Analysis and functional annotation of expressed sequence tags from the aquatic midge (Chironomus tentans)

Environmental stressors, including pesticides, heavy metals, nutrients, and oxygen depletion, are detrimental to organisms and have now become a growing global concern. This research is to develop an expressed sequence tag (EST) database from the aquatic midge (Chironomus tentans). From 10,368 random cDNA clones sequenced, we retained 10,367 high-quality ESTs with an average length of 896 bp after preprocessing. These ESTs were assembled into 2,912 unique sequences including 2,095 singletons and 817 contigs. Blast search resulted in 2,152 putative transcripts that were functionally annotated and sorted into 10 molecular function categories: binding (37.6%), catalytic (37.5), transporter (12.1), structural molecule (6.7), molecular transducer (1.3), antioxidant (1.1), enzyme regulator (1.0), translation regulator (1.0), transcription regulator (1.0), and motor (0.5) activities. Eighty nine transcripts likely encode different types of hemoglobin involved in oxygen storage and/or transport, whereas at least 28 encode various cytochrome P450 monooxygenases involved in xenobiotic metabolism. These ESTs are expected to help us develop a DNA microarray for studying the mechanism of stressor’s effects, and cellular and molecular responses of the midge to environmental stressors.