Effect of photoperiod on clock gene expression and subcellular distribution of PERIOD in the circadian clock neurons of the blow fly Protophormia terraenovae

Apr 17, 2010Cell and tissue research

Day length effects on daily clock gene activity and protein location in the time-keeping nerve cells of the blow fly Protophormia terraenovae

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Abstract

The mRNA levels of circadian clock genes per and tim oscillated in the brain of the blow fly, Protophormia terraenovae, under both short-day and long-day conditions.

Oscillations of per and tim mRNA levels peaked around lights-off and troughs around lights-on, persisting even in constant darkness.
The distribution of PER protein in neurons varied over time, with the highest number of cells showing PER in the nucleus 12 hours after lights-off.
Photoperiod appears to influence the nuclear translocation of PER, indicating a potential mechanism for how light cycles affect circadian rhythms.
Neurons were grouped based on temporal changes in PER localization, revealing distinct responses to photoperiod between different types of clock neurons.

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We examined the effect of photoperiod on the expression of circadian clock genes period (per) and timeless (tim), using quantitative real-time polymerase chain reaction (PCR), and the effect of photoperiod on subcellular distribution of PERIOD (PER), using immunocytochemistry, in the blow fly, Protophormia terraenovae. Under both short-day and long-day conditions, the mRNA levels of per and tim in the brain oscillated, and their peaks and troughs occurred around lights-off and lights-on, respectively. The oscillations persisted even under constant darkness. In the large ventral lateral neurons (l-LN(v)s), small ventral lateral neurons (s-LN(v)s), dorsal lateral neurons (LN(d)s), and medial dorsal neurons (DN(m)s), the subcellular distribution of PER-immunoreactivity changed with time. The number of cells with PER-immunoreactivity in the nucleus was highest 12 h after lights-off and lowest 12 h after lights-on, regardless of photoperiod, suggesting that PER nuclear translocation entrains to photoperiod. When temporal changes in the nuclear localization of PER were compared, the neurons could be classified into 2 groups: the l-LN(v)s were similar to the s-LN(v)s, and the LN(d)s were similar to DN(m)s. In LN(d)s and DN(m)s, decreasing rates of the number of cells with PER immunoreactivity in the nucleus per brain from the maximum were large as compared with those in l-LN(v)s and s-LN(v)s under short-day conditions. These results suggest that photoperiodic information is reflected in the expression patterns of circadian clock genes per and tim and in the subcellular distribution of PER. This observation suggests that the 2 different groups of clock neurons respond to photoperiod in slightly different manners.

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Effect of photoperiod on clock gene expression and subcellular distribution of PERIOD in the circadian clock neurons of the blow fly Protophormia terraenovae

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