Transcriptomic analysis of light-induced genes in Nasonia vitripennis: possible implications for circadian light entrainment pathways

Circadian entrainment to the environmental day-night cycle is essential for the optimal use of environmental resources. In insects, opsin-based photoreception in the compound eye and ocelli, and CRYPTOCHROME1 (CRY1) in circadian clock neurons are thought to be involved in sensing photic information, but genetic regulation of circadian light entrainment in species without light-sensitive CRY1 remains unclear. To elucidate a possible CRY1-independent light transduction cascade, we analysed light-induced gene expression through RNA-sequencing in Nasonia vitripennis. Entrained wasps were subjected to a light pulse in the subjective night to reset the circadian clock and light-induced changes in gene expression were characterized at four different time points in wasp heads. We used co-expression, functional annotation, and transcription factor binding motif analyses to gain insight into the molecular pathways in response to acute light stimulus and form a hypothesis about the circadian light resetting pathway. Maximal gene induction was found after 2h of light stimulation (1432 genes), including the opsin opblue and the core clock genes cry2 and npas2. Pathway and cluster analyses revealed light activation of glutamatergic and GABA-ergic neurotransmission, including CREB and AP-1 transcription pathway signalling. This suggests that circadian photic entrainment in Nasonia may require pathways that are similar to mammals. We propose a model for hymenopteran circadian light resetting that involves opsin-based photoreception, glutamatergic neurotransmission, and gene induction of cry2 and npas2 to reset the circadian clock.