Yes / Animals have evolved diverse seasonal variations in physiology and reproduction to accommodate yearly changes in environmental and climatic conditions. These changes in physiology are initiated by changes in photoperiod (daylength) and are mediated through melatonin, which relays photoperiodic information to the pars tuberalis of the pituitary gland. Melatonin drives thyroidâstimulating hormone transcription and synthesis in the pars tuberalis, which, in turn, regulates thyroid hormone and retinoic acid synthesis in the tanycytes lining the third ventricle of the hypothalamus. Seasonal variation in central thyroid hormone signalling is conserved among photoperiodic animals. Despite this, different species adopt divergent phenotypes to cope with the same seasonal changes. A common response amongst different species is increased hypothalamic cell proliferation/neurogenesis in short photoperiod. That cell proliferation/neurogenesis may be important for seasonal timing is based on (i) the neurogenic potential of tanycytes; (ii) the fact that they are the locus of striking seasonal morphological changes; and (iii) the similarities to mechanisms involved in de novo neurogenesis of energy balance neurones. We propose that a decrease in hypothalamic thyroid hormone and retinoic acid signalling initiates localised neurodegeneration and apoptosis, which leads to a reduction in appetite and body weight. Neurodegeneration induces compensatory cell proliferation from the neurogenic niche in tanycytes and new cells are born under short photoperiod. Because these cells have the potential to differentiate into a number of different neuronal phenotypes, this could provide a mechanistic basis to explain the seasonal regulation of energy balance, as well as reproduction. This cycle can be achieved without changes in thyroid hormone/retinoic acid and explains recent data obtained from seasonal animals held in natural conditions. However, thyroid/retinoic acid signalling is required to synchronise the cycles of apoptosis, proliferation and differentiation. Thus, hypothalamic neurogenesis provides a framework to explain diverse photoperiodic responses. / MRC. Grant Number: MR/P012205/1 - Scottish Government - BBSRC. Grant Number: BB/K001043/1 - Physiological Society
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/16819 |
| Date | 26 December 2018 |
| Creators | Helfer, Gisela, Barrett, P., Morgan, P.J. |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Article, Accepted manuscript |
| Rights | © 2019 Wiley This is the peer reviewed version of the following article: Helfer G, Barrett P and Morgan PJ (2019) A unifying hypothesis for control of body weight and reproduction in seasonally breeding mammals. Journal of Neuroendocrinology. 31(3): e12680, which has been published in final form at https://doi.org/10.1111/jne.12680. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. |
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