Comparative transcriptomics uncovers apoptosis in brain impairment in newly pupated honeybee worker under cold stress

Abstract Background Honeybees have a much narrower developmental temperature range compared to other insects, making it an ideal model species for studying temperature effect on insect metamorphosis. Cold exposure during pupal stage resulted in impaired learning, memory, and foraging ability in adults. So far, the understanding of molecular mechanisms and physiological processes underlying the impaired brain development of honeybee pupae under cold exposure is unclear. Result The transcriptome data used in this study were collected from the heads of white-eyed honeybee pupae between control group and cold-treated groups. A total of 736 significantly differentially expressed genes (DEGs) were found to be shared by the different durations of cold treatment, and three gene clusters with significant expression patterns were identified using gene expression trend analysis, and RT-qPCR verification was performed on six genes. Enrichment analyses of each cluster using GO and KEGG database showed that upregulated DEGs followed by a plateau were significantly enriched in apoptosis, axon regeneration and signalling pathways regulating pluripotency of stem cells genes, consistently upregulated DEGs were significantly enriched in MAPK signalling pathway, and the downregulated DEGs followed by a plateau were related to insect ecdysteroids synthesis (phm and spookiest), epigenetic regulation of genes associated with brain development (LSD1), endoplasmic reticulum-associated protein degradation (RNF5 and SVIP) and regulation of endoplasmic reticulum stress-associated cell apoptosis (FBXO32, PET191 and UBL5). Conclusion Our study suggests that cold stress will inhibit the synthesis of ecdysteroids, disrupt gene epigenetic regulation, and intensify endoplasmic reticulum stress-associated brain cell apoptosis, thus hinder brain development in new pupal heads.