Ancestral TSH mechanism signals summer in a photoperiodic mammal

Elodie A. Hanon, Gerald A. Lincoln, Jean-Michel Fustin, Hugues Dardente, Mireille Masson-Pevet, Peter J. Morgan, David G. Hazlerigg

Research output: Contribution to journalArticlepeer-review


In mammals, day-length-sensitive (photoperiodic) seasonal breeding cycles depend on the pineal hormone melatonin, which modulates secretion of reproductive hormones by the anterior pituitary gland [1]. It is thought that melatonin acts in the hypothalamus to control reproduction through the release of neurosecretory signals into the pituitary portal blood supply, where they act on pituitary endocrine cells [2]. Contrastingly, we show here that during the reproductive response of Soay sheep exposed to summer day lengths, the reverse applies: Melatonin acts directly on anterior-pituitary cells, and these then relay the photoperiodic message back into the hypothalamus to control neuroendocrine output. The switch to long clays causes melatonin-responsive cells in the pars tuberalis (PT) of the anterior pituitary to increase production of thyrotrophin (TSH). This acts locally on TSH-receptor-expressing cells in the adjacent mediobasal hypothalamus, leading to increased expression of type 11 thyroid hormone deiodinase (13102). DIO2 initiates the summer response by increasing hypothalamic tri-iodothyronine (T3) levels. These data and recent findings in quail [3] indicate that the TSH-expressing cells of the PT play an ancestral role in seasonal reproductive control in vertebrates. In mammals this provides the missing link between the pineal melatonin signal and thyroid-dependent seasonal biology.

Original languageEnglish
Pages (from-to)1147-1152
Number of pages6
JournalCurrent Biology
Issue number15
Publication statusPublished - 5 Aug 2008


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