Takashi Yoshimura

Animals that inhabit mid- to high-latitude regions exhibit various adaptive behaviors, such as migration, reproduction, molting and hibernation in response to seasonal cues. These adaptive behaviors are tightly regulated by seasonal changes in photoperiod, the relative day length vs night length. Recently, the regulatory pathway of seasonal reproduction has been elucidated using quail. In birds, deep brain photoreceptors receive and transmit light information to the pars tuberalis in the pituita

Most vertebrates living outside the tropical zone show robust physiological responses in response to seasonal changes in photoperiod, such as seasonal reproduction, molt, and migration. The highly sophisticated photoperiodic mechanism in Japanese quail has been used to uncover the mechanism of seasonal reproduction. Molecular analysis of quail mediobasal hypothalamus (MBH) revealed that local thyroid hormone activation within the MBH plays a critical role in the photoperiodic response of gonads.

Organisms living outside the tropics measure the changes in the length of the day to adapt to seasonal changes in the environment. Animals that breed during spring and summer are called long-day breeders, while those that breed during fall are called short-day breeders. Although the influence of thyroid hormone in the regulation of seasonal reproduction has been known for several decades, its precise mechanism remained unknown. Recent studies revealed that the activation of thyroid hormone withi

Thyroid-stimulating hormone (TSH; thyrotropin) is a glycoprotein secreted from the pituitary gland. Pars distalis-derived TSH (PD-TSH) stimulates the thyroid gland to produce thyroid hormones (THs), whereas pars tuberalis-derived TSH (PT-TSH) acts on the hypothalamus to regulate seasonal physiology and behavior. However, it had not been clear how these two TSHs avoid functional crosstalk. Here, we show that this regulation is mediated by tissue-specific glycosylation. Although PT-TSH is released

Circadian rhythms are generated by an internal biological clock. The suprachiasmatic nucleus (SCN) in the hypothalamus is known to be the dominant biological clock regulating circadian rhythms in mammals. In birds, two nuclei, the so-called medial SCN (mSCN) and the visual SCN (vSCN), have both been proposed to be the avian SCN. However, it remains an unsettled question which nuclei are homologous to the mammalian SCN. We have identified circadian clock genes in Japanese quail and demonstrated t

In temperate zones, animals use changes in day length as a calendar to time their breeding season. However, the photoreceptive and neuroendocrine mechanisms of seasonal reproduction are considered to differ markedly between birds and mammals. This can be understood from the fact that the eye is the only photoreceptive organ, and melatonin mediates the photoperiodic information in mammals, whereas in birds, photoperiodic information is directly received by the deep brain photoreceptors and melato