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Circadian activity rhythm and molecular clock in Hemiptera D2 楊 斌

2013/06/09 16:57 に Takashi Matsuo が投稿

In response to the changing seasonality, insects have evolved circadian activity rhythm in the timing of development, reproduction and diapause state by using photoperiodic circadian clock. To receive light and synchronize with the circadian activity rhythm, insects utilize visual system composed of compound eyes and ocelli or photoreceptors such as cryptochrome [1]. 
Hemipteran insects exhibit a clear photoperiodic response for the induction of adult reproductive diapause so that they are good materials to study circadian clock [2]. Circadian system such as clock cell bodies in the brain was described in both larvae and adult stages in Rhodnius prolixus [3]. Circadian clock genes were isolated from Riptortus pedestris in which vrille (vri), and mammalian-type cryptochrome (cry-m) were first reported in hemimetabolous insects [4]. The lack of cry-m in Drosophila melanogaster indicated the difference of clockwork between these two species. Gene modification by RNAi was performed in R. pedestris revealed that period (per), cycle (cyc) and cry-m were core components of the circadian clock [5, 6]. These clock genes were upstream cascade of juvenile hormone (JH) secretion [7]. In contrast, in the linden bug, Pyrrhocoris apterus, clock genes were suggested to work at downstream of JH by observing the effect of an endocrine gland on circadian clock gene expression [8]. In addition, another studies showed organ-autonomous, yet noncircadian, involvement of clock genes and hormonal signaling in diapause regulation [9].  
These results suggest that the circadian activity rhythm was controlled by complicated factors of both circadian clock and endocrine system, but the intact mechanism was still unknown. Recent application of whole genome sequencing in the studies of circadian clock, may clarify the regulatory mechanisms of circadian activity rhythm.

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