Closing the Gap: Comparative Approaches to Studying Insect Development in the Red Flour Beetle Tribolium castaneum and Other Short and Intermediate Germ Insects

Abstract

The homeotic gene studies of Ed Lewis [1] and the embryonic patterning studies of Christiane Nüsslein- Volhard and Eric Wieschaus [2-4] are landmarks of insect developmental genetics that continue to inspire the work of developmental geneticists today. The genes they discovered were subsequently shown to be evolutionarily conserved and are now considered to be basic components of the genetic toolkit that is deployed during development in virtually all metazoans, albeit with specific roles that vary between animal groups. Their systematic approach, which combined the power of genetics with molecular and experimental biology, established Drosophila as a premier model organism for developmental studies. Pioneering work in the field of evo-devo (evolution of development) extended the Drosophila studies to other insect and arthropod groups to determine the extent to which these genes and their regulatory networks have general applications to insect development or reflect the unique phylogenetic history of the Diptera. The systematic approach that has been so successful in Drosophila has been applied in other insects that are amenable to genetic manipulation, perhaps most successfully in the genetic analysis of homeotic genes in the red flour beetle, Tribolium castaneum. However, most non-drosophilid insects are difficult to rear in the lab or are not candidates for facile genetic analysis. As a result, comparative studies are often limited to inferring function from the expression patterns of candidate genes. There is hope, however, of narrowing the gap in technical sophistication that separates Drosophila from other insects. Recently, the reverse genetics technique of RNA interference (RNAi) has made it possible to determine gene function even in the absence of mutants. Moreover, the genomic sequence of several insects, including Tribolium, will soon be available. Here we review recent advances in the study of insect development made possible by RNAi analysis, which have whetted our appetites for the large-scale comparative genomic approaches that will soon be possible. Keywords: Insect development, segmentation, homeotic genes, RNAi