Circadian Clock Genes Regulate Temperature-Dependent Diapause Induction in Silkworm Bombyx mori

Abstract

The bivoltine strain of the domestic silkworm, Bombyx mori, exhibits a facultative diapause phenotype that is determined by maternal environmental conditions during embryonic and larval development. Although a recent study implicated a circadian clock gene period (per) in circadian rhythms and photoperiod-induced diapause, the roles of other core feedback loop genes, including timeless (tim), Clock (Clk), cycle (cyc), and cryptochrome2 (cry2), have to be clarified yet. Therefore, the aim of this study was to elucidate the roles of circadian clock genes in temperature-dependent diapause induction. To achieve this, per, tim, Clk, cyc, and cry2 knockout (KO) mutants were generated, and the percentages of diapause and non-diapause eggs were determined. The results show that per, tim, Clk, cyc, and cry2 regulated temperature-induced diapause by acting upstream of cerebral γ-aminobutyric acid (GABA)ergic and diapause hormone signaling pathways. Moreover, the temporal expression of the clock genes in wild-type (wt) silkworms was significantly different from that of thermosensitive transient receptor potential ankyrin 1 (TRPA1) KO mutants during embryonic development. Overall, the findings of this study provide target genes for regulating temperature-dependent diapause induction in silkworms.

Mutation of the clock gene timeless disturbs diapause induction and adult emergence rhythm in Helicoverpa armigera

“…In a recent study, a Per ‐knockout strain of Bombyx mori lost the ability to enter photoperiod‐induced embryonic diapause 24 . Moreover, temperature‐dependent embryonic diapause can be disturbed by knockout of Tim or Per gene in Bombyx mori 25 . Although H. armigera diapauses in the pupal stage are different from silkworm, our results suggest that the clock gene Tim is involved in diapause induction in H. armigera .…”

“…Diapause has been observed in diverse embryonic stages, larval instars, pupae, and adults; however, for any given species, the potential for diapause is usually restricted to a single stage 20 . Insect photoperiodism is closely linked to circadian clock 21–25 . Insect circadian clocks may measure the photoperiod and temperature and translate this information into downstream endocrine signals 18,19 .…”

“…The circadian clock genes ( period and cycle ) are important for photoperiodic diapause in bean bug Riptortus pedestris 28 . Additionally, clock genes contribute to egg diapause in Bombyx mori 23,25 . In the sugar beet moth, Scrobipalpa ocellatella , TIM and PER immunoreactivity cells in the brain of non‐diapause pupae are less abundant than in that of diapause pupae 29 .…”

Multiomic Analysis of Adult Diapause inDrosophila melanogasterIdentifies Hallmarks of Cellular Quiescence

“…6A). The diapause-associated changes to circadian gene expression—such as the upregulation of period and downregulation of clock— was observed through our analysis, suggesting our experimental design accurately represents diapause physiology (Salminen et al, 2015; Homma et al, 2022). In addition, JH-responsive genes Obp99a and Fad2 showed expected changes in transcription according to the presence or absence of S-methoprene, demonstrating the success of our supplementation approach (supplemental fig.…”

Knockouts of positive and negative elements of the circadian clock disrupt photoperiodic diapause induction in the silkworm,Bombyx mori

“…Our results agree with Ikeda et al (2021) that found that knocking out per in Kosetsu, another bivoltine strain, inhibits the diapause egg production induced by a short-day condition during the larval stage. Recently, Homma et al (2022) reported that core clock genes regulate temperature-dependent diapause induction in B . mori using TALEN-mediated knockouts in the Kosetsu strain.…”