title: MicroRNAs are involved in cadmium tolerance in Daphnia pulex.
abstract: Daphnia can develop tolerance to cadmium (Cd) after multi-generational exposures. Until now, Cd tolerance in this crustacean was thought to be mainly due to its sequestration via induction of metallothioneins (MTs). Our research supports other studies showing microRNAs (miRNAs) also play a role in this enhanced tolerance. We induced Cd tolerance in Daphnia pulex after exposing them for 25 generations and examined the maintenance of enhanced Cd tolerance under a Cd-free environment for an additional three generations. Acute Cd tolerance as well as long-term effects on population dynamics were measured in selected generations via 48h LC50 tests and 21 d reproductive tests, respectively. Cd tolerance was associated with differential expression of 10 miRNAs (miR-2, miR-33, miR-92, miR-96, miR-153, miR-252, miR-279, miR-283, miR-305 and miR-615). Pathway analysis revealed these miRNAs might increase Cd tolerance by suppressing cellular growth and proliferation by GTPase and cuticle protein pathways, which switch cellular energy allocation to detoxification processes. Moreover, we found increased Cd tolerance is related with induction of MT3 and MT4 and a subsequent downregulation of MT1 and MT3 expression when animals are moved to a Cd-free environment. This is the first study linking aquatic invertebrate miRNAs with induced tolerance to environmental stressors.
authors.affiliation: Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN, USA.
authors.forename: Shuai
authors.initials: S
authors.lastname: Chen
authors.affiliation: Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN, USA; Conservation Biology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, National Ocean and Atmospheric Administration, Seattle, WA, USA.
authors.forename: Krista M
authors.initials: KM
authors.lastname: Nichols
authors.affiliation: School for the Environment, University of Massachusetts, Boston, MA, USA.
authors.forename: Helen C
authors.initials: HC
authors.lastname: Poynton
authors.affiliation: Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN, USA. Electronic address: mssepulv@purdue.edu.
authors.forename: Maria S
authors.initials: MS
authors.lastname: Sepúlveda
mesh_terms: D000818:Animals; D002104:Cadmium / Q000633:toxicity*; D003621:Daphnia / Q000187:drug effects / Q000502:physiology*; D004361:Drug Tolerance; D020558:GTP Phosphohydrolases / Q000378:metabolism; D008668:Metallothionein / Q000378:metabolism; D035683:MicroRNAs / Q000378:metabolism; D012098:Reproduction / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D035683:MicroRNAs; D014874:Water Pollutants, Chemical; D002104:Cadmium; D008668:Metallothionein; D020558:GTP Phosphohydrolases
keywords: Daphnia; Heavy metal; Metallothioneins; MicroRNA; Toleranec