The evolution of invertebrate photopigments and photoreceptors

Abstract

The advent of new tools in genetics, labeling, and imaging has led to a revolution in the ability to investigate the genetic and cellular evolution of invertebrate photoreceptor pigments and cells. All opsins, invertebrate and vertebrate, derive from a common ancestral G-protein-coupled receptor, whose descendants form four distinct groups (one of which, the "cnidops," is strictly limited to invertebrates). Today's invertebrate opsins associate with a bewildering assortment of G-proteins and often have unusual properties, including functional bistability and occasionally the capacity to act as photoisomerases for visual pigment chromophores. In this chapter, we review our state of knowledge of how invertebrate opsins-the proteins underlying all visual pigments-have evolved and become functionally specialized as well as how the photoreceptive cells in which they are housed have diversified from a common ancestor-or ancestors-early in animal evolution.