Heterogeneity and Developmental Connections between Cell Types Inhabiting Teeth

Abstract

Every tissue is composed of multiple cell types that are developmentally, evolutionary and functionally integrated into the unit we call an organ. Teeth, our organs for biting and mastication, are complex and made of many different cell types connected or disconnected in terms of their ontogeny. In general, epithelial and mesenchymal compartments represent the major framework of tooth formation. Thus, they give rise to the two most important matrix–producing populations: ameloblasts generating enamel and odontoblasts producing dentin. However, the real picture is far from this quite simplified view. Diverse pulp cells, the immune system, the vascular system, the innervation and cells organizing the dental follicle all interact, and jointly participate in transforming lifeless matrix into a functional organ that can sense and protect itself. Here we outline the heterogeneity of cell types that inhabit the tooth, and also provide a life history of the major populations. The mouse model system has been indispensable not only for the studies of cell lineages and heterogeneity, but also for the investigation of dental stem cells and tooth patterning during development. Finally, we briefly discuss the evolutionary aspects of cell type diversity and dental tissue integration.

Single-Cell RNA-Sequencing From Mouse Incisor Reveals Dental Epithelial Cell-Type Specific Genes

“…Enamel formation processes are coordinated by strictly synchronized functions of the dental epithelium ( Krivanek et al, 2017 ). SI cells cover the ameloblast layer and may contribute to ameloblast differentiation through Shh signaling ( Koyama et al, 2001 ).…”

“…During tooth development, DESCs give rise to all types of dental epithelial cells that involve amelogenesis ( Juuri et al, 2013 ). They may be classified into the following five types: ameloblast and its progenitor inner enamel epithelium (IEE), outer enamel epithelium (OEE), cuboidal cells surrounding the outer layer of the enamel organ, stratum intermedium (SI), squamous cells that cover ameloblast, and stellate reticulum (SR), having a spindle shape ( Krivanek et al, 2017 ). All these cell types are essential for proper enamel formation ( Liu H. et al, 2016 ).…”

Attachment and spatial organisation of human mesenchymal stem cells on poly(ethylene glycol) hydrogels

“…Additionally, PDL cells have been known to produce collagen and exhibit certain osteoblast-like features [18]. Even though different components of the tooth originate from different germ origins during early odontogenesis, most of the specialised cells within the periodontium arise from neural crest cells [19,20]. As illustrated in Figure 3, PDL fibroblasts are products of the mesenchymal lineage, while the gingival epithelium originates from oral epithelial cells (not shown in the Figure) [21].…”

Dental cell type atlas reveals stem and differentiated cell types in mouse and human teeth

“…ammalian teeth are formed by the ectoderm of the first pharyngeal arch and neural crest-derived ectomesenchyme. Developmental interactions between these tissue types enable the construction of solid dental structures composed of epithelium-derived crown enamel and ectomesenchyme-derived dentin [1][2][3][4] . In humans, teeth primordia are formed in utero and complete their growth before adulthood, at which point the progenitor populations disappear.…”

“…We next focused on the most striking aspects of population complexity of epithelial (Figs. [2][3][4] and mesenchymal (Figs. 5-7) compartments, their human analogues (Figs.…”