Human induced pluripotent stem cells (iPSCs) provide great potential as a tool for basic biologic... more Human induced pluripotent stem cells (iPSCs) provide great potential as a tool for basic biological discovery, disease modeling, and ultimately for cell based regenerative medicine but the full realization of these stem cells requires an ability to precisely edit their genome in an efficient way. The relative efficiencies of CRISPR/Cas9 and TALENs were quantified in human iPSC lines for inducing both homologous donor-based precise genome editing and nonhomologous end joining (NHEJ)-mediated gene disruption; genome wide off-target mutagenesis was also assessed by targeted deep sequencing. The specificity of Cas9 was further tested by targeting either the mutant or the wild-type allele of disease causing single nucleotide variants (SNVs) with gRNAs and testing their cleavage at the intended target or the other genotype differing by a single nucleotide; little disruption was observed at the other allele differing by a single nucleotide alone. Overall, these results demonstrate the adva...
We present a rapid, scalable, user-friendly method for in vitro production of high-purity single-... more We present a rapid, scalable, user-friendly method for in vitro production of high-purity single-stranded DNA (ssDNA) ranging from 89–3315 nucleotides in length. PCR with a forward primer bearing a methanol-responsive polymer generates a tagged amplicon that enables selective precipitation of the modified strand under denaturing conditions. We demonstrate that the recovered ssDNA can be used for CRISPR/Cas9 homology-directed repair in human cells, DNA-origami folding, and fluorescent in situ hybridization.
Multiplex genome editing is the simultaneous introduction of multiple distinct modifications to a... more Multiplex genome editing is the simultaneous introduction of multiple distinct modifications to a given genome. Though in its infancy, maturation of this field will facilitate powerful new biomedical research approaches, and will enable a host of far-reaching biological engineering applications, including new therapeutic modalities and industrial applications, as well as 'genome writing' and de-extinction efforts. In this perspective, we focus on multiplex editing of large eukaryotic genomes. We describe the current state of multiplexed genome editing, the current limits of our ability to multiplex edits, and provide perspective on the many applications that fully-realized multiplex editing technologies would enable in higher eukaryotic genomes. We offer a broad look at future directions, covering emergent CRISPR-based technologies, advances in intracellular delivery, and new DNA assembly approaches that may enable future genome editing on a massively multiplexed scale.
Derivation of pluripotent stem cells (iPSCs) induced from somatic cell types and the subsequent g... more Derivation of pluripotent stem cells (iPSCs) induced from somatic cell types and the subsequent genetic modifications of disease-specific or patient-specific iPSCs are crucial steps in their applications for disease modeling as well as future cell and gene therapies. Conventional procedures of these processes require co-culture with primary mouse embryonic fibroblasts (MEFs) to support self-renewal and clonal growth of human iPSCs as well as embryonic stem cells (ESCs). However, the variability of MEF quality affects the efficiencies of all these steps. Furthermore, animal sourced feeders may hinder the clinical applications of human stem cells. In order to overcome these hurdles, we established immortalized human feeder cell lines by stably expressing human telomerase reverse transcriptase, Wnt3a, and drug resistance genes in adult mesenchymal stem cells. Here, we show that these immortalized human feeders support efficient derivation of virus-free, integration-free human iPSCs and...
We have exploited the repetitive nature of transposable elements of the human genome to generate ... more We have exploited the repetitive nature of transposable elements of the human genome to generate synthetic circuits. Transposable elements such as LINE-1 and Alu have successfully replicated in mammalian genomes throughout evolution to reach a copy number ranging from thousands to more than a million. Targeting these repetitive elements with programmable DNA nucleases such as CRISPR-Cas9 rapidly induce extremely high levels of cell death. We use this genotoxic feature to build synthetic biocontainment circuits: CRISPR defense system (CRISPR-DS) capable of preventing CRISPR genome editing, and we introduce the proof-of-concept of CRISPR Safety-Switch, an inducible, stringent and non-leaky kill-switch capable of clearing out cell lines resistant to DNA breaks.
Human pluripotent stem cells (PSCs) hold great potential for regenerative medicine and currently ... more Human pluripotent stem cells (PSCs) hold great potential for regenerative medicine and currently are being used as a research tool for basic discovery and disease modeling. To evaluate the role of a single genetic variant, a system of genome editing is needed to precisely mutate any desired DNA sequence in isolation and measure its effect on phenotype when compared to the isogenic parental PSC from which it was derived. This protocol describes the general targeting schemes used by researchers to edit PSCs to knock out, knock-in, or precisely alter a single nucleotide, covering conditions for electroporation, clonal isolation, and screening of edited PSCs for the targeted mutation. These recent advances simplify the procedure for genome editing, allowing individual researchers to induce nearly any desired mutation to further study its function or to reverse a disease-causing variant for future applications in regenerative medicine.
Human induced pluripotent stem cells (iPSCs) and genome editing provide a precise way to generate... more Human induced pluripotent stem cells (iPSCs) and genome editing provide a precise way to generate gene-corrected cells for disease modeling and cell therapies. Human iPSCs generated from sickle cell disease (SCD) patients have a homozygous missense point mutation in the HBB gene encoding adult β-globin proteins, and are used as a model system to improve strategies of human gene therapy. We demonstrate that the CRISPR/Cas9 system designer nuclease is much more efficient in stimulating gene targeting of the endogenous HBB locus near the SCD point mutation in human iPSCs than ZFNs and TALENs. Using a specific guide RNA and Cas9, we readily corrected one allele of the SCD HBB gene in human iPSCs by homologous recombination with a donor DNA template containing the wild-type HBB DNA and a selection cassette that was subsequently removed to avoid possible interference of HBB transcription and translation. We chose targeted iPSC clones that have one corrected and one disrupted SCD allele fo...
Efficient and precise genome editing is crucial for realizing the full research and therapeutic p... more Efficient and precise genome editing is crucial for realizing the full research and therapeutic potential of human induced pluripotent stem cells (iPSCs). Engineered nucleases including CRISPR/Cas9 and transcription activator like effector nucleases (TALENs) provide powerful tools for enhancing gene-targeting efficiency. In this study, we investigated the relative efficiencies of CRISPR/Cas9 and TALENs in human iPSC lines for inducing both homologous donorbased precise genome editing and nonhomologous end joining (NHEJ)-mediated gene disruption. Significantly higher frequencies of NHEJ-mediated insertions/deletions were detected at several endogenous loci using CRISPR/ Cas9 than using TALENs, especially at nonexpressed targets in iPSCs. In contrast, comparable efficiencies of inducing homologous donor-based genome editing were observed at disease-associated loci in iPSCs. In addition, we investigated the specificity of guide RNAs used in the CRISPR/Cas9 system in targeting disease-associated point mutations in patient-specific iPSCs. Using myeloproliferative neoplasm patient-derived iPSCs that carry an acquired JAK2-V617F point mutation and α1-antitrypsin (AAT) deficiency patient-derived iPSCs that carry an inherited Z-AAT point mutation, we demonstrate that Cas9 can specifically target either the mutant or the wild-type allele with little disruption at the other allele differing by a single nucleotide. Overall, our results demonstrate the advantages of the CRISPR/Cas9 system in allele-specific genome targeting and in NHEJ-mediated gene disruption.
Culture-expanded human mesenchymal stem cells (MSCs) are increasingly used in clinics, yet full c... more Culture-expanded human mesenchymal stem cells (MSCs) are increasingly used in clinics, yet full characterization of the genomic compositions of these cells is lacking. We present a whole-genome investigation on the genetic dynamics of cultured MSCs under ex vivo establishment (passage 1 [p1]) and serial expansion (p8 and p13). We detected no significant changes in copy-number alterations (CNAs) and low levels of single-nucleotide changes (SNCs) until p8. Strikingly, a significant number (677) of SNCs were found in p13 MSCs. Using a sensitive Droplet Digital PCR assay, we tested the nonsynonymous SNCs detected by whole-genome sequencing and found that they were preexisting low-frequency mutations in uncultured mononuclear cells ($0.01%) and early-passage MSCs (0.1%-1% at p1 and p8) but reached 17%-36% in p13. Our data demonstrate that human MSCs maintain a stable genomic composition in the early stages of ex vivo culture but are subject to clonal growth upon extended expansion.
Human induced pluripotent stem cells (iPSCs) provide great potential as a tool for basic biologic... more Human induced pluripotent stem cells (iPSCs) provide great potential as a tool for basic biological discovery, disease modeling, and ultimately for cell based regenerative medicine but the full realization of these stem cells requires an ability to precisely edit their genome in an efficient way. The relative efficiencies of CRISPR/Cas9 and TALENs were quantified in human iPSC lines for inducing both homologous donor-based precise genome editing and nonhomologous end joining (NHEJ)-mediated gene disruption; genome wide off-target mutagenesis was also assessed by targeted deep sequencing. The specificity of Cas9 was further tested by targeting either the mutant or the wild-type allele of disease causing single nucleotide variants (SNVs) with gRNAs and testing their cleavage at the intended target or the other genotype differing by a single nucleotide; little disruption was observed at the other allele differing by a single nucleotide alone. Overall, these results demonstrate the adva...
We present a rapid, scalable, user-friendly method for in vitro production of high-purity single-... more We present a rapid, scalable, user-friendly method for in vitro production of high-purity single-stranded DNA (ssDNA) ranging from 89–3315 nucleotides in length. PCR with a forward primer bearing a methanol-responsive polymer generates a tagged amplicon that enables selective precipitation of the modified strand under denaturing conditions. We demonstrate that the recovered ssDNA can be used for CRISPR/Cas9 homology-directed repair in human cells, DNA-origami folding, and fluorescent in situ hybridization.
Multiplex genome editing is the simultaneous introduction of multiple distinct modifications to a... more Multiplex genome editing is the simultaneous introduction of multiple distinct modifications to a given genome. Though in its infancy, maturation of this field will facilitate powerful new biomedical research approaches, and will enable a host of far-reaching biological engineering applications, including new therapeutic modalities and industrial applications, as well as 'genome writing' and de-extinction efforts. In this perspective, we focus on multiplex editing of large eukaryotic genomes. We describe the current state of multiplexed genome editing, the current limits of our ability to multiplex edits, and provide perspective on the many applications that fully-realized multiplex editing technologies would enable in higher eukaryotic genomes. We offer a broad look at future directions, covering emergent CRISPR-based technologies, advances in intracellular delivery, and new DNA assembly approaches that may enable future genome editing on a massively multiplexed scale.
Derivation of pluripotent stem cells (iPSCs) induced from somatic cell types and the subsequent g... more Derivation of pluripotent stem cells (iPSCs) induced from somatic cell types and the subsequent genetic modifications of disease-specific or patient-specific iPSCs are crucial steps in their applications for disease modeling as well as future cell and gene therapies. Conventional procedures of these processes require co-culture with primary mouse embryonic fibroblasts (MEFs) to support self-renewal and clonal growth of human iPSCs as well as embryonic stem cells (ESCs). However, the variability of MEF quality affects the efficiencies of all these steps. Furthermore, animal sourced feeders may hinder the clinical applications of human stem cells. In order to overcome these hurdles, we established immortalized human feeder cell lines by stably expressing human telomerase reverse transcriptase, Wnt3a, and drug resistance genes in adult mesenchymal stem cells. Here, we show that these immortalized human feeders support efficient derivation of virus-free, integration-free human iPSCs and...
We have exploited the repetitive nature of transposable elements of the human genome to generate ... more We have exploited the repetitive nature of transposable elements of the human genome to generate synthetic circuits. Transposable elements such as LINE-1 and Alu have successfully replicated in mammalian genomes throughout evolution to reach a copy number ranging from thousands to more than a million. Targeting these repetitive elements with programmable DNA nucleases such as CRISPR-Cas9 rapidly induce extremely high levels of cell death. We use this genotoxic feature to build synthetic biocontainment circuits: CRISPR defense system (CRISPR-DS) capable of preventing CRISPR genome editing, and we introduce the proof-of-concept of CRISPR Safety-Switch, an inducible, stringent and non-leaky kill-switch capable of clearing out cell lines resistant to DNA breaks.
Human pluripotent stem cells (PSCs) hold great potential for regenerative medicine and currently ... more Human pluripotent stem cells (PSCs) hold great potential for regenerative medicine and currently are being used as a research tool for basic discovery and disease modeling. To evaluate the role of a single genetic variant, a system of genome editing is needed to precisely mutate any desired DNA sequence in isolation and measure its effect on phenotype when compared to the isogenic parental PSC from which it was derived. This protocol describes the general targeting schemes used by researchers to edit PSCs to knock out, knock-in, or precisely alter a single nucleotide, covering conditions for electroporation, clonal isolation, and screening of edited PSCs for the targeted mutation. These recent advances simplify the procedure for genome editing, allowing individual researchers to induce nearly any desired mutation to further study its function or to reverse a disease-causing variant for future applications in regenerative medicine.
Human induced pluripotent stem cells (iPSCs) and genome editing provide a precise way to generate... more Human induced pluripotent stem cells (iPSCs) and genome editing provide a precise way to generate gene-corrected cells for disease modeling and cell therapies. Human iPSCs generated from sickle cell disease (SCD) patients have a homozygous missense point mutation in the HBB gene encoding adult β-globin proteins, and are used as a model system to improve strategies of human gene therapy. We demonstrate that the CRISPR/Cas9 system designer nuclease is much more efficient in stimulating gene targeting of the endogenous HBB locus near the SCD point mutation in human iPSCs than ZFNs and TALENs. Using a specific guide RNA and Cas9, we readily corrected one allele of the SCD HBB gene in human iPSCs by homologous recombination with a donor DNA template containing the wild-type HBB DNA and a selection cassette that was subsequently removed to avoid possible interference of HBB transcription and translation. We chose targeted iPSC clones that have one corrected and one disrupted SCD allele fo...
Efficient and precise genome editing is crucial for realizing the full research and therapeutic p... more Efficient and precise genome editing is crucial for realizing the full research and therapeutic potential of human induced pluripotent stem cells (iPSCs). Engineered nucleases including CRISPR/Cas9 and transcription activator like effector nucleases (TALENs) provide powerful tools for enhancing gene-targeting efficiency. In this study, we investigated the relative efficiencies of CRISPR/Cas9 and TALENs in human iPSC lines for inducing both homologous donorbased precise genome editing and nonhomologous end joining (NHEJ)-mediated gene disruption. Significantly higher frequencies of NHEJ-mediated insertions/deletions were detected at several endogenous loci using CRISPR/ Cas9 than using TALENs, especially at nonexpressed targets in iPSCs. In contrast, comparable efficiencies of inducing homologous donor-based genome editing were observed at disease-associated loci in iPSCs. In addition, we investigated the specificity of guide RNAs used in the CRISPR/Cas9 system in targeting disease-associated point mutations in patient-specific iPSCs. Using myeloproliferative neoplasm patient-derived iPSCs that carry an acquired JAK2-V617F point mutation and α1-antitrypsin (AAT) deficiency patient-derived iPSCs that carry an inherited Z-AAT point mutation, we demonstrate that Cas9 can specifically target either the mutant or the wild-type allele with little disruption at the other allele differing by a single nucleotide. Overall, our results demonstrate the advantages of the CRISPR/Cas9 system in allele-specific genome targeting and in NHEJ-mediated gene disruption.
Culture-expanded human mesenchymal stem cells (MSCs) are increasingly used in clinics, yet full c... more Culture-expanded human mesenchymal stem cells (MSCs) are increasingly used in clinics, yet full characterization of the genomic compositions of these cells is lacking. We present a whole-genome investigation on the genetic dynamics of cultured MSCs under ex vivo establishment (passage 1 [p1]) and serial expansion (p8 and p13). We detected no significant changes in copy-number alterations (CNAs) and low levels of single-nucleotide changes (SNCs) until p8. Strikingly, a significant number (677) of SNCs were found in p13 MSCs. Using a sensitive Droplet Digital PCR assay, we tested the nonsynonymous SNCs detected by whole-genome sequencing and found that they were preexisting low-frequency mutations in uncultured mononuclear cells ($0.01%) and early-passage MSCs (0.1%-1% at p1 and p8) but reached 17%-36% in p13. Our data demonstrate that human MSCs maintain a stable genomic composition in the early stages of ex vivo culture but are subject to clonal growth upon extended expansion.
Uploads
Papers by Cory Smith