Genomic basis of evolutionary change: evolving immunity

Abstract

Complex traits are manifestations of intricate gene interaction networks. Evolution of complex traits revolves around the genetic variation in such networks. Genomics has increased our ability to investigate the complex gene interaction networks, and characterize the extent of genetic variation in these networks. Immunity is a complex trait, for which the ecological drivers and molecular networks are fairly well understood in Drosophila. By characterizing the natural variation in immunity, and mapping how the genome changes during the evolution of immunity in Drosophila, we can integrate our knowledge on the complex genetic architecture of traits and the molecular basis of evolutionary processes.

Keywords: adaptation; complex traits; evolution; gene interaction networks; innate immunity; molecular mechanisms; parasitoid resistance.

FIGURE 1

Schematic representation of the genetic networks in immunity. (A) Several interconnected networks coordinate the responses to an immune challenge. These networks consist of proteins (represented by circles) that interact with each in a signal transduction cascade to regulate the expression of transcription factors (represented by hexagonals). The activation of the core signal transduction pathways (e.g., IMD, Toll, or Jak/Stat, indicated by thick lines among proteins) results in the production of effector molecules, such as antimicrobial peptides (represented by pie-shaped symbols) and the proliferation and differentiation of specialized (blood) cells (cloud-shaped figures). Extracellular and membrane-bound receptor molecules (moon-shaped figures) induce the pathways. The activity can be further modulated by many other proteins that interact with the pathways and cross-talk with other pathways and genetic networks (indicated by the thin lines among proteins). (B) The central components of the genetic networks in immunity, e.g., the transcription factors and the proteins in direct contact with these transcription factors, are often strongly conserved across phyla. Evolutionary diversification is found more extensively toward the peripheries of the networks.