Cryptochrome-mediated integration of circadian rhythms into seasonal cycles in the silkworm Bombyx mori

Abstract

The domesticated silkworm Bombyx mori is both a major sericultural species and a powerful model for studying how environmental cues are converted into developmental decisions. A central seasonal trait in this species is embryonic diapause, a maternally programmed developmental arrest whose incidence is shaped by genetic background and environmental conditions experienced during the maternal generation. Recent genome-editing studies have provided new functional evidence for the role of circadian clock genes in this process, particularly the two silkworm cryptochromes, BmCRY1 and BmCRY2. BmCRY1 belongs to the Drosophila -type CRY lineage and retains features consistent with a light-input function, whereas BmCRY2 belongs to the mammalian-type insect CRY lineage and displays structural motifs expected for a nuclear transcriptional repressor. Loss of Bmcry1 disrupts embryonic hatching and adult eclosion rhythms and impairs photoperiodic modulation of diapause, while temperature-dependent diapause induction under constant darkness is largely retained. By contrast, Bmcry2 mutants show reduced temperature-dependent diapause induction, although the direct role of BmCRY2 in the silkworm clockwork remains unresolved. Together, available evidence suggests that BmCRY1 and BmCRY2 act through distinct clock-related entry points that ultimately influence, directly or indirectly, the neuroendocrine pathway controlling diapause hormone release and maternal diapause commitment. These findings place silkworm cryptochromes at a key interface between environmental sensing, circadian timing and seasonal developmental control, with potential implications for sericulture.