Cohen, K. E. | bioRxiv Science

bioRxiv2025

Shark tooth regeneration: RNAseq reveals genes for unlimited dental renewal

Sharks are masters of tooth regeneration with a rapid and unlimited tooth supply. We present a comprehensive transcriptomic analysis across five distinct compartments from the embryonic shark mouth, capturing the full sequence of shark tooth development. Differential gene expression and gene regulatory network analyses reveal novel candidate markers upregulated within epithelial stem cells of the dental lamina. We show a potential role for this conserved regenerative network in the regulation of tooth production in sharks. Notably, we find the proto-oncogene mycn co-expressed with a definitive dental stem cell marker, sox2. Perturbation of mycn disrupts stem cell proliferation, underscoring its role in regulating dental stem cells in sharks. Our data showcase the power of transcriptome-based developmental approaches in the identification of predictive gene networks governing unlimited dental regeneration. The shark dental lamina provides an accessible system for the study of regeneration, offering exciting opportunities for investigating translational mechanisms of natural tooth renewal. TeaserSequencing dental stem cells in sharks reveals new genes necessary for lifelong tooth development.

developmental biology↗

bioRxiv2025

Teeth Outside the Jaw: Evolution and Development of the Toothed Head Clasper in Chimaeras

Chimaeras (Holocephali) are an understudied group of mostly deep-ocean cartilaginous fishes (Chondrichthyes) with unique characteristics that distinguish them from their distant relatives, sharks, skates, and rays. Unlike sharks, chimaeras lack scales and do not have serially replacing rows of serrated teeth crowned with enameloid. Instead, they possess a fused dentition of dentine toothplates. Additionally, male chimaeras develop an articulated cartilaginous facial appendage, the tenaculum, which is covered in an arcade of tooth-like structures. These seeming extraoral teeth remain poorly understood, and their evolutionary origin is unclear. We investigate the development of the tenaculum and its teeth throughout the ontogeny of the Spotted Ratfish, Hydrolagus colliei, to assess homology and convergence between this novel craniofacial feature and oral jaws. Our study aims to: (1) describe the development of the tenaculum, (2) assess tenaculum tooth development in comparison to oral teeth and denticles, and (3) characterize the genes and tissues responsible for tenaculum tooth emergence. We found that juvenile male chimaeras develop a full tenaculum before tooth development is complete and that only mature males possess a fully toothed tenaculum. These extraoral teeth emerge from within the tenaculum rather than from the surrounding epithelium. We integrate our developmental data with fossil evidence of the tenacula dentition from the Carboniferous holocephalan Helodus simplex. Our findings show that the tenaculum is closely associated with the upper jaw and that tenacula dentition resembles separate shark-like oral tooth whorls more than modified dermal denticles. Significance StatementThe development and evolutionary history of extraoral dentition in vertebrates remain largely unexplored. This study investigates the ontogeny of the male tenaculum, a unique feature of chimaeras, revealing a tooth development pathway similar to the oral dentition in sharks. By integrating fossil data and molecular techniques, we hypothesize that tenaculum teeth are homologous to oral teeth rather than modified skin denticles, providing key insights into the plasticity of odontogenesis and craniofacial diversity in vertebrates.

developmental biology↗