Most dentate vertebrates, including humans, replace their teeth and yet the process is poorly understood. Here, we investigate whether dental epithelial stem cells exist in a polyphyodont species, the leopard gecko (Eublepharis macularius). Since the gecko dental epithelium lacks a histologically distinct site for stem cells analogous to the mammalian hair follicle bulge, we performed a pulse-chase experiment on juvenile geckos to identify label-retaining cells (LRCs). We detected LRCs exclusively on the lingual side of the dental lamina, which exhibits low proliferation rates and is not involved in tooth morphogenesis. Lingual LRCs were organized into pockets of high density close to the successional lamina. A subset of the LRCs expresses Lgr5 and other genes that are markers of adult stem cells in mammals. Also similar to mammalian stem cells, the LRCs appear to proliferate in response to gain of function of the canonical Wnt pathway. We suggest that the LRCs in the lingual dental lamina represent a population of stem cells, the immediate descendents of which form the successional lamina and, ultimately, the replacement teeth in the gecko. Furthermore, their location on the non-tooth-forming side of the dental lamina implies that dental stem cells are sequestered from signals that might otherwise induce them to differentiate.
"In one experiment, cells that express genes that are markers of adult stem cells in mammals were found in pockets close to the successional dental lamina. Perhaps they represent a stemcell population whose descendants form the successional lamina and then the replacement teeth, and these dental stem cells are sequestered from signals that might otherwise induce them to differentiate earlier (Handrigan et al. 2010; Richman and Handrigan 2011). An epithelial stem-cell niche also is present in zebrafish and other fish (Huysseune and Thesleff 2004). "
"These issues with current developmental models have led to a recent surge in studies focused on natural tooth replacement in a variety of polyphodont and diphyodont (two sets of teeth) species     . "
[Show abstract][Hide abstract] ABSTRACT: This review considers the diversity observed during both the development and evolution of tooth replacement throughout the vertebrates in a phylogenetic framework from basal extant chondrichthyan fish and more derived teleost fish to mammals. We illustrate the conservation of the tooth regeneration process among vertebrate clades, where tooth regeneration refers to multiple tooth successors formed de novo for each tooth position in the jaws from a common set of retained dental progenitor cells. We discuss the conserved genetic mechanisms that might be modified to promote morphological diversity in replacement dentitions. We review current research and recent progress in this field during the last decade that have promoted our understanding of tooth diversity in an evolutionary developmental context, and show how tooth replacement and dental regeneration have impacted the evolution of the tooth-jaw module in vertebrates.
Seminars in Cell and Developmental Biology 01/2014; 25–26. DOI:10.1016/j.semcdb.2013.12.013 · 6.27 Impact Factor
"Jarvien et al. showed that, in the ferret, Usag-1(also known as Sostdc1, Ectodin, and Wise) is expressed in the elongating successional dental lamina at the interface between the lamina and deciduous tooth, as well as the buccal side of the dental lamina, suggesting that Sostdc1 plays a role in defining the identity of the dental lamina(Jar‐ vinen et al., 2009). Handrigan et al. analysed successional tooth formation in the snake and in lizard, and proposed that dental epithelium stem cells are responsible for the formation of successional lamina, and Wnt signaling may regulate the dental eithelial stem cell fate in these cells (Handrigan et al., 2010). Maintenance or reactivation of component dental lamina is thus pivotal for the replacement tooth and supernumerary formation. "
New Trends in Tissue Engineering and Regenerative Medicine - Official Book of the Japanese Society for Regenerative Medicine, Edited by Hideharu Hibi, Minoru Ueda, 01/2014: chapter 5; InTech., ISBN: 978-953-51-1724-7
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