Cell proliferation and apoptosis in enamelin null mice

Abstract

Enamelin is a secreted glycoprotein that is critical for dental enamel formation. Ameloblasts in enamelin (Enam) null mice develop atypical features that include the absence of a Tomes’ process, expanded endoplasmic reticulum, apparent loss of polarity, and pooling of extracellular matrix in all directions, including between ameloblasts and the stratum intermedium. We hypothesized that ameloblast pathological changes may be associated with increased cell apoptosis. Our objective was to assess apoptotic activity in maxillary first molars of wild-type, Enam+/−, and Enam−/− mice at postnatal days 5, 7, 9, 14, and 17. Mouse maxillae were characterized by light microscopy after terminal deoxynucleotidyl transferase (TdT)-mediated biotin–dUTP nick-end labelling (TUNEL) or 5-bromo-2′-deoxyuridine (BrdU) staining. Following the initial deposition of dentin matrix, ameloblasts became highly dysplastic and no enamel crystal ribbons were deposited. Ameloblast apoptosis was observed in the Enam null mice starting in the secretory stage and with no apparent alteration in cell proliferation. We conclude that in the absence of enamelin and subsequent shutdown of enamel formation, ameloblasts undergo pathological changes early in the secretory stage that are evident as radically altered cell morphology, detachment from the tooth surface, apoptosis, and formation of ectopic calcifications both outside and inside the dystrophic enamel organ.

Enamel ribbons, surface nodules, and octacalcium phosphate in C57BL/6Amelx−/−mice andAmelx+/−lyonization

“…; Hu et al. ); however, Tomes’ processes were not observed penetrating into the surface of the thin Amelx − / − enamel. Immunohistochemistry of Amelx +/+ , Amelx +/ − , and Amelx − / − mandibular incisor cross sections using affinity‐purified polyclonal antibodies raised against recombinant mouse amelogenin (Simmer et al.…”

Ultrastructure of early amelogenesis in wild‐type, Amelx ‐/‐ , and Enam ‐/‐ mice: enamel ribbon initiation on dentin mineral and ribbon orientation by ameloblasts

“…The ameloblasts become increasingly pathological and dysfunctional with time, with the progression of time being evident from the increasing dentin thickness (Hu et al. , ). The FIB series detailing the absence of enamel ribbon formation following the formation of a continuous and expanding layer of dentin is provided in Figures S13–S21.…”

Dental Enamel Development: Proteinases and Their Enamel Matrix Substrates

“…This was attributed to ameloblastin playing a role in cell adhesion. However, ablation of the enamelin gene results in a near identical progressive dysplastic ameloblast layer morphology as is observed in the Ambn mutated mouse [177]. An alternative explanation for the dysplastic ameloblast layer morphology may be that since no enamel layer forms in the Ambn mutated and Enam ablated mice, ameloblasts could fail to adhere to the unnatural surface even if their attachment apparatus remained intact.…”

“…Furthermore, wild-type ameloblasts move back as the enamel layer rapidly thickens and cell proliferation at the cervical loop compensates for this movement of ameloblasts away from the dentin. So, when enamel thickening is absent, as in the case with Ambn and Enam mutations, the ameloblasts occupy a smaller surface than normal that could contribute to their dysplastic morphology [177]. Although the Ambn mutant mice have an ameloblast layer morphology that is disrupted after the early secretory stage, this may be a secondary effect from the almost complete absence of the rapidly thickening enamel layer.…”