Current Stem Cell Research & Therapy - Volume 13, Issue 1, 2018

Background: Tooth loss occurs with age and significantly impacts the quality of elderly's life both physically and psychologically. It has been well known that odontogenesis is a complicated process with sequential and reciprocal interactions between epithelial and mesenchymal tissues and different types of dental tissue-derived stem cells involve in it. However, only a small portion of the intricate mechanisms has been defined nowadays. Among them, epigenetics has become an increasingly important mechanism for tooth development and regeneration. Objective: This review aims at illustrating the function of epigenetic regulation in odontogenesis, which plays an important role in dental tissue-derived stem cell self-renewal and differentiation nowadays and would be a new strategy for tooth regeneration. Results: In this review, we introduced the natural process of tooth development and the functions of stem cells involved in. Furthermore, we summarized the current knowledge on epigenetic regulation including DNA methylation, histone modification, and non-coding RNAs during odontogenesis, providing the theoretical basis for tooth regeneration. Conclusion: Along with a deeper understanding of odontogenesis, the epigenetic mechanism involved in has become increasingly important. Therefore, it's necessary to further study the functions of epigenetic regulation in tooth development and regeneration, which may make tooth regeneration a reality in the future.

Background: The Hippo signaling pathway serves as a main regulator of tissue growth and organ size through the moderation of cell cycle dynamics across many different species. In mammals, the two downstream transcriptional regulators of this pathway are Yes-associated protein (YAP) and transcriptional co-activator with PDZ binding motif (TAZ). Recent studies found in addition to the core Hippo signaling pathway, other signaling pathways can also regulate YAP/TAZ activity, either directly or through crosstalk with the Hippo pathway. Objective: In this review, we discuss what is known about the regulation of YAP/TAZ from studies conducted using both cell line and mouse models. Conclusion: To add to the complexity of YAP/TAZ regulation, the activity of YAP/TAZ is also controlled by mechanical and cytoskeletal cues and by multiple extracellular factors.

Background: Bone mesenchymal stem cells (BMSCs) are multipotent stromal cells providing a useful cell source for treating bone diseases and metabolic disorders. BMSCs fate determination and lineage progression are controlled by multiple cytokines, transcriptional factors, signaling pathways, and microRNAs (miRNAs). MiRNAs are small non-coding RNAs that inhibit the posttranscriptional gene expression or degrade their targets. They are closely involved in controlling the key steps of osteogenesis and adipogenesis of BMSCs. Objective: We aim to summarize the roles of miRNAs and their pathways in regulating osteogenic and adipogenic differentiation of BMSCs, and sketch its preliminary applications in bone regeneration. Method: We reviewed the published literature about the microRNA regulation in osteogenic and adipogenic differentiation of BMSCs. Results: Most of miRNAs are expressed in BMSCs, perform as negative regulators of osteogenesis and have bidirectional effects on adipogenesis. Runx2 and PPARγ are two key transcriptional factors in osteogenesis and adipogenesis, respectively. Conclusion: Anti-miRNAs or miRNA mimics is potential therapeutic strategy to repress pathological miRNAs for cellular therapies to bone diseases. The preliminary applications of miRNAs in BMSCs strongly suggested their bright future in bone regeneration.

Background: Epigenetic modifications have been evidenced to participate in eukaryotic stem cell fate decision. Among the most studied, 5-methylcytosine (m5C) and its derivatives are wellestablished epigenetic codes that play important roles in stem cell pluripotency and differentiation. Based on improved detection techniques, recent studies have succeeded in defining N6-adenine methylation (m6A) in eukaryotic DNA and RNA. The abundant m6A methylation in RNA was shown to be involved in multiple cellular metabolisms while the presence and functional potential of DNA m6A methylation in different species advanced our knowledge in the m6A-mediated biological processes. Conclusion: m6A modification has been observed during embryogenesis and has been proposed to fine-tune stem cell regulation. The m6A methyltransferases and demethylases work together to control the dynamic state of m6A marks in genomic DNA and RNA to ensure proper cell fate transition and determination, which are vital to the development and survival of eukaryotes.

Background: Mesenchymal stem cells (MSCs) in teeth have been exploited as vital seed cells for stem cell-based dental medicine. To date, several mesenchymal stem cell populations originated from odontogenic tissue have been isolated and characterized by their expression of MSC surface markers and capacity of multi-lineage differentiation, including dental pulp stem cells (DPSCs), stem cells from human exfoliated deciduous teeth (SHED), stem cells from apical papilla (SCAP) and so on. However, their identity in vivo remains elusive, which hinders further understanding of their application in stem cell-based tooth regeneration. Label retaining and lineage tracing analyses, which serve as gold standards for identification of stem cells in vivo, provide feasibility for identifying MSCs in teeth. Objectives: In this review, we will discuss the issues of MSCs, including the origin and identification of both odontogenic and non-odontogenic MSCs, and address the role of nerve-derived Sonic hedgehog (Shh) in the regulation of MSCs in the neurovascular bundle (NVB). Conclusion: Based on label retaining and lineage tracing analyses, latest studies have found new populations of non-odontogenic MSCs in teeth, periarterial-derived and glial-derived, regulated by the Shh derived from nerves in the NVB, which provides a new hope for tooth regeneration.

Background: Epithelial tissues have the ability to self-renew throughout animal's life due to the presence of the epithelial stem cells. Except for complicated genes regulation, the fate of epithelial stem cells is also regulated by the epigenetics, including DNA methylation, histone modification and microRNAs, which are emerging as vital elements of epigenetic regulation for epithelial stem cells self-renewal and differentiation. However, the mechanisms underlying these are still poorly understood. Objective: In this review, we focus on the epigenetic regulation of gene expression in epithelial stem cells fate, using intestinal and epidermal stem cells as models. Meanwhile, a brief description of recent research about the possible impact of network regulation in epithelial stem cell-based amelogenesis by epigenetic regulation is therefore, being discussed. Conclusion: Epigenetic modification plays a vital role in the epithelial stem cells fate choice through the gene expression. The interaction between epigenetic modification and molecular signaling in epithelial stem cells fate choice still needs further exploration.

Background: Long non-coding RNAs (LncRNAs) are non-protein coding transcripts longer than 200 nucleotides in length. Instead of being “transcriptional noise”, lncRNAs are emerging as a key modulator in various biological processes and disease development. Mesenchymal stem cells can be isolated from various adult tissues, such as bone marrow and dental tissues. The differentiation processes into multiple lineages, such as osteogenic differentiation, are precisely orchestrated by molecular signals in both genetic and epigenetic ways. Recently, several lines of evidence suggested the role of lncRNAs participating in cell differentiation through the regulation of gene transcriptions. And the involvement of lncRNAs may be associated with initiation and progression of mesenchymal stem cell-related diseases. Objective: We aimed at addressing the role of lncRNAs in the regulation of osteogenesis of mesenchymal stem cells derived from bone marrow and dental tissues, and discussing the potential utility of lncRNAs as biomarkers and therapeutic targets for mesenchymal stem cell-related diseases. Results: Numerous lncRNAs were differentially expressed during osteogenesis or odontogenesis of mesenchymal stem cells, and some of them were confirmed to be able to regulate the differentiation processes through the modifications of chromatin, transcriptional and post-transcriptional processes. LncRNAs were also associated with some diseases related with pathologic differentiation of mesenchymal stem cells. Conclusion: LncRNAs involve in the osteogenic differentiation of bone marrow and dental tissuederived mesenchymal stem cells, and they could become promising therapeutic targets and prognosis parameters. However, the mechanisms of the role of lncRNAs are still enigmatic and require further investigation.

Background: Some research studies provided evidence for the differentiation capacity of adult stem cells (ASCs) into germ cells (GCs). Since the generation of GCs from stem cells (SCs) has been proposed as a potential way for treatment of infertility, many research groups have begun their creative studies on generation of new GCs both in vitro and in vivo, and utilized different ASC types such as bone marrow mesenchymal stem cells (BM-MSCs), skin stem cells, pancreatic stem cells, and adipose tissue MSCs. Despite many interesting reports with promising results, an obvious problem in the research projects was the functionality of the produced GCs. Objective: In this paper, we have reviewed the results of almost all previously published reports on derivation of male and female GCs from ASCs to provide a better insight into this field of research. Results: The most evaluated papers have shown that ASCs from various tissues can differentiate into GCs but rarely were the produced GCs functional and could form fertile gametes neither in vitro, nor in vivo (after transplantation into the gonads). Conclusion: There are still so many unknown issues about gametogenesis. Perhaps making alterations in treatment methods and utilizing creative techniques like tissue engineering and gene targeting help to achieve a standard method of in vitro GC production from ASCs.