Thyroid hormone and hypothalamic stem cells in seasonal functions

Area of Science:

• Endocrinology
• Neuroscience
• Chronobiology

Background:

• Seasonal rhythms are crucial for organismal life cycles, regulated by internal circannual clocks.
• Daylength (photoperiod) is a primary environmental cue for these clocks.
• In vertebrates, photoperiodic information is transduced via the pituitary pars tuberalis (PT) and thyroid hormones (TH).

Purpose of the Study:

• To review the molecular and neuroendocrine pathways linking photoperiod to seasonal physiological changes.
• To discuss the role of tanycytes, TH, and cell proliferation in seasonal timing.
• To highlight the tanycyte as a potential photoperiod-sensitive stem cell niche.

Main Methods:

• Literature review of molecular and neuroendocrine mechanisms.
• Analysis of the photoperiodic control of TSH production.
• Investigation of tanycyte regulation of deiodinases (Dio 2/3) and TH availability.

Main Results:

• Photoperiod regulates TSH production in the PT, influencing hypothalamic TH levels.
• Tanycytes, regulated by PT-TSH, control local TH availability via Dio 2/3.
• TH influences cell proliferation and differentiation, suggesting a role in seasonal tanycyte stem cell dynamics.

Conclusions:

• Tanycytes are key mediators in translating photoperiodic signals into seasonal physiological adjustments.
• Seasonal control of tanycyte proliferation is a potential mechanism for synchronizing physiological rhythms.
• Understanding this pathway offers insights into the neuroendocrine basis of seasonal timing.