Acute Thiamethoxam exposure in Apis mellifera : Absence of both stress-induced changes in mRNA splicing and synergistic effects of common fungicide and herbicide

Abstract

Running title: Neonicotinoid toxicity is not enhanced by common fungicide and herbicide ABSTRACT Securing food supply for a growing population is a major challenge and heavily relies on the use of agrochemicals to maximize crop yield. Neonicotinoids are globally one of the most widely used insecticides. It is increasingly recognized, that some neonicotinoids have a negative impact on non-target organisms, including important pollinators such as the European honeybee Apis mellifera. Toxicity of neonicotinoids may be enhanced through simultaneous exposure with additional pesticides, which could help explain, in part, the global decline of honeybee colonies. Here we examined whether exposure effects of the neonicotinoid Thiamethoxam are enhanced by the commonly used fungicide Carbendazim and the herbicide Glyphosate. We also analysed alternative splicing changes upon pesticide exposure in the honeybee. In particular, we examined transcripts of three genes: i) the stress sensor gene X box binding protein-1 (Xbp1), ii) the Down Syndrome Cell Adhesion Molecule (Dscam) gene and iii) the embryonic lethal/abnormal visual system (elav) gene, which are important for neuronal function. Our results showed that acute neonicotinoid exposure is not enhanced by Carbendazim, nor Glyphosate. Toxicity of the compounds did not trigger stress-induced, alternative splicing in the analysed mRNAs, thereby leaving dormant a cellular response pathway to these man-made environmental perturbations.

Srrm234, but not canonical SR and hnRNP proteins, drive inclusion of Dscam exon 9 variable exons

“…Such a factor has not been identified for exon 4 and 9 clusters, and for the factors tested, we did not observe splicing together of variable exons. Intriguingly, a newly annotated exon 4.0 in the beginning of the bee Dscam exon 4 cluster is spliced to exon 4.6 (Decio et al, 2019). This unexpected finding, however, is not compatible with the model described for Hrp36 in the exon 6 cluster, but might involve a repressive sequence element around exon 4.0 similar the element discovered in the beginning of the exon 6 cluster, which when deleted results only in inclusion of exon 6.1 (May et al 2011).…”