Evolution of deuterostome immune systems

Abstract

Contemporary theory on the evolution of metazoan immune systems is primarily derived of work on a few historically established model species (including Drosophila, human, and mouse). Though these species have provided invaluable insight into the molecular and cellular components of immunity, they nonetheless cannot alone provide sufficient phylogenetic contrast to accurately capture the nuances of immunity evolution. In the modern sequencing era of comparative biology, studies leveraging transcriptomic and genomic datasets have provided valuable insight into the ancestry of immunity molecular toolkits within Deuterostomia – a superphylum comprised of Hemichordata (acorn worms and pterobranchs), Echinodermata (urchins, sea stars, and their allies), and Chordates (tunicates, lancelets, and vertebrates). In my PhD thesis, I focus on remedying a gap in knowledge by improving representation of hemichordates in the context of immunity and place these findings in the framework of deuterostome evolution.

This dissertation contains one literature review and three research chapters (Chapters 2-5). Chapter 2 is zoological account of the hemichordate clade, Enteropneusta (commonly called acorn worms). In addition to overviewing the anatomy, physiology, and diversity within the clade, this publication also highlights the sparsity of immunology within the phylum. Chapter 3 focuses on the Toll-like receptor (TLR) pathway, a central component of pathogen recognition and innate immunity signaling. This chapter was the first published work of my dissertation, and its findings provided the groundwork for the subsequent chapters. Chapter 4 concerns the molecular toolkit involved in antiviral immunity in the acorn worm hemichordate, Saccoglossus kowalevskii. The capacity for S. kowalevskii to recognize and transcriptionally react to viral stimulus is described. This work is a critical step forward for hemichordate immunology and towards inferring the ancestry of deuterostome immunity evolution. The final data chapter (Chapter 5) expands upon the work of Chapter 3 by investigating the evolution of key innate immunity proteins across Metazoa, with focus on deuterostome taxa. For this work, I developed a bioinformatic tool called TIAMMAt (Taxon-Informed Adjustment of Markov Model Attributes). This study highlights the value of improving the representation of non-model species in comparative evolutionary studies using immunity as a case study.