Temporal Dynamics of Type 2 Deiodinase Expression after Melatonin Injections in Syrian Hamsters

Abstract

In many species living in temperate zones, reproduction is controlled by the photoperiod. Recent findings have clarified that type 2 iodothyronine deiodinase (Dio2) plays a significant role in the photoperiodic response of gonads in the mediobasal hypothalamus, converting the prohormone T(4) into bioactive T(3). In mammals, Dio2 expression is suppressed by long-term melatonin injections, although the signal transduction pathways that link the melatonin signal to Dio2 expression are unknown. As a first step to approach the problem, we have here investigated the temporal dynamics of the melatonin effect on Dio2 expression using male Syrian hamsters. Dio2 mRNA levels were found to show diurnal rhythms under long-day conditions in an area adjacent to the tuberoinfundibular sulcus and in the ependymal cell layer lining the ventrobasal walls of the third ventricle. Daily sc melatonin injections given in the late afternoon under long-day condition suppressed the Dio2 mRNA levels already at the first day after the onset of the treatment in the ependymal cell layer lining the ventrobasal walls of the third ventricle, and 1 d later in an area adjacent to the tuberoinfundibular sulcus. These suppressive effects were sustained for at least 2 d after a single injection. Furthermore, we examined the temporal changes of the Dio2 expression after the onset of the treatment, showing that the suppression did not occur until midday of the next day. These data suggest that melatonin is involved in the signal transduction mechanisms controlling the photoperiodic response of gonads by acting on Dio2 expression rather rapidly through indirect pathways.

The saccus vasculosus of fish is a sensor of seasonal changes in day length

“…S7), indicating that the isolated SV is a photoperiodic sensor. Both TSHb and DIO2 appeared to exhibit circadian variation, as has also been reported in hamster 19 . However, despite the changes in protein levels, we did not observe significant changes in the corresponding messenger RNA levels by real-time quantitative PCR (Q-PCR) (Fig.…”

Melatonin Transmits Photoperiodic Signals through the MT1 Melatonin Receptor

“…This was also found in CBA/N mice , Djungarian hamsters (Barrett et al, 2007;Watanabe et al, 2007b), and Japanese quail (Yasuo et al, 2005). Dio2 expression did not respond to photoperiodic changes in wild-type C3H, whereas it was strongly induced by long-day condition in CBA/N mice , Syrian hamsters (Revel et al, 2006;Yasuo et al, 2007), and Japanese quail (Yoshimura et al, 2003;Yasuo et al, 2005). In Djungarian hamsters, Dio2 expression was induced when animals were transferred from short to long days, but it did not change when animals were transferred from long to short days (Watanabe et al, 2004(Watanabe et al, , 2007bBarrett et al, 2007).…”

“…This molecular machinery is conserved in mammals. The expression of Dio2 and Dio3 is regulated by the photoperiod and melatonin in Syrian and Djungarian hamsters (Watanabe et al, 2004;Revel et al, 2006;Watanabe et al, 2007b;Yasuo et al, 2007), and TSHB is involved in the photoperiodic regulation of Dio2 in sheep (Hanon et al, 2008). Most interestingly, the expression of Dio2, Dio3, and TSHB is also under photoperiodic control in mice whose gonadal size is not affected by the photoperiod .…”

Thyroid hormones and seasonal reproductive neuroendocrine interactions

“…Further, T 3 administered exogenously under short-day conditions was observed to mimic the effects of long-day conditions on gonadal growth in hamsters (Barrett et al 2007, Freeman et al 2007). In addition, it has been reported that the expressions of DIO2 and DIO3 are regulated by melatonin in mammals (Watanabe et al 2004, Revel et al 2006, Barrett et al 2007, Yasuo et al 2007a. It is also noteworthy that in goats, which breed under short-day conditions, a long-day stimulus suppressed the expression of DIO2; this effect was contrary to that observed in species that breed under longday conditions ).…”

“…Although some interspecies differences exist with regard to the relative importance of DIO2 and DIO3 in photoperiodism, the photoperiodic regulation of DIO2 and/or DIO3 expression has been confirmed in various mammalian species, including the Djungarian (Siberian) hamster (Watanabe et al 2004, Barrett et al 2007, Freeman et al 2007), Syrian hamster (Revel et al 2006, Yasuo et al 2007a, rat (Yasuo et al 2007b), and goat . Further, T 3 administered exogenously under short-day conditions was observed to mimic the effects of long-day conditions on gonadal growth in hamsters (Barrett et al 2007, Freeman et al 2007).…”