Nuclear factor-kappa B pathways in Drosophila.

The nuclear factor kappa B (NF-kappaB) pathways in Drosophila are multi-component pathways, as in vertebrates, that regulate the expression of many genes responsible for the formation of dorsal-ventral polarity in the early embryo, the innate immune response to infection with Gram- negative and positive bacteria and fungi, the cellular immune response and hematopoiesis. Overactivation of the fly pathway can result in developmental defects, overproliferation of hemocytes and the formation of melanotic tumors or nodules. The extracellular events leading to the maturation of the ligand for initiation of the Drosophila NF-kappaB pathway is not conserved between flies and vertebrates, but the Toll receptor and downstream events are remarkably similar. NF-kappaB proteins have been identified in mollusks, and arthropods such as horseshoe crabs and beetles, indicating that this pathway has been established more than 500 million years ago. The fly NF-kappaB pathways are less complex than those in vertebrates, with the involvement of fewer proteins, but they are, nonetheless, just as important as their vertebrate counterparts for the life of the fly.