Date of Award

Summer 8-2014

Embargo Period

11-18-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Advisor(s)

Veronica Hinman

Abstract

Study of Gene Regulatory Networks (GRNs) is essential for the understanding of developmental processes because GRNs describe the genetic specification mechanisms that instruct an egg to become a complex organism. Additionally, because cell types, organs, tissues, and other morphological features are specified during development, changes to the underlying GRNs lead to differences in such features. Therefore, an understanding of developmental GRNs is required to understand how morphology evolves. Echinoderms offer an attractive group of model organisms for the study of GRN evolution. A variety of echinoderm species have publically available genomic or transcriptomic information, their development is well characterized, and for some species and cell types extensive GRNs have already been elucidated, all of which greatly facilitate comparative approaches. Furthermore, echinoderms are deuterostomes, just as vertebrates are. Therefore, studies of echinoderm developmental GRNs can enhance our understanding of vertebrate evolution and development. Here, we take multiple approaches to understanding the processes of developmental GRN evolution. We first survey recent literature with the aim of ascertaining the significance and prevalence of transcription factor changes to GRN evolution and morphological novelty. Next, we present a recent publication from our lab which describes a previously uncharacterized source of modularity within orthologous Tbrain (Tbr) transcription factor DNA-binding abilities. We maintain that this type of modularity could be an important contributor to the evolution of novel features. After this, we characterize a new GRN for the specification of serotonergic neurons in the sea star dorsal ganglia. This structure exhibits versatile morphologies among echinoderms and is important for understanding the origins of the vertebrate forebrain as it is thought to be similar to the ancestral deuterostome central nervous system precursor. Finally, we propose a new line of research intended to determine whether modular DNA- binding among orthologous Tbr transcription factors has impacted the evolution of this interesting neuronal structure.

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