Histogenesis of Swiss white mouse secondary palate from nine and one‐half days to fifteen and one‐half days In utero. I. Epithelial‐mesenchymal relationships—light and electron microscopy

Abstract

Development of the secondary palate in Swiss white mouse embryos was studied from age nine-and-one-half days in utel-o to the stage of mesenchymal coalescence in the secondary palate (approximately fifteen-and-one-half days). The greatest changes observed occur in the mesenchyme. At early stages, mesenchymal cells underlying oral ectoderm of the head are few and only occasionally contact the ectoderm. Electron micrographs show large intercellular spaces between the ectodermal cells. As embryogenesis continues, the mesenchymal cells become more numerous, closer to each other and closer to the epithelium. Just prior to horizontal transposition of shelves, the mesen,chymal cells spread farther from each other and from the palatal epithelium and epithelium of the palatal tip becomes stretched. important to study earlier stages of secondary palate histogenesis. In this paper, we describe palatal development from a stage where neither tongue nor palate are present to the stage of mesenchymal coalescence in the secondary palate. METHODS AND MATERIALSSwiss white female mice were bred in the evening. If a plug was found the next morning, 2:OO AM of that morning was considered day 0 of gestation. Embryos were removed at various time intervals from 9 days, 6 hours to 15 days, 12 hours. They were fixed in 10% neutral formalin or Bouin's and embedded in paraplast, or fixed in 1% (phosphate buffered) OsOd and embedded in Epon (Luft, '61). With younger embryos, the entire body was fixed, while only the head of older embryos was used. Coronal and sagittal sections of

Teratogenicity of arotinoid ethyl ester (RO 13‐6298) in mice

“…It is clear, however, that retinoid-sensitive stages occur as early as day 9. This observation appears to be in contrast to earlier morphological findings that showed that palate development takes place from days 12-15 [48,49]. Owing to the susceptibility of palate development to arotinoid RO 13-6298 on days 8 or 9 of development, precursor processes or primary cells may be directly affected by the compound; alternatively, the closure of the palate may be disturbed indirectly by anatomical abnormalities of the craniofacial system induced on days 8 or 9 [50].…”

Modulations of the epithelial phenotype during embryogenesis and cancer progression

“…Local apoptosis [33,34] or an EMT involving the medial edge cells [35] has been suggested to participate in this event. Recently, vital dye staining shows clearly migrating medial edge cells leaving the midline epithelial seam and migrating towards oral and nasal epithelia, into which they become incorporated [36,37].…”

The Unknown Epithelial and Mesenchymal States Cannot Support Epithelial-Mesenchymal Transition as a Meaningful Concept

“…It is believed that EMT drives the formation of migratory neural crest cells from neuroectoderm, leading to loss of the original neuroepithelial morphology and gain of migratory phenotype with a fibroblast-like shape (Bronner, 2012;Duband et al, 1995;Nieto et al, 1994;Mancilla and Mayor, 1996;Strobl-Mazzulla and Bronner, 2012;Theveneau and Mayor, 2012). During organogenesis, EMT has been reported to involve in the formation of many different types of cells or tissues in an animal, such as fetal liver stroma (Chagraoui et al, 2003), the cardiac cushion tissue (Markwald et al, 1977;Markwald et al, 1996;Person et al, 2005), and oral palatal shelves (Ferguson, 1988;Fitchett and Hay, 1989;Sweney and Shapiro, 1970).…”