Desiccation and hypoxic stress-induced changes in gene expression in the red flour beetle, Tribolium castaneum (Herbst)

Tribolium castaneum is a serious pest of stored products and represents a group of desiccation-resistant coleopteran insects.  The genome sequence assembly includes >97% of the euchromatin, of which >90% has been mapped onto the linkage groups. Based on computerized predictions for ~16,000 putative genes, we have designed an oligonucleotide microarray (Combimatrix) containing ~12,000 unigene 35-mer probes for this insect.  We used this microarray to investigate genome-wide changes in gene expression in response to desiccation and hypoxic stress in the larval stage.  Candidate genes were ranked by the following criteria: P value, fold-change, and normalized fluorescence values.  Based on our criteria, a total of 372 candidate genes were found to be differentially expressed; 206 and 210 genes were differentially expressed for desiccation and hypoxic stress, respectively, and 44 genes were overlapping.  Of particular interest were a large number of candidate genes associated with cuticle metabolism.  Microarray data were validated by qRT-PCR for a select set of candidate genes. Under desiccation stress, up-regulation was confirmed for genes encoding purine biosynthesis protein PURH (2x) and chitinase 9 (1.8x).  Confirmed down-regulated genes included J domain-containing heatshock protein binding protein (11x), arylsulfatase B (3.5x), and cathepsin B (4.3x).  Under hypoxic stress, up-regulation was confirmed for genes encoding death-associated small cytoplasmic leucine-rich protein SCLP (2.3x) and cartilage leucine-rich protein (9.4x).  Down-regulation during hypoxia was confirmed for genes encoding chymotrypsin BII (1.7x), as well as for two genes that were also down-regulated during desiccation stress, namely J domain-containing heatshock protein binding protein (2.1x) and cathepsin B (1.7x).  The results indicate that there are both unique and common stress-responsive genes in both arid and hypoxic conditions.