Your browser version may not work well with NCBI's Web applications. More information here...
1: Curr Biol. 2008 Aug 5;18(15):1147-52.
Related Articles, Links
Click here to read Click here to read
Comment in:
Ancestral TSH mechanism signals summer in a photoperiodic mammal.

Hanon EA, Lincoln GA, Fustin JM, Dardente H, Masson-Pévet M, Morgan PJ, Hazlerigg DG.

School of Biological Sciences, University of Aberdeen, Aberdeen, Scotland.

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 days 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 II thyroid hormone deiodinase (DIO2). 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.

Publication Types:
PMID: 18674911 [PubMed - indexed for MEDLINE]