MicroRNA\nmiR-210\nModulates the Water Flea Daphnia magna Response to Cyanobacterial Toxicity

As a key form of post-transcriptional\nregulation, microRNAs\n(miRNAs)\nregulate gene expression by binding to target mRNAs, leading to mRNA\ndecay or translational repression. Recently, the role of miRNAs in\nthe response of aquatic organisms to environmental stressors has emerged. Daphnia, widely distributed cladocerans, play a crucial\nrole in aquatic ecosystems. Cyanobacterial blooms often cause Daphnia populations to decrease, thereby disrupting\necosystem functionality and water quality. However, the post-transcriptional\nmechanisms behind Daphnia’s\nresponse to toxic cyanobacteria are insufficiently understood. This\nstudy investigated the role of miR-210, a multifunctional miRNA involved\nin stress response and toxicity pathways, and its target genes (<i>MLH3</i>, <i>CDHR5</i>, and <i>HYOU1</i>) in two Daphnia magna clones exposed\nto toxic Microcystis aeruginosa. Results\nshowed that M. aeruginosa inhibited\nsomatic growth rates, led to microcystin accumulation, caused abnormal\nultrastructural alterations in the digestive tract, and induced DNA\ndamage in both clones. Notably, exposure significantly increased miR-210\nexpression and decreased the expression of its target genes compared\nwith the controls. We identified miR-210s regulation on clonal-tolerance\nvariations in D. magna to M. aeruginosa, emphasizing miRNAs’ contribution\nto adaptive responses. Our work uncovered a novel post-transcriptional\nmechanism of cyanobacterial impact on zooplankton and provided essential\ninsights for assessing cyanobacterial toxicity risks.