The Function and Evolution of Nuclear Receptors in Insect Embryonic Development.

Nuclear receptors are a family of transcription factors that are often responsive to small ligands, allowing for efficient gene expression-level responses to a stimulus. The average insect has 21 genes encoding nuclear receptors, whose functions are especially well studied in developmental transitions during the insect life cycle, such as metamorphosis and molting. However, their utility as well-controlled transcriptional regulators also lends them to important roles in embryogenesis, neurogenesis, metabolism, and organogenesis. Such developmental functions have been explored in depth in the model organism Drosophila melanogaster. More recently, advances in genomic resources and functional genomic methodologies have allowed for comparison of nuclear receptor function among a wider range of insect species. As has been the trend throughout the field of Evo-Devo, these new data sets reveal that many genes are shared, but the ways in which they are utilized in different lineages are more variable. In this chapter, we describe the suite of nuclear receptor genes found in Drosophila and their developmental functions. We then compare and contrast these genes and their functions in diverse insects.