Genetic recombination pathways and their application for genome modification of human embryonic stem cells

CRISPR/Cas-Mediated Knockin in Human Pluripotent Stem Cells

Fluorescent reporter and epitope-tagged human pluripotent stem cells (hPSCs) greatly facilitate studies on the pluripotency and differentiation characteristics of these cells. Unfortunately traditional procedures to generate such lines are hampered by a low targeting efficiency that necessitates a lengthy process of selection followed by the removal of the selection cassette. Here we describe a procedure to generate fluorescent reporter and epitope tagged hPSCs in an efficient one-step process using the CRISPR/Cas technology. Although the method described uses our recently developed iCRISPR platform, the protocols can be adapted for general use with CRISPR/Cas or other engineered nucleases. The transfection procedures described could also be used for additional applications, such as overexpression or lineage tracing studies.

Construction of a eukaryotic expression plasmid encoding the human HSF2 gene and its expression in Caco-2 cells

AIM: To construct a eukaryotic expression plasmid encoding the human heat shock factor 2 (HSF2) gene and to examine its expression and localization in Caco-2 cells, a human colon adenocarcinoma cell line using FLAG tag as a reporter.

METHODS: The coding sequence of the HSF2 gene was amplified by PCR using human HSF2 cDNA as the template and subcloned into pCMV-Myc vector after digestion with EcoR I and Knp I. After the identity of recombinant plasmid was verified by direct sequencing, the plasmid was transfected into Caco-2 cells using Lipofectamine. Total RNA was extracted, reverse transcribed into cDNA, and tested by PCR. The expression of HSF2 and the recombinant fusion protein in Caco-2 cells was detected by Western blot. The expression and localization of HSF2 and the recombinant fusion protein in Caco-2 cells were observed by laser scanning confocal microscopy.

RESULTS: The coding sequence of the HSF2 gene was successfully inserted into the pCMV-Myc vector. Restriction enzyme digestion analysis showed that the length of the insert was 1557 bp, matching the expected size. The mRNA level of HSF2 in cells transfected with the recombinant plasmid was higher than those in non-transfected cells and cells transfected with empty vector. The expression of recombinant HSF2-FLAG fusion protein, which had a molecular weight of 70 kDa, was detected by Western blot. The expression of HSF2 in cells transfected with the recombinant plasmid increased dramatically in comparison with matched groups. The HSF2 and recombinant HSF2-FLAG protein were localized predominantly to the cytoplasm but partially aggregated around the nuclear envelope in Caco-2 cells.

CONCLUSION: The recombinant plasmid pCMV-HSF2-FLAG has been successfully constructed, which provides the basis for further study of possible roles of HSF2 in ulcerative colitis.

Efficient and accurate homologous recombination in hESCs and hiPSCs using helper-dependent adenoviral vectors

Low efficiencies of gene targeting via homologous recombination (HR) have limited basic research and applications using human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs). Here, we show highly and equally efficient gene knockout and knock-in at both transcriptionally active (HPRT1, KU80, LIG1, LIG3) and inactive (HB9) loci in these cells using high-capacity helper-dependent adenoviral vectors (HDAdVs). Without the necessity of introducing artificial DNA double-strand breaks, 7-81% of drug-resistant colonies were gene-targeted by accurate HR, which were not accompanied with additional ectopic integrations. Even at the motor neuron-specific HB9 locus, the enhanced green fluorescent protein (EGFP) gene was accurately knocked in in 23-57% of drug-resistant colonies. In these clones, induced differentiation into the HB9-positive motor neuron correlated with EGFP expression. Furthermore, HDAdV infection had no detectable adverse effects on the undifferentiated state and pluripotency of hESCs and hiPSCs. These results suggest that HDAdV is one of the best methods for efficient and accurate gene targeting in hESCs and hiPSCs and might be especially useful for therapeutic applications.

Pluripotent stem cell models of cardiac disease and their implication for drug discovery and development

Recent advances in pluripotent stem cell biology now make it possible to generate human cardiomyocytes in vitro from both healthy individuals and from patients with cardiac abnormalities. This offers unprecedented opportunities to study cardiac disease development 'in a dish' and establish novel platforms for drug discovery, either to prevent disease progression or to reverse it. In this review paper, we discuss some of the genetic diseases that affect the heart and illustrate how these new paradigms could assist our understanding of cardiac pathogenesis and aid in drug discovery. In particular, we highlight the limitations of other commonly used model systems in predicting the consequences of drug exposure on the human heart.

Targeted gene correction of laminopathy-associated LMNA mutations in patient-specific iPSCs

Combination of stem cell-based approaches with gene-editing technologies represents an attractive strategy for studying human disease and developing therapies. However, gene-editing methodologies described to date for human cells suffer from technical limitations including limited target gene size, low targeting efficiency at transcriptionally inactive loci, and off-target genetic effects that could hamper broad clinical application. To address these limitations, and as a proof of principle, we focused on homologous recombination-based gene correction of multiple mutations on lamin A (LMNA), which are associated with various degenerative diseases. We show that helper-dependent adenoviral vectors (HDAdVs) provide a highly efficient and safe method for correcting mutations in large genomic regions in human induced pluripotent stem cells and can also be effective in adult human mesenchymal stem cells. This type of approach could be used to generate genotype-matched cell lines for disease modeling and drug discovery and potentially also in therapeutics.

Cardiomyocyte differentiation of pluripotent stem cells and their use as cardiac disease models

More than 10 years after their first isolation, human embryonic stem cells are finally 'coming of age' in research and biotechnology applications as protocols for their differentiation and undifferentiated expansion in culture become robust and scalable, and validated commercial reagents become available. Production of human cardiomyocytes is now feasible on a daily basis for many laboratories with tissue culture expertise. An additional recent surge of interest resulting from the first production of human iPSCs (induced pluripotent stem cells) from somatic cells of patients now makes these technologies of even greater importance since it is likely that (genetic) cardiac disease phenotypes can be captured in the cardiac derivatives of these cells. Although cell therapy based on replacing cardiomyocytes lost or dysfunctional owing to cardiac disease are probably as far away as ever, biotechnology and pharmaceutical applications in safety pharmacology and drug discovery will probably impact this clinical area in the very near future. In the present paper, we review the cutting edge of this exciting area of translational research.