Expression of cuticle genes and insecticide resistance in Triatoma infestans

CALDERÓN FERNÁNDEZ, GUSTAVO M.

Mar del Plata

Congreso; X Congreso de Protozoología y Enfermedades Parasitarias; 2014

Sociedad Argentina de Protozoología

The insect integument, or exoesqueleton, covers the surface of the insect body; it comprises the cuticle and the epidermal tissue. The cuticle consists of an outer thin epicuticle, formed by lipids and lipoproteins, and an inner thick procuticle, mostly formed by chitin embedded in a matrix of cuticular proteins. Shortly after its formation, the cuticle is sclerotized in an enzyme-mediated sequence of reactions, becoming hard and rigid. The epidermis is the cell layer that underlies the insect cuticle and is primarily responsible for its formation. It includes several different types of cells with specific roles, such as epidermal cells, oenocytes, dermal glands, and hair forming cells. The cuticle lipids include mostly hydrocarbons, fatty alcohols, waxes and fatty acids. Fatty acid synthases (FAS), fatty acid elongases (ELOVL) and fatty acid reductases (FAR) are key enzymes of cuticle lipid synthesis. Structural cuticle proteins represent several families of chitin-binding proteins involved in forming the bulk of the cuticle; the CPR family includes most of the cuticle proteins found in the cuticle. The integument plays a crucial role in the fitness, general metabolism, communication and survival of insects. Evidence has also been gathered showing that this tissue might be involved in several aspects of insecticide resistance. In T. infestans, the cuticle thickness and hydrocarbon content were shown to be related to insecticide resistance. The sequences of several genes related to the metabolism of cuticle components were obtained from a sequencing project of T. infestans epidermal tissue transcriptome. Present work showed a differential expression pattern of several ELOVL and FAR genes in insecticide resistant T. infestans compared to susceptible insects, further supporting the cuticle barrier role. Very importantly, several cuticle protein genes, and also genes coding for detoxifying enzymes such as cytochrome P450s, were differentially expressed in resistant insects. These results suggest that the differential expression of integument genes may contribute to insecticide resistance in T. infestans through mechanisms not only involving a delayed penetration through the cuticle, but also an increased detoxification as the insecticide is transported through the epidermis.