Characterizing a Mammalian Circannual Pacemaker

@article{Lincoln2006CharacterizingAM,
  title={Characterizing a Mammalian Circannual Pacemaker},
  author={Gerald Lincoln and Iain J Clarke and Roelof A. Hut and David G. Hazlerigg},
  journal={Science},
  year={2006},
  volume={314},
  pages={1941 - 1944}
}
Many species express endogenous cycles in physiology and behavior that allow anticipation of the seasons. The anatomical and cellular bases of these circannual rhythms have not been defined. Here, we provide strong evidence using an in vivo Soay sheep model that the circannual regulation of prolactin secretion, and its associated biology, derive from a pituitary-based timing mechanism. Circannual rhythm generation is seen as the product of the interaction between melatonin-regulated timer cells… 

A Physiological Model of a Circannual Oscillator

A physiological model of a circannual rhythm generator centered in the pituitary gland based on the interaction between melatonin-responsive cells in the pars tuberalis that act to decode photoperiod, and lactotroph cells of the adjacent pars distalis that secrete prolactin is presented.

Mammalian circannual pacemakers.

It is proposed that circannual timing involves mechanisms that are integral to the ontogenetic life-history programme where annual transitions are generated by cell birth, death and tissue regeneration throughout the life cycle--the histogenesis hypothesis.

Stem Cell Regulation of Circannual Rhythms

This chapter conjecture that all three mechanisms can contribute to the generation of the seasonal phenotype in complex organisms, different for each species, and that an evolutionally conserved, cell-autonomous mechanism may be expressed in stem cells to act as a pacemaker for circannual timing.

Circannual rhythms in birds

The present review outlines the basics ofcircannual rhythms, its interaction with environmental factors, differences between the two mechanisms that regulate seasonal responses in organisms i.e. photoperiodism and circannual rhythm, and also presents some experiments which have demonstrated circann annual rhythm in reproduction, migration and molt behaviour of birds.

Circannual prolactin rhythms: calendar-like timer revealed in the pituitary gland

  • M. Duncan
  • Biology, Medicine
    Trends in Endocrinology & Metabolism
  • 2007

Circadian Timekeeping and Multiple Timescale Neuroendocrine Rhythms

The recent evidence suggesting that the circadian clock genes that pace the authors' daily rhythms may also contribute to the regulation of pituitary pulsatility, even in the non 24‐h range is summarized.

A riot of rhythms: neuronal and glial circadian oscillators in the mediobasal hypothalamus

These results provide the first single cell resolution of endogenous circadian rhythms in clock gene expression in any intact tissue outside the SCN, reveal the cellular basis for tissue level damping in extra-SCN oscillators and demonstrate that an oscillator in the ME/PT is responsive to changes in metabolism.

Epigenetic Mechanisms Regulating Circannual Rhythms

A Dual Compartmentalization Model is proposed in which the first compartment is composed of stem/primordial cells and provides the initiation signal for the circannual cycle, and the second compartment is formed of differentiated cells that propagate and amplify the circANNual cycle.

Hypothesis: cyclical histogenesis is the basis of circannual timing.

The authors propose that circannual rhythm generation depends on tissue-autonomous, reiterated cycles of cell division, functional differentiation, and cell death, and see the feedback control influencing localized stem cell niches as crucial to this cyclical histogenesis hypothesis.
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