Transcript profiles of mitochondrial and cytoplasmic manganese superoxide dismutases in Exopalaemon carinicauda under ammonia stress

Superoxide dismutase(SOD) is one of the most important antioxidant defense enzymes,and is considered as the first line against oxidative stress. In this study,we cloned a mitochondrial manganese(Mn) SOD( m Mn SOD) c DNA from the ridgetail white prawn E xopalaemon carinicauda by using rapid amplification of c DNA ends(RACE) methods. The full-length c DNA for m Mn SOD was 1 014-bp long,containing a 5′-untranslated region(UTR) of 37-bp,a 3′-UTR of 321-bp with a poly(A) tail,and included a 657-bp open reading frame encoding a protein of 218 amino acids with a 16-amino-acid signal peptide. The protein had a calculated molecular weight of 23.87 k Da and a theoretical isoelectric point of 6.75. The m Mn SOD sequence included two putative N-glycosylation sites(NHT and NLS),the Mn SOD signature sequence 1 80 DVWEHAYY 187,and four putative Mn binding sites(H48,H96,D180,and H184). Sequence comparison showed that the m Mn SOD deduced amino acid sequence of E. carinicauda shared 97%,95%,89%,84%,82%,72%,and 69% identity with that of M acrobrachium rosenbergii,M acrobrachium nipponense,Fenneropeneaus chinensis,Callinectes sapidus,P erisesarma b idens,D anio r erio,and Homo sapiens,resectively. Quantitative real-time RT-PCR analysis showed that m Mn SOD transcripts were present in all E. carinicauda tissues examined,with the highest levels in the hepatopancreas. During an ammonia stress treatment,the transcript levels of m Mn SOD and c Mn SOD were up-regulated at 12 h in hemocytes and at 24 h in the hepatopancreas. As the duration of the ammonia stress treatment extended to 72 h,the transcript levels of m Mn SOD and c Mn SOD significantly decreased both in hemocytes and hepatopancreas. These findings indicate that the SOD system is induced to respond to acute ammonia stress,and may be involved in environmental stress responses in E. carinicauda.