Qi-Long Ying

Bio: Qi-Long Ying is an academic researcher from University of Southern California. The author has contributed to research in topics: Embryonic stem cell & Stem cell. The author has an hindex of 31, co-authored 82 publications receiving 13077 citations. Previous affiliations of Qi-Long Ying include University of Edinburgh & Peking Union Medical College.

The ground state of embryonic stem cell self-renewal

Abstract: In the three decades since pluripotent mouse embryonic stem (ES) cells were first described they have been derived and maintained by using various empirical combinations of feeder cells, conditioned media, cytokines, growth factors, hormones, fetal calf serum, and serum extracts. Consequently ES-cell self-renewal is generally considered to be dependent on multifactorial stimulation of dedicated transcriptional circuitries, pre-eminent among which is the activation of STAT3 by cytokines (ref. 8). Here we show, however, that extrinsic stimuli are dispensable for the derivation, propagation and pluripotency of ES cells. Self-renewal is enabled by the elimination of differentiation-inducing signalling from mitogen-activated protein kinase. Additional inhibition of glycogen synthase kinase 3 consolidates biosynthetic capacity and suppresses residual differentiation. Complete bypass of cytokine signalling is confirmed by isolating ES cells genetically devoid of STAT3. These findings reveal that ES cells have an innate programme for self-replication that does not require extrinsic instruction. This property may account for their latent tumorigenicity. The delineation of minimal requirements for self-renewal now provides a defined platform for the precise description and dissection of the pluripotent state.

Conversion of embryonic stem cells into neuroectodermal precursors in adherent monoculture.

Abstract: Mouse embryonic stem (ES) cells are competent for production of all fetal and adult cell types. However, the utility of ES cells as a developmental model or as a source of defined cell populations for pharmaceutical screening or transplantation is compromised because their differentiation in vitro is poorly controlled. Specification of primary lineages is not understood and consequently differentiation protocols are empirical, yielding variable and heterogeneous outcomes. Here we report that neither multicellular aggregation nor coculture is necessary for ES cells to commit efficiently to a neural fate. In adherent monoculture, elimination of inductive signals for alternative fates is sufficient for ES cells to develop into neural precursors. This process is not a simple default pathway, however, but requires autocrine fibroblast growth factor (FGF). Using flow cytometry quantitation and recording of individual colonies, we establish that the bulk of ES cells undergo neural conversion. The neural precursors can be purified to homogeneity by fluorescence activated cell sorting (FACS) or drug selection. This system provides a platform for defining the molecular machinery of neural commitment and optimizing the efficiency of neuronal and glial cell production from pluripotent mammalian stem cells.

Changing potency by spontaneous fusion

Abstract: Recent reports have suggested that mammalian stem cells residing in one tissue may have the capacity to produce differentiated cell types for other tissues and organs (1–9). Here we define a mechanism by which progenitor cells of the central nervous system can give rise to non-neural derivatives. Cells taken from mouse brain were co-cultured with pluripotent embryonic stem cells. Following selection for a transgenic marker carried only by the brain cells, undifferentiated stem cells are recovered in which the brain cell genome has undergone epigenetic reprogramming. However, these cells also carry a transgenic marker and chromosomes derived from the embryonic stem cells. Therefore the altered phenotype does not arise by direct conversion of brain to embryonic stem cell but rather through spontaneous generation of hybrid cells. The tetraploid hybrids exhibit full pluripotent character, including multilineage contribution to chimaeras. We propose that transdetermination consequent to cell fusion (10) could underlie many observations otherwise attributed to an intrinsic plasticity of tissue stem cells (9).

Niche-independent symmetrical self-renewal of a mammalian tissue stem cell.

Abstract: Pluripotent mouse embryonic stem (ES) cells multiply in simple monoculture by symmetrical divisions In vivo, however, stem cells are generally thought to depend on specialised cellular microenvironments and to undergo predominantly asymmetric divisions Ex vivo expansion of pure populations of tissue stem cells has proven elusive Neural progenitor cells are propagated in combination with differentiating progeny in floating clusters called neurospheres The proportion of stem cells in neurospheres is low, however, and they cannot be directly observed or interrogated Here we demonstrate that the complex neurosphere environment is dispensable for stem cell maintenance, and that the combination of fibroblast growth factor 2 (FGF-2) and epidermal growth factor (EGF) is sufficient for derivation and continuous expansion by symmetrical division of pure cultures of neural stem (NS) cells NS cells were derived first from mouse ES cells Neural lineage induction was followed by growth factor addition in basal culture media In the presence of only EGF and FGF-2, resulting NS cells proliferate continuously, are diploid, and clonogenic After prolonged expansion, they remain able to differentiate efficiently into neurons and astrocytes in vitro and upon transplantation into the adult brain Colonies generated from single NS cells all produce neurons upon growth factor withdrawal NS cells uniformly express morphological, cell biological, and molecular features of radial glia, developmental precursors of neurons and glia Consistent with this profile, adherent NS cell lines can readily be established from foetal mouse brain Similar NS cells can be generated from human ES cells and human foetal brain The extrinsic factors EGF plus FGF-2 are sufficient to sustain pure symmetrical self-renewing divisions of NS cells The resultant cultures constitute the first known example of tissue-specific stem cells that can be propagated without accompanying differentiation These homogenous cultures will enable delineation of molecular mechanisms that define a tissue-specific stem cell and allow direct comparison with pluripotent ES cells

Pluripotency of mesenchymal stem cells derived from adult marrow

Abstract: We report here that cells co-purifying with mesenchymal stem cells--termed here multipotent adult progenitor cells or MAPCs--differentiate, at the single cell level, not only into mesenchymal cells, but also cells with visceral mesoderm, neuroectoderm and endoderm characteristics in vitro. When injected into an early blastocyst, single MAPCs contribute to most, if not all, somatic cell types. On transplantation into a non-irradiated host, MAPCs engraft and differentiate to the haematopoietic lineage, in addition to the epithelium of liver, lung and gut. Engraftment in the haematopoietic system as well as the gastrointestinal tract is increased when MAPCs are transplanted in a minimally irradiated host. As MAPCs proliferate extensively without obvious senescence or loss of differentiation potential, they may be an ideal cell source for therapy of inherited or degenerative diseases.

Genome-wide maps of chromatin state in pluripotent and lineage-committed cells

Abstract: We report the application of single-molecule-based sequencing technology for high-throughput profiling of histone modifications in mammalian cells By obtaining over four billion bases of sequence from chromatin immunoprecipitated DNA, we generated genome-wide chromatin-state maps of mouse embryonic stem cells, neural progenitor cells and embryonic fibroblasts We find that lysine 4 and lysine 27 trimethylation effectively discriminates genes that are expressed, poised for expression, or stably repressed, and therefore reflect cell state and lineage potential Lysine 36 trimethylation marks primary coding and non-coding transcripts, facilitating gene annotation Trimethylation of lysine 9 and lysine 20 is detected at satellite, telomeric and active long-terminal repeats, and can spread into proximal unique sequences Lysine 4 and lysine 9 trimethylation marks imprinting control regions Finally, we show that chromatin state can be read in an allele-specific manner by using single nucleotide polymorphisms This study provides a framework for the application of comprehensive chromatin profiling towards characterization of diverse mammalian cell populations

Histone H3K27ac separates active from poised enhancers and predicts developmental state

Abstract: Developmental programs are controlled by transcription factors and chromatin regulators, which maintain specific gene expression programs through epigenetic modification of the genome. These regulatory events at enhancers contribute to the specific gene expression programs that determine cell state and the potential for differentiation into new cell types. Although enhancer elements are known to be associated with certain histone modifications and transcription factors, the relationship of these modifications to gene expression and developmental state has not been clearly defined. Here we interrogate the epigenetic landscape of enhancer elements in embryonic stem cells and several adult tissues in the mouse. We find that histone H3K27ac distinguishes active enhancers from inactive/poised enhancer elements containing H3K4me1 alone. This indicates that the amount of actively used enhancers is lower than previously anticipated. Furthermore, poised enhancer networks provide clues to unrealized developmental programs. Finally, we show that enhancers are reset during nuclear reprogramming.