophormia terraenovae and Riptortus
circadian clock to produce a 48-hourpedestris develop ovaries on long days but
behavioral rhythm, and we are studying theenter diapause with ovary development
neural mechanisms underlying this uniquesuppressed by short days.
rhythm.

Figure 1: Photoperiodic response in the blowfly

Figure 2: Circadian clock cells (blue) mapped in theoptic lobe in the bean bug Riptortus pedestris. Pigmentdispersing factor immunoreactive neurons (green), andanterior lobula neurons (mazenta) are shown involved in
the photoperiodic response in this bug.

D iv e rsity of a nim a l b e ha v iora nd p hys iolog y is a s tonis hing .
T he re a re inte re sting re se a rc h
sub je c ts tha t no one ha s d one
ye t. L e t's ta ke on thisc ha lle ng e tog e the r.

Department of Biological Sciences
Graduate School of Science, Osaka University
1-1, Machikaneyama-cho, Toyonaka, Osaka
560-0043, Japan
TEL: +81-6-6850-5423
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