HomeGCOE Researchers >Takashi YOSHIMURA

GCOE Researchers

Takashi YOSHIMURA

Affiliation
/Position
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
address takashiy@agr.nagoya-u.ac.jp
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+81-52-789-4050
  Laboratory

Outline of research

 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.

References

  1. Yasuo S. et al. (2009) Melatonin transmits photoperiodic signals through the MT1 melatonin receptor. J. Neurosci. 29: 2885-2889.
  2. Tomida S. et al. (2009) Identification of Usp46, encoding a ubiquitin specific peptidase, as a quantitative trait gene regulating mouse immobile behavior in the tail suspension test and the forced swimming test. Nature Genet. 41: 688-695.
  3. Ono H. et al. (2008) Involvement of thyrotropin in photoperiodic signal transduction in mice. Proc. Natl. Acad. Sci. USA. 105: 18238-18242.
  4. Nakao N. et al., (2008) Thyrotrophin in the pars tuberalis triggers photoperiodic response. Nature 452: 317-322.
  5. Takagi T. et al. (2007) Involvement of TGFa in the photoperiodic regulation of reproduction in birds. Endocrinology 148: 2788-2792.
  6. Nakao N. et al. (2007) Circadian clock gene regulation of steroidogenic acute regulatory protein gene expression in pre-ovulatory ovarian follicles. Endocrinology 148: 3031-3038.
  7. Yasuo S. et al. (2006) Long day suppressed expression of type 2 deiodinase gene in the mediobasal hypothalamus of the Saanen goat, a short day breeder: Implication for seasonal window of thyroid hormone action on reproductive neuroendocrine axis. Endocrinology 147: 432-440.
  8. Yasuo S. et al. (2005) The reciprocal switching of two thyroid hormone activating and inactivating enzyme genes is involved in the photoperiodic gonadal response of Japanese quail. Endocrinology 146: 2551-2554.
  9. Watanabe M. et al. (2004) Photoperiodic regulation of type 2 deiodinase gene in Djungarian hamster: possible homologies between avian and mammalian photoperiodic regulation of reproduction. Endocrinology 145: 1546-1549.
  10. Yoshimura T. et al. (2003) Light-induced hormone conversion of T4 to T3 regulates photoperiodic response of gonads in birds. Nature 426: 178-181.