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Molecular Endocrinology Group, Division of Obesity and Metabolic Health and Aberdeen Centre for Energy Regulation and Obesity (ACERO), Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, UK
¹ Faculty of Life Sciences, University of Manchester, Stopford Building, Oxford Road, Manchester M13 9PT, UK
² School of Biomedical Sciences, University of Nottingham Medical School, Nottingham NG7 2UH, UK

(Requests for offprints should be addressed to P Barrett; Email: pb{at}rri.sari.ac.uk)

(Current address of E Scott Graham is Department of Pharmacology, Medical and Health Sciences, University of Auckland, Auckland, New Zealand)

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.

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