Gene expression in the gut of keratin-feeding clothes moths (Tineola) and keratin beetles (Trox) revealed by subtracted cDNA libraries

Few lineages of insects are able to feed on keratin (hair, feathers) and it remains unknown which genes enable this metabolism and what is their evolutionary origin. We conducted a transcriptomic study of two keratin-feeding insects, the clothes moth Tineola bisselliella (Lepidoptera) and the keratin beetle Trox sp. (Coleoptera). Using subtracted cDNA libraries enriched for gut-expressed transcripts, a total of 672 clones sequenced per library resulted in >150 tentative unique sequences for each species. Sequence similarity predictions identified 22.4% (Tineola) and 6.8% (Trox) of the ESTs as proteases, and mainly as serine proteases of the trypsin and chymotrypsin type, while lacking cysteine proteases. None of the sequences showed similarity to subtilisin type proteases that confers keratinolytic activities in prokaryotes and fungi. Neighbor-Joining trees grouped Tineola and Trox serine proteases near other lepidopteran and coleopteran sequences, respectively, but distant from each other. A few abundant ESTs had no database matches but their presence suggests a role specific to these keratin-feeding insects. While high expression of specific serine proteases appears linked to keratin digestion in both species, it remains to be established if their action requires additional enzymatic or physiological functions to initiate the degradation of the abundant cysteine bonds of keratins. These catabolic pathways are of great interest in the leather industry for the removal of hair, while proteinase inhibitors could prevent damage from clothes moths.