Decoding photoperiodic time through Per1 and ICER gene amplitude - PubMed (original) (raw)

Decoding photoperiodic time through Per1 and ICER gene amplitude

S Messager et al. Proc Natl Acad Sci U S A. 1999.

Abstract

The mammalian Per1 gene is expressed in the suprachiasmatic nucleus of the hypothalamus, where it is thought to play a critical role in the generation of circadian rhythms. Per1 mRNA also is expressed in other tissues. Its expression in the pars tuberalis (PT) of the pituitary is noteworthy because, like the suprachiasmatic nucleus, it is a known site of action of melatonin. The duration of the nocturnal melatonin signal encodes photoperiodic time, and many species use this to coordinate physiological adaptations with the yearly climatic cycle. This study reveals how the duration of photoperiodic time, conveyed through melatonin, is decoded as amplitude of Per1 and ICER (inducible cAMP early repressor) gene expression in the PT. Syrian hamsters display a robust and transient peak of Per1 and ICER gene expression 3 h after lights-on (Zeitgeber time 3) in the PT, under both long (16 h light/8 h dark) and short (8 h light/16 h dark) photoperiods. However, the amplitude of these peaks is greatly attenuated under a short photoperiod. The data show how amplitude of these genes may be important to the long-term measurement of photoperiodic time intervals.

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Figures

Figure 1

Figure 1

Effect of photoperiod on the temporal pattern of expression of Per1 and ICER mRNA in the PT of the Syrian hamster. (A) Autoradiographs showing the expression of Per1 and ICER mRNA and 2-[125I]iodomelatonin binding in the PT and adjacent brain areas. Coronal sections (20 μm) show gene expression or radioligand binding at ZT3 under LD and SD. Sections a–c are consecutive sections showing antisense labeling for Per1 (a) and ICER (c) and 2-[125I]iodomelatonin binding (b) under LD. Sections f_–_h are consecutive sections showing antisense labeling for Per1 (f) and ICER (h) and 2-[125I]iodomelatonin binding (g) under SD. Sections d and e show sense labeling for Per1 (d) and ICER (e) under LD. (Bar = 4 mm.) (B and C) Diurnal pattern of expression of Per1 (B) and ICER (C) riboprobe-specific hybridization in the pars tuberalis in LD (□) and SD (●). Each value is the mean ± SEM of two to six animals per time point. The horizontal solid bars represent the dark period for LD and SD. (D) A schematic showing the effect of changing from LD to SD on the endogenous melatonin rhythm when the time of lights-on is kept the same for both photoperiods, as used in this experiment. The melatonin rhythm decompresses slowly over several cycles toward lights-off (20).

Figure 2

Figure 2

(A) Effect of exogenous melatonin on the expression of Per1 (a) and ICER (b) mRNA at ZT3 in the PT of Syrian hamsters held under LD. Animals received no treatment (control), were injected with 25 μg of melatonin 1 h before lights-on (mel), or were injected with vehicle (saline). Each value is the mean ± SEM from three animals (∗, P < 0.05). (B) Expression of Per1 (a) and ICER (b) mRNA in the PT 1, 2, 5, and 14 days after a switch from LD to SD. Each value is the mean ± SEM of three animals (∗∗, P < 0.001). (C) Schematic showing the effect of changing from LD to SD on the endogenous melatonin rhythm when the timing of lights-off is held constant as in this experiment. The melatonin rhythm decompresses slowly over many cycles toward lights-on (20).

Figure 3

Figure 3

Effect of photoperiod on the temporal pattern of expression of Per1 and ICER mRNA in the SCN of the Syrian hamster. (A) Autoradiographs showing the expression of Per1 and ICER mRNA and 2-[125I]iodomelatonin binding in the SCN and adjacent brain areas. Coronal sections (20 μm) show gene expression or radioligand binding at ZT3 under LD and SD. Sections a–c are consecutive sections showing antisense labeling for Per1 (a) and ICER (c) and 2-[125I]iodomelatonin binding (b) under LD. Sections f_–_h are consecutive sections showing antisense labeling of Per1 (f) and ICER (h) and 2-[125I]iodomelatonin binding (g) under SD. Sections d and e show sense labeling for Per1 (d) and ICER (e) under LD. (Bar = 4 mm.) (B and C) Diurnal pattern of expression of Per1 (B) and ICER (C) riboprobe-specific hybridization in the SCN in LD (□) and SD (●). Each value is the mean ± SEM of two to six animals per time point. The horizontal solid bars represent the dark period for LD and SD. The time of lights-on was held constant between LD and SD as described in Fig. 1.

Figure 4

Figure 4

Expression of Per1 (A) and ICER (B) mRNA at ZT3 in the SCN 1, 2, 5, and 14 days after a switch from LD to SD. The time of lights-off was held constant between LD and SD (see Fig. 2_C_). Each value is the mean ± SEM of three animals. (∗, P < 0.01).

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