Temporal transcriptional responses of insulin-associated metabolic genes during chilling-induced embryonic diapause termination in Bombyx mori.

Understanding how low-temperature signals are integrated into transcriptional regulatory networks is essential for elucidating the mechanisms underlying chilling-induced termination of embryonic diapause. In Bombyx mori, several signaling pathways, including insulin signaling, have been implicated in this process; however, the transcriptional behavior of metabolism-related genes associated with insulin signaling during prolonged chilling remains incompletely characterized. In this study, I examined the temporal expression patterns of a targeted set of insulin-associated genes, including components of insulin signaling (insulin receptor [InR], forkhead box protein O [FOXO]), glycogen and glucose metabolism (glycogen synthase [Glys], glycogen phosphorylase [Glyp], glucose-6-phosphate dehydrogenase [G6PD]), and the transcription factors (myocyte enhancer factor 2 [Mef2] and microphthalmia-associated transcription factor [Mitf]), during chilling-induced diapause termination. By initiating chilling 2 or 15 days after oviposition, diapause eggs with weaker or stronger diapause intensity, respectively, were obtained. Their temporal responses to chilling were compared with those kept at 25 °C. Upon transfer to 5 °C at 2 days post-oviposition, InR transcripts increased 15 days after transfer and then maintained a relatively higher level thereafter. Increased FOXO transcripts were also detected between 30 and 60 days after transfer. While other genes showed gene-specific expression patterns during chilling. Following transfer to 5 °C at 15 days post-oviposition, all examined genes showed increased expression compared with those maintained at 25 °C. Returning eggs that had been chilled for 30 days to 25 °C resulted in reduced expression of FOXO, Glys, Glyp, G6PD, Mef2, and Mitf, indicating that a 30-day chilling period is not sufficient to sustain elevated transcription of these genes. These results provide a temporal framework describing chilling-dependent transcriptional regulation of selected insulin-associated metabolic genes during embryonic diapause termination in B. mori. While the findings do not directly assess metabolic activity, they identify candidate regulatory components whose functional roles in carbohydrate metabolism and diapause termination warrant further investigation.