Steroid hormones are one of the major bioactive molecules responsible for the coordinated regulation of biological processes in multicellular organisms. In insects, the principal steroid hormones are ecdysteroids, including 20-hydroxyecdysone. A great deal of research has investigated the roles played by ecdysteroids during insect development, especially the regulatory role in inducing molting and metamorphosis. However, little attention has been paid to the roles of these hormones in post-developmental processes, despite their undisputed presence in the adult insect body. Recently, molecular genetics of the fruit fly Drosophila melanogaster has revealed that ecdysteroid biosynthesis and signaling are indeed active in adult insects, and involved in diverse processes, including oogenesis, stress resistance, longevity, and neuronal activity. In this review, we focus on very recent progress in the understanding of two adult biological events that require ecdysteroid biosynthesis and/or signaling in Drosophila at the molecular level: germline development and the circadian clock.
Photoperiodic regulation of development is a common strategy for insects in the temperate zone to adapt to the seasonally changing environment. Although the circadian clock is generally thought to be involved, the underlying time measurement mechanism is still elusive. Here, we demonstrate that the circadian clock gene period (per) plays an essential role in the photoperiodic regulation of nymphal development in the cricket Modicogryllus siamensis. Nymphal development of this cricket depends on photoperiods, being accelerated by long days and slowed down by short days. We examined the role of per in the nymphal photoperiodic response as well as circadian rhythm generation using parental RNA interference (pRNAi). per mRNA levels in nymphal heads showed a rhythmic expression with the pattern dependent on photoperiods, and pRNAi significantly suppressed the per mRNA level with no significant rhythmicity in the early nymphal stage. Irrespective of photoperiods, nymphs treated with per pRNAi showed adult emergence patterns neither of intact nymphs nor of DsRed2 pRNAi nymphs kept under long days or under short days but similar to those kept under constant dark conditions. Most per pRNAi adults showed arrhythmic or aberrant circadian locomotor activity. These results suggest that the photoperiodic time measurement requires the normal circadian clock that is controlled by the per gene.
Many physiological functions of insects show a rhythmic change to adapt to daily environmental cycles. These rhythms are controlled by a multi-clock system. A principal clock located in the brain usually organizes the overall behavioral rhythms, so that it is called the "central clock". However, the rhythms observed in a variety of peripheral tissues are often driven by clocks that reside in those tissues. Such autonomous rhythms can be found in sensory organs, digestive and reproductive systems. Using Drosophila melanogaster as a model organism, researchers have revealed that the peripheral clocks are self-sustained oscillators with a molecular machinery slightly different from that of the central clock. However, individual clocks normally run in harmony with each other to keep a coordinated temporal structure within an animal. How can this be achieved? What is the molecular mechanism underlying the oscillation? Also how are the peripheral clocks entrained by light-dark cycles? There are still many questions remaining in this research field. In the last several years, molecular techniques have become available in non-model insects so that the molecular oscillatory mechanisms are comparatively investigated among different insects, which give us more hints to understand the essential regulatory mechanism of the multi-oscillatory system across insects and other arthropods. Here we review current knowledge on arthropod's peripheral clocks and discuss their physiological roles and molecular mechanisms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.