Yumei Luo

Derivation and characterization of human embryonic stem cell lines from poor quality embryos.

Poor quality embryos discarded from in vitro fertilization (IVF) laboratories are good sources for deriving human embryonic stem cell (hESC) lines. In this study, 166 poor quality embryos donated from IVF centers on day 3 were cultured in a blastocyst medium for 2 days, and 32 early blastocysts were further cultured in a blastocyst optimum culture medium for additional 2 days so that the inner cell masses (ICMs) could be identified and isolated easily. The ICMs of 17 blastocysts were isolated by a mechanical method, while those of the other 15 blastocysts were isolated by immunosurgery. All isolated ICMs were inoculated onto a feeder layer for subcultivation. The rates of ICM attachment, primary ICM colony formation and the efficiency of hESC derivation were similar between the ICMs isolated by the two methods (P>0.05). As a result, four new hESC lines were established. Three cell lines had normal karyotypes and one had an unbalanced Robertsonian translocation. All cell lines showed normal hESC characteristics and had the differentiation ability. In conclusion, we established a stable and effective method for hESC isolation and culture, and it was confirmed that the mechanical isolation was an effective method to isolate ICMs from poor embryos. These results further indicate that hESC lines can be derived from poor quality embryos discarded by IVF laboratories.

Targeted Inhibition of the miR-199a/214 Cluster by CRISPR Interference Augments the Tumor Tropism of Human Induced Pluripotent Stem Cell-Derived Neural Stem Cells under Hypoxic Condition

The human induced pluripotent stem cell (hiPSC) provides a breakthrough approach that helps overcoming ethical and allergenic challenges posed in application of neural stem cells (NSCs) in targeted cancer gene therapy. However, the tumor-tropic capacity of hiPSC-derived NSCs (hiPS-NSCs) still has much room to improve. Here we attempted to promote the tumor tropism of hiPS-NSCs by manipulating the activity of endogenous miR-199a/214 cluster that is involved in regulation of hypoxia-stimulated cell migration. We first developed a baculovirus-delivered CRISPR interference (CRISPRi) system that sterically blocked the E-box element in the promoter of the miR-199a/214 cluster with an RNA-guided catalytically dead Cas9 (dCas9). We then applied this CRISPRi system to hiPS-NSCs and successfully suppressed the expression of miR-199a-5p, miR-199a-3p, and miR-214 in the microRNA gene cluster. Meanwhile, the expression levels of their targets related to regulation of hypoxia-stimulated cell migration, such as HIF1A, MET, and MAPK1, were upregulated. Further migration assays demonstrated that the targeted inhibition of the miR-199a/214 cluster significantly enhanced the tumor tropism of hiPS-NSCs both in vitro and in vivo. These findings suggest a novel application of CRISPRi in NSC-based tumor-targeted gene therapy.

Genetic and epigenetic X-chromosome variations in a parthenogenetic human embryonic stem cell line.

PurposeTo assess the genetic and epigenetic status of parthenogenetic human embryonic stem cells (phESCs).MethodsCytogenetics, X chromosome inactivation (XCI) and gene expression patterns were analyzed in one phESC line (FY-phES-018) that was derived from our laboratory.ResultsFY-phES-018 cells displayed the classical characteristics of normal hESCs. These cells had a 46, XX karyotype, and no inactive X chromosomes were observed before passage 20. After being cultured long term in vitro, some cells lost one X, and the proportion of cells with only one X gradually increased. At passage 35, almost all the cells displayed a 45, XO karyotype. Interestingly, at passage 45, the recovery of the X-chromosome was observed, and XCI became detectable; the mosaic ratio of 46, XX to 45, XO was 67:33. After passage 60, most cells displayed the 46, XX karyotype again with a mosaic ratio of 97:3. Some aberrant genomic imprinting was also observed in these cells.ConclusionsThe phESCs line FY-phES-018 is both genetically and epigenetically unstable; therefore, further research is needed before using these cells.

High-resolution chromosomal microarray analysis of early-stage human embryonic stem cells reveals an association between X chromosome instability and skewed X inactivation.

X chromosome inactivation (XCI) is a dosage compensation mechanism that silences the majority of genes on one X chromosome in each female cell via a random process. Skewed XCI is relevant to many diseases, but the mechanism leading to it remains unclear. Human embryonic stem cells (hESCs) derived from the inner cell mass (ICM) of blastocyst-stage embryos have provided an excellent model system for understanding XCI initiation and maintenance. Here, we derived hESC lines with random or skewed XCI patterns from poor-quality embryos and investigated the genome-wide copy number variation (CNV) and loss of heterozygosity (LOH) patterns at the early passages of these two groups of hESC lines. It was found that the average size of CNVs on the X chromosomes in the skewed group is twice as much as that in the random group. Moreover, the LOH regions of the skewed group covered the gene locus of either XIST or XACT, which are master long non-coding RNA (lncRNA) effectors of XCI in human pluripotent stem cells. In conclusion, our work has established an experimentally tractable hESC model for study of skewed XCI and revealed an association between X chromosome instability and skewed XCI.

Developmental potential of human oocytes reconstructed by transferring somatic cell nuclei into polyspermic zygote cytoplasm

The generation of patient-specific nuclear transfer embryonic stem cells holds huge promise in modern regenerative medicine and cell-based drug discovery. Since human in vivo matured oocytes are not readily available, human therapeutic cloning is developing slowly. Here, we investigated for the first time whether human polyspermic zygotes could support preimplantation development of cloned embryos. Our results showed that polyspermic zygotes could be used as recipients for human somatic cell nuclear transfer (SCNT). The preimplantation developmental potential of SCNT embryos from polyspermic zygotes was limited to the 8-cell stage. Since ES cell lines can be derived from single blastomeres, these results may have important significance for human ES cells derived by SCNT. In addition, confocal images demonstrated that all of the SCNT embryos that failed to cleave showed abnormal microtubule organization. The results of the present study suggest that polyspermic human zygotes could be used as a potential source of recipient cytoplasm for SCNT.

Modeling induced pluripotent stem cells from fibroblasts of Duchenne muscular dystrophy patients

The generation of disease-specific induced pluripotent stem cell (iPS cell) lines from patients with incurable diseases is a promising approach for studying disease mechanisms and for drug screening. Such innovation enables us to obtain autologous cell sources for regenerative medicine. Herein, we report the generation and characterization of iPS cells from the fibroblasts of patients with a family history of Duchenne muscular dystrophy (DMD); these fibroblasts were obtained from patients at 22 gestational weeks of age and exhibit exon duplication from exons 16 to 42. The DMD-iPS cells were generated by the ectopic expression of four transcription factors: OCT4, SOX2, KLF4, and c-MYC; the DMD-iPS cells expressed several pluripotency markers and could be differentiated into various somatic cell types both in vitro and in vivo. Furthermore, DMD-iPSCs showed the differentiation potential to neuronal lineage. Thus, DMD-iPS cells are expected to serve as an in vitro disease model system, which will lay a foundation for the production of autologous cell therapies that avoid immune rejection and enable the correction of gene defects prior to tissue reconstitution.

Integrative Analysis of CRISPR/Cas9 Target Sites in the Human HBB Gene

Recently, the clustered regularly interspaced short palindromic repeats (CRISPR) system has emerged as a powerful customizable artificial nuclease to facilitate precise genetic correction for tissue regeneration and isogenic disease modeling. However, previous studies reported substantial off-target activities of CRISPR system in human cells, and the enormous putative off-target sites are labor-intensive to be validated experimentally, thus motivating bioinformatics methods for rational design of CRISPR system and prediction of its potential off-target effects. Here, we describe an integrative analytical process to identify specific CRISPR target sites in the human β-globin gene (HBB) and predict their off-target effects. Our method includes off-target analysis in both coding and noncoding regions, which was neglected by previous studies. It was found that the CRISPR target sites in the introns have fewer off-target sites in the coding regions than those in the exons. Remarkably, target sites containing certain transcriptional factor motif have enriched binding sites of relevant transcriptional factor in their off-target sets. We also found that the intron sites have fewer SNPs, which leads to less variation of CRISPR efficiency in different individuals during clinical applications. Our studies provide a standard analytical procedure to select specific CRISPR targets for genetic correction.

Uniparental disomy of the entire X chromosome in Turner syndrome patient-specific induced pluripotent stem cells.

The human induced pluripotent stem cell (iPSC) technique promises to provide an unlimited, reliable source of genetically matched pluripotent cells for personalized therapy and disease modeling. Recently, it is observed that cells with ring chromosomes 13 or 17 autonomously correct the defects via compensatory uniparental disomy during cellular reprogramming to iPSCs. This breakthrough finding suggests a potential therapeutic approach to repair large-scale chromosomal aberrations. However, due to the scarceness of ring chromosome samples, the reproducibility of this approach in different individuals is not carefully evaluated yet. Moreover, the underlying mechanism and the applicability to other types of chromosomal aberrations remain unknown. Here we generated iPSCs from four 45,X chorionic villous fibroblast lines and found that only one reprogrammed line acquired 46,XX karyotype via uniparental disomy of the entire X chromosome. The karyotype correction was reproducible in the same cell line by either retroviral or episomal reprogramming. The karyotype-corrected iPSCs were subject to X chromosome inactivation and obtained better colony morphology and higher proliferation rate than other uncorrected ones. Further transcriptomic comparison among the fibroblast lines identified a distinct expression pattern of cell cycle regulators in the uncorrectable ones. These findings demonstrate that the iPSC technique holds the potential to correct X monosomy, but the correction rate is very low, probably due to differential regulation of cell cycle genes between individuals. Our data strongly suggest that more systematic investigations are needed before defining the iPSC technique as a novel means of chromosome therapy.

Generation of an induced pluripotent stem cell line from an adult male with 45,X/46,XY mosaicism

Turner syndrome (TS) with 45,X/46,XY mosaic karyotype is a rare sex chromosome disorder with an occurrence of 0.15‰ at birth. We report the generation of an induced pluripotent stem cell (iPSC) line from peripheral blood mononuclear cells of a Chinese adult male with 45,X/46,XY mosaicism. The iPSC line retains the original 45,X/46,XY mosaic karyotype, expresses pluripotency markers and undergoes trilineage differentiation. Therefore, it offers an unprecedented cellular model to investigate the profound symptoms like infertility of TS in the male, and serve as a useful tool to develop therapies for the disease.