The control of neural stem cells by morphogenic signals

A complex orchestration of stem-cell specification, expansion and differentiation is required for the proper development of the nervous system. Although progress has been made on the role of individual genes in each of these processes, there are still unresolved questions about how gene function translates to the dynamic assembly of cells into tissues. Recently, stem-cell biology has emerged as a bridge between the traditional fields of cell biology and developmental genetics. In addition to their potential therapeutic role, stem cells are being exploited as experimental 'logic chips' that integrate information and exhibit self-organizing properties. Recent studies provide new insights on how morphogenic signals coordinate major stem cell decisions to regulate the size, shape and cellular diversity of the nervous system.     

Convergence of human pluripotent stem cell,organoid, and genome editing technologies

The last decade has seen many exciting technological breakthroughs that greatly expanded the toolboxes for biological and biomedical research, yet few have had more impact than induced pluripotent stem cells and modern-day genome editing. These technologies are providing unprecedented opportunities to improve physiological relevance of experimental models, further our understanding of developmental processes, and develop novel therapies. One of the research areas that benefit greatly from these technological advances is the three-dimensional human organoid culture systems that resemble human tissues morphologically and physiologically. Here we summarize the development of human pluripotent stem cells and their differentiation through organoid formation. We further discuss how genetic modifications, genome editing in particular, were applied to answer basic biological and biomedical questions using organoid cultures of both somatic and pluripotent stem cell origins. Finally, we discuss the potential challenges of applying human pluripotent stem cell and organoid technologies for safety and efficiency evaluation of emerging genome editing tools.     

Understanding cornea epithelial stem cells and stem cell deficiency: Lessons learned using vertebrate model systems

Animal models have contributed greatly to our understanding of human diseases. Here, we focus on cornea epithelial stem cell (CESC) deficiency (commonly called limbal stem cell deficiency, LSCD). Corneal development, homeostasis and wound healing are supported by specific stem cells, that include the CESCs. Damage to or loss of these cells results in blindness and other debilitating ocular conditions. Here we describe the contributions from several vertebrate models toward understanding CESCs and LSCD treatments. These include both mammalian models, as well as two aquatic models, Zebrafish and the amphibian, Xenopus. Pioneering developments have been made using stem cell transplants to restore normal vision in patients with LSCD, but questions still remain about the basic biology of CESCs, including their precise cell lineages and behavior in the cornea. We describe various cell lineage tracing studies to follow their patterns of division, and the fates of their progeny during development, homeostasis, and wound healing. In addition, we present some preliminary results using the Xenopus model system. Ultimately, a more thorough understanding of these cornea cells will advance our knowledge of stem cell biology and lead to better cornea disease therapeutics.     

Potential of embryonic and adult stem cells in vitro

Recent developments in the field of stem cell research indicate their enormous potential as a source of tissue for regenerative therapies. The success of such applications will depend on the precise properties and potentials of stem cells isolated either from embryonic, fetal or adult tissues. Embryonic stem cells established from the inner cell mass of early mouse embryos are characterized by nearly unlimited proliferation, and the capacity to differentiate into derivatives of essentially all lineages. The recent isolation and culture of human embryonic stem cell lines presents new opportunities for reconstructive medicine. However, important problems remain; first, the derivation of human embryonic stem cells from in vitro fertilized blastocysts creates ethical problems, and second, the current techniques for the directed differentiation into somatic cell populations yield impure products with tumorigenic potential. Recent studies have also suggested an unexpectedly wide developmental potential of adult tissue-specific stem cells. Here too, many questions remain concerning the nature and status of adult stem cells both in vivo and in vitro and their proliferation and differentiation/transdifferentiation capacity. This review focuses on those issues of embryonic and adult stem cell biology most relevant to their in vitro propagation and differentiation. Questions and problems related to the use of human embryonic and adult stem cells in tissue regeneration and transplantation are discussed.     

MicroRNAs对动物皮肤和毛发发育调控作用的研究进展

MicroRNAs是近年来发现的一类由19-25个核苷酸组成的非编码单链小RNA分子,它们通过与靶基因mRNA3’UTR结合抑制靶基因的翻译,在转录后水平调控基因表达.MicroRNAs参与了包括细胞分化、增殖和凋亡及免疫系统应答在内的一系列发育调控和生物学过程.最近研究发现MicroRNAs在多种哺乳动物皮肤中均表达,并参与了哺乳动物皮肤及毛发发育的调控过程,这些都为研究这个新颖的调控因子在干细胞生物学和发育生物学中的功能奠定了基础.本文综述了近年来MicroRNAs对哺乳动物皮肤和毛发发育调控作用的研究状况.     

Photomodulatable fluorescent proteins for imaging cell dynamics and cell fate

An organism arises from the coordinate generation of different cell types and the stereotypical organization of these cells into tissues and organs. Even so, the dynamic behaviors, as well as the ultimate fates, of cells driving the morphogenesis of an organism, or even an individual organ, remain largely unknown. Continued innovations in optical imaging modalities, along with the discovery and evolution of improved genetically-encoded fluorescent protein reporters in combination with model organism, stem cell and tissue engineering paradigms are providing the means to investigate these unresolved questions. The emergence of fluorescent proteins whose spectral properties can be photomodulated is one of the most significant new developments in the field of cell biology where they are primarily used for studying protein dynamics in cells. Likewise, the use of photomodulatable fluorescent proteins holds great promise for use in developmental biology. Photomodulatable fluorescent proteins also represent attractive and emergent tools for studying cell dynamics in complex populations by facilitating the labeling and tracking of individual or defined groups of cells. Here, we review the currently available photomodulatable fluorescent proteins and their application in model organisms. We also discuss prospects for their use in mice, and by extension in embryonic stem cell and tissue engineering paradigms.     

Cell biology of stem cells: an enigma of asymmetry and self-renewal

Stem cells present a vast, new terrain of cell biology. A central question in stem cell research is how stem cells achieve asymmetric divisions to replicate themselves while producing differentiated daughter cells. This hallmark of stem cells is manifested either strictly during each mitosis or loosely among several divisions. Current research has revealed the crucial roles of niche signaling, intrinsic cell polarity, subcellular localization mechanism, asymmetric centrosomes and spindles, as well as cell cycle regulators in establishing self-renewing asymmetry during stem cell division. Much of this progress has benefited from studies in model stem cell systems such as Drosophila melanogaster neuroblasts and germline stem cells and mammalian skin stem cells. Further investigations of these questions in diverse types of stem cells will significantly advance our knowledge of cell biology and allow us to effectively harness stem cells for therapeutic applications.     

Gene correction in patient-specific iPSCs for therapy development and disease modeling

The discovery that mature cells can be reprogrammed to become pluripotent and the development of engineered endonucleases for enhancing genome editing are two of the most exciting and impactful technology advances in modern medicine and science. Human pluripotent stem cells have the potential to establish new model systems for studying human developmental biology and disease mechanisms. Gene correction in patient-specific iPSCs can also provide a novel source for autologous cell therapy. Although historically challenging, precise genome editing in human iPSCs is becoming more feasible with the development of new genome-editing tools, including ZFNs, TALENs, and CRISPR. iPSCs derived from patients of a variety of diseases have been edited to correct disease-associated mutations and to generate isogenic cell lines. After directed differentiation, many of the corrected iPSCs showed restored functionality and demonstrated their potential in cell replacement therapy. Genome-wide analyses of gene-corrected iPSCs have collectively demonstrated a high fidelity of the engineered endonucleases. Remaining challenges in clinical translation of these technologies include maintaining genome integrity of the iPSC clones and the differentiated cells. Given the rapid advances in genome-editing technologies, gene correction is no longer the bottleneck in developing iPSC-based gene and cell therapies; generating functional and transplantable cell types from iPSCs remains the biggest challenge needing to be addressed by the research field.     

LeX/ssea-1 is expressed by adult mouse CNS stem cells,identifying them as nonependymal

Adult neural stem cells are rare, and little is known about their unique characteristics, leaving their in vivo identity enigmatic. We show that Lewis X (LeX), a carbohydrate expressed by embryonic pluripotent stem cells, is made by adult mouse subventricular zone (SVZ) stem cells and shed into their environment. Only 4% of acutely isolated SVZ cells are LeX(+); this subpopulation, purified by FACS, contains the SVZ stem cells. Ependymal cells are LeX(-), and purified ependymal cells do not make neurospheres, resolving the controversial claim that these are stem cells. Thus, LeX expression by adult CNS stem cells aids their in vivo identification, allows their enrichment, and raises new questions about the role of this unusual carbohydrate in stem cell biology.     

The Emergence of Stem Cell‐Based Brain Organoids: Trends and Challenges

Recent developments in 3D cultures exploiting the self‐organization ability of pluripotent stem cells have enabled the generation of powerful in vitro systems termed brain organoids. These 3D tissues recapitulate many aspects of human brain development and disorders occurring in vivo. When combined with improved differentiation methods, these in vitro systems allow the generation of more complex “assembloids,” which are able to reveal cell diversities, microcircuits, and cell–cell interactions within their 3D organization. Here, the ways in which human brain organoids have contributed to demystifying the complexities of brain development and modeling of developmental disorders is reviewed and discussed. Furthermore, challenging questions that are yet to be addressed by emerging brain organoid research are discussed.     

果蝇干细胞研究进展

本文主要介绍了果蝇五种干细胞,包括生殖干细胞、神经干细胞、造血干细胞、小肠干细胞、肾干细胞及其微环境（niche）的组成成份;简述了五种干细胞系统对应的分子标记;最后重点介绍了调控每种干细胞系统的信号通路。     

Chemical genetics: adding to the developmental biology toolbox

Recent advances in cell and molecular biology have generated important tools to probe developmental questions. In addition, new genetic model systems such as Danio rerio now make large-scale vertebrate early developmental mutant screens feasible. Nonetheless, some developmental questions remain difficult to study because of the need for finer temporal, spatial, or tuneable control of gene function within a developmental system. New uses for old teratogens as well as novel chemical modulators of development have begun to fill this void.     

Derivation of rhesus monkey parthenogenetic embryonic stem cells and its microRNA signature

Parthenogenetic embryonic stem cells are considered as a promising resource for regeneration medicine and powerful tools for developmental biology. A lot of studies have revealed that embryonic stem cells have distinct microRNA expression pattern and these microRNAs play important roles in self-renewal and pluripotency of embryonic stem cells. However, few studies concern about microRNA expression pattern in parthenogenetic embryonic stem cells, especially in non-human primate--the ideal model species for human, largely due to the limited rhesus monkey parthenogenetic embryonic stem cells (rpESCs) available and lack of systematic analysis of the basics of rpESCs. Here, we derived two novel rpESCs lines and characterized their microRNA signature by Solexa deep sequencing. These two novel rpESCs shared many properties with other primate ESCs, including expression of pluripotent markers, capacity to generate derivatives representative of all three germ layers in vivo and in vitro, maintaining of euploid karyotype even after long culture. Additionally, lack of some paternally expressed imprinted genes and identity of Single-nucleotide Polymorphism (SNP) compare to their oocyte donors support their parthenogenesis origin. By characterizing their microRNA signature, we identified 91 novel microRNAs, except those are also detected in other primate ESCs. Moreover, these two novel rpESCs display a unique microRNA signature, comparing to their biparental counterpart ESCs. Then we analyzed X chromosome status in these two novel rpESCs; results suggested that one of them possesses two active X chromosomes, the other possesses only one active X chromosome liking biparental female embryonic stem cells. Taken together, our novel rpESCs provide a new alternative to existing rhesus monkey embryonic stem cells, microRNA information expands rhesus monkey microRNA data and may help understanding microRNA roles in pluripotency and parthenogenesis.     

Separation technologies for stem cell bioprocessing

Stem cells have been the focus of an intense research due to their potential in Regenerative Medicine, drug discovery, toxicology studies, as well as for fundamental studies on developmental biology and human disease mechanisms. To fully accomplish this potential, the successful application of separation processes for the isolation and purification of stem cells and stem cell‐derived cells is a crucial issue. Although separation methods have been used over the past decades for the isolation and enrichment of hematopoietic stem/progenitor cells for transplantation in hemato‐oncological settings, recent achievements in the stem cell field have created new challenges including the need for novel scalable separation processes with a higher resolution and more cost‐effective. Important examples are the need for high‐resolution methods for the separation of heterogeneous populations of multipotent adult stem cells to study their differential biological features and clinical utility, as well as for the depletion of tumorigenic cells after pluripotent stem cell differentiation. Focusing on these challenges, this review presents a critical assessment of separation processes that have been used in the stem cell field, as well as their current and potential applications. The techniques are grouped according to the fundamental principles that govern cell separation, which are defined by the main physical, biophysical, and affinity properties of cells. A special emphasis is given to novel and promising approaches such as affinity‐based methods that take advantage of the use of new ligands (e.g., aptamers, lectins), as well as to novel biophysical‐based methods requiring no cell labeling and integrated with microscale technologies. Biotechnol. Bioeng. 2012; 109: 2699–2709. © 2012 Wiley Periodicals, Inc.     

Human neural stem cells: a new tool for studying cortical development in Down's syndrome

The clinical characteristics of Down's syndrome (DS), or trisomy 21, are caused by errors that occur during development. In addition to mental retardation, DS individuals have craniofacial abnormalities, clinical defects of the heart, gut and immune system, as well as predisposition to certain diseases, such as leukemias and Alzheimer's disease. To explain the developmental mechanisms that cause these traits, it is necessary to look at how developmental processes in DS compare to normal development. The neurological characteristics of DS are established during the prenatal and early postnatal period in humans, when the bulk of brain development occurs. Mouse models of DS have provided a useful way of studying DS neural development. However, there are clearly significant differences between rodent and human biology that may not be reflected in mouse models. Recent advances in stem cell biology now allow the generation of human neural tissue in the culture dish ( Ostenfeld & Svendsen 2003 ). Stem cells offer a novel model system to study alterations in neuron development in developmental disorders such as DS.     

Embryonic stem cells and cardiomyocyte differentiation: phenotypic and molecular analyses

Embryonic stem (ES) cell lines, derived from the inner cell mass (ICM) of blastocyst-stage embryos, are pluripotent and have a virtually unlimited capacity for self-renewal and differentiation into all cell types of an embryoproper. Both human and mouse ES cell lines are the subject of intensive investigation for potential applications in developmental biology and medicine. ES cells from both sources differentiate in vitro into cells of ecto-, endoand meso-dermal lineages, and robust cardiomyogenic differentiation is readily observed in spontaneously differentiating ES cells when cultured under appropriate conditions. Molecular, cellular and physiologic analyses demonstrate that ES cell-derived cardiomyocytes are functionally viable and that these cell derivatives exhibit characteristics typical of heart cells in early stages of cardiac development. Because terminal heart failure is characterized by a significant loss of cardiomyocytes, the use of human ES cell-derived progeny represents one possible source for cell transplantation therapies. With these issues in mind, this review will focus on the differentiation of pluripotent embryonic stem cells into cardiomyocytes as a developmental model, and the possible use of ES cell-derived cardiomyocytes as source of donor cells.     

体细胞重编程逆转为干细胞的研究进展

目前细胞和发育生物学上的研究成果为生物医学研究提供了广泛的前景.将完全分化的细胞重编程,不经过胚胎逆转为多能干细胞状态,这点燃了再生医学应用的新希望,这一成果从法律、道德、伦理等不同方面被人们所接受.通过体细胞克隆胚胎获得干细胞所面临的破坏胚胎的伦理限制,促使研究者去寻求将分化细胞重编程逆转为干细胞的新方法.主要论述了体细胞重编程的原理、过程及不经过胚胎逆转为多能干细胞的方法.     

Induced pluripotent stem cells,a giant leap for mankind therapeutic applications

Induced pluripotent stem cells (iPSC) technology has propelled the field of stem cells biology, providing new cells to explore the molecular mechanisms of pluripotency, cancer biology and aging. A major advantage of human iPSC, compared to the pluripotent embryonic stem cells, is that they can be generated from virtually any embryonic or adult somatic cell type without destruction of human blastocysts. In addition, iPSC can be generated from somatic cells harvested from normal individuals or patients, and used as a cellular tool to unravel mechanisms of human development and to model diseases in a manner not possible before. Besides these fundamental aspects of human biology and physiology that are revealed using iPSC or iPSC-derived cells, these cells hold an immense potential for cell-based therapies, and for the discovery of new or personalized pharmacological treatments for many disorders. Here, we review some of the current challenges and concerns about iPSC technology. We introduce the potential held by iPSC for research and development of novel health-related applications. We briefly present the efforts made by the scientific and clinical communities to create the necessary guidelines and regulations to achieve the highest quality standards in the procedures for iPSC generation, characterization and long-term preservation. Finally, we present some of the audacious and pioneer clinical trials in progress with iPSC-derived cells.