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Hypothesis: cyclical histogenesis is the basis of circannual timing.
MedLine Citation:
PMID:  22215606     Owner:  NLM     Status:  In-Data-Review    
Circannual rhythms are innately timed long-term (tau ≈ 12 months) cycles of physiology and behavior, crucial for life in habitats ranging from the equator to the Poles. Here the authors propose that circannual rhythm generation depends on tissue-autonomous, reiterated cycles of cell division, functional differentiation, and cell death. They see the feedback control influencing localized stem cell niches as crucial to this cyclical histogenesis hypothesis. Analogous to multi-oscillator circadian organization, circannual rhythm generation occurs in multiple tissues with hypothalamic and pituitary sites serving as central pacemakers. Signals including day length, nutrition, and social factors can synchronize circannual rhythms through hormonal influences, notably via the thyroid and glucocorticoid axes, which have profound effects on histogenesis. The authors offer 4 arguments in support of this hypothesis: (1) Cyclical histogenesis is a prevalent process in seasonal remodeling of physiology. It operates over long time domains and exhibits tissue autonomy in its regulation. (2) Experiments in which selected peripheral endocrine signals are held constant indicate that circannual rhythms are not primarily the product of interacting hormonal feedback loops. (3) Hormones known to control cell proliferation, differentiation, and organogenesis profoundly affect circannual rhythm expression. (4) The convergence point between photoperiodic input pathways and circannual rhythm expression occurs in histogenic regions of the hypothalamus and pituitary. In this review, the authors discuss how testing this hypothesis will depend on the use of cellular/molecular tools and animal models borrowed from developmental biology and neural stem cell research.
David G Hazlerigg; Gerald A Lincoln
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Journal of biological rhythms     Volume:  26     ISSN:  1552-4531     ISO Abbreviation:  J. Biol. Rhythms     Publication Date:  2011 Dec 
Date Detail:
Created Date:  2012-01-04     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  8700115     Medline TA:  J Biol Rhythms     Country:  United States    
Other Details:
Languages:  eng     Pagination:  471-85     Citation Subset:  IM    
*Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, Scotland, UK.
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