Elsevier

Archives of Oral Biology

Volume 50, Issue 2, February 2005, Pages 131-136
Archives of Oral Biology

Dental epithelial histo-morphogenesis in the mouse: positional information versus cell history

https://doi.org/10.1016/j.archoralbio.2004.09.007Get rights and content

Summary

Reciprocal epithelial–mesenchymal interactions control odontogenesis and the cap stage tooth germ mesenchyme specifies crown morphogenesis. The aim of this work was to determine whether this mesenchyme could also control epithelial histogenesis. Dental mesenchyme and enamel organ were dissociated from mouse first lower molars at E14. At this early cap stage, the enamel organ consists of four cell types forming the inner dental epithelium (IDE), primary enamel knot (PEK), outer dental epithelium (ODE) and the stellate reticulum (SR). Pelleted trypsin-dissociated single dental epithelial cells, which had lost all positional information, were reassociated to either dental mesenchyme or dissociated mesenchymal cells and cultured in vitro. Although with different timings, teeth developed in both types of experiments showing a characteristic dental epithelial histogenesis, cusp formation, and the differentiation of functional odontoblasts and ameloblasts. The rapid progression of the initial steps of histogenesis suggested that the cell history was not memorized. The dental mesenchyme, as well as dissociated mesenchymal cells, induced the formation of a PEK indicating that no specific organisation in the mesenchyme is required for this step. However, the proportion of well-formed multicusped teeth was much higher when intact mesenchyme was used instead of dissociated mesenchymal cells. The mesenchymal cell dissociation had consequences for the functionality of the newly-formed PEK.

Introduction

Reciprocal epithelial–mesenchymal interactions control all steps of odontogenesis. Crown morphogenesis (i.e. cusp number, size and position) is specific for each molar in the upper and lower jaws. Tissue reassociation experiments have shown that crown morphogenesis is controlled by the dental mesenchyme.1, 2

Epithelial histogenesis is already initiated at the bud stage since two cell types can be distinguished morphologically. Cells in contact with the basement membrane are elongated, while internal epithelial cells are small and round. Positional information might thus be involved in specifying the cell shape and cell fate as illustrated for other models.3, 4, 5, 6 At the early cap stage, epithelial histogenesis becomes much more complex when the inner dental epithelium (IDE) and outer dental epithelium (ODE), the stellate reticulum (SR) and the primary enamel knot (PEK) become distinct. The molecular mechanisms, which control dental epithelial histogenesis, involve cell–cell and cell–matrix interactions as well as diffusible signaling molecules.7, 8, 9, 10, 11, 12, 13, 14, 15 The aim of the present work was to determine whether the mesenchyme could control epithelial histogenesis. For this purpose, the dental mesenchyme from the cap stage (E14) was reassociated with pelleted single dental epithelial cells, which had lost all positional information, and cultured in vitro. In complementary experiments, dissociated single dental mesenchymal cells were pelleted and reassociated with epithelial cells to test whether the potentialities of the mesenchyme required any specific tissue organisation.

Section snippets

Materials and methods

ICR mice were mated overnight and the detection of the vaginal plug was determined as Embryonic day (E)0. The first lower molars (n = 2420) were dissected from embryos at E14 under a stereomicroscope (Leica MZ9).

Results

Mouse first lower molars were trypsin-dissociated in order to separate the mesenchyme from the epithelium at E14, when the PEK was formed and expressed transcripts for signaling molecules.16 Reassociations between the dental mesenchyme and dissociated single epithelial cells were cultured in vitro (Fig. 1). Complementary experiments were also performed by reassociating pelleted dissociated mesenchymal cells and pelleted dissociated epithelial cells (Fig. 1). In both experimental groups, the

Discussion

When epithelial cells were dissociated, the enamel organ already comprised four distinct cell populations (IDE, PEK, ODE and SR). Their specific fate may be determined by positional information,3, 4, 5 which can be specified by differential cell–cell interactions,8, 9, 15, 17 cell–matrix interactions7, 10, 11, 12, 14, 18 and signaling molecules.13, 19, 20 After trypsin treatment, the breakdown of the basement membrane and cell-surface molecules resulted in the loss of positional information.

Acknowledgement

The authors wish to thank Mr. A. Ackermann for histology.

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