Organogenesis of the juxta‐oral organ in mice

Abstract

The juxta-oral organ is a bilateral organ in the mammalian bucca. It consists of epithelial cords with surrounding mesenchyme. It develops from embryonic oral epithelium, but its macroscopic morphology in mice is less studied and seems to be very different from that of humans. The juxta-oral organ in mice extends more widely from the subcutaneous tissue of the mandible near the lateral fascia of the masseter to the submucosa of the soft palate. In this paper, we report that the mutant mouse allele Bmp7 lacZ presented intense lacZ expression in the epithelial component of the juxta-oral organ in its homo-and heterozygous states. The main aims of this study were to show that this mutant mouse allele is suitable for observing macroscopic structure of the juxta-oral organ and to describe the development of this organ during embryonic and postnatal stages. Whole-mount β-gal staining of this strain of mouse showed that the juxta-oral organ in mice appeared at E12.0 from oral epithelium and lost connection with it before E12.5. Then, the juxta-oral organ extended anteriorly to the lateral fascia of the masseter and posteriorly to the submucosal layer of the soft palate via the orbit. The mature juxta-oral organ had no connection to other epithelia such as those of the bucca and parotid duct. It persisted until adulthood and there seemed to be no tendency to regress. Transmission electron microscopy showed that each part of the juxta-oral organ was an epithelial cord surrounded by a basement membrane and mesenchymal tissue.

Development of the Juxta‐Oral Organ in Rat Embryo

“…At E15, the JOO was disconnected from the epithelium of origin. In mice, the JOO appeared in the same region at E12 (Ito et al, 2009). Previously, we have observed an epithelial thickening in the proximity of the mandibular nerve, at Carnegie's stage 16 of human embryos (M erida-Velasco et al, 2005).…”

“…Although the molecular mechanisms of the development of the JOO are not known, these appear to differ from the classical epithelium-mesenchyme interaction of other epithelial organs (M erida-Velasco et al, 2005;Ito et al, 2009). We have reported that in human development the mesenchyme surrounding the JOO is loose, while that surrounding the bud of the parotid gland is condensed.…”

“…Previously, we have observed an epithelial thickening in the proximity of the mandibular nerve, at Carnegie's stage 16 of human embryos (M erida-Velasco et al, 2005). Grü neberg (1971) studying mice, found three parts in the JOO, the cauda, corpus, and cervix, whereas Ito et al (2009) called them anterior, middle, and posterior portions, respectively. Examining rats, we observed that the location of JOO is similar, as the anterior part is related to the masseter muscle; the middle part to the temporal muscle, whereas the posterior part is related to the medial pterygoid and the tensor veli palatini muscles, being located near the posterior part of the tongue.…”

“…In humans, the possibility of a receptor function of the JOO has been raised (D'Andrea et al, 1999;Pantanowitz and Balogh, 2003;M erida-Velasco et al, 2005). Recently, Ito et al (2009), studying mice, considered the JOO to be a sensory receptor. Developmentally, mechanoreceptive neuromasts and electroreceptive ampullary organs have been suggested to have arisen from epithelial placodes in amphibians and fish (Northcutt et al, 1995;Gibbs and Northcutt, 2004).…”

“…Zenker's group referred to the persistence of a neuroepithelial organ that they termed the ''juxtaoral organ'' (Salzer and Zenker, 1962). The presence of the juxta-oral organ (JOO) has been reported in a wide range of species such as fish, amphibians, reptiles, birds, and mammals (Zenker and Halz, 1953;Grü neberg, 1971;Jeanneret-Gris, 1980;Ito et al, 2009). In adult humans, the JOO is a neuroepithelial structure located between the temporal and buccinator muscles and near the pterigomandibular raphe (Kramer and Zenker, 1974).…”