Fate of the Molar Dental Lamina in the Monophyodont Mouse

Abstract

The successional dental lamina (SDL) plays an essential role in the development of replacement teeth in diphyodont and polyphyodont animals. A morphologically similar structure, the rudimental successional dental lamina (RSDL), has been described in monophyodont (only one tooth generation) lizards on the lingual side of the developing functional tooth. This rudimentary lamina regresses, which has been proposed to play a role in preventing the formation of future generations of teeth. A similar rudimentary lingual structure has been reported associated with the first molar in the monophyodont mouse, and we show that this structure is common to all murine molars. Intriguingly, a lingual lamina is also observed on the non-replacing molars of other diphyodont mammals (pig and hedgehog), initially appearing very similar to the successional dental lamina on the replacing teeth. We have analyzed the morphological as well as ultrastructural changes that occur during the development and loss of this molar lamina in the mouse, from its initiation at late embryonic stages to its disappearance at postnatal stages. We show that loss appears to be driven by a reduction in cell proliferation, down-regulation of the progenitor marker Sox2, with only a small number of cells undergoing programmed cell death. The lingual lamina was associated with the dental stalk, a short epithelial connection between the tooth germ and the oral epithelium. The dental stalk remained in contact with the oral epithelium throughout tooth development up to eruption when connective tissue and numerous capillaries progressively invaded the dental stalk. The buccal side of the dental stalk underwent keratinisation and became part of the gingival epithelium, while most of the lingual cells underwent programmed cell death and the tissue directly above the erupting tooth was shed into the oral cavity.

Heterochronic truncation of odontogenesis in theropod dinosaurs provides insight into the macroevolution of avian beaks

“…Though the precise mechanism by which keratinized oral epithelia would affect the aborally located dental lamina is unclear, acceleration of postnatal growth of the keratinized beak could overgrow alveoli and would likely induce alveolar remodeling. Keratinous epithelial appendages are associated with delayed tooth eruption and truncation of odontogenesis in a range of tetrapods at various embryonic and postnatal ontogenetic stages (26,(30)(31)(32), and cytokeratin expression is up-regulated during degradation of the successional dental lamina in monophyodont (33,34) and diphyodont (35) amniotes. Given that a functional dental lamina and appropriate expression of odontogenic pathways are essential prerequisites for vertebrate tooth formation (5,7,36), dental lamina damage, loss of epithelial-mesenchymal interaction, or even misexpression of odontogenic signals caused by jaw bone remodeling and/or rhamphotheca growth could have led to the tooth reduction in theropods.…”

Evolutionary aspects of the development of teeth and baleen in the bowhead whale

“…Dosedělová et al. () found that a weak crest that projects lingually from the monophyodontic teeth of terrestrial mammals (mouse, hedgehog, pig) is a likely remnant of a developing permanent tooth. This is similar to the crest we observed in the lower dentition of bowhead whales, and we interpret the bowhead tooth bells as part of the primary (deciduous) dentition, and hypothesize that these tooth germs represent the single tooth generation of fossil toothed mysticetes such as aetiocetids.…”

Current Perspectives on Tooth Implantation, Attachment, and Replacement in Amniota

“…Dentition is limited to 2 dental generations over the life of the animal (Figure 4A ). The interruption of tooth replacement is caused by a resorption of the dental lamina after the second generation has started its development ( Dosedělová et al, 2015 ).…”