title: Mesenchymal Remodeling during Palatal Shelf Elevation Revealed by Extracellular Matrix and F-Actin Expression Patterns.
abstract: During formation of the secondary palate in mammalian embryos, two vertically oriented palatal shelves rapidly elevate into a horizontal position above the tongue, meet at the midline, and fuse to form a single entity. Previous observations suggested that elevation occurs by a simple 90° rotation of the palatal shelves. More recent findings showed that the presumptive midline epithelial cells are not located at the tips of palatal shelves before elevation, but mostly toward their medial/lingual part. This implied extensive tissue remodeling during shelf elevation. Nevertheless, it is still not known how the shelf mesenchyme reorganizes during this process, and what mechanism drives it. To address this question, we mapped the distinct and restricted expression domains of certain extracellular matrix components within the developing palatal shelves. This procedure allowed to monitor movements of entire mesenchymal regions relative to each other during shelf elevation. Consistent with previous notions, our results confirm a flipping movement of the palatal shelves anteriorly, whereas extensive mesenchymal reorganization is observed more posteriorly. There, the entire lingual portion of the vertical shelves moves close to the midline after elevation, whereas the mesenchyme at the original tip of the shelves ends up ventrolaterally. Moreover, we observed that the mesenchymal cells of elevating palatal shelves substantially align their actin cytoskeleton, their extracellular matrix, and their nuclei in a ventral to medial direction. This indicates that, like in other morphogenetic processes, actin-dependent cell contractility is a major driving force for mesenchymal tissue remodeling during palatogenesis.
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Medical Faculty, School of Dental Medicine, University of Bern Bern, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Chiquet
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Medical Faculty, School of Dental Medicine, University of Bern Bern, Switzerland.
authors.forename: Susan
authors.initials: S
authors.lastname: Blumer
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Medical Faculty, School of Dental Medicine, University of Bern Bern, Switzerland.
authors.forename: Manuela
authors.initials: M
authors.lastname: Angelini
authors.affiliation: Orofacial Development and Regeneration, Center for Dental Medicine, Institute for Oral Biology, University of Zurich Zurich, Switzerland.
authors.forename: Thimios A
authors.initials: TA
authors.lastname: Mitsiadis
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Medical Faculty, School of Dental Medicine, University of Bern Bern, Switzerland.
authors.forename: Christos
authors.initials: C
authors.lastname: Katsaros
keywords: actin; extracellular matrix; mouse embryo; palatal shelf elevation; palate morphogenesis; tissue remodeling