A research group led by Professor Takashi Yoshimura of Nagoya University, in collaboration with the National Institute for Basic Biology/Center for Life Creation Exploration, has revealed that medaka fish have a ``circadian clock'' that ticks endogenous rhythms. For the first time in the world, we have identified the ``circadian gene'' that determines the rhythm of the year.
Through the process of evolution, living things have acquired mechanisms to predict and proactively respond to the seasonal changes that inevitably occur every year, such as breeding in the spring and migrating or hibernating in the winter. This is the ``circadian clock,'' an internal body clock that keeps track of the endogenous rhythms of the year. However, there is no living organism whose mechanism has been clarified.
The research group raised medaka fish outdoors for two years under natural conditions and observed changes in the development of their gonads (ovaries). As a result, they found that the ovaries of female medaka develop in April and May every year, and after regressing during the rainy season, they develop again in July and August, showing a clear rhythm.
Furthermore, when the hypothalamus and pituitary gland of the medaka brain were collected and analyzed every month for two years, 2 genes were found to have a yearly rhythm. Among them, they identified 3,341 ``circadian genes'' that have a rhythm of approximately 1 year under constant conditions in the laboratory without seasonal changes. Of these 1 genes, 518 genes are thought to be particularly important because they share a yearly rhythm both under natural outdoor conditions and under constant conditions in the laboratory, and analysis revealed that genes involved in cell division and differentiation. It turned out that there are many.
In humans, heart disease, cerebrovascular disease, pneumonia, influenza, and mental illnesses such as depression, bipolar disorder, and schizophrenia become more severe in winter, and mortality rates rise markedly in winter, but the mechanism is unclear. In the future, progress in circadian genetic research is expected to elucidate the molecular mechanisms of seasonal rhythms in various organisms, including the molecular mechanisms of seasonal diseases in humans.
Paper information:[Proceedings of the National Academy of Sciences, USA] A transcriptional program underlying the circannual rhythms of gonadal development in medaka
