Circadian Clock Genes and Photoperiodism: Comprehensive Analysis of Clock Gene Expression in the Mediobasal Hypothalamus, the Suprachiasmatic Nucleus, and the Pineal Gland of Japanese Quail under Various Light Schedules
In birds, the mediobasal hypothalamus (MBH) including the infundibular nucleus, inferior hypothalamic nucleus, and median eminence is considered to be an important center that controls the photoperiodic time measurement. Here we show expression patterns of circadian clock genes in the MBH, putative suprachiasmatic nucleus (SCN), and pineal gland, which constitute the circadian pacemaker under various light schedules. Although expression patterns of clock genes were different between long and short photoperiod in the SCN and pineal gland, the results were not consistent with those under night interruption schedule, which causes testicular growth. These results indicate that different expression patterns of the circadian clock genes in the SCN and pineal gland are not an absolute requirement for encoding and decoding of seasonal information. In contrast, expression patterns of clock genes in the MBH were stable under various light conditions, which enables animals to keep a steady-state photoinducible phase.
"tion - based oscillatory loop that serves as an internal bi - ological clock . The oscillatory loop involves BMAL1 , Clock , and Period ( PER ; Reppert and Weaver , 2002 ) . Expression of BMAL1 in chicken is modulated by the duration of light , and the expression patterns of the clock genes are affected by photoperiod in the SCN and pineal gland ( Yasuo et al . , 2003 ) . Luteinizing hormone acts additively with Clock / BMAL1 to enhance StAR gene expression and stimulates Per2 gene expression in the presence of Clock / BMAL1 . This latter observation is consistent with control of the timing of ovulation by the circadian rhythm ( Nakao et al . , 2007 ) . This background information led us to suspect t"
"Changes in photoperiod have also been shown to alter the pattern of Fos expression within the MBH and ME, reinforcing roles for these regions in transducing photoperiod into an endocrine response (Meddle and Follett, 1997). The expression of multiple clock genes within both the MBH and the suprachiasmatic nuclei (SCN) has suggested a location within the hypothalamus for the photoperiodic clock (Yasuo et al., 2003). In parallel with these findings, It has been known for many years that thyroid hormones play a critically important role in regulating the avian photoperiodic response (Follett and Nicholls, 1985) but a series of recent studies by Yoshimura and colleagues have placed these observations into a physiological context suggesting that long daylengths regulate thyroid hormone metabolism within the MBH itself (Nakao et al., 2008; Yoshimura et al., 2003). "
"Of note, daily variations in this gene have been highlighted in the SCN of a diurnal non-human primate, the capuchin monkey (Valenzuela et al., 2008). Furthermore, in other classes of vertebrates, Clock oscillations have also been found in diurnal birds such as the quail (Yasuo et al., 2003). Therefore, this comparative phylogenetic survey gives clues to our assertion. "
[Show abstract][Hide abstract] ABSTRACT: A major challenge in the field of circadian rhythms is to understand the neural mechanisms controlling the oppositely phased temporal organization of physiology and behaviour between night- and day-active animals. Most identified components of the master clock in the suprachiasmatic nuclei (SCN), called circadian genes, display similar oscillations according to the time of day, independent of the temporal niche. This has led to the predominant view that the switch between night- and day-active animals occurs downstream of the master clock, likely also involving differential feedback of behavioral cues onto the SCN. The Barbary striped grass mouse, Lemniscomys barbarus is known as a day-active Muridae. Here we show that this rodent, when housed in constant darkness, displays a temporal rhythmicity of metabolism matching its diurnal behaviour (i.e., high levels of plasma leptin and hepatic glycogen during subjective midday and dusk, respectively). Regarding clockwork in their SCN, these mice show peaks in the mRNA profiles of the circadian gene Period1 (Per1) and the clock-controlled gene Vasopressin (Avp), which occur during the middle and late subjective day, respectively, in accordance with many observations in both diurnal and nocturnal species. Strikingly, expression of the circadian gene Clock in the SCN of the Barbary striped grass mouse was not constitutive as in nocturnal rodents, but it was rhythmic. As this is also the case for the other diurnal species investigated in the literature (sheep, marmoset, and quail), a hypothesis is that the transcriptional control of Clock within the SCN participates in the mechanisms underlying diurnality and noctumality.
Brain Research 11/2014; 1594. DOI:10.1016/j.brainres.2014.10.063 · 2.84 Impact Factor
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