Oral vestibule in the mouse.

<p>In the mouse lower jaw (<b>A</b>), the anterior lower oral vestibule (VO) is a free space of oral cavity bounded externally (labial) by the mucosa of the lips and orally by the alveolar mucosa, gingiva, and teeth (<b>B, C</b>). It originates as a vestibular lamina (VE) adjacent to the dental epithelium (DE), which is a developmental base of functional incisors (FI) comprising epithelial (yellow) and mesenchymal (orange) material. Vestibular lamina itself gives rise to the epithelial lining of the oral vestibule space in an adult mouse lower jaw.</p

One Odontogenic Cell-Population Contributes to the Development of the Mouse Incisors and of the Oral Vestibule

<div><p>The area of the oral vestibule is often a place where pathologies appear (e.g., peripheral odontomas). The origin of these pathologies is not fully understood. In the present study, we traced a cell population expressing Sonic hedgehog (<i>Shh</i>) from the beginning of tooth development using Cre-LoxP system in the lower jaw of wild-type (WT) mice. We focused on <i>Shh</i> expression in the area of the early appearing rudimentary incisor germs located anteriorly to the prospective incisors. The localization of the labelled cells in the incisor germs and also in the inner epithelial layer of the vestibular anlage showed that the first very early developmental events in the lower incisor area are common to the <i>vestibulum oris</i> and the prospective incisor primordia in mice. Scanning electron microscopic analysis of human historical tooth-like structures found in the vestibular area of jaws confirmed their relation to teeth and thus the capability of the vestibular tissue to form teeth. The location of labelled cells descendant of the early appearing <i>Shh</i> expression domain related to the rudimentary incisor anlage not only in the rudimentary and functional incisor germs but also in the externally located anlage of the oral vestibule documented the odontogenic potential of the vestibular epithelium. This potential can be awakened under pathological conditions and become a source of pathologies in the vestibular area.</p></div

Tooth-like structures in a historical skull confirm the odontogenic potential of the vestibular epithelium.

<p>During rescue archaeological research in 2007 and 2008 at the Gan locality (Galanta district, Slovak Republic, the Migration Period, 5th - 6th c. AD), three tooth-like structures were found in a female skull excavated from grave AH19 (<b>A-F</b>). Two tooth-like structures were located in the mandible (<b>A-B</b>) externally to the alveoli (a), one on the surface of the mandibular bone (orange arrowhead, <b>A, C, E</b>) and one within the mandibular bone (black arrowhead, <b>B</b>). One dental particle was found free among the bone fragments (blue arrowhead, <b>C, D, F</b>). Scanning electron microscopy (<b>D-F</b>) showed aprismatic (Ap) and prismatic enamel (p) with tubercles (t) and fossae (f) or grooves (g) formation on the surface of the scanned denticles. Openings (o) presumably for vessels or nerves were detected.</p

Table of the used material—Cre-loxP system Nr.2.

<p>Numbers of harvested embryos (obtained using the tamoxifen inducible Cre-loxP system Nr.2: LacZ x B6.129S6-Shh/J) 24/48/72/96 and 120 hours (h) after tamoxifen injection at embryonic day (E)11.5 positive for X-gal staining.</p

Table of the used material—Cre-loxP system Nr.1.

<p>Numbers of harvested embryos (obtained using the Cre-loxP system Nr.1: LacZ x B6.Cg-<i>Shh</i>^tm1(EGFP/cre)Cjt/J) positive for X-gal staining.</p

Col2a1-CreERT2/R26DTA mouse embryo E17.5

Col2a1-CreERT2/R26DTA mouse embryo injected with 2.5 mg tamoxifen at E12.5 and analysed at embryonic day E17.

(INV6b-C2)/(DEL-90-C2) E17.5

Inversion of the genomic region (INV6b-C2) and Deletion of the genomic region (DEL-90-C2) analyzed at embryonic day E17.

Six1, Six4, double knockout E18.5

Six1, Six4, double knockout analyzed at embryonic day E18.

Nkx2.2-Cre/Shhfloxed/floxed embryos E12.5

Nkx2.2-Cre/Shhfloxed/floxed mouse embryo analyzed at embryonic day E12.

mouse control embryo E18.5

mouse control embryo analyzed at embryonic day E18.