Molecular genetics and hormonal regulation of exoskeleton differentiation in an insect model, Apis mellifera

Abstract

The exoskeleton, or cuticle, not only gives shape to the insects, but also provides other essential biological properties, such as locomotion, protection against desiccation, parasites and pathogens, to this large group of Arthropoda. This rigid (sclerotized) structure produced by epidermis is composed of a variety of proteins (cuticle proteins) and a type of polysaccharide, chitin, and is periodically renewed during insect growth. The periodicity of this process, or molt, is mainly controlled by ecdysteroids, while the regulation of exoskeleton maturation has been attributed to ecdysteroids as well as to bursicon, a peptide produced by the brain. Recently, the sequencing and annotation of the genome of some insect species have given new dimension to the study of the exoskeleton. A significant number of genes that potentially encode cuticle proteins - the 'cuticle genes' - were identified. Chitin binding motifs, and other conserved regions, allowed the classification of these proteins into 12 families, thus revealing the complexity of the structural components of the exoskeleton. However, the application of this knowledge to understand both (1) the differential gene expression, and its regulation, as well as (2) the changes undergone by the epidermis during the successive molting events (apolysis, cuticle synthesis, cuticle differentiation or sclerotization, and ecdysis), is still incipient. The objective of this project is to use the honeybee Apis mellifera as a biological model in a multiple methodological approach (microarray, real time RT-PCR, in situ hybridization, RNA interference) aiming (1) to identify genes differentially expressed in epidermis during the successive molting events that lead to the adult exoskeleton formation; (2) to characterize the differential gene expression in response to the changing ecdysteroid titer during this period, and (3) to investigate the role of bursicon in the induction of genes encoding enzymes of potential importance for exoskeleton maturation. Concurrently, we intend to characterize the sub-cellular changes that occur in epidermis during exoskeleton formation. With this approach, we expect to deepen our understanding on exoskeleton formation and differentiation at the molecular and sub-cellular levels. (AU)