Seasonal regulation of the lncRNA LDAIR modulates self-protective behaviours during the breeding season.

To cope with seasonal environmental changes, animals adapt their physiology and behaviour in response to photoperiod. However, the molecular mechanisms underlying these adaptive changes are not completely understood. Here, using genome-wide expression analysis, we show that an uncharacterized long noncoding RNA (lncRNA), LDAIR, is strongly regulated by photoperiod in Japanese medaka fish (Oryzias latipes). Numerous transcripts and signalling pathways are activated during the transition from short- to long-day conditions; however, LDAIR is one of the first genes to be induced and its expression shows a robust daily rhythm under long-day conditions. Transcriptome analysis of LDAIR knockout fish reveals that the LDAIR locus regulates a gene neighbourhood, including corticotropin releasing hormone receptor 2, which is involved in the stress response. Behavioural analysis of LDAIR knockout fish demonstrates that LDAIR affects self-protective behaviours under long-day conditions. Therefore, we propose that photoperiodic regulation of corticotropin releasing hormone receptor 2 by LDAIR modulates adaptive behaviours to seasonal environmental changes.

Dynamic plasticity in phototransduction regulates seasonal changes in color perception.

To cope with seasonal changes in the environment, organisms adapt their physiology and behavior. Although color perception varies among seasons, the underlying molecular basis and its physiological significance remain unclear. Here we show that dynamic plasticity in phototransduction regulates seasonal changes in color perception in medaka fish. Medaka are active and exhibit clear phototaxis in conditions simulating summer, but remain at the bottom of the tank 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 pathways. Behavioral analysis of photopigment-null fish shows significant differences from wild type, suggesting that plasticity in color perception is crucial for the emergence of seasonally regulated behaviors.Animal coloration and behavior can change seasonally, but it is unclear if visual sensitivity to color shifts as well. Here, Shimmura et al. show that medaka undergo seasonal behavioral change accompanied by altered expression of opsin genes, resulting in reduced visual sensitivity to mates during winter-like conditions.

The saccus vasculosus of fish is a sensor of seasonal changes in day length.

The pars tuberalis of the pituitary gland is the regulatory hub for seasonal reproduction in birds and mammals. Although fish also exhibit robust seasonal responses, they do not possess an anatomically distinct pars tuberalis. Here we report that the saccus vasculosus of fish is a seasonal sensor. We observe expression of key genes regulating seasonal reproduction and rhodopsin family genes in the saccus vasculosus of masu salmon. Immunohistochemical studies demonstrate that all of these genes are expressed in the coronet cells of the saccus vasculosus, suggesting the existence of a photoperiodic signalling pathway from light input to neuroendocrine output. In addition, isolated saccus vasculosus has the capacity to respond to photoperiodic signals, and its removal abolishes photoperiodic response of the gonad. Although the physiological role of the saccus vasculosus has been a mystery for several centuries, our findings indicate that the saccus vasculosus acts as a sensor of seasonal changes in day length in fish.