This work was funded in part by NIH/NIDDK (R01DK096239) and New York State Stem Cell Science (NYSTEM C029156). Z.Z. was supported by the NYSTEM postdoctoral fellowship from the Center for Stem Cell Biology of the Sloan Kettering Institute.

<ol>
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The authors have nothing to disclose.

Time Considerations for Generating Mutant Lines
Although recent approaches based on CRISPR/Cas systems for genome editing have led to successful targeting, a more efficacious and universal platform would be preferable for larger-scale analyses of gene function. The iCRISPR platform offers a rapid and efficient method to introduce mutations to any gene of interest5,9. First, the PCR-based gRNA synthesis method allows the production of hundreds of gRNAs in arrayed format in one day without the time-consuming cloning steps. Second, with doxycycline-inducible Cas9 expression in iCas9 hPSCs, the step involving gRNA transfection requires only a minimal amount of work, and thus, multiple gRNA targeting experiments can be conducted concurrently. Third, due to the high targeting efficiencies attainable with our system, the analysis of ~ 24 - 48 colonies per gRNA transfected should be sufficient to establish multiple monoallelic and biallelic mutant lines for a single gene, although efficiencies vary depending on the target locus. Since it is feasible for a trained individual to mechanically pick 384 colonies (4 x 96-well plates) in one sitting, which should take ~ 4 h under a dissecting microscope, a trained individual can be expected to generate mutant lines affecting 12 genes within 1 - 2 months. The streamlined generation of hPSC mutants in a short time allows for the systematic analysis of an array of transcription factors and/or signaling pathway components that interact with each other, regulating the developmental process9. Additionally, efficient multiplexed gene targeting also opens the door to investigating genetic interactions underlying complex human traits.
Generation of Precise Genetic Modifications
The derivation of patient-specific iPSCs from easily accessible somatic cell types and the differentiation into disease-relevant cell types provide a great opportunity for the functional validation of disease-associated mutations. However, due to the considerable variability in genetic background between individuals, direct comparisons between iPSCs from patients and from healthy donors may not allow one to distinguish disease phenotypes from background effects. Therefore, it is necessary to generate isogenic control iPSCs by correcting the disease mutation back to the wild-type sequence or to introduce the patient-specific mutations into a wild-type hPSC background, as proposed by others25,26. In addition to loss-of-function (null) mutations, one may now more precisely dissect disease mechanisms through the introduction of a patient-specific sequence alterations into the endogenous locus in hPSCs, including hypermorphic, hypomorphic, neomorphic, or dominant-negative patient mutations.
Precise genetic modification employs HDR for DSB repair in the presence of a repair template. Since it is much less efficient than NHEJ-mediated DNA repair, a donor plasmid containing the patient-specific mutation, a drug selection cassette, and homology arms has been previously used as the repair template2. After drug selection and verification of the patient-specific mutation, a second step is generally needed to remove the drug selection cassette. While the most widely used Cre-loxP and FLP-FRT systems leave behind residual sequence in the endogenous locus, the use of piggyBac transposon has allowed for the seamless removal of the drug selection cassette27. More recently, short ssDNA templates have also been shown to support efficient HDR with engineered DNA endonucleases28. Compared to a donor plasmid, ssDNA can be directly synthesized and thus circumvents the time-consuming cloning step. Here, it has been shown that, by co-transfecting gRNA and an ssDNA template to induce homology-directed repair, iCRISPR can be used to introduce specific nucleotide modifications with high efficiency. This is critical for not only dissecting the role of essential nucleotides within protein functional domains, but also for modeling human disease mutations and potentially correcting these disease-associated mutations for therapeutic intervention. Due to the large number of susceptibility loci that are each associated with multiple sequence variants, modeling complex and multigenic diseases such as diabetes has been a challenge for geneticists. As the iCRISPR platform is permissive for the rapid generation of an allelic series or for multiplexable gene targeting, it can facilitate the investigation of multiple disease-associated loci, either individually or in combination with isogenic backgrounds.
Targeting Efficiencies and Off-target Effects
We have found a good correlation between the T7E1 and RFLP assay results and the number of mutant lines identified by sequencing. This emphasizes the importance of performing these assays in parallel with the establishment of clonal lines. While the targeting efficiencies attained may vary depending on the genomic loci, in most single-gene-targeting experiments, 20 - 60% of the clones were found with both alleles mutated (including in-frame and frameshift mutations)9. In cases where multiplexed gene targeting was performed, triple biallelic mutant clones with 5-10% efficiencies were obtained5. ssDNA-mediated HDR of several genes were also performed to obtain precise genetic alterations, with the efficiencies of obtaining homozygous knock-in clones ranging from 1 - 10%5. Working with CRISPR/Cas in hPSCs, any mutations in potential off-target sites that do not share the same gRNA target sequence are yet to be detected5,9,12. Whole-genome sequencing performed in a recent study has also failed to identify substantial off-target mutations in clonal hPSC lines generated using CRISPR/Cas29. Nevertheless, to minimize any potential effect of confounding phenotypes introduced by mutations at off-target effect sites, it is suggested to generate independent mutant lines using at least two independent gRNAs targeting different sequences within the same gene. Similar phenotypes observed in multiple lines generated using different gRNAs could principally rule out the possibility that the phenotype comes from an off-target effect.
Feeder-dependent versus Independent Culture and Targeting
Traditional methods for hPSC culture involve their maintenance and expansion on feeder cells in media containing serum or serum replacement that includes animal products, such as bovine serum albumin. Feeder cells, serum, serum replacement, and albumin all contain complex, undefined components and show considerable batch variability. Adapting to the feeder-free and chemically defined condition significantly reduces the efforts for hPSC maintenance and, more importantly, increases the consistency of differentiation experiments. At present, there are very few studies that describe genome editing procedures on hPSCs cultured in fully defined culture conditions30. We have found higher CRISPR targeting efficiencies when gRNA transfection and clonal deposition were performed in feeder-free conditions compared to feeder-dependent culture conditions. We believe that this is due to increased cell survival after transfection and single-cell seeding for colony formation. Moreover, feeder cells have previously been shown to sequester transfection reagents, thereby lowering the transfection efficiency.
Combining Genome Editing with Directed Differentiation
Previous differentiation protocols have yielded only a small fraction of insulin-positive cells, the majority of which were polyhormonal and resembled fetal endocrine cells23. Recent progress has permitted the differentiation of hPSCs into more mature glucose-responsive beta-like cells16,17,19,20. We can routinely obtain at least 75% definitive endoderm cells, 40% PDX1+NKX6.1+ pancreatic progenitors, and around 20% NKX6.1+CPEP+ glucose-responsive beta-like cells using HUES8 hPSCs9. When combined with the iCRISPR genome editing system, this more robust differentiation protocol has facilitated the analysis of transcription factors that are crucial to the pancreatic progenitor and endocrine stages of pancreatic differentiation. This will make it possible, in future studies, to examine a large number of candidate disease genes for the functional validation and investigation into the mechanisms that underlie diabetes9.
Future Applications or Directions
Our iCRISPR system may facilitate the generation of more complex genomic modifications, such as the creation of reporter alleles through HDR-mediated gene targeting using long donor DNA templates encoding protein tags or fluorescent reporters12. We have shown that, due to the high CRISPR targeting efficiencies attained in the system, this process can be performed in hPSCs, without the need for further drug selection12.&#160; Furthermore, multiplexed gene targeting can be used to investigate genetic interactions underlying complex human disease, as shown in our recent study, which we believe is the first example of such work31. iCRISPR can also be used to understand gene regulatory control by creating deletions either in noncoding RNAs or in gene regulatory regions, such as promoters and enhancers. To efficiently generate regulatory mutants using iCRISPR, gRNAs can be designed to disrupt the binding site of a DNA-binding protein, including but not restricted to the basal transcriptional machinery or a tissue-specific transcription factor. ssDNA template-mediated HDR can also be used to mutate specific protein-binding sites. Finally, we envisage that further optimization would enable the use of the iCRISPR platform in hPSCs for higher throughput genetic analyses of pluripotency phenotypes or disease phenotypes when combined with an in vitro differentiation protocol. These iCRISPR-mediated studies may allow for the more rapid identification of candidate disease-associated genes and studies of their functional relevance.

Human pluripotent stem cells (hPSCs) have the ability to both self-renew and give rise to all derivatives of the three embryonic germ lineages. They provide a valuable resource for cell replacement therapy and disease modeling by serving as a unique platform to recapitulate cellular processes in a human developmental context. They are also a source of experimental cells for scalable, high-throughput analyses. However, progress has been limited because of two main challenges: the lack of efficient genetic modification tools and the difficulty in recapitulating the complex embryonic developmental steps in a culture dish.
Genetic modification is an indispensable tool to study gene function in normal development and disease. However, while classical gene targeting approaches via homologous recombination have proven to be a powerful tool to dissect gene function in mouse embryonic stem cells (mESCs)1, this approach has been extremely inefficient when applied to hPSCs2,3. The recent brisk accession of programmable, site-specific nucleases from nature to laboratory use, including zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) systems4, means that genome engineering has become a much easier task in a wide range of organisms and cell lines, including in hPSCs. These gene editing tools take advantage of the fact that chimeric nucleases such as the Cas9 endonuclease can permit a whole range of genetic modifications by inducing double-stranded breaks (DSBs) at precise locations, triggering the endogenous DNA repair machinery to activate either non-homologous end joining (NHEJ) or homology-directed repair (HDR). Both mechanisms may be exploited for genetic manipulation by inducing either random insertion and deletion mutations (indels; via NHEJ), to create frameshift mutations that nullify gene alleles, or precise nucleotide substitutions (via HDR), to recapitulate patient mutations for human disease modeling or to correct a disease-causing mutation for gene therapy.
CRISPR/Cas-mediated genome engineering requires two components: the constant RNA-guided Cas9 endonuclease necessary for DNA cleavage and a variable CRISPR RNA (crRNA) and trans-activating (tracrRNA) duplex that specifies DNA target recognition. The crRNA/tracrRNA duplex can be replaced with a single chimeric guide RNA (gRNA), which have been found to work more efficiently5,6,7. While the CRISPR/Cas9 system has been adapted to most experimental organisms and cell lines, the delivery and expression of Cas9 and gRNA varies significantly and needs to be further optimized to achieve efficient genome editing in many systems, including hPSCs8. An efficient genome-editing platform, iCRISPR, has been established in hPSCs5. In this system, a TALEN-mediated approach has been used to target both alleles of the &#34;transgene safe harbor locus&#34; AAVS1 in trans, one allele with a reverse tetracycline-controlled transactivator (M2rtTA) and the other with a tetracycline response element (TRE) driving the expression of Cas9 (iCas9) in the hPSCs. In established clonal lines (iCas9 hPSCs), Cas9 is highly expressed with doxycycline treatment. Meanwhile, due to its small size (100 nt), single or multiple gRNAs can be easily delivered into iCas9 hPSCs with high efficiency and can direct Cas9 for site-specific cleavage, enabling efficient NHEJ-mediated gene disruption, as well as HDR-mediated precise nucleotide modifications in the presence of short single-stranded DNA (ssDNA) donor templates. The iCRISPR system can be used to successfully generate a panel of disease-mimicking hPSC lines with biallelic (homozygous or compound heterozygous) or heterozygous loss-of-function mutations in important developmental genes5,9. While a number of groups have reported efficient gene editing using CRISPR/Cas in hPSCs, the success remains limited to a small number of technologically adept laboratories. The iCRISPR platform offers an efficient yet simple solution for routine gene editing by researchers of different skill levels, and it has already been used in a number of published studies by our group and others9,10,11,12. This approach has also been further extended to inducible silencing based on the expression of dCas9-KRAB13.
Along with the progress in genome-editing technology, significant improvements have also been achieved in hPSC maintenance and directed differentiation. Culture conditions for hPSCs have evolved from irradiated mouse embryonic fibroblast (iMEF) feeder-dependent to feeder-free conditions on defined extracellular matrix components, and from complex media formulations to chemically defined medium conditions14. Such improvements have reduced the variability in hPSCs due to batch-to-batch differences in iMEF preparation and knockout serum replacement components, and thus provide a more reproducible environment for hPSC differentiation. Meanwhile, improved knowledge of signaling pathways governing human embryonic development, as well as discoveries from high-throughput drug screenings, have led to improved differentiation protocols15,16,17,18. These protocols more closely mimic in vivo developmental steps and generate cell types that closely recapitulate their in vivo counterparts. For hPSC differentiation into the pancreatic lineage, initial protocols mimicked early pancreatic development relatively well but eventually generated polyhormonal &#946; cells that were of immature fetal phenotypes and responded poorly to glucose stimulation. Recent advancements16,17,19,20 have allowed for the generation of glucose-responsive pancreatic &#946;-like cells, which will enable us to investigate later events, such as the formation and the further maturation of monohormonal &#946; cells.
Here, we detail the application of genome-modified lines for the study of pancreatic development by combining the iCRISPR system with the hPSC-based in vitro differentiation platform towards glucose-responsive pancreatic &#946;-like cells. This coupling of powerful genome editing tools with an improved hPSC differentiation protocol not only offers the speed and scale necessary to meet the growing demand for validating disease causality, but also enables sophisticated genetic manipulations for further mechanistic investigations into transcriptional control underlying normal development and disease9.

<table border="0" cellpadding="0" cellspacing="0" width="847">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:368px;">Chemically defined medium (E8)</td>
			<td style="width:261px;">Thermo Fisher Scientific</td>
			<td style="width:131px;">A1517001</td>
			<td style="width:87px;">Essential 8 basal medium and Essential 8 supplement included</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Truncated recombinant human form of vitronectin</td>
			<td>Thermo Fisher Scientific</td>
			<td>A14700</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">ROCK inhibitor Y-27632</td>
			<td>Selleck Chemicals</td>
			<td>S1049</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Dissociation reagent (TrypLE Select enzyme)</td>
			<td>Thermo Fisher Scientific</td>
			<td>12563029</td>
			<td>1X, animal origin free, recombinant enzyme</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">G418 Sulfate</td>
			<td>Thermo Fisher Scientific</td>
			<td>10131035</td>
			<td>Geneticin Selective Antibiotic</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Puromycin dihydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>P8833</td>
			<td>Puromycin Selective Antibiotic</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DNA Polymerase (Herculase II Fusion)</td>
			<td>Agilent Technologies</td>
			<td>600679</td>
			<td>PCR kit</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MEGAshortscript T7 Transcription kit</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM1354</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MEGAclear Transcription Clean-Up Kit</td>
			<td>Thermo Fisher Scientific</td>
			<td>AM1908</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Doxycycline hyclate</td>
			<td>Sigma-Aldrich</td>
			<td>D9891</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Opti-MEM medium</td>
			<td>Thermo Fisher Scientific</td>
			<td>31985062</td>
			<td>Reduced Serum Medium</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Lipofectamine RNAiMAX Transfection Reagent</td>
			<td>Thermo Fisher Scientific</td>
			<td>13778150</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DNeasy Blood &#38; Tissue Kit</td>
			<td>QIAGEN</td>
			<td>69504</td>
			<td>Genomic DNA extraction kit</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Proteinase K</td>
			<td>Roche</td>
			<td>3115879001</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MCDB 131 medium</td>
			<td>Thermo Fisher Scientific</td>
			<td>10372-019</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">BLAR medium</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td>Custom-made with a published formulation (Rezania et al., 2014)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">L-glutamine supplement (GlutaMAX)</td>
			<td>Thermo Fisher Scientific</td>
			<td>35050061</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">NaHCO3</td>
			<td>Thermo Fisher Scientific</td>
			<td>144-55-8</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G8769</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">BSA</td>
			<td>LAMPIRE Biological Laboratories</td>
			<td>7500855</td>
			<td>Fatty acid free</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">GDF8</td>
			<td>PeproTech</td>
			<td>120-00</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">CHIR-99021</td>
			<td>Stemgent</td>
			<td>04-0004</td>
			<td>GSK-3 inhibitor</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">L-Ascorbic acid</td>
			<td>Sigma-Aldrich</td>
			<td>A4544</td>
			<td>Vitamin C</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">FGF7</td>
			<td>R&#38;D Systems</td>
			<td>251-KG</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SANT1</td>
			<td>Tocris Bioscience</td>
			<td>1974</td>
			<td>Hedgehog inhibitor</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">RA</td>
			<td>Sigma-Aldrich</td>
			<td>R2625</td>
			<td>Retinoic acid</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">LDN</td>
			<td>Stemgent</td>
			<td>04-0019</td>
			<td>BMP inhibitor</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">IWP-2</td>
			<td>Tocris Bioscience</td>
			<td>3533</td>
			<td>Wnt antagonist&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">ITS-X</td>
			<td>Thermo Fisher Scientific</td>
			<td>51500-056</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TPB</td>
			<td>EMD Millipore</td>
			<td>565740-1MG</td>
			<td>PKC activator</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">3,3&#8217;,5-Triiodo-L-thyronine (T3)</td>
			<td>Sigma-Aldrich</td>
			<td>T6397</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">ALK5i II</td>
			<td>Enzo Life Sciences</td>
			<td>ALX-270-445</td>
			<td>ALK5 inhibitor II</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">ZnSO4</td>
			<td>Sigma-Aldrich</td>
			<td>Z0251</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Heparin</td>
			<td>Sigma-Aldrich</td>
			<td>H3149</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">GSiXX</td>
			<td>EMD Millipore</td>
			<td>565789</td>
			<td>Gamma secretase inhibitor XX, NOTCH signaling inhibitor</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">N-Cys (N-acetyl cysteine)</td>
			<td>Sigma-Aldrich</td>
			<td>A9165</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Trolox</td>
			<td>EMD Millipore</td>
			<td>648471</td>
			<td>Vitamin E analogue</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">R428</td>
			<td>Selleck Chemicals</td>
			<td>S2841</td>
			<td>AXL receptor tyrosine kinase inhibitor</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">24mm Transwell with insert</td>
			<td>Corning Life Sciences</td>
			<td>3414</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Gene Pulser Xcell Electroporation System</td>
			<td>Bio-Rad</td>
			<td>1652660</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">0.4 cm Electroporation Cuvettes</td>
			<td>Bio-Rad</td>
			<td>1652081</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">AAVS1-TALEN-L</td>
			<td>Addgene</td>
			<td>59025</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">AAVS1-TALEN-R</td>
			<td>Addgene</td>
			<td>59026</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">AAVS1-Neo-M2rtTA</td>
			<td>Addgene</td>
			<td>60843</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">AAVS1-Puro-iCas9</td>
			<td>Addgene</td>
			<td>58409</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">T7 Endonuclease I</td>
			<td>NEB</td>
			<td>M0302L</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Buffer 2</td>
			<td>NEB</td>
			<td>B7002S</td>
			<td>NEBuffer 2</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Long oligonucleotide</td>
			<td>Eton Bioscience or IDT</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SOX17 antibody</td>
			<td>R&#38;D Systems</td>
			<td>AF1924</td>
			<td>1: 500</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">FOXA2 antibody</td>
			<td>Millipore</td>
			<td>07-633</td>
			<td>1: 100</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">CXCR4-APC antibody</td>
			<td>R&#38;D Systems</td>
			<td>FAB170A</td>
			<td>1: 25</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">PDX1 antibody</td>
			<td>R&#38;D Systems</td>
			<td>AF2419</td>
			<td>1: 500</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">NKX6.1 antibody</td>
			<td>DSHB</td>
			<td>F55A12</td>
			<td>1: 500</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">NKX2.2 antibody</td>
			<td>DSHB</td>
			<td>74.5A5</td>
			<td>1: 100</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">NEUROD1 antibody</td>
			<td>Santa Cruz Biotechnology</td>
			<td>sc-1084</td>
			<td>1: 100</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Insulin antibody</td>
			<td>Dako</td>
			<td>A0564</td>
			<td>1: 2000</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">C-peptide antibody</td>
			<td>DSHB</td>
			<td>GN-ID4-c</td>
			<td>1: 2000</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Glucagon antibody</td>
			<td>Sigma-Aldrich</td>
			<td>G2654</td>
			<td>1: 1000</td>
		</tr>
	</tbody>
</table>

genome editing and directed differentiation of hpscs for interrogating lineage determinants in human pancreatic development

Interrogating gene function in self-renewing or differentiating human pluripotent stem cells (hPSCs) offers a valuable platform towards understanding human development and dissecting disease mechanisms in a dish. To capitalize on this potential application requires efficient genome-editing tools to generate hPSC mutants in disease-associated genes, as well as in vitro hPSC differentiation protocols to produce disease-relevant cell types that closely recapitulate their in vivo counterparts. An efficient genome-editing platform for hPSCs named iCRISPR has been developed through the TALEN-mediated targeting of a Cas9 expression cassette in the AAVS1 locus. Here, the protocols for the generation of inducible Cas9 hPSC lines using cells cultured in a chemically defined medium and a feeder-free condition are described. Detailed procedures for using the iCRISPR system for gene knockout or precise genetic alterations in hPSCs, either through non-homologous end joining (NHEJ) or via precise nucleotide alterations using a homology-directed repair (HDR) template, respectively, are included. These technical procedures include descriptions of the design, production, and transfection of CRISPR guide RNAs (gRNAs); the measurement of the CRISPR mutation rate by T7E1 or RFLP assays; and the establishment and validation of clonal mutant lines. Finally, we chronicle procedures for hPSC differentiation into glucose-responsive pancreatic &#946;-like cells by mimicking in vivo pancreatic embryonic development. Combining iCRISPR technology with directed hPSC differentiation enables the systematic examination of gene function to further our understanding of pancreatic development and diabetes disease mechanisms.

Watch this Scientific Journal Video about Genome Editing and Directed Differentiation of hPSCs for Interrogating Lineage Determinants in Human Pancreatic Development at JoVE.com

Genome Editing and Directed Differentiation of hPSCs for Interrogating Lineage Determinants in Human Pancreatic Development

Protocols to generate hPSC mutant lines using the iCRISPR platform and to differentiate hPSCs into glucose-responsive &#946;-like cells are described. Combining genome editing technology with hPSC-directed differentiation provides a powerful platform for the systematic analysis of the role of lineage determinants in human development and disease progression.

Interrogating gene function in self-renewing or differentiating human pluripotent stem cells (hPSCs) offers a valuable platform towards understanding ...

genome-editing-directed-differentiation-hpscs-for-interrogating

Research

JoVE Journal

Genetics

13.0K Views.  Sloan Kettering Institute. Protocols to generate hPSC mutant lines using the iCRISPR platform and to differentiate hPSCs into glucose-responsive β-like cells are described. Combining genome editing technology with hPSC-directed differentiation provides a powerful platform for the systematic analysis of the role of lineage determinants in human development and disease progression.

Video: Genome Editing and Directed Differentiation of hPSCs for Interrogating Lineage Determinants in Human Pancreatic Development

A Standard Methodology to Examine On-site Mutagenicity As a Function of Point Mutation Repair Catalyzed by CRISPR/Cas9 and SsODN in Human Cells

Combinatorial gene editing using CRISPR/Cas9 and single-stranded oligonucleotides is an effective strategy for the correction of single-base point mutations, which often are responsible for a variety of human inherited disorders. Using a well-established cell-based model system, the point mutation of a single-copy mutant eGFP gene integrated into HCT116 cells has been repaired using this combinatorial approach. The analysis of corrected and uncorrected cells reveals both the precision of gene editing and the development of genetic lesions, when indels are created in uncorrected cells in the DNA sequence surrounding the target site. Here, the specific methodology used to analyze this combinatorial approach to the gene editing of a point mutation, coupled with a detailed experimental strategy to measuring indel formation at the target site, is outlined. This protocol outlines a foundational approach and workflow for investigations aimed at developing CRISPR/Cas9-based gene editing for human therapy. The conclusion of this work is that on-site mutagenesis takes place as a result of CRISPR/Cas9 activity during the process of point mutation repair. This work puts in place a standardized methodology to identify the degree of mutagenesis, which should be an important and critical aspect of any approach destined for clinical implementation.

This protocol outlines the workflow of a CRISPR/Cas9-based gene editing system for the repair of point mutations in mammalian cells. Here, we use a combinatorial approach to gene editing with a detailed follow-on experimental strategy for measuring indel formation at the target site&#8212;in essence, analyzing onsite mutagenesis.

Combinatorial gene editing using CRISPR/Cas9 and single-stranded oligonucleotides is an effective strategy for the correction of single-base point ...

Microinjection of CRISPR/Cas9 Protein into Channel Catfish, Ictalurus punctatus, Embryos for Gene Editing

The complete genome of the channel catfish, Ictalurus punctatus, has been sequenced, leading to greater opportunities for studying channel catfish gene function. Gene knockout has been used to study these gene functions in vivo. The clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9 (CRISPR/Cas9) system is a powerful tool used to edit genomic DNA sequences to alter gene function. While the traditional approach has been to introduce CRISPR/Cas9 mRNA into the single cell embryos through microinjection, this can be a slow and inefficient process in catfish. Here, a detailed protocol for microinjection of channel catfish embryos with CRISPR/Cas9 protein is described. Briefly, eggs and sperm were collected and then artificial fertilization performed. Fertilized eggs were transferred to a Petri dish containing Holtfreter's solution. Injection volume was calibrated and then guide RNAs/Cas9 targeting the toll/interleukin 1 receptor domain-containing adapter molecule (TICAM 1) gene and rhamnose binding lectin (RBL) gene were microinjected into the yolk of one-cell embryos. The gene knockout was successful as indels were confirmed by DNA sequencing. The predicted protein sequence alterations due to these mutations included frameshift and truncated protein due to premature stop codons.

Microinjection of CRISPR/Cas9 Protein into Channel Catfish, Ictalurus punctatus, Embryos for Gene Editing

A simple and efficient microinjection protocol for gene editing in channel catfish embryos using the CRISPR/Cas9 system is presented. In this protocol, guide RNAs and Cas9 protein were microinjected into the yolk of one-cell embryos. This protocol has been validated by knocking out two channel catfish immune-related genes.

The complete genome of the channel catfish, Ictalurus punctatus, has been sequenced, leading to greater opportunities for studying channel catfish gene ...

Targeted Next-generation Sequencing and Bioinformatics Pipeline to Evaluate Genetic Determinants of Constitutional Disease

Next-generation sequencing (NGS) is quickly revolutionizing how research into the genetic determinants of constitutional disease is performed. The technique is highly efficient with millions of sequencing reads being produced in a short time span and at relatively low cost. Specifically, targeted NGS is able to focus investigations to genomic regions of particular interest based on the disease of study. Not only does this further reduce costs and increase the speed of the process, but it lessens the computational burden that often accompanies NGS. Although targeted NGS is restricted to certain regions of the genome, preventing identification of potential novel loci of interest, it can be an excellent technique when faced with a phenotypically and genetically heterogeneous disease, for which there are previously known genetic associations. Because of the complex nature of the sequencing technique, it is important to closely adhere to protocols and methodologies in order to achieve sequencing reads of high coverage and quality. Further, once sequencing reads are obtained, a sophisticated bioinformatics workflow is utilized to accurately map reads to a reference genome, to call variants, and to ensure the variants pass quality metrics. Variants must also be annotated and curated based on their clinical significance, which can be standardized by applying the American College of Medical Genetics and Genomics Pathogenicity Guidelines. The methods presented herein will display the steps involved in generating and analyzing NGS data from a targeted sequencing panel, using the ONDRISeq neurodegenerative disease panel as a model, to identify variants that may be of clinical significance.

Targeted next-generation sequencing is a time- and cost-efficient approach that is becoming increasingly popular in both disease research and clinical diagnostics. The protocol described here presents the complex workflow required for sequencing and the bioinformatics process used to identify genetic variants that contribute to disease.

Next-generation sequencing (NGS) is quickly revolutionizing how research into the genetic determinants of constitutional disease is performed. The ...

Enhanced Genome Editing with Cas9 Ribonucleoprotein in Diverse Cells and Organisms

Site-specific eukaryotic genome editing with CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated) systems has quickly become a commonplace amongst researchers pursuing a wide variety of biological questions. Users most often employ the Cas9 protein derived from Streptococcus pyogenes in a complex with an easily reprogrammed guide RNA (gRNA). These components are introduced into cells, and through a base pairing with a complementary region of the double-stranded DNA (dsDNA) genome, the enzyme cleaves both strands to generate a double-strand break (DSB). Subsequent repair leads to either random insertion or deletion events (indels) or the incorporation of experimenter-provided DNA at the site of the break.
The use of a purified single-guide RNA and Cas9 protein, preassembled to form an RNP and delivered directly to cells, is a potent approach for achieving highly efficient gene editing. RNP editing particularly enhances the rate of gene insertion, an outcome that is often challenging to achieve. Compared to the delivery via a plasmid, the shorter persistence of the Cas9 RNP within the cell leads to fewer off-target events. 
Despite its advantages, many casual users of CRISPR gene editing are less familiar with this technique. To lower the barrier to entry, we outline detailed protocols for implementing the RNP strategy in a range of contexts, highlighting its distinct benefits and diverse applications. We cover editing in two types of primary human cells, T cells and hematopoietic stem/progenitor cells (HSPCs). We also show how Cas9 RNP editing enables the facile genetic manipulation of entire organisms, including the classic model roundworm Caenorhabditis elegans and the more recently introduced model crustacean, Parhyale hawaiensis.

Utilizing a preassembled Cas9 ribonucleoprotein complex (RNP) is a powerful method for precise, efficient genome editing. Here, we highlight its utility across a broad range of cells and organisms, including primary human cells and both classic and emerging model organisms.

Site-specific eukaryotic genome editing with CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated) systems has ...

CRISPR/Cas9 Gene Editing to Make Conditional Mutants of Human Malaria Parasite P. falciparum

Malaria is a significant cause of morbidity and mortality worldwide. This disease, which primarily affects those living in tropical and subtropical regions, is caused by infection with Plasmodium parasites. The development of more effective drugs to combat malaria can be accelerated by improving our understanding of the biology of this complex parasite. Genetic manipulation of these parasites is key to understanding their biology; however, historically the genome of P. falciparum has been difficult to manipulate. Recently, CRISPR/Cas9 genome editing has been utilized in malaria parasites, allowing for easier protein tagging, generation of conditional protein knockdowns, and deletion of genes. CRISPR/Cas9 genome editing has proven to be a powerful tool for advancing the field of malaria research. Here, we describe a CRISPR/Cas9 method for generating glmS-based conditional knockdown mutants in P. falciparum. This method is highly adaptable to other types of genetic manipulations, including protein tagging and gene knockouts.

CRISPR/Cas9 Gene Editing to Make Conditional Mutants of Human Malaria Parasite P. falciparum

We describe a method for generating glmS-based conditional knockdown mutants in Plasmodium falciparum using CRISPR/Cas9 genome editing.

Malaria is a significant cause of morbidity and mortality worldwide. This disease, which primarily affects those living in tropical and subtropical ...

CRISPR-mediated Genome Editing of the Human Fungal Pathogen Candida albicans

This method describes the efficient CRISPR mediated genome editing of the diploid human fungal pathogen Candida albicans. CRISPR-mediated genome editing in C. albicans requires Cas9, guide RNA, and repair template. A plasmid expressing a yeast codon optimized Cas9 (CaCas9) has been generated. Guide sequences directly upstream from a PAM site (NGG) are cloned into the Cas9 expression vector. A repair template is then made by primer extension in vitro. Cotransformation of the repair template and vector into C. albicans leads to genome editing. Depending on the repair template used, the investigator can introduce nucleotide changes, insertions, or deletions. As C. albicans is a diploid, mutations are made in both alleles of a gene, provided that the A and B alleles do not harbor SNPs that interfere with guide targeting or repair template incorporation. Multimember gene families can be edited in parallel if suitable conserved sequences exist in all family members. The C. albicans CRISPR system described is flanked by FRT sites and encodes flippase. Upon induction of flippase, the antibiotic marker (CaCas9) and guide RNA are removed from the genome. This allows the investigator to perform subsequent edits to the genome. C. albicans CRISPR is a powerful fungal genetic engineering tool, and minor alterations to the described protocols permit the modification of other fungal species including C. glabrata, N. castellii, and S. cerevisiae.

CRISPR-mediated Genome Editing of the Human Fungal Pathogen Candida albicans

Efficient genome engineering of Candida albicans is critical to understanding the pathogenesis and development of therapeutics. Here, we described a protocol to quickly and accurately edit the C. albicans genome using CRISPR. The protocol allows investigators to introduce a wide variety of genetic modifications including point mutations, insertions, and deletions.

This method describes the efficient CRISPR mediated genome editing of the diploid human fungal pathogen Candida albicans. CRISPR-mediated genome editing ...

Genome Editing in Mammalian Cell Lines using CRISPR-Cas

The clustered regularly interspaced short palindromic repeats (CRISPR) system functions naturally in bacterial adaptive immunity, but has been successfully repurposed for genome engineering in many different living organisms. Most commonly, the wildtype CRISPR associated 9 (Cas9) or Cas12a endonuclease is used to cleave specific sites in the genome, after which the DNA double-stranded break is repaired via the non-homologous end joining (NHEJ) pathway or the homology-directed repair (HDR) pathway depending on whether a donor template is absent or present respectively. To date, CRISPR systems from different bacterial species have been shown to be capable of performing genome editing in mammalian cells. However, despite the apparent simplicity of the technology, multiple design parameters need to be considered, which often leave users perplexed about how best to carry out their genome editing experiments. Here, we describe a complete workflow from experimental design to identification of cell clones that carry desired DNA modifications, with the goal of facilitating successful execution of genome editing experiments in mammalian cell lines. We highlight key considerations for users to take note of, including the choice of CRISPR system, the spacer length, and the design of a single-stranded oligodeoxynucleotide (ssODN) donor template. We envision that this workflow will be useful for gene knockout studies, disease modeling efforts, or the generation of reporter cell lines.

CRISPR-Cas is a powerful technology to engineer the complex genomes of plants and animals. Here, we detail a protocol to efficiently edit the human genome using different Cas endonucleases. We highlight important considerations and design parameters to optimize editing efficiency.

The clustered regularly interspaced short palindromic repeats (CRISPR) system functions naturally in bacterial adaptive immunity, but has been ...

Single-cell RNA Sequencing and Analysis of Human Pancreatic Islets

Pancreatic islets comprise of endocrine cells with distinctive hormone expression patterns. The endocrine cells show functional differences in response to normal and pathological conditions. The goal of this protocol is to generate high-quality, large-scale transcriptome data of each endocrine cell type with the use of a droplet-based microfluidic single-cell RNA sequencing technology. Such data can be utilized to build the gene expression profile of each endocrine cell type in normal or specific conditions. The process requires careful handling, accurate measurement, and rigorous quality control. In this protocol, we describe detailed steps for human pancreatic islets dissociation, sequencing, and data analysis. The representative results of about 20,000 human single islet cells demonstrate the successful application of the protocol.

Here, we present a protocol to generate high-quality, large-scale transcriptome data of single cells from isolated human pancreatic islets using a droplet-based microfluidic single-cell RNA sequencing technology.

Pancreatic islets comprise of endocrine cells with distinctive hormone expression patterns. The endocrine cells show functional differences in response to ...

Transforming, Genome Editing and Phenotyping the Nitrogen-fixing Tropical Cannabaceae Tree Parasponia andersonii

Parasponia andersonii is a fast-growing tropical tree that belongs to the Cannabis family (Cannabaceae). Together with 4 additional species, it forms the only known non-legume lineage able to establish a nitrogen-fixing nodule symbiosis with rhizobium. Comparative studies between legumes and P. andersonii could provide valuable insight into the genetic networks underlying root nodule formation. To facilitate comparative studies, we recently sequenced the P. andersonii genome and established Agrobacterium tumefaciens-mediated stable transformation and CRISPR/Cas9-based genome editing. Here, we provide a detailed description of the transformation and genome editing procedures developed for P. andersonii. In addition, we describe procedures for the seed germination and characterization of symbiotic phenotypes. Using this protocol, stable transgenic mutant lines can be generated in a period of 2-3 months. Vegetative in vitro propagation of T0 transgenic lines allows phenotyping experiments to be initiated at 4 months after A. tumefaciens co-cultivation. Therefore, this protocol takes only marginally longer than the transient Agrobacterium rhizogenes-based root transformation method available for P. andersonii, though offers several clear advantages. Together, the procedures described here permit P. andersonii to be used as a research model for studies aimed at understanding symbiotic associations as well as potentially other aspects of the biology of this tropical tree.

Transforming, Genome Editing and Phenotyping the Nitrogen-fixing Tropical Cannabaceae Tree Parasponia andersonii

Parasponia andersonii is a fast-growing tropical tree that belongs to the Cannabis family (Cannabaceae) and can form nitrogen-fixing root nodules in association with the rhizobium. Here, we describe a detailed protocol for reverse genetic analyses in P. andersonii based on Agrobacterium tumefaciens-mediated stable transformation and CRISPR/Cas9-based genome editing.

Parasponia andersonii is a fast-growing tropical tree that belongs to the Cannabis family (Cannabaceae). Together with 4 additional species, it forms the ...

Characterization of In Vitro Differentiation of Human Primary Keratinocytes by RNA-Seq Analysis

Human primary keratinocytes are often used as in vitro models for studies on epidermal differentiation and related diseases. Methods have been reported for in vitro differentiation of keratinocytes cultured in two-dimensional (2D) submerged manners using various induction conditions. Described here is a procedure for 2D in vitro keratinocyte differentiation method by contact inhibition and subsequent molecular characterization by RNA-seq. In brief, keratinocytes are grown in defined keratinocyte medium supplemented with growth factors until they are fully confluent. Differentiation is induced by close contacts between the keratinocytes and further stimulated by excluding growth factors in the medium. Using RNA-seq analyses, it is shown that both 1) differentiated keratinocytes exhibit distinct molecular signatures during differentiation and 2) the dynamic gene expression pattern largely resembles cells during epidermal stratification. As for comparison to normal keratinocyte differentiation, keratinocytes carrying mutations of the transcription factor p63 exhibit altered morphology and molecular signatures, consistent with their differentiation defects. In conclusion, this protocol details the steps for 2D in vitro keratinocyte differentiation and its molecular characterization, with an emphasis on bioinformatic analysis of RNA-seq data. Because RNA extraction and RNA-seq procedures have been well-documented, it is not the focus of this protocol. The experimental procedure of in vitro keratinocyte differentiation and bioinformatic analysis pipeline can be used to study molecular events during epidermal differentiation in healthy and diseased keratinocytes.

Presented here is a stepwise procedure for in vitro differentiation of human primary keratinocytes by contact inhibition followed by characterization at the molecular level by RNA-seq analysis.

Human primary keratinocytes are often used as in vitro models for studies on epidermal differentiation and related diseases. Methods have been reported ...