Differential gene expression of Malpighi tubule transcriptomes of Melipona scutellaris exposed to thiamethoxam

Author(s)

Lucas Miotelo

• Document type: Master's Dissertation
• Press: Rio Claro. 2022-08-26.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2022-07-28
• Advisor: Osmar Malaspina; Milene Ferro

Abstract

In Brazil, using neonicotinoid insecticides, such as thiamethoxam (TMX), is common in crops. The indiscriminate use of TMX affects non-target insects such as bees. For example, Melipona scutellaris is a species of stingless bee that was included in an IBAMA list, along with TMX, for toxicological studies to be carried out. The present study analyzed differential gene expression of Malpighian tubules (Mt) of foragers bees of M. scutellaris exposed to LC50/100 of TMX through transcriptomic analysis. In addition, the immunostaining of heat shock proteins (HSP) 70 and 90 were evaluated, searching for HSPs expressed in the transcriptome and applying the TUNEL method to detect cell death. After de novo assembly, 237 differentially expressed genes (DEGs) were identified and grouped into nine clusters. DEGs involved in detoxification, excretion, tissue regeneration, cellular respiration, oxidative stress, apoptosis, cell signaling, and the immune system were found. HSP70 immunostaining increased within one day and decreased within eight days of exposure to TMX. At the same time, HSP90 decreased by one day and increased by eight. The TUNEL method detected DNA fragmentation only in eight days. In addition, there are no DEGs related to HSPs, and through the analysis of TPM (transcripts per million), it was identified that HSP70 was the most expressed heat shock protein. Regarding the transcriptome results, cell metabolism in Mt was mainly affected after eight days of exposure. Nine genes were selected from different clusters and validated by RT-qPCR. According to our results, TMX promotes several types of damage in Mt cells at the molecular level. Therefore, interference in different cellular processes directly affects the health of M. scutellaris, compromising essential functions of Mt. The data obtained for HSPs (immunostaining and transcriptome analysis) are conflicting since there are no DEGs on the transcriptome. However, the immunostaining showed differences between the control and exposed groups. These differences may result from the high sensitivity of this immunomarkers. The present study was the first to evaluate the effects of a neonicotinoid on the gene expression of stingless bees and highlighted the importance of molecular analyzes for ecotoxicological studies. (AU)

• FAPESP's process: 20/03527-3 - Differential gene expression of Melipona scutellaris Malpighi tubule transcriptomes exposed to thiamethoxam
• Grantee: Lucas Miotelo
• Support Opportunities: Scholarships in Brazil - Master