In partial fulfillment of the requirements for the degree of

Doctor of Philosophy in Biology

In the

School of Biological Sciences

Talha Mubeen

Will defend his dissertation

FROM CELLS TO MOLECULES: AN OVERVIEW ON THE DYNAMICS OF ACCELERATED WHOLE TOOTH REGENERATION

Tuesday, July 23rd, 2024

12 PM

In-person details:

Classroom 230
Kendeda Building, 
422 Ferst Dr NW, Atlanta, GA 30313

Virtual details:
https://gatech.zoom.us/j/98670235019?pwd=bItHr4Hqr7elyiFSjgFzBcbHc97oXe.1

 Thesis Advisor:

Jeffrey Todd Streelman, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Committee Members:

Shuyi Nie, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Liang Han, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Alberto Stolfi, Ph.D.

School of Biological Sciences

Georgia Institute of Technology

Gareth Fraser, Ph.D.

Department of Biology

University of Florida

ABSTRACT: 

Healthy teeth play a vital role in our well-being, affecting everything from what we eat to how we interact with the world. Losing teeth, whether from injury, disease, lack of nutrients, or birth defects, can have serious consequences for our physical and social health.  Therefore, to advance the development of effective regenerative therapies and improve dental health, a comprehensive understanding of tooth biology is essential. Tooth development (morphogenesis) is a complex process involving interactions between embryonic epithelium and ectomesenchyme, leading to the formation of specialized dental structures through distinct stages. While the basic process of tooth development is conserved across species, the ability to repair and regenerate teeth differs. Humans and many mammals have two sets of teeth with limited reparative capacity, while rodents can continually renew dental tissues lost due to gnawing. On the other end of the spectrum, a wide array of species, including numerous bony fish and reptiles, along with other vertebrates, demonstrate a remarkable ability for lifelong tooth replacement. The current paradigm in dental research largely focuses on models such as mice which lack the ability to replace their dentition. This significantly limits our understanding of tooth replacement mechanisms, making it imperative to broaden our investigative lens to incorporate alternative models. 

                  Lake Malawi Cichlids exhibit remarkable ability to continuously replace teeth every ~ sixty days throughout life (polyphyodonty), offer a powerful model to study this fascinating regenerative process. This evolutionary adaptation stems from the persistence of an embryonic dental lamina, a specialized tissue responsible for tooth replacement. However, the cellular and molecular makeup of replacement teeth in polyphyodonts, along with the intricate mechanisms driving their continuous tooth regeneration, remain unknown. To address this gap, we transcriptionally profiled meticulously dissected individual replacement teeth and adjacent oral lamina in Lake Malawi cichlids using single nuclei RNA sequencing (snRNA-seq) to make two main discoveries. First, despite hundreds of millions of years of evolution, we demonstrate conservation of cell type gene expression across vertebrate teeth (fish, mouse, human). Second, we used an approach that combines marker gene expression and developmental potential of dental cells to uncover the transcriptional signature of stem-like cells in regenerating teeth. 

                            To further delve into the intricacies of cellular and molecular signatures governing the lifelong tooth replacement in cichlids, we developed a plucking-induced tooth replacement model by combining tooth removal as microinjury with vital staining techniques. An accelerated rate of tooth replacement was observed on the plucked side after two weeks, which was consistent across species with diverse tooth formulas. We next coupled this pluck-control paradigm with snRNA-seq of cichlid dental apparatus to model dental embryonic cell fate specification and provide a temporal account of cellular and molecular events during the first seven days following tooth removal.  We demonstrate a cascade of sequential interactions between cell populations which involved not only communication within dental cells but also extension to supporting cells like immune and bone cells. The interaction pattern mimicked the process of tooth formation with intense crosstalk between epithelial and mesenchymal sub-populations, orchestrated by Collagen, Semaphorin, Slit-Robo, Notch, BMP, and MMP signaling pathways. In addition, we shed light on the hierarchy and remarkable plasticity of the dental epithelium. We propose a more nuanced role of supporting non-ameloblast epithelial cells in response to tooth removal mediated by immune and nerve guidance cues. In summary, this work significantly emphasizes the value of a comparative framework in the study of vertebrate oral and regenerative biology. It provides new insights into cellular and molecular interactions that can accelerate tooth replacement thereby laying robust groundwork for understanding tooth eruption syndromes and advancements in regeneration.