SequentialShhexpression in the development of the mouse upper functional incisor

Abstract

The mouse incisor is a frequently used model in studies of the molecular control of organ development. The appropriate interpretation of data on normogenesis is essential for understanding the data obtained in mutant mice. For this reason, we performed a very detailed investigation of the development of the upper incisor in wild-type mice from embryonic day (ED) 11.5 till 14.5. A combination of histology, whole mount in situ hybridization, computer-aided three-dimensional reconstructions, and fluorescent microscopy, has been used. Several sonic hedgehog (Shh) expression domains have been detected in the upper incisor region during early prenatal development. At ED11.5-13.5, there was a single Shh positive domain present in the anterior part of left or right upper jaw arches, corresponding to the epithelial thickening. More posteriorly, a new Shh expression domain appeared in the incisor bud in the developmentally more advanced ED13.5 embryos. At ED14.5, only this posterior Shh expression in the incisor germ remained detectable. This study brings new insights into the early development of the upper incisor in mice and completes the data on normal mouse incisor development. The temporal-spatial pattern of Shh expression reflects the development of two tooth generations, being detectable in two successive, antero-posteriorly located areas in the prospective incisor region in the upper jaw. The first, anterior and superficial Shh expression domain reflects the rudimentary tooth development suppressed during evolution. Only the subsequent, posterior and deeper Shh expression region, appearing at ED13.5, correlates with the prospective upper functional incisor in wild-type mice.

The Grooved Rodent Incisor Recapitulates Rudimentary Teeth Characteristics of Ancestral Mammals

“…To further study the development of the rudimentary dental primordia in the gerbil upper incisor, we analyzed the expression patterns of Shh, an initial marker for early odontogenesis (Sarkar et al 2000;Hovorakova et al 2013). At E18.5, a single strip of Shh transcription domain appeared in the labial dental epithelium in each upper incisor quadrant ( Fig.…”

“…Typically, extra incisors in the mice could only be gotten from the trimmed explants at or prior to the bud stage (Munne et al 2009), at a time point before the labial expression of Shh disappeared (Hovorakova et al 2013), suggesting that the extra incisors may result from the reviving of the rudimentary primordia. A reviving of rudimentary primordia in vitro may shed light on the incisor patterns during evolution.…”

“…Peterkova et al (1993Peterkova et al ( , 2006 proposed that the functional incisors originate from the integration of 3 primordia in the mandible and 5 to 6 primordia in the maxilla based on histological and 3-dimensional (3D) reconstruction analyses. Further molecular analysis detected 2 labial and superficial Shh expressed domains in the vestigial primordia, as well as 1 lingual and deeper Shh expressed domain in the functional incisor (Hovorakova et al 2013). In contrast, some studies described that the incisor in mouse corresponds to the medial incisor of eutherian dental formula, while the other 2 primordia are lost (Strassburg et al 1971;Charles et al 2011).…”

“…In contrast, some studies described that the incisor in mouse corresponds to the medial incisor of eutherian dental formula, while the other 2 primordia are lost (Strassburg et al 1971;Charles et al 2011). A concentration of apoptosis occurs at the anterior limit of the functional incisor primordium in the lower (Kieffer et al 1999) and upper (Hovorakova et al 2013) jaws, relating to the suppression of the rudimentary incisor primordia in both cases Hovorakova et al 2013). Moreover, it has been proven that both integration and regression play roles in the morphogenesis of the first molar in mouse (Prochazka et al 2010;Lagronova-Churava et al 2013).…”

“…At the initiation stage, the transcription of Shh in the thickened epithelium represents odontogenesis (Sarkar et al 2000;Hovorakova et al 2013). Prior to the bud stage, the tooth inductive potential resides in the epithelium.…”