The genomic structure of
manganese superoxide dismutase (
Mn-SOD) was characterized in Hemibarbus mylodon (Teleostei, Cypriniformes), an endangered freshwater fish species, and changes in
Mn-SOD mRNA expression in response to various stimuli, such as challenge with
lipopolysaccharide (LPS), bacteria, or
heavy metals, were examined. H. mylodon
Mn-SOD possesses well-conserved features of vertebrate Mn-SODs, including its homologous quinquepartite gene structure (five exons interrupted by four introns) and high sequence identity with vertebrate orthologs in coding regions, including a typical eukaryotic
Mn-SOD signature. The 5'-regulatory upstream region of the H. mylodon
Mn-SOD gene lacked a canonical TATA sequence; however, it displayed various
transcription factor binding elements that may be involved in immune and stress responses, as well as the modulation of
enzymes that mediate the metabolism of metals and other
xenobiotics. Bioinformatic analysis of
Mn-SOD genes from fish and mammalian genome databases revealed chromosomal synteny of the
Mn-SOD locus in the vertebrate lineage.
Mn-SOD transcripts were ubiquitously detected in diverse tissues with variable levels of basal expression using an RT-PCR assay.
Mn-SOD expression in the liver and kidney were significantly modulated by injection of LPS (1, 5, or 10 microg g(-1)
body weight), Edwardsiella tarda challenge (5 x 10(3) or 5 x 10(5) cells/fish), and
heavy metal exposure (Cd, Cu, or Zn at 5 microM). Results from this study suggest that
Mn-SOD plays an important role in the host defence against oxidative damage caused by
infection-mediated
inflammation and/or toxicant related stress in this species.