In partial fulfillment of the requirements for the degree of

Doctor of Philosophy in Biology

In the

School of Biological Sciences

Chris Johnson

Will defend his dissertation

Investigating the Mechanisms Underlying Metamorphosis in the Chordate Ciona robusta

18, 4, 2024

3PM

Krone Engineered Biosystems Building (EBB) CHOA Room 1005

https://gatech.zoom.us/j/93986623573?pwd=eURpcHRrcXFwUENmcWNXRFBKZlpFUT09

 Thesis Advisor:

Alberto Stolfi, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Committee Members:

Annalise Paaby, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Brian Hammer, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

William Ratcliff, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Pengpeng Bi, Ph.D.

Department of Genetics and Center for Molecular Medicine

University of Georgia

ABSTRACT:

Tunicates are our closes living invertebrate relative, and as such, have given us tremendous insight on tunicate/vertebrate development and evolution. For this presentation, I discuss two projects that are tied together and contribute to the ongoing investigation underlying metamorphosis in tunicates.

The first chapter discusses our work on the transcriptional regulation governing the pattering of cells comprising the three sensory adhesive papillae of the Ciona robusta larva. Through the discovery and use of novel genetic markers and reporter constructs, we visualized and tracked the differentiation of various papilla cell types which range from collocytes responsible for secreting adhesive material, to ciliated neurons initiating metamorphosis and axial columnar cells potentially possessing chemosensory and contractile properties. Using CRISPR/Cas9, overexpression, and pharmacological perturbations, we identified the molecular mechanisms underlying the specification of these cell types and their contributions to metamorphic processes.

The second chapter describes the transcriptional regulation of adult Ciona muscle cell fusion. In vertebrates, all skeletal muscles form multinucleated myofibers through myoblast fusion. In tunicates like Ciona, only adult muscles form multinucleated fibers through cell fusion, while larvae have mononucleated muscles instead. I show that this is achieved through combinatorial regulation that activates the expression of a key myoblast fusion factor only in adult muscles.