Download - metallothionein -Biomarker
Zn>Cd &Hg>Cu
Pathiratne et al(2009) and Ghedtra et al (2010) Richard (1994) -MT induction -liver : Hg > Ag> Cu > Zn.
Metallothionein - a potential biomarker to assess the metal contamination in marine fishes-A review
Metal
Transcription -of MT genes
MT synthesis
•Cd can induce MT expression in Fishes. (Chen et al. 2005, Rovira et al. 2005, Choi et al. 2007) •MT transcript proteins -bivalent metal - Zn, Cu, Pb, Fe, Co and Hg. ( Ikebuchi et al. 1986; Carginale et al. 1998; Riggio et al. 2003 )• Thiele in 1992- MT gene expression ὰ Metal concentration.•4 MT genes-common promoter-several MREs- which binds to metal transcription factors-synthesis of MT.(Kling and Olsson in 1993).
Factors Affecting the Metallothionein Estimations
age
Sexual maturity- max variation-femaleOlsson et al ( 1987) - Rainbow Trout –hepatic MT levels
Sex
Liver
Muscle
Kidney
brainSkin
Gills
Tissue type
Route of exposure and experimental conditions
MT Levels
fish species
tissue physiology
experimental conditions
• Chowdhury et al (2005) -Rainbow trout -sub lethal concentration -waterborne Cd (0 or 3 μg/L) or dietary Cd (0 or 500 mg/kg dry wt) -30 days• Waterborne exposure group- highest MT- kidney - Gills – liver.• Dietary exposure group-kidney >> cecae and posterior intestine > liver and stomach > midintestine > gills.
Exogenous and endogenous substances
Experimental problems with MTs
Olsson 1996
Metal Type
Seasonal variations
Future prospects
1. Inorganic Hg Invitro studies Cell culture
Invivo influence
Not clear
Organic-mercury complex
2. Standardization of methods 3.Different methodology used by researchers
•Thiele D J (1992).Metal Regulated Transscription in Eukaryotes. Nucleic Acid Research.210;1183-1188.•Kling, P. & Olsson. P. E. (1993). Metal regulation of the rainbow trout metallothionein-A gene. In: proceedings of the Seventh International Symposium on Responses of Marine Organisms to Pollutants.•Geroge S.G.,Hadgson P.A.,Tybler .P.,Tedd.K.,(1996).Inducability of Metallothionein mRNA expression and Cadmium tolerance in larva of teleosts the turbot (Scophthalmus maximus).Fundamental Application of Toxicology 33:91-99.•Singh M R. (2007). Impurities-heavy metals: IR prespective.(George et al.,1996)
Reference
Vijaya * and R. Jayakumar** *Research Scholar, **Assistant Professor, Department of Environmental Science, GITAM University, Bengaluru Campus, Nagadenahalli-562 163. KARNATAKA. E-mail:[email protected]
MT as Biomarker
•Ubiquitous , stable & inducible proteins, Mw 6-8kDa, pI-8.3•High cysteine content (20-30%) - 61 amino acids - no aromatic amino acids.• Binds to metals - metal thiolate bonds.•Metal homeostasis –Zn ,Cu & detoxification – Cd, Hg, Pt, Ag
Introduction
Metallothionein (MTs)
Cd Higher affinity to MTs tan Zn
Displace Zn from MT binding site
(Hollis L.C and C.M.Wood, 2001)
Maximum induction
MTs in Tilapia 2mg/kg of Cd No further change
(Y.F.Ueng et al. 1996)