The circadian clock gene (Clock) regulates photoperiodic time measurement and its downstream process determining maternal induction of embryonic diapause in a cricket

Shin G Goto,Masatoshi Nagata

doi:10.14411/eje.2022.002

Abstract

In response to short days in autumn, most temperate multivoltine insects enter diapause, a state in which development or reproduction is suppressed or arrested, which serves to coordinate their development and physiology (or that of offspring) with annual changes in the environment (i.e. photoperiodism). This response is mediated by a measurement of time based on photoperiod (photoperiodic time measurement), which is thought to be regulated by a circadian clock. However, some studies also demonstrate the involvement of the circadian clock in an output process that generates phenotypes associated with diapause. To gain further insight into this, we silenced the Clock (Clk) gene, the main regulator of the circadian clock, in the band-legged ground cricket Dianemobius nigrofasciatus (Orthoptera: Trigonidiidae). Silencing the Clk gene using RNA interference (Clk RNAi) in female crickets resulted in abnormal circadian rhythms under constant darkness and light-dark conditions, thereby indicating the central role of this gene in the circadian clock mechanism. Clk RNAi females exhibited long-day oviposition behaviour, even when reared under short-day conditions, thereby indicating the involvement of Clk in photoperiodic time measurement. In addition, Clk RNAi females immediately laid non-diapause-type eggs, which was not recorded in control females under either short-day or long-day conditions and cannot be explained in terms of dysfunction of photoperiodic time measurement. Accordingly, we speculate that Clk could also be involved in a downstream process that results in the laying of diapause-type eggs.

Highlights

Organisms have evolved a seasonal timing system that enables them to coordinate their development and physiology with annual changes in the environment, using day length as a cue (Tauber et al, 1986; Danks, 1987)
To gain further insight in this regard, we investigated the role of Clk, a main component of the circadian clock (Zhao et al, 2003; Kilman & Allada, 2009), in photoperiod induced diapause in the band-legged ground cricket Dianemobius nigrofasciatus (Matsumura) (Orthoptera: Trigonidiidae)
In female crickets maintained under short-day conditions, dsClk was injected on day 1 and Clk mRNA levels in the head were quantified at ZT 6 on day 15 (Fig. 2b), which revealed that Clk mRNA levels in the dsClk-injected females were lower than those in the control crickets

Summary

Introduction

Organisms have evolved a seasonal timing system that enables them to coordinate their development and physiology (or that of their offspring) with annual changes in the environment, using day length (photoperiod) as a cue (Tauber et al, 1986; Danks, 1987). This property is termed photoperiodism and an organism’s response to photoperiod is referred to as a photoperiodic response. Organisms measure the length of night or day using a measurement of time based on photoperiod (photoperiodic time measurement) In this regard, the most well-established photoperiodic event in insects is diapause, where development or reproduction is suppressed or arrested in conjunction with an extensive shutdown of metabolic activity (Košťál, 2006). The period sensitive to photoperiod, during which an insect receives photoperiodic cues that trigger the photoperiodic response, occurs in advance of diapause, the most extreme example of which is when this sensitive stage occurs in one generation and diapause in the (i.e. a maternal effect) (Mousseau & Dingle, 1991)

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