Towards understanding molecular mechanisms ofinfradian rhythms
Takashi YoshimuraInstitute of Transformative Bio-Molecules (WPI-ITbM)
Graduate School of Bioagricultural Sciences
Nagoya University
Furo-cho, Chikusa-ku, Nagoya, JapanThe appropriate timing of various seasonal processes, such as reproduction,
migration, and hibernation, is crucial for the survival of animals living in temperateregions. Although this phenomenon attracts great interest, its underlying
mechanisms were not well understood. Drosophila and mouse are undoubtedly goodmodels for understanding various aspects of physiology and behavior. However, theseanimals do not show clear seasonal responses. Therefore, it is better to choose“non-model animals” that show robust and dramatic seasonal responses, tounderstand the underlying mechanism of seasonality. With the use of non-modelorganisms that have highly sophisticated seasonal responses, we have uncovered theuniversality and diversity of the signal transduction pathway that regulate seasonal
rhythms in vertebrates.
Although humans are not typically considered seasonal animals, someevidence suggests that seasonal variation in physiology and behavior also exists inhumans. For example, the wavelength settings for the unique yellow hue are shiftedto shorter wavelengths in summer when compared to those in winter. Seasonalaffective disorder patients experience recurrent winter episodes of depressed mood,overeating, and hypersomnia along with electroretinogram changes in winterassociated with lower sensitivity when compared to healthy subjects. Theseobservations highlight the potential importance of the retina in seasonality. We havediscovered dynamic plasticity in phototransduction regulates seasonal changes incolor perception in Japanese medaka fish (Oryzias latipes), making it an excellent
model for studying seasonal adaptation. Furthermore, we observed decreasedsociability and increased anxiety-like behavior in medaka exposed to winter-likeconditions. Chemical genomics approach uncovered molecular mechanisms
underlying winter depression-like behavior in medaka. Moreover, we are studying
seasonal changes in physiology of rhesus macaques kept under natural outdoor
conditions. We believe that exploring the regulation of seasonal traits in animalmodels will provide insight into human seasonality and aid in the understanding of
human diseases, such as seasonal affective disorder.
The existence of circannual and circalunar clock has been demonstrated inseveral organisms. However, their underlying molecular mechanisms remain mystery.
We are currently attempting to uncover these mechanisms using medaka and grass
puffer as model species.

CaMKIIα is involved in the coupling of theevening and morning circadian oscillators in mice
Tomoko Yoshikawa1,2,3, Ken-ichi Honma2
Sato Honma2
1Hokkaido

University Graduate School of Medicine,of Anatomy and Neurobiology, Kindai
University Faculty of Medicine
3Organization for International Education and Exchange,
University of Toyama
2Department

The circadian pacemaker in mammals is located in the hypothalamicsuprachiasmatic nucleus (SCN) and yields photoperiodic response to transfer
seasonal information to physiology and behavior. Photoperiodic changes in behavior,especially in the length of activity time in nocturnal rodents, are ascribed to thephase-relation between two circadian oscillators which differentially respond to light,
and respectively regulate the onset and offset of activity band of circadian behavior
rhythms (Pittendrigh and Daan, 1976). The two oscillators are called the evening (E)for the onset and the morning (M) oscillators for the offset. We identified the regions
corresponding to these two oscillators in the mouse SCN by using bioluminescenceimaging (Yoshikawa et al. 2017). However, the dynamics and mechanism of coupling
between the oscillators is not well understood.
Ca2+/calmodulin-dependent protein kinase IIα (CaMKIIα) activity is essential for
not only the cellular oscillation but also synchronization among oscillators in the SCN(Kon et al., 2014). The knock-in mouse with a kinase-dead mutation in CaMKIIα(K42R mouse) showed weakened behavioral rhythm and elicited decoupling between
the E and M oscillators. Under prolonged DD, the activity time (α) was gradually
expanded (α decompression) in association with an increase of circadian period of theactivity offset. When α reached a critical length of about 18 hours, abrupt shorteningof α (α compression) took place by phase-delay shifts of the activity onset andphase-advance shift of the activity offset. The amounts of the phase shifts weresignificantly larger in the activity offset than onset, suggesting that the internal
coupling between the E and M oscillators is bidirectional but with different strength.
Disrupted coupling of the E and M oscillator was also seen in the course ofre-entrainment to a short photoperiod (LD6:18), where α decompression wasaccompanied. CaMKIIα was suggested to be involved in the coupling of the E and M
oscillators. Possible mechanism of the coupling will be discussed.

Time to update the external coincidence model inArabidopsis
Motomu Endo and Akane KubotaNara Institute of Science
Physiology, Nara, JapanandTechnology,Plant

Many organisms developed seasonal responses in order toadopt to changing environment throughout a year. In plants, regulation of seasonal
flowering is a representative example of photoperiodism and is important forsuccessful propagation.
It is widely known that the expression of the gene that encodes florigen,
FLOWERING LOCUS T (FT), is induced by specific photoperiod and promotes
flowering in plants. Photoperiodic induction of FT expression is interpreted by amodel called "external coincidence model", in which FT activation occurs when plants
receive the light on the specific timing of the day. In long-day model plant,
Arabidopsis thaliana, it was proposed that light- and clock-mediated activation of
CONSTANSE (CO), one of the major transcriptional regulators of FT, is the actual
mechanism of external coincidence model. CO-FT module fits well to the concept of“external coincident model”, and has been widely validated in various plant species
under laboratory conditions, where temperature remains constant and artificial lightsources are used.
However, under natural long-day conditions, where plants are exposed tosunlight and daily fluctuation of temperature, FT is highly induced both in themorning and evening and promotes flowering. In different with the evening FT, theinduction of morning FT requires both far-red signaling and long-day photoperiod.
Interestingly, the induction levels of morning FT increased gradually as theday-length becomes longer. Since light exposure from dawn to the peak expression ofmorning FT (ZT4) is the same under any photoperiod condition, these results suggestthat photoperiod information from the day before determines the induction levels ofmorning FT, and that current external coincidence model cannot fully explain
long-day dependent FT induction in the morning.
To further analyze how day length affects FT expression, we applied transient
jet-lag experiments and found that the timing of dawn and dusk determines theinduction levels of morning and evening FT, respectively. Under this jet-lag condition,
morning FT induction occurs even in the absence of far-red light, implying that
far-red signaling and photoperiod independently regulate morning FT. In addition,
the responses of each clock gene to the new light-dark cycle are slightly different.
While morning-expressed gene CIRCADIAN CLOCK ASSOCIATED1 (CCA1) rapidly
adjusted to the new light-dark cycle, evening-expressed LUX ARRHYTHMO (LUX)
partially remains original phase, implying the transient decoupling between clock
genes and FT expression.
Here, we discuss how the light-dark cycle affects the expressions of FT andcircadian clock genes, and propose a possible model that explains photoperiodic
flowering responses of Arabidopsis in nature.

Diet- and hibernation season- dependentenhancement of hepatic cold resistance in a
mammalian hibernator Syrian hamster
Yoshifumi Yamaguchi
Hibernation metabolism, physiology, and developmentgroup, Institute of Low Temperature Science, Hokkaido
University, Sapporo, Japan

Mammalian hibernation is a strategy to survives during the harsh season
with cold and little food by reducing basal metabolism and thermogenesis. In small
mammalian hibernators, hibernation consists of multiday hypothermic deep torporand normothermic periodic arousal. Deep torpor is characterized by the profoundsuppression of metabolism, body temperature, heart rate, and locomotive activity. The
drastic alterations in physiology associated with hibernation can lead to multiple
organ dysfunction and death in non-hibernators such as mice and humans, whereas
hibernators tolerate these physiological extremes. The mechanisms responsible forsuch extremes remain poorly understood.
Syrian golden hamster (Mesocricetus auratus) is a facultative hibernator, inthat they are induced to hibernate under a winter-like, short photoperiodic cold
condition independent of circannual rhythm. When transferred from summer-like
conditions to winter-like conditions, they begin to hibernate after several months ofthe pre-hibernation remodeling period. We found that hepatocytes from Syrian
hamsters exhibited remarkable intrinsic resistance to prolonged cold culture, whereas
murine hepatocytes underwent cold-induced cell death. The cold-induced cell death
fulfills the hallmarks of a recently identified regulate cell death, ferroptosis, such as
necrotic morphology, lipid peroxidation and prevention by an iron chelator.
Unexpectedly, the resistance to cold in hepatocytes from Syrian hamsters was lost in a
diet-dependent manner. The diet-dependent resistance in Syrian hamsters wasattributed to their superior ability to retain dietary -tocopherol (T), a vitamin E
analog in the liver and blood. We also found that Syrian hamsters also increased
plasma T concentration in a hibernation-season dependent manner. These results
suggest that the cold resistance of Syrian hamsters is established by the ability toutilize T effectively to prevent lipid peroxidation and ferroptosis, both of which canoccurs by the repeated cooling and rewarming processes during hibernation.

Organizing complex seasonality: bird migration
gives clues
Prof. Barbara Helm
Groningen Institute for Evolutionary
University of Groningen, Netherlands

LifeSciences,

Over recent years, we have witnessed great strides in the neuroendocrine
understanding and molecular decoding of photoperiodic stimulation of vertebrate
reproduction, thanks in particular to research by the laureate Takashi Yoshimura.
Apart from reproductive activation, the mechanisms driving further major transitionsin the vertebrate annual cycle are still largely unknown. Yet ultimately,
understanding the regulation of annual cycles requires knowledge of driving
mechanisms of all phases, as well as of their integration.
Migratory birds are a particularly challenging, but potentially also rewarding, system
for such an integrative understanding. The birds’ change of location imposes
photoperiodic change and uncertainty, but at the same time, major physiologicaltransitions must be initiated well in advance. Thus, the birds’ long-distance flights
must be accurately timed relative to the anticipated environmental resources months
later, at destination areas that can be several thousand kilometres away. Because ofsuch high demands on biological time-keeping, bird migration has been a classicalstudy system in chronobiology from its early days, including of photoperiodic pioneers
such as William Rowan, and of circannual pioneers such as Eberhard Gwinner.
Given their complex environmental input and annual cycle, migratory birds require atiming system that selectively uses photoperiodic input during some phases of theannual cycle, and might individually time different phases of the annual cycle.
Additionally, given the demands of their mobile life styles, it is likely that thefine-tuning of migratory timing involves integration of multiple physiologicalprocesses. Now, new data from multiple sources give clues to contributing factors.
Circannual and photoperiodic studies of migratory birds suggest modularorganization of the annual cycle, such that phases can be independently modified andmay differ in free-running circannual period length. Data from wild migrants show
good correspondence with captivity studies, and theory of migratory timing programs
can accurately explain striking behaviour in the wild. Long-term data from wild birds
confirm that through evolution and plasticity, different phases can be independently
modified. Lastly, genomic studies of wild birds point to molecular components of thefine-tuning of annual timing. At present, these studies yield diverse, sometimes
surprising, results, which however can inform hypotheses for future mechanistic
studies.
Disentangling this multi-piece puzzle is a grand challenge, but bird migration offers
unique pathways for relating complex rhythmic organization to the lives of free-living
animals. New insights from migratory birds are likely to reveal fundamental
regulatory mechanisms that may also play a role in less complex systems, where theymight be less conspicuous and thus more easily overlooked.