Clocks for all seasons: unwinding the roles and mechanisms of circadian and interval timers in the hypothalamus and pituitary

Wood, Shona H.; Loudon, A. S. I.

doi:10.1530/joe-14-0141e

Cited by 37 publications

(51 citation statements)

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“…This most likely reflects the well‐characterised susceptibility of PRL secretion to various unpredictable stressors such as noise or human activity and temperature fluctuations, which are common in open barns but very limited in our light‐tight building. PRL displays a seasonal pattern of secretion, with higher levels during spring and summer and a rapid increase or decrease upon acute exposure to longer or shorter daylengths, respectively . Photoperiodic history also affects the long‐day response of PRL secretion in ewes .…”

Section: Discussionmentioning

confidence: 99%

“…To achieve this, melatonin targets a peculiar population of thyrotrophs within the pars tuberalis (PT) of the pituitary, leading to seasonal expression of Tshb and hundreds of genes expressed in the PT and mediobasal hypothalamus (MBH) . PT‐specific thyrotrophin ( TSH ) appears to be the crux of photoperiod‐dependent seasonal timing because it connects melatonin input with local hypothalamic triiodothyronine (T3) output via the induction of deiodinase 2 ( Dio2 ) in tanycytes lining the infra‐lateral walls of the adjacent third ventricle . Although the basics of this TSH‐DIO2‐T3 axis have been well characterised in birds and mammals, cellular and molecular mechanisms that link T3 to seasonal gonadotrophin‐releasing hormone (GnRH) output, and hence to control of the pituitary response and gonadal axis, remain unclear.…”

Section: Introductionmentioning

confidence: 99%

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Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

Dardente

Lomet

Chesneau

et al. 2019

J Neuroendocrinology

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In mammals, melatonin is responsible for the synchronisation of seasonal cycles to the solar year. Melatonin is secreted by the pineal gland with a profile reflecting the duration of the night and acts via the pituitary pars tuberalis (PT), which in turn modulates hypothalamic thyroid hormone status via seasonal changes in the production of locally-acting thyrotrophin. Recently, we demonstrated that, in the Soay sheep, photoperiodic induction of Tshb expression and consequent downstream hypothalamic changes occur over a narrow range of photoperiods between 12 and 14 hours in duration. In the present study, we aimed to extend our molecular characterisation of this pathway, based on transcriptomic analysis of photoperiodic changes in the pituitary and hypothalamus of ovariectomised, oestradiol-implanted Ile-de-France ewes. We demonstrate that photoperiodic treatments applied before the winter solstice elicit two distinctive modes of accelerated reproductive switch off compared to ewes held on a simulated natural photoperiod, with shut-down occurring markedly faster on photoperiods of 13 hours or more than on photoperiods of 12 hours and less. This pattern of response was reflected in gene expression profiles of photoperiodically sensitive markers, both in the PT (Tshb, Fam150b, Vmo1, Ezh2 and Suv39H2) and in tanycytes (Tmem252 and Dct). Unexpectedly, the expression of Dio2 in tanycytes did not show any noticeable increase in expression with lengthening photoperiods. Finally, the expression of Kiss1, the key activator of gonadotrophin-releasing hormone release, was proportionately decreased by lengthening photoperiods, in a pattern that correlated strongly with gonadotrophin suppression. These data show that stepwise increases in photoperiod lead to graded molecular responses at the level of the PT, a progressive suppression of Kiss1 in the hypothalamic arcuate nucleus and luteinising hormone/ follicle-stimulating hormone release by the pituitary, despite apparently unchanged Dio2 expression in tanycytes. We hypothesise that this apparent discontinuity in the seasonal neuroendocrine response illustrates the transient nature of the thyroid hormone-mediated response to long days in the control of circannual timing.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

Dardente

Lomet

Chesneau

et al. 2019

J Neuroendocrinology

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show abstract

“…Although thyroid secretion of the prohormone T4 does not change seasonally [27], hypothalamic expression of deiodinase enzymes catabolizing T4 into the receptor-active triiodothyronine T3 (DIO2) or the receptor-inactive enantiomer (DIO3) are regulated by changes in photoperiod [2829303132], providing a seasonal gating mechanism for thyroid hormone receptor signaling. Winter photoperiods elevate dio3 expression, quench T3 signaling, and inhibit gonadotropin secretion, whereas spring/summer photoperiods elevate dio2 expression, enhance T3 signaling, and stimulate gonadotropin release [282930313233]. …”

Section: Discussionmentioning

confidence: 99%

Chronobiological Hypothesis about the Association Between Height Growth Seasonality and Geographical Differences in Body Height According to Effective Day Length

Yokoya

Higuchi

2016

J Circadian Rhythms

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Studies on growth hormone therapy in children have shown that height velocity is greater in summer than in winter and that this difference increases with latitude. It is hypothesized that summer daylight is a causative factor and that geographical distribution of body height will approximate the distribution of summer day length over time. This is an ecological analysis of prefecture-level data on the height of Japanese youth. Mesh climatic data of effective day length were collated. While height velocity was greatest during the summer, the height of Japanese youth was strongly and negatively correlated with the distribution of winter effective day length. Therefore, it is anticipated that summer height velocity is greater according to winter day length (dark period). This may be due to epigenetic modifications, involving reversible DNA methylation and thyroid hormone regulation found in the reproductive system of seasonal breeding vertebrates. If the function is applicable to humans, summer height growth may quantitatively increase with winter day length, and height growth seasonality can be explained by thyroid hormone activities that-induced by DNA methylation-change depending on the seasonal difference in day length. Moreover, geographical differences in body height may be caused by geographical differences in effective day length, which could influence melatonin secretion among subjects who spend a significant time indoors.

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“…By stark contrast to the molecular gears of the circadian clock, which have been unravelled in several model organisms, our current understanding of the mechanisms driving seasonal switches in physiology is fragmentary. In both mammals and birds, the current model emphasises the role of the pars tuberalis (PT) of the pituitary . The PT translates the photoperiodic message into a seasonal output of thyroid‐stimulating hormone ( TSH) , which then acts on tanycytes of the neighbouring mediobasal hypothalamus (MBH) through its cognate TSH receptor (TSHR).…”

Section: Introductionmentioning

confidence: 99%

Photoperiod and thyroid hormone regulate expression of l‐dopachrome tautomerase (Dct), a melanocyte stem‐cell marker, in tanycytes of the ovine hypothalamus

Dardente

Lomet

2018

J Neuroendocrinology

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The pars tuberalis (PT) of the pituitary is central to the control of seasonal breeding. In mammals, the PT translates the photoperiodic message carried by melatonin into an endocrine thyroid-stimulating hormone output, which controls local thyroid hormone (TH) signalling in tanycytes of the neighbouring hypothalamus. In the present study, we identify l-dopachrome tautomerase (Dct) as a novel marker of ovine tanycytes and show that Dct displays marked seasonal variations in expression, with higher levels during spring and summer. This seasonal profile is photoperiod-dependent because an acute exposure to long days induces Dct expression. In addition, we find that TH also modulates Dct expression. DCT functions as an enzyme in the melanin synthesis pathway within skin melanocytes, whereas expression in other tissues is comparatively low. We demonstrate that both Tyr and Tyrp1, which are enzymes that intervene upstream and downstream of Dct in the melanin synthesis pathway, respectively, are expressed at very low levels in the ovine hypothalamus. This suggests that Dct in tanycytes may not be involved in melanin synthesis. We speculate that DCT function is linked to its protective role towards oxidative stress and/or its function in the control of neural progenitor cell proliferation.

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Clocks for all seasons: unwinding the roles and mechanisms of circadian and interval timers in the hypothalamus and pituitary

Cited by 37 publications

References 0 publications

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

Discontinuity in the molecular neuroendocrine response to increasing daylengths in Ile‐de‐France ewes: Is transient Dio2 induction a key feature of circannual timing?

Chronobiological Hypothesis about the Association Between Height Growth Seasonality and Geographical Differences in Body Height According to Effective Day Length

Photoperiod and thyroid hormone regulate expression of l‐dopachrome tautomerase (Dct), a melanocyte stem‐cell marker, in tanycytes of the ovine hypothalamus

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