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.