ECE2019 Symposia Circadian clocks: from pathophysiology to chronomedicine (3 abstracts)
Japan.
Appropriate timing of various seasonal processes, such as reproduction, migration and hibernation, is crucial to the survival of animals living in temperate regions. Although this phenomenon has been studied for decades, the underlying mechanisms of seasonal changes in behavior are not well understood. Medaka fish (Oryzias latipes) are an excellent model for studying seasonal adaptation, as they are active and exhibit clear phototaxis in conditions simulating summer, but are inactive and fail to exhibit phototaxis in conditions simulating winter. Mate preference tests using virtual fish created with computer graphics demonstrate that medaka are more attracted to orange-red-colored model fish in summer than in winter. Transcriptome analysis of the eye reveals dynamic seasonal changes in the expression of genes encoding photopigments and their downstream signaling components, suggesting that plasticity in phototransduction is crucial for seasonal changes in color perception. We have also performed transcriptome analysis using medaka hypothalamus and pituitary gland and found that an uncharacterized long non-coding RNA (lncRNA) is strongly regulated by photoperiod. Since knockout medaka of this lncRNA show different responses to stress, we propose that photoperiodic regulation of this lncRNA modulates seasonal changes in behavior. Although humans are not typically considered seasonal, some evidence suggests that seasonal variation in physiology and behavior do exist. Seasonal affective disorder patients, experiencing recurrent winter episodes of depressed mood, show electroretinogram changes in winter with lower sensitivity compared with healthy subjects. I will discuss how we can better understand seasonal changes in behavior using unique animal models.