Developmental transcriptome evolution supporting the independent evolution of mouse upper molars

Lower and upper molar development mostly rely on the same genes, so correlated evolution is expected. Yet major innovations occurred where their two shapes evolved independently, as with the iconic example of tribosphenic molars in early mammals, or the murine dental plan. Here we studied the latter case to understand how such independent evolution is achieved. Mouse upper molars (but not lower molars) evolved a third row of cusps. We contrasted mouse to hamster, which kept the ancestral dental plan for both upper and lower molar. To study the developmental evolution which enabled this independent evolution, we generated transcriptome timeseries for each species, covering homologous time periods when the tooth crown and its cusps form from soft tissues in the embryo. We also generated bulk transcriptomes for the epithelial and mesenchymal part of tooth germs at specific timepoints, as well as transcriptomes from the buccal and lingual part of the tooth germ, where the new cusps will form. Results are currently published on bioRxiv: https://www.biorxiv.org/content/10.1101/2020.04.22.043422v2