Expression Patterns of Cysteine Peptidase Genes throughout the Tribolium castaneum Life Cycle

The red flour beetle, Tribolium castaneum, is a major agricultural pest responsible for considerable loss of stored grains and cereals worldwide.  Like other tenebrionid insects, T. castaneum larvae have an adapted and highly compartmentalized gut capable of degrading serine peptidase inhibitors found in cereals.  The gut is organized with cysteine peptidases mostly in the acidic anterior portion of the midgut, and serine peptidases in the alkaline posterior midgut.  T. castaneum larvae have approximately 25 putative cysteine peptidase genes (types B, L, O, F, and K) localized mostly on chromosomes 3, 7, 8, and 10, many in tandem as apparently duplicated gene events.  Most cysteine peptidase genes are highly expressed in the larval gut for protein digestion, but others are found in cells and serve lysosomal functions.  Previous work has shown cysteine peptidase gene expression in the gut is responsive to ingested inhibitors, where specific genes are upregulated to manage the deleterious effects of specific inhibitors.  We hypothesize that gene expression is not only responsive to dietary changes in the gut, but also specific to life stages.  We have used high throughput sequencing to further study cysteine peptidase genes in T. castaneum and characterized their relative expression among developmental stages (egg, larvae, pupae, and adult).  Understanding the expression patterns and regulation of cysteine peptidase genes in T. castaneum will be helpful in developing new pest control strategies for tenebrionid pests.