 oxidants are important in the regulation of signal transduction and gene expression . 
 multiple classes of genes are transcriptionally activated by oxidants and are implicated in different phenotypic responses . in the present study , we performed differential mrna display to elucidate genes that are induced or repressed after exposure of rat lung epithelial ( rle ) cells to h2o2 or crocidolite asbestos , a pathogenic mineral that generates oxidants . 
 after 8 or 24 hr of exposure , rna was extracted , reverse transcribed , and amplified by polymerase chain reaction with degenerate primers to visualize alterations in gene expression . 
 the seven clones obtained were sequenced and encoded the mitochondrial genes , nadh dehydrogenase subunits nd5 and nd6 , and 16s ribosomal rna . 
 evaluation of their expression by northern blot analysis revealed increased expression of 16s rrna after 1 or 2 hr of exposure to h2o2 . at later time periods ( 4 and 24 hr ) , mrna levels of 16s rrna and nadh dehydrogenase 
 were decreased in h2o2-treated rle cells when compared to sham controls . 
 crocidolite asbestos caused increases in 16s rrna levels after 8 hr of exposure , whereas after 24 hr of exposure to asbestos , 16s rrna levels were decreased in comparison to sham controls . 
 in addition to these oxidants , the nitric oxide generator spermine nonoate caused similar decreases in nadh dehydrogenase mrna levels after 4 hr of exposure . 
 the present data and previous studies demonstrated that all oxidants examined resulted in apoptosis in rle cells during the time frame where alterations of mitochondrial gene expression were observed . 
 as the mitochondrion is a major organelle that controls apoptosis , alterations in expression of mitochondrial genes may be involved in the regulation of apoptosis.imagesfigure 1figure 2figure 3figure 4figure 5 
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