UC San Diego

Sox genes regulate multiple aspects of neurogenesis, including ectoderm and neuroectoderm specification, maintenance of neural stem cells, and sensory neuron specification and maintenance. Homozygous knockout of the SoxB1 transcription factor gene Sox1 causes epileptic seizures in mice. However, the genes regulated by Sox1 in the adult nervous system or the roles that its abnormal function plays in disease are largely unknown. Planarian flatworms are excellent models for studying the roles of transcription factors in adult neurogenesis; these animals regenerate a molecularly complex central and peripheral nervous system following injury or amputation from a large population of adult stem cells. Thus, we wanted to use planarians as a model system to study SoxB1 function during regenerative neurogenesis in planarians. In order to do this, my dissertation work had two broad goals: 1) the further development of methods to assess the effects of perturbations to neurogenesis in planarian flatworms and 2) to assess the roles soxB1 genes play in planarian neurogenesis. In the first chapter, I describe the current state-of-knowledge of planarian neurogenesis. In the second and third chapters, I demonstrate the strides we have taken to produce more antibodies and methods to use antibodies to label multiple planarian cell types and tissues. And finally, in Chapter 4, I present our work surveying soxB1 function in planarian neurogenesis. Through this work, we found that inhibition of soxB1-2 caused a seizure-like movement phenotype. By using single cell RNA sequencing data (scRNA-seq), we were able to identify an ectodermal progenitor in planarians that is marked by soxB1-2 expression. Functional and expression analysis of 86 downstream genes of soxB1-2 revealed 17 genes with loss-of-function phenotypes that recapitulated aspects of the soxB1-2(RNAi) phenotype. 16 of these genes have confirmed expression in neurons and by coupling expression and function of a subset of these genes, we have identified at the molecular level a rheosensory (water flow sensory) population in planarians. While some downstream genes are implicated in genetic causes of epilepsy disorders (EDs) in humans, additional genes represent novel candidates, in particular, genes encoding components of calcium signaling linked to primary cilia function, which represents a new field in epilepsy research. Thus, these studies will aid in establishing planarians as a genetic model in which to study the molecular basis of seizure disorders in humans.