Search Results
You are looking at 1 - 4 of 4 items for
- Author: Andrew Loudon x
- Refine by access: All content x
Search for other papers by Shona Wood in
Google Scholar
PubMed
Search for other papers by Andrew Loudon in
Google Scholar
PubMed
Adaptation to the environment is essential for survival, in all wild animal species seasonal variation in temperature and food availability needs to be anticipated. This has led to the evolution of deep-rooted physiological cycles, driven by internal clocks, which can track seasonal time with remarkable precision. Evidence has now accumulated that a seasonal change in thyroid hormone (TH) availability within the brain is a crucial element. This is mediated by local control of TH-metabolising enzymes within specialised ependymal cells lining the third ventricle of the hypothalamus. Within these cells, deiodinase type 2 enzyme is activated in response to summer day lengths, converting metabolically inactive thyroxine (T4) to tri-iodothyronine (T3). The availability of TH in the hypothalamus appears to be an important factor in driving the physiological changes that occur with season. Remarkably, in both birds and mammals, the pars tuberalis (PT) of the pituitary gland plays an essential role. A specialised endocrine thyrotroph cell (TSH-expressing) is regulated by the changing day-length signal, leading to activation of TSH by long days. This acts on adjacent TSH-receptors expressed in the hypothalamic ependymal cells, causing local regulation of deiodinase enzymes and conversion of TH to the metabolically active T3. In mammals, the PT is regulated by the nocturnal melatonin signal. Summer-like melatonin signals activate a PT-expressed clock-regulated transcription regulator (EYA3), which in turn drives the expression of the TSHβ sub-unit, leading to a sustained increase in TSH expression. In this manner, a local pituitary timer, driven by melatonin, initiates a cascade of molecular events, led by EYA3, which translates to seasonal changes of neuroendocrine activity in the hypothalamus. There are remarkable parallels between this PT circuit and the photoperiodic timing system used in plants, and while plants use different molecular signals (constans vs EYA3) it appears that widely divergent organisms probably obey a common set of design principles.
Search for other papers by Shona Wood in
Google Scholar
PubMed
Search for other papers by Andrew Loudon in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Perry Barrett in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Elena Ivanova in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by E Scott Graham in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Alexander W Ross in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Dana Wilson in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Helene Plé in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Julian G Mercer in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Francis J Ebling in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Sandrine Schuhler in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Sandrine M Dupré in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Andrew Loudon in
Google Scholar
PubMed
Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK
Search for other papers by Peter J Morgan in
Google Scholar
PubMed
Tanycytes in the ependymal layer of the third ventricle act both as a barrier and a communication gateway between the cerebrospinal fluid, brain and portal blood supply to the pituitary gland. However, the range, importance and mechanisms involved in the function of tanycytes remain to be explored. In this study, we have utilized a photoperiodic animal to examine the expression of three unrelated gene sequences in relation to photoperiod-induced changes in seasonal physiology and behaviour. We demonstrate that cellular retinoic acid-binding protein 1 (CRBP1), a retinoic acid transport protein, GPR50, an orphan G-protein-coupled receptor and nestin, an intermediate filament protein, are down-regulated in short-day photoperiods. The distribution of the three sequences is very similar, with expression located in cells with tanycyte morphology in the region of the ependymal layer where tanycytes are located. Furthermore, CRBP1 expression in the ependymal layer is shown to be independent of a circadian clock and altered testosterone levels associated with testicular regression in short photo-period. Pinealectomy of Siberian hamsters demonstrates CRBP1 expression is likely to be dependent on melatonin output from the pineal gland. This provides evidence that tanycytes are seasonally responsive cells and are likely to be an important part of the mechanism to facilitate seasonal physiology and behaviour in the Siberian hamster.
Search for other papers by Perry Barrett in
Google Scholar
PubMed
Search for other papers by Elena Ivanova in
Google Scholar
PubMed
Search for other papers by E Scott Graham in
Google Scholar
PubMed
Search for other papers by Alexander W Ross in
Google Scholar
PubMed
Search for other papers by Dana Wilson in
Google Scholar
PubMed
Search for other papers by Helene Plé in
Google Scholar
PubMed
Search for other papers by Julian G Mercer in
Google Scholar
PubMed
Search for other papers by Francis J Ebling in
Google Scholar
PubMed
Search for other papers by Sandrine Schuhler in
Google Scholar
PubMed
Search for other papers by Sandrine M Dupré in
Google Scholar
PubMed
Search for other papers by Andrew Loudon in
Google Scholar
PubMed
Search for other papers by Peter J Morgan in
Google Scholar
PubMed
