Hematopoietic progenitors express embryonic stem cell and germ layer genes

Cell therapy for tissue regeneration requires cells with high self-renewal potential and with the capacity to differentiate into multiple differentiated cell lineages, like embryonic stem cells (ESCs) and adult somatic cells induced to pluripotency (iPSCs) by genetic manipulation. Here we report that normal adult mammalian bone marrow contains cells, with the cell surface antigen CD34, that naturally express genes characteristic of ESCs and required to generate iPSCs. In addition, these CD34+ cells spontaneously express, without genetic manipulation, genes characteristic of the three embryonic germ layers: ectoderm, mesoderm and endoderm. In addition to the neural lineage genes we previously reported in these CD34+ cells, we found that they express genes of the mesodermal cardiac muscle lineage and of the endodermal pancreatic lineage as well as intestinal lineage genes. Thus, these normal cells in the adult spontaneously exhibit characteristics of embryonic-like stem cells.     

Identification of neural progenitors in the adult mammalian eye

We have shown that the embryonic mammalian retina contains neural progenitors which display stem cell properties in vitro. Here we report the characterization of neural progenitors isolated from the adult mammalian eye. These quiescent cells, located in the pigmented ciliary bodies, proliferate in the presence of FGF2 and express the neuroectodermal marker nestin. The proliferating cells give rise to neural spheres and are multipotential; they express cell type-specific markers corresponding to neurons and glia. In addition, neural progenitors can generate secondary neural spheres, thus displaying potential to self-renew. The ciliary body-derived neural progenitors display retina-specific properties; the undifferentiated cells express Chx10, a retinal progenitor marker, and upon differentiation express markers corresponding to specific retinal cell types. Therefore, the pigmented ciliary body in the adult mammalian eye harbors neural progenitors that display stem cell properties and have the capacity to give rise to retinal neurons in vitro.     

Identification and culture of olfactory neural progenitors from GFP mice

The olfactory epithelium (OE) is one of the best sources for obtaining adult stem cells from the nervous system, because it contains neural progenitors that regenerate continuously throughout life. The OE is accessible through the nasal cavity, which facilitates stem cell harvest for examination and transplantation. The mitotic activity of OE progenitors can be stimulated by intranasal irrigation with zinc sulfate (ZnSO₄). In the study reported here, we focused on OE from a transgenic mouse line transfected with green fluorescent protein (GFP). Histological examination demonstrated the site of highest yield of OE in the transgenic and wild type littermates. Cultures were established from that site four days in vitro following ZnSO₄ exposure. The GFP-derived primary cultures contained a heterogeneous population of fluorescent cells. After 10-12 days, a population of round, mitotically active cells emerged that formed fluorescent neurospheres. The neurosphere forming cells (NSFCs) were collected and subcultured up to four times. The NSFCs were primarily neuronal with only a few cells of glial lineage. Furthermore, the NSFCs were nestin positive and keratin negative, suggesting that they were neural progenitors. The endogenous GFP fluorescence of these cells provides a readily identifiable label that will facilitate their identification following transplantation into nontransfected hosts. They should provide a useful model for evaluating the potential therapeutic utility of OE progenitors in neurodegenerative diseases and neurotrauma repair.     

Progressive restriction in fate potential by neural progenitors during cerebral cortical development

During early stages of cerebral cortical development, progenitor cells in the ventricular zone are multipotent, producing neurons of many layers over successive cell divisions. The laminar fate of their progeny depends on environmental cues to which the cells respond prior to mitosis. By the end of neurogenesis, however, progenitors are lineally committed to producing upper-layer neurons. Here we assess the laminar fate potential of progenitors at a middle stage of cortical development. The progenitors of layer 4 neurons were first transplanted into older brains in which layer 2/3 was being generated. The transplanted neurons adopted a laminar fate appropriate for the new environment (layer 2/3), revealing that layer 4 progenitors are multipotent. Mid-stage progenitors were then transplanted into a younger environment, in which layer 6 neurons were being generated. The transplanted neurons bypassed layer 6, revealing that layer 4 progenitors have a restricted fate potential and are incompetent to respond to environmental cues that trigger layer 6 production. Instead, the transplanted cells migrated to layer 4, the position typical of their origin, and also to layer 5, a position appropriate for neither the host nor the donor environment. Because layer 5 neurogenesis is complete by the stage that progenitors were removed for transplantation, restrictions in laminar fate potential must lag behind the final production of a cortical layer. These results suggest that a combination of intrinsic and environmental cues controls the competence of cortical progenitor cells to produce neurons of different layers.     

Identification of microRNAs associated with hyperthermia-induced cellular stress response

MicroRNAs (miRNAs) are a class of small RNAs that play a critical role in the coordination of fundamental cellular processes. Recent studies suggest that miRNAs participate in the cellular stress response (CSR), but their specific involvement remains unclear. In this study, we identify a group of thermally regulated miRNAs (TRMs) that are associated with the CSR. Using miRNA microarrays, we show that dermal fibroblasts differentially express 123 miRNAs when exposed to hyperthermia. Interestingly, only 27 of these miRNAs are annotated in the current Sanger registry. We validated the expression of the annotated miRNAs using qPCR techniques, and we found that the qPCR and microarray data was in well agreement. Computational target-prediction studies revealed that putative targets for the TRMs are heat shock proteins and Argonaute-2—the core functional unit of RNA silencing. These results indicate that cells express a specific group of miRNAs when exposed to hyperthermia, and these miRNAs may function in the regulation of the CSR. Future studies will be conducted to determine if other cells lines differentially express these miRNAs when exposed to hyperthermia.     

Identification and characterization of lineage-specific genes in Populus trichocarpa

Species- or lineage-specific genes can facilitate studying the unique characteristics of biological processes. Updated genome sequences in Populus trichocarpa were screened against thirty newly sequenced or resequenced plant genomes to identify a set of species-specific genes (PtSS). Forty PtSS genes have been isolated with no similarity to any sequence outside the P. trichocarpa genome, therefore have no annotated functions. Protein motif, intron/exon features, subcellular localization and gene expression were analyzed in these PtSS genes. Results reflect their basic genic characters, expression analysis and primary function exploration might provide insight to their possible involvements in lineage specific biological process in woody plants.     

microRNA与神经系统发育

microRNA(miRNA)介导的基因沉默是生物体内普遍存在的重要基因表达调控方式,其调控失常与很多人类疾病相关.miRNA在神经组织表达丰富.神经系统miRNA的功能研究是近年非常活跃的新领域.基于近期的研究进展,本文重点讨论了miRNA在神经轴模式化、神经元命运决定、神经细胞发生、神经元突触形成及成熟神经元突触重塑中的重要作用.     

A clonal analysis of neural progenitors during axolotl spinal cord regeneration reveals evidence for both spatially restricted and multipotent progenitors

Complete regeneration of the spinal cord occurs after tail regeneration in urodele amphibians such as the axolotl. Little is known about how neural progenitor cells are recruited from the mature tail, how they populate the regenerating spinal cord, and whether the neural progenitor cells are multipotent. To address these issues we used three types of cell fate mapping. By grafting green fluorescent protein-positive (GFP(+)) spinal cord we show that a 500 microm region adjacent to the amputation plane generates the neural progenitors for regeneration. We further tracked single nuclear-GFP-labeled cells as they proliferated during regeneration, observing their spatial distribution, and ultimately their expression of the progenitor markers PAX7 and PAX6. Most progenitors generate descendents that expand along the anterior/posterior (A/P) axis, but remain close to the dorsal/ventral (D/V) location of the parent. A minority of clones spanned multiple D/V domains, taking up differing molecular identities, indicating that cells can execute multipotency in vivo. In parallel experiments, bulk labeling of dorsally or ventrally restricted progenitor cells revealed that ventral cells at the distal end of the regenerating spinal cord switch to dorsal cell fates. Analysis of PAX7 and PAX6 expression along the regenerating spinal cord indicated that these markers are expressed in dorsal and lateral domains all along the spinal cord except at the distal terminus. These results suggest that neural progenitor identity is destabilized or altered in the terminal vesicle region, from which clear migration of cells into the surrounding blastema is also observed.     

FGF receptor signalling is required to maintain neural progenitors during Hensen's node progression

Previous analyses of labelled clones of cells within the developing nervous system of the mouse have indicated that descendants are initially dispersed rostrocaudally followed by more local proliferation, which is consistent with the progressing node's contributing descendants from a resident population of progenitor cells as it advances caudally. Here we electroporated an expression vector encoding green fluorescent protein into the chicken embryo near Hensen's node to test and confirm the pattern inferred in the mouse. This provides a model in which a proliferative stem zone is maintained in the node by a localized signal; those cells that are displaced out of the stem zone go on to contribute to the growing axis. To test whether fibroblast growth factor (FGF) signalling could be involved in the maintenance of the stem zone, we co-electroporated a dominant-negative FGF receptor with a lineage marker, and found that it markedly alters the elongation of the spinal cord primordium. The results indicate that FGF receptor signalling promotes the continuous development of the posterior nervous system by maintaining presumptive neural progenitors in the region near Hensen's node. This offers a potential explanation for the mixed findings on FGF in the growth and patterning of the embryonic axis.