The evolution of signalling systems in animals: insights from vision and chemokines

The evolution of animals from unicellular ancestors to obligate multicellular organisms has deeply influenced their biology. Integral to this transformation is the development of distinct cell types that, while fulfilling specialized roles, must communicate and coordinate to uniformly respond to internal and external stimuli. Consequently, cell signalling systems are of fundamental importance in animals. This thesis delves into the evolution of two prominent biological processes in animals underpinned by cell signalling: vision and the chemokine system.

Vision, widespread in animals, has origins in the early stages of animal evolution. It relies on a photosensitive molecule, the opsin bound to a vitamin A derivative, that when hit by light, triggers a phototransduction pathway within photoreceptor cells. The phototransduction pathway involves a diverse suite of molecular components whose evolutionary journey is meticulously explored, as well as the regulatory genes involved in photoreceptor cell identity, in Chapter 3. While the evolutionary history of enzymes involved in the vitamin A metabolism is explored in Chapter 4.

The chemokine system is instrumental in directing cell migration during immunity, homeostasis, and development in vertebrate. This system is composed of ligand and receptor components, with both essential "canonical" elements and additional "non-canonical" elements that interact with the system. This intricate molecular diversity is investigated in Chapter 5.

Using comprehensive phylogenetic and bioinformatic methodologies, the evolution of these signalling systems is dissected. The research paints a detailed evolutionary picture of each molecular component in both systems. A recurrent theme emerged, highlighting the significance of gene family expansions at critical species nodes.