title: Cd-metallothioneins in three additional tetrahymena species: intragenic repeat patterns and induction by metal ions.
abstract: Ciliate metallothioneins (MTs) possess many unique features compared to the "classic" MTs in other organisms, but they have only been studied in a small number of species. In this study, we investigated cDNAs encoding subfamily 7a metallothioneins (CdMTs) in three Tetrahymena species (T. hegewischi, T. malaccensis, and T. mobilis). Four CdMT genes (ThegMT1, ThegMT2, TmalMT1, and TmobMT1) were cloned and characterized. They share high sequence similarity to previously identified subfamily 7a MT members. Tetrahymena CdMTs exhibit a remarkably regular intragenic repeat homology. The CdMT sequences were divided into two main types of modules, which had been previously described, and which we name "A" and "B". ThegMT2 was identified as the first MT isoform solely composed of module "B". A phylogenetic analysis of individual modules of every characterized Tetrahymena CdMT rigorously documents the conclusion that modules are important units of CdMT evolution, which have undergone frequent and rapid gain/loss and shuffling. The transcriptional activity of the four newly identified genes was measured under different heavy metal exposure (Cd, Cu, Zn, Pb) using real-time quantitative PCR. The results showed that these genes were differentially induced after short (1 h) or long (24 h) metal exposure. The evolutionary diversity of Tetrahymena CdMTs is further discussed with regard to their induction by metal ions.
authors.affiliation: Key Laboratory of Aquatic Biodiversity and Conservation, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China; Graduate School of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Yue
authors.initials: Y
authors.lastname: Chang
authors.forename: Guanglong
authors.initials: G
authors.lastname: Liu
authors.forename: Lina
authors.initials: L
authors.lastname: Guo
authors.forename: Hongbo
authors.initials: H
authors.lastname: Liu
authors.forename: Dongxia
authors.initials: D
authors.lastname: Yuan
authors.forename: Jie
authors.initials: J
authors.lastname: Xiong
authors.forename: Yingzhi
authors.initials: Y
authors.lastname: Ning
authors.forename: Chengjie
authors.initials: C
authors.lastname: Fu
authors.forename: Wei
authors.initials: W
authors.lastname: Miao
mesh_terms: D008668:Metallothionein / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D060888:Real-Time Polymerase Chain Reaction; D013768:Tetrahymena / Q000235:genetics* / Q000378:metabolism*
chemical_list: D008668:Metallothionein
keywords: ciliate; heavy metal stress; metallothionein evolution; modular repeat; real-time quantitative PCR