Diurnal and photoperiodic changes in thyrotrophin-stimulating hormone β expression and associated regulation of deiodinase enzymes (DIO2, DIO3) in the female juvenile chicken hypothalamus.

I C Dunn,A S I Loudon,P J Sharp,P W Wilson,D W Burt,Y Shi

doi:10.1111/jne.12554

Abstract

Increased thyrotrophin‐stimulating hormone β (TSHβ) expression in the pars tuberalis is assumed to be an early step in the neuroendocrine mechanism transducing photoperiodic information. The present study aimed to determine the relationship between long‐photoperiod (LP) and diurnal TSHβ gene expression in the juvenile chicken by comparing LP‐photostimulated birds with groups kept on a short photoperiod (SP) for 1 or 12 days. TSHβ expression increased by 3‐ and 23‐fold after 1 and 12 days of LP‐photostimulation both during the day and at night. Under both SP and LP conditions, TSHβ expression was between 3‐ and 14‐fold higher at night than in the day, suggesting that TSHβ expression cycles in a diurnal pattern irrespective of photoperiod. The ratio of DIO2/3 was decreased on LPs, consequent to changes in DIO3 expression, although there was no evidence of any diurnal effect on DIO2 or DIO3 expression. Plasma prolactin concentrations revealed both an effect of LPs and time‐of‐day. Thus, TSHβ expression changes in a dynamic fashion both diurnally and in response to photoperiod.

Highlights

Increased thyrotrophin-stimulating hormone β (TSHβ) expression in the pars tuberalis is assumed to be an early step in the neuroendocrine mechanism transducing photoperiodic information to the reproductive axis, driving thyroid hormone conversion in adjacent ependymal tanycyte cells of the ventral hypothalamus.[1]
We have demonstrated that juvenile domesticated chickens have as robust a photoperiodic response in terms of TSHβ expression and changes in the ratio of DIO2/3 expression as that previously observed in quail.[1]
In the present study, there is no evidence that DIO2 is affected by photostimulation in juvenile chickens as it is in quail

Summary

Introduction

Increased thyrotrophin-stimulating hormone β (TSHβ) expression in the pars tuberalis is assumed to be an early step in the neuroendocrine mechanism transducing photoperiodic information to the reproductive axis, driving thyroid hormone conversion in adjacent ependymal tanycyte cells of the ventral hypothalamus.[1]. EYA3 is a transcriptional activator of the TSHβ promoter and fulfills the requirements to be part of the internal coincidence model proposed to explain the interaction of light and the circadian system.[10] The pars tuberalis is known to regulate other seasonal hormones, such as prolactin via paracrine regulation of adjacent lactotroph cells, with this not involving thyroid hormone conversion. A number of pars tuberalis-specific signals have been proposed as prolactin

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