New insight into dental epithelial stem cells:Identification,regulation,and function in tooth homeostasis and repair

Tooth enamel,a highly mineralized tissue covering the outermost area of teeth,is always damaged by dental caries or trauma.Tooth enamel rarely repairs or renews itself,due to the loss of ameloblasts and dental epithelial stem cells(DESCs)once the tooth erupts.Unlike human teeth,mouse incisors grow continuously due to the presence of DESCs that generate enamel-producing ameloblasts and other supporting dental epithelial lineages.The ready accessibility of mouse DESCs and wide availability of related transgenic mouse lines make mouse incisors an excellent model to examine the identity and heterogeneity of dental epithelial stem/progenitor cells;explore the regulatory mechanisms underlying enamel formation;and help answer the open question regarding the therapeutic development of enamel engineering.In the present review,we update the current understanding about the identification of DESCs in mouse incisors and summarize the regulatory mechanisms of enamel formation driven by DESCs.The roles of DESCs during homeostasis and repair are also discussed,which should improve our knowledge regarding enamel tissue engineering.

Injury-associated reacquiring of intestinal stem cell function

Epithelial layer of the intestine relies upon stem cells for maintaining homeostasis and regeneration.Two types of stem cells are currently defined in intestinal crypts:the cycling crypt base columnar cells and quiescent cells.Though several candidate markers and regulators of rapidly cycling and quiescent stem cells have been identified so far,the exact nature of quiescent cells is still questionable since investigations mainly focused on candidate markers rather than the label-retaining population itself.Recent results,however,have streng-thened the argument for functional plasticity.Using a lineage tracing strategy label-retaining cells(LRCs)of the intestinal epithelium were marked,then followed by a pulse-chase analysis it was found that during homeostasis,LRCs were Lgr5-positive and were destined to become Paneth and neuroendocrine cells.Nevertheless,it was demonstrated that LRCs are capable of clonogenic growth by recall to the self-renewing pool of stem cells in case of epithelial injury.These new findings highlight on the hierarchical and spatial organization of intestinal epithelial homeostasis and the important plasticity of progenitors during tissue regeneration,moreover,provide a motivation for studying their role in disorders like colorectal cancer.

Adult stem-like cells in kidney

Human pluripotent cells are promising for treatment for kidney diseases, but the protocols for derivation of kidney cell types are still controversial. Kidney tissue regeneration is well confirmed in several lower vertebrates such as fish, and the repair of nephrons after tubular damages is commonly observed after renal injury. Even in adult mammal kidney, renal progenitorcell or system is reportedly presents suggesting that adult stem-like cells in kidney can be practical clinical targets for kidney diseases. However, it is still unclear if kidney stem cells or stem-like cells exist or not. In general, stemness is defined by several factors such as self-renewal capacity, multi-lineage potency and characteristic gene expression profiles. The definite use of stemness may be obstacle to understand kidney regeneration, and here we describe the recent broad findings of kidney regeneration and the cells that contribute regeneration.