|Graduate School of Bioagricultural Sciences, Department of Applied Molecular Biosciences, Professor; Avian Bioscience Research Center, Director|
|Doctorate||Doctor of Agriculture|
|Research interests||Mechanism of seasonal time measurement in vertebrates|
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The appropriate timing of various seasonal processes, such as migration, hibernation, and reproduction, is crucial to the survival of animals living in temperate regions. Reproductive seasonality ensures the birth of young in spring or summer, as is appropriate for survival. The goal of our project is to understand the molecular basis of seasonal time measurement in vertebrates.
Among various vertebrates, birds have evolved especially sophisticated photoperiodic mechanisms, and among them, the Japanese quail (Coturnix japonica) has proved to be an excellent model for examining photoperiodism. The chain of events, all of which lie within the brain, involves a photoreceptor, a clock (calendar) to measure daylength, and neural circuitry to trigger the increased secretion of gonadotropin releasing hormone (GnRH) and, hence, gonadotropin from the pituitary gland. Many of these functions are thought to involve areas within the mediobasal hypothalamus (MBH). Using Japanese quail as a model species, we have recently uncovered a gene cascade for these effects. Functional genomics analysis has shown that long day stimulus induces production of thyrotropin (thyroid stimulating hormone: TSH) in the pars tuberalis of the pituitary gland, which triggers the expression of thyroid hormone-activating enzyme (Dio2) in the MBH. Dio2 converts the prohormone, thyroxine (T4), into its bioactive form, triiodothyronine (T3). Local thyroid hormone catabolism within the MBH by Dio2 regulates seasonal reproduction. Using TSH receptor-null mice we have also demonstrated that above mentioned gene cascades are conserved in mammals. Seasonal reproduction is a rate-limiting factor for animal production. The results of our project will contribute to the improvement of animal production.