Death is the major fate of medial edge epithelial cells and the cause of basal lamina degradation during palatogenesis.
ABSTRACT During mammalian development, a pair of shelves fuses to form the secondary palate, a process that requires the adhesion of the medial edge epithelial tissue (MEE) of each shelf and the degeneration of the resulting medial epithelial seam (MES). It has been reported that epithelial-mesenchymal transformation (EMT) occurs during shelf fusion and is considered a fundamental process for MES degeneration. We recently found that cell death is a necessary process for shelf fusion. These findings uncovered the relevance of cell death in MES degeneration; however, they do not discard the participation of other processes. In the present work, we focus on the evaluation of the processes that could contribute to palate shelf fusion. We tested EMT by traditional labeling of MEE cells with a dye, by infection of MEE with an adenovirus carrying the lacZ gene, and by fusing wild-type shelves with the ones from EGFP-expressing mouse embryos. Fate of MEE labeled cells was followed by culturing whole palates, or by a novel slice culture system that allows individual cells to be followed during the fusion process. Very few labeled cells were found in the mesenchyme compartment, and almost all were undergoing cell death. Inhibition of metalloproteinases prevented basal lamina degradation without affecting MES degeneration and MEE cell death. Remarkably, independently of shelf fusion, activation of cell death promoted the degradation of the basal lamina underlying the MEE ('cataptosis'). Finally, by specific labeling of periderm cells (i.e. the superficial cells that cover the basal epithelium), we observed that epithelial triangles at oral and nasal ends of the epithelial seam do not appear to result from MEE cell migration but rather from periderm cell migration. Inhibition of migration or removal of these periderm cells suggests that they have a transient function controlling MEE cell adhesion and survival, and ultimately die within the epithelial triangles. We conclude that MES degeneration occurs almost uniquely by cell death, and for the first time we show that this process can activate basal lamina degradation during a developmental process.
- Current Topics in Developmental Biology - CURR TOP DEVELOP BIOL. 01/2005; 66:65-133.
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ABSTRACT: Background: Retinoic acid (RA) is a key regulator of embryonic development and linked to several birth defects including cleft lip and palate (CLP). The aim was to investigate the effects of RA on proliferation and gene expression of human palatal keratinocytes (KCs) in vitro. Methods: KCs from children with and without CLP were cultured with 2 and 5 μM RA. Proliferation was measured by quantification of DNA after 2, 4, 6, and 8 days. In addition, we analysed the effects of RA on messenger RNA expression of genes for proliferation, differentiation, apoptosis, and RA receptors. Results: RA similarly inhibited proliferation of palatal KC from cleft and non-cleft subjects. The proliferation of KCs from cleft subjects was reduced to 59.8±13.4% (2 μM) and 41.5±14.0% (5 μM, Day 6), while that of cells from age-matched non-cleft subjects was reduced to 66.9±12.1% (2 μM) and 33.9±10.1% (5 μM). RA treatment reduced the expression of several of the investigated genes; the proliferating cell nuclear antigen (PCNA) was reduced in CLP KCs only. Keratins 10 and 16 were downregulated in keratinocytes from both cleft and non-cleft subjects. P63, a master regulator for epithelial differentiation, was only downregulated in KCs from cleft subjects, as was the RXRa receptor. Two P63 target genes (GJB6 and DLX5) were strongly downregulated by RA in all cell lines. None of the apoptosis genes was affected. Conclusion: Overall, RA similarly inhibits proliferation of palatal KCs from cleft and non-cleft subjects and reduces the expression of specific genes.The European Journal of Orthodontics 02/2014; · 1.08 Impact Factor
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ABSTRACT: This paper describes the design and development of an experimental machine capable of drawing metallic rod or wire without the use of metal forming dies as used in conventional wire/rod drawing process. Conventional wire and rod forming processes have a number of drawbacks which include die wear, lubrication requirements, pre-cleaning of precursor stock and a requirement for multiple passes through dies to achieve significant reductions in diameter. Consequently, a dieless drawing system has been developed to address the aforementioned drawbacks. This novel system can effect a reduction in diameter of a metallic rod without the use of drawing dies by heating a localised area of the rod while a tensile load is applied along its longitudinal axis. The dieless drawing process was feasible through precise control of process parameters such as drawing velocity, temperature and rates of both heating and cooling. The machine operated in a closed-loop system where identification of the onset of yield in the workpiece material was used to control the process, and consequently, allow steady state dieless drawing. The machine was designed to draw both mild steel and high carbon steel rods at elevated temperatures.The results of an experimental programme carried out with the machine indicate that the dieless forming method is feasible for the production of metallic materials in wire or bar form.CIRP Journal of Manufacturing Science and Technology 01/2011; 4(1):110-117.