A.J.M. created the original concept that led to the development of CRISPR-EZ and produced the figures. C.K.D. compiled and adapted the internal and published protocols for this current manuscript. A.J.M. is supported by NIH (R00HD096108).

<ol>
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There are no relevant financial declarations by the authors.

Presented here is a straightforward and highly efficient mouse genome editing technology. Electroporation can be used to generate modified embryos in 1-2 weeks (Figure 1) and can produce edited mice within 6 weeks9. Compared to contemporaneously developed electroporation-based protocols that deliver RNPs7,10,11,12,<sup class="xref...

Genome editing in live mice has been considerably simplified and has become accessible and more affordable since the emergence of CRISPR editing1,2,3. Initial animal editing attempts used microinjection to deliver CRISPR Cas9 mRNA/sgRNA into pronuclear-stage embryos4,5,6. While microinjection is quite effective, the amount of practice required to fully master it might not be appropriate for trainees and students and also requires expensive equipment that a modestly funded lab is unable to afford. Microinjection is normally performed by expert technicians at transgenic facilities with schedules and service prices that are rate-limiting for many researchers. A more accessible approach is that of electroporation, which has been demonstrated to be quite effective for the delivery of CRISPR Cas9 mRNA/sgRNA into pronuclear-stage embryos7. Further improvements in CRISPR genome editing and delivery strategies suggested that pre-assembled RNPs already engaged with sgRNAs may be an effective means to reduce mosaicism8.
The rationale behind the development and use of this protocol was to bypass many of the limitations and obstacles associated with microinjection. As the name implies, an easy, in-house, and cost-effective method that could quickly determine whether untested sgRNA designs would be worthwhile using during a microinjection experiment would be a very convenient first pass quality control step (Figure 1). While this method cannot replace microinjection for more complex strategies, like introducing long donor DNA sequences for recombination-based outcomes, it is ideal for less complex strategies like small deletions or insertions and tagging genes. This method is appropriate for researchers with basic embryo manipulation skills who have simple editing needs, would like to test their hypothesis within the timeframe of preimplantation development, or prefer to test sgRNAs in embryos before scheduling an appointment with a microinjection specialist. Here, editing reagents are transiently delivered into pronuclear-stage embryos as Cas9/sgRNA RNPs via electroporation (a series of electrical pulses) to maximize efficiency while decreasing mosaicism8. Using an embryo genotyping method, editing results are available in approximately 1 week9, thus reducing the need for various microinjection applications at a significantly reduced cost.
This method&#39;s effectiveness peaks at the pronuclear embryo stage, when the embryo has not yet fused the maternal and paternal pronuclei or entered S-phase (Figure 2). Superovulation is used to maximize the number of zygotes but produces both pronuclear zygotes and unfertilized eggs. Healthy zygotes can also be pre-selected before electroporation to increase the overall efficiency. As other electroporation protocols have efficiently edited zygotes without the need to include a similar step7,10,11,12,13,14,15, an optional step of this protocol is the slight erosion of the zona pellucida (ZP). The ZP is a glycoprotein layer that aids spermatozoa binding, acrosome response, and fertilization surrounding pronuclear-stage embryos. In our experience, we found that a gentle acid-based erosion of the ZP provides reliable Cas9 RNP electroporation delivery with only a marginal impact on viability.
We have observed RNP delivery rates of up to 100% efficiency via electroporation in mouse strains that are commonly used in research like C57BL/6J and C57BL/6N9,16. Independent groups have also developed electroporation-based procedures with efficiencies greater than or matching microinjection11,12,13,14,15,17, with electroporation protocols functioning well in rat18,19, pig20,21,22 and cow23, so we suggest that readers compare the protocols to find the conditions that best suit their experimental and equipment needs. The system described here uses common materials and equipment, requiring only basic embryo manipulation skills. This technique is effective for a range of editing strategies, making this method broadly accessible to the research community.
Designing ideal small guide RNAs (sgRNAs) is essential for efficient editing. We recommend screening two to three sgRNA strategies per target site directly in mouse embryos, especially if mouse line generation is desired. Once designed, cloning-free methods like in vitro transcription (IVT) to produce high-quality sgRNAs are recommended3. The RNPs and sgRNAs are mixed with 30-50 processed pronuclear-stage embryos and exposed to a series of electrical pulses to first temporarily permeabilize the ZP and cell membrane, with subsequent pulses to keep the pores open and electrophorese the RNPs through the zygote24. After optimization, we found that six 3 ms pulses at 30 V for bulk embryos (~50) were optimal for editing effectiveness and viability, providing highly efficient Cas9/sgRNA RNP delivery9,16,25. Editing events in individual mouse morula can be confirmed using a variety of validation strategies common for CRISPR editing, such as restriction fragment length polymorphism (RFLP), T7 endonuclease digestion, and Sanger sequencing of the region of interest26.
The current method is most appropriate for simple editing schemes (Figure 3), such as insertion/deletions (indels), exon-sized deletions on the order of 500-2000 bp, and the delivery of point mutations and small insertions such as C- or N-Terminal tags (e.g., FLAG, HA, or V5)9,16,27. The potential for complex genome editing, like large insertions of fluorescent tags or conditional alleles, remains uncertain and is the present focus of upcoming improvements.
This method is easily mastered and can be used to quickly test sgRNAs in cultured mouse embryos in 1 week9 (Figure 1). Presented in this work is a six-step protocol, which includes 1) sgRNA design; 2) sgRNA synthesis; 3) superovulation and mating; 4) embryo culture, collection, and processing; 5) RNP assembly and electroporation; 6) embryo culture and genotyping. Information about all the materials used is provided (Table of Materials). As a positive control, reagents to edit the Tyrosinase (Tyr) locus9,16 have been included in the Supplementary Table 1.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.1-cm-gap electroporation cuvette</td>
			<td>Bio-Rad</td>
			<td>cat. no. 1652089</td>
			<td>Electroporation</td>
		</tr>
		<tr>
			<td>26-G, 1/2-inch needle</td>
			<td>BD</td>
			<td>cat. no. 305111</td>
			<td>Superovulation</td>
		</tr>
		<tr>
			<td>3&#8211;8-month-old male mice and 3- to 5-week-old female mice</td>
			<td>JAX</td>
			<td>cat. no. 000664</td>
			<td>Superovulation</td>
		</tr>
		<tr>
			<td>35-mm Tissue culture dish</td>
			<td>Greiner Bio-One,</td>
			<td>cat. no. 627-160</td>
			<td>Embryo Culture</td>
		</tr>
		<tr>
			<td>60-mm Tissue culture dish</td>
			<td>Greiner Bio-One,</td>
			<td>cat. no. 628-160</td>
			<td>Embryo Processing</td>
		</tr>
		<tr>
			<td>6x loading dye</td>
			<td>Thermo Fisher Scientific</td>
			<td>cat. no. R0611</td>
			<td>sgRNA Synthesis and Genotyping</td>
		</tr>
		<tr>
			<td>Acidic Tyrode&#39;s (AT) solution, embryo culture grade</td>
			<td>Sigma-Aldrich,</td>
			<td>cat. no. T1788</td>
			<td>Embryo Processing</td>
		</tr>
		<tr>
			<td>BSA, embryo culture grade</td>
			<td>Sigma-Aldrich</td>
			<td>cat. no. A3311</td>
			<td>Embryo Processing and Culture</td>
		</tr>
		<tr>
			<td>Cas9 protein</td>
			<td>Alt-R S.p. Cas9 nuclease 3NLS</td>
			<td>cat. no. 1074181</td>
			<td>Electroporation</td>
		</tr>
		<tr>
			<td>DNase I, RNase-free</td>
			<td>New England BioLabs,</td>
			<td>cat. no. M0303</td>
			<td>sgRNA Synthesis</td>
		</tr>
		<tr>
			<td>DPBS(calcium and magnesium free)</td>
			<td>Gibco</td>
			<td>cat. no. 14190-144</td>
			<td>Embryo Processing</td>
		</tr>
		<tr>
			<td>EcoRI</td>
			<td>NEB</td>
			<td>cat. no. R3101S</td>
			<td>Genotyping</td>
		</tr>
		<tr>
			<td>EDTA, anhydrous</td>
			<td>Sigma-Aldrich</td>
			<td>cat. no. EDS-100G</td>
			<td>RNP Buffer</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Koptec</td>
			<td>cat. no. V1016</td>
			<td>sgRNA Synthesis</td>
		</tr>
		<tr>
			<td>Gelatin (powder) type B, laboratory grade</td>
			<td>Fisher,</td>
			<td>cat. no. G7-500</td>
			<td>Lysis Buffer</td>
		</tr>
		<tr>
			<td>Glycerol,&#160;molecular-biology grade</td>
			<td>Fisher</td>
			<td>cat. no. BP229</td>
			<td>RNP Buffer</td>
		</tr>
		<tr>
			<td>Taq Polymerase</td>
			<td>Promega</td>
			<td>cat. no. M712</td>
			<td>Genotyping</td>
		</tr>
		<tr>
			<td>HEPES, cell culture grade</td>
			<td>Sigma-Aldrich</td>
			<td>cat. no. H4034</td>
			<td>RNP Buffer</td>
		</tr>
		<tr>
			<td>HinfI (10,000 U/mL)</td>
			<td>NEB</td>
			<td>cat. no. R0155S</td>
			<td>Genotyping</td>
		</tr>
		<tr>
			<td>HiScribe T7 High Yield RNA Synthesis Kit</td>
			<td>New England BioLabs,</td>
			<td>cat. no. E2040</td>
			<td>sgRNA Synthesis</td>
		</tr>
		<tr>
			<td>Human chorion gonadotropin, lyophilized&#160;(hCG)</td>
			<td>Millipore</td>
			<td>cat. no. 230734</td>
			<td>Superovulation</td>
		</tr>
		<tr>
			<td>Hyaluronidase/M2</td>
			<td>Millipore</td>
			<td>cat. no. MR-051-F</td>
			<td>Embryo Processing</td>
		</tr>
		<tr>
			<td>KSOMaa Evolve medium (potassium-supplemented simplex-optimized medium plus amino acids)</td>
			<td>Zenith Biotech</td>
			<td>cat. no. ZEKS-050</td>
			<td>Embryo Culture</td>
		</tr>
		<tr>
			<td>LE agarose, analytical grade</td>
			<td>BioExpress</td>
			<td>cat. no. E-3120-500</td>
			<td>sgRNA Synthesis and Genotyping</td>
		</tr>
		<tr>
			<td>M2 medium</td>
			<td>Zenith Biotech</td>
			<td>cat. no. ZFM2-050</td>
			<td>Embryo Processing</td>
		</tr>
		<tr>
			<td>Magnesium chloride, anhydrous (MgCl2)</td>
			<td>Sigma-Aldrich</td>
			<td>cat. no. M8266</td>
			<td>RNP and Lysis Buffer</td>
		</tr>
		<tr>
			<td>Mineral Oil</td>
			<td>Millipore</td>
			<td>cat. no. ES-005C</td>
			<td>Embryo Culture</td>
		</tr>
		<tr>
			<td>Nonidet P-40,substitute (NP-40)</td>
			<td>Sigma-Aldrich</td>
			<td>cat. no. 74385</td>
			<td>Lysis Buffer</td>
		</tr>
		<tr>
			<td>Nuclease-free water, molecular-biology grade</td>
			<td>Ambion</td>
			<td>cat. no. AM9937</td>
			<td>sgRNA Synthesis and Genotyping</td>
		</tr>
		<tr>
			<td>Oligos for sgRNA synthesis, donor oligo and PCR primers for genotyping</td>
			<td>Integrated DNA Technologies</td>
			<td>custom orders</td>
			<td>sgRNA Design</td>
		</tr>
		<tr>
			<td>Reduced serum medium</td>
			<td>Thermo Fisher Scientific</td>
			<td>cat. no. 31985062</td>
			<td>Embryo Culture</td>
		</tr>
		<tr>
			<td>High-fidelity DNA polymerase</td>
			<td>New England BioLabs,</td>
			<td>cat. no. M0530</td>
			<td>sgRNA Synthesis</td>
		</tr>
		<tr>
			<td>Potassium chloridemolecular-biology grade (KCl)</td>
			<td>Sigma-Aldrich</td>
			<td>cat. no. P9333</td>
			<td>RNP and Lysis Buffer</td>
		</tr>
		<tr>
			<td>Pregnant mare serum gonadotropin lyophilizd ((PMSG)</td>
			<td>ProspecBio</td>
			<td>cat. no. HOR-272</td>
			<td>Superovulation</td>
		</tr>
		<tr>
			<td>Proteinase K, molecular-biology grade</td>
			<td>Fisher</td>
			<td>cat. no. BP1700-100</td>
			<td>Lysis Buffer</td>
		</tr>
		<tr>
			<td>RNase-free 1.5-mL microcentrifuge tube</td>
			<td>VWR</td>
			<td>cat. no. 20170-333</td>
			<td>sgRNA Synthesis and Genotyping</td>
		</tr>
		<tr>
			<td>RNase-free eight-well PCR strip tubes</td>
			<td>VWR</td>
			<td>cat. no. 82006-606</td>
			<td>sgRNA Synthesis and Genotyping</td>
		</tr>
		<tr>
			<td>Magnetic purification beads</td>
			<td>GE Healthcare</td>
			<td>cat. no. 65152105050250</td>
			<td>sgRNA Synthesis</td>
		</tr>
		<tr>
			<td>Tris (2-carboxyethyl) phosphine hydrochloride (TCEP)</td>
			<td>Sigma-Aldrich</td>
			<td>cat. no. C4706</td>
			<td>RNP Buffer</td>
		</tr>
		<tr>
			<td>Tris-HCl solution, pH 8.5 molecular-biology grade</td>
			<td>Teknova</td>
			<td>cat. no. T1085</td>
			<td>Lysis Buffer</td>
		</tr>
		<tr>
			<td>Tween 20 molecular-biology grade</td>
			<td>Sigma-Aldrich</td>
			<td>cat. no. P7949-500</td>
			<td>Lysis Buffer</td>
		</tr>
	</tbody>
</table>

efficient genome editing of mice by crispr electroporation of zygotes

With exceptional efficiency, accuracy, and ease, the CRISPR/Cas9 system has significantly improved genome editing in cell culture and lab animal experiments. When generating animal models, the electroporation of zygotes offers higher efficiency, simplicity, cost, and throughput as an alternative to the gold standard method of microinjection. Electroporation is also gentler, with higher viability, and reliably delivers Cas9/single-guide RNA (sgRNA) ribonucleoproteins (RNPs) into the zygotes of common laboratory mouse strains (e.g., C57BL/6J and C57BL/6N) that approaches 100% delivery efficiency. This technique enables insertion/deletion (indels) mutations, point mutations, the deletion of whole genes or exons, and small insertions in the range of 100-200 bp to insert LoxP or short tags like FLAG, HA, or V5. While constantly being improved, here we present the current state of CRISPR-EZ in a protocol that includes sgRNA production through in vitro transcription, embryo processing, RNP assembly, electroporation, and the genotyping of preimplantation embryos. A graduate-level researcher with minimal experience manipulating embryos can obtain genetically edited embryos in less than 1 week using this protocol. Here, we offer a straightforward, low-cost, efficient, high-capacity method that could be used with mouse embryos.

This method generates more than 100 &#181;g of sgRNA (20 &#181;L at &#62;6,000 ng/L concentration) for efficient Cas9/sgRNA RNP assembly. The routine superovulation method described here typically produces 10-20 viable embryos per plugged female. Due to handling errors and typical losses associated with embryo manipulation, an expected 80% of embryos are fertilized, viable, and in excellent condition after electroporation. To aid researchers in executing a successful experiment, we have provided an example strategy to ta...

Watch this Scientific Journal Video about Efficient Genome Editing of Mice by CRISPR Electroporation of Zygotes at JoVE.com

Efficient Genome Editing of Mice by CRISPR Electroporation of Zygotes

Here, we describe a simple technique intended for the efficient generation of genetically modified mice called CRISPR RNP Electroporation of Zygotes (CRISPR-EZ). This method delivers editing reagents by electroporation into embryos at an efficiency approaching 100%. This protocol is effective for point mutations, small genomic insertions, and deletions in mammalian embryos.

With exceptional efficiency, accuracy, and ease, the CRISPR/Cas9 system has significantly improved genome editing in cell culture and lab animal ...

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JoVE Journal

Developmental Biology

2.7K Views.  The University of Pennsylvania. Here, we describe a simple technique intended for the efficient generation of genetically modified mice called CRISPR RNP Electroporation of Zygotes (CRISPR-EZ). This method delivers editing reagents by electroporation into embryos at an efficiency approaching 100%. This protocol is effective for point mutations, small genomic insertions, and deletions in mammalian embryos.

Video: Efficient Genome Editing of Mice by CRISPR Electroporation of Zygotes

Efficient Gene Transfer in Chick Retinas for Primary Cell Culture Studies: An Ex-ovo Electroporation Approach

The cone photoreceptor-enriched cultures derived from embryonic chick retinas have become an indispensable tool for researchers around the world studying the biology of retinal neurons, particularly photoreceptors. The applications of this system go beyond basic research, as they can easily be adapted to high throughput technologies for drug development. However, genetic manipulation of retinal photoreceptors in these cultures has proven to be very challenging, posing an important limitation to the usefulness of the system. We have recently developed and validated an ex&#160;ovo plasmid electroporation technique that increases the rate of transfection of retinal cells in these cultures by five-fold compared to other currently available protocols1. In this method embryonic chick eyes are enucleated at stage 27, the RPE is removed, and the retinal cup is placed in a plasmid-containing solution and electroporated using easily constructed custom-made electrodes. The retinas are then dissociated and cultured using standard procedures. This technique can be applied to overexpression studies as well as to the downregulation of gene expression, for example via the use of plasmid-driven RNAi technology, commonly achieving transgene expression in 25% of the photoreceptor population. The video format of the present publication will make this technology easily accessible to researchers in the field, enabling the study of gene function in primary retinal cultures. We have also included detailed explanations of the critical steps of this procedure for a successful outcome and reproducibility.

Efficient Gene Transfer in Chick Retinas for Primary Cell Culture Studies: An Ex-ovo Electroporation Approach

Embryonic chick retinal cell cultures constitute valuable tools for the study of photoreceptor biology. We have developed an efficient gene transfer technique based on ex&#160;ovo plasmid electroporation of the retinas prior to culture. This technique considerably increases transfection efficiencies over currently available protocols, making genetic manipulation feasible for this system.

The cone photoreceptor-enriched cultures derived from embryonic chick retinas have become an indispensable tool for researchers around the world studying ...

Culture of Embryonic Mouse Cochlear Explants and Gene Transfer by Electroporation

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair cells are aligned in one row of inner hair cells and three rows of outer hair cells that extend along the basal to apical axis of the cochlea. The explant culture technique described here provides an efficient method to isolate and maintain cochlear explants from the embryonic mouse inner ear. Also, the morphology and molecular characteristics of sensory hair cells and nonsensory supporting cells within the cochlear explant cultures resemble those observed in vivo and can be studied within its intrinsic cellular environment. The cochlear explants can serve as important experimental tools for the identification and characterization of molecular and genetic pathways that are involved in cellular specification and patterning. Although transgenic mouse models provide an effective approach for gene expression studies, a considerable number of mouse mutants die during embryonic development thereby hindering the analysis and interpretation of developmental phenotypes. The organ of Corti from mutant mice that die before birth can be cultured so that their in vitro development and responses to different factors can be analyzed. Additionally, we describe a technique for electroporating embryonic cochlear explants ex vivo which can be used to downregulate or overexpress specific gene(s) and analyze their potential endogenous function and test whether specific gene product is necessary or sufficient in a given context to influence mammalian cochlear development1-8.

We present a method that describes isolation and culture of cochlear explants from embryonic mouse inner ear. We also demonstrate a method for gene transfer into cochlear explants via square-wave electroporation. The in vitro explant culture coupled with gene transfer technique enables researchers to study the effects of altering gene expression during development.

Auditory hair cells located within the mouse organ of Corti detect and transmit sound information to the central nervous system. The mechanosensory hair ...

Genome-wide Snapshot of Chromatin Regulators and States in Xenopus Embryos by ChIP-Seq

The recruitment of chromatin regulators and the assignment of chromatin states to specific genomic loci are pivotal to cell fate decisions and tissue and organ formation during development. Determining the locations and levels of such chromatin features in vivo will provide valuable information about the spatio-temporal regulation of genomic elements, and will support aspirations to mimic embryonic tissue development in vitro. The most commonly used method for genome-wide and high-resolution profiling is chromatin immunoprecipitation followed by next-generation sequencing (ChIP-Seq). This protocol outlines how yolk-rich embryos such as those of the frog Xenopus can be processed for ChIP-Seq experiments, and it offers simple command lines for post-sequencing analysis. Because of the high efficiency with which the protocol extracts nuclei from formaldehyde-fixed tissue, the method allows easy upscaling to obtain enough ChIP material for genome-wide profiling. Our protocol has been used successfully to map various DNA-binding proteins such as transcription factors, signaling mediators, components of the transcription machinery, chromatin modifiers and post-translational histone modifications, and for this to be done at various stages of embryogenesis. Lastly, this protocol should be widely applicable to other model and non-model organisms as more and more genome assemblies become available.

Genome-wide Snapshot of Chromatin Regulators and States in Xenopus Embryos by ChIP-Seq

The question of how chromatin regulators and chromatin states affect the genome in vivo is key to our understanding of how early cell fate decisions are made in the developing embryo. ChIP-Seq&#8212;the most popular approach to investigate chromatin features at a global level&#8212;is outlined here for Xenopus embryos.

The recruitment of chromatin regulators and the assignment of chromatin states to specific genomic loci are pivotal to cell fate decisions and tissue and ...

Efficient Generation of hiPSC Neural Lineage Specific Knockin Reporters Using the CRISPR/Cas9 and Cas9 Double Nickase System

Gene targeting is a critical approach for characterizing gene functions in modern biomedical research. However, the efficiency of gene targeting in human cells has been low, which prevents the generation of human cell lines at a desired rate. The past two years have witnessed a rapid progression on improving efficiency of genetic manipulation by genome editing tools such as the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas (CRISPR-associated) system. This manuscript describes a protocol for generating lineage specific human induced pluripotent stem cell (hiPSC) reporters using CRISPR/Cas system assisted homologous recombination. Procedures for obtaining necessary components for making neural lineage reporter lines using the CRISPR/Cas system, focusing on construction of targeting vectors and single guide RNAs, are described. This protocol can be extended to platform establishment and mutation correction in hiPSCs.

Genome editing tools such as the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas (CRISPR-associated) system have greatly improved gene targeting efficiency in human induced pluripotent stem cells (hiPSCs). This manuscript describes a protocol for generating lineage specific hiPSC reporter using CRISPR/Cas system assisted homologous recombination.

Gene targeting is a critical approach for characterizing gene functions in modern biomedical research. However, the efficiency of gene targeting in human ...

Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation

Chicken embryos are ideal model systems for studying embryonic development as manipulations of gene function can be conducted with relative ease in ovo. The inner ear auditory sensory organ is critical for our ability to hear. It houses a highly specialized sensory epithelium that consists of mechano-transducing hair cells (HCs) and surrounding glial-like supporting cells (SCs). Despite structural differences in the auditory organs, molecular mechanisms regulating the development of the auditory organ are evolutionarily conserved between mammals and aves. In ovo electroporation is largely limited to early stages at E1 - E3. Due to the relative late development of the auditory organ at E5, manipulations of the auditory organ by in ovo electroporation past E3 are difficult due to the advanced development of the chicken embryo at later stages. The method presented here is a transient gene transfer method for targeting genes of interest at stage E4 - E4.5 in the developing chicken auditory sensory organ via in ovo micro-electroporation. This method is applicable for gain- and loss-of-functions with conventional plasmid DNA-based expression vectors and can be combined with in ovo cell proliferation assay by adding EdU (5-ethynyl-2&#180;-deoxyuridine) to the whole embryo at the time of electroporation. The use of green or red fluorescent protein (GFP or RFP) expression plasmids allows the experimenter to quickly determine whether the electroporation successfully targeted the auditory portion of the developing inner ear. In this method paper, representative examples of GFP electroporated specimens are illustrated; embryos were harvested 18 - 96 hr&#160;after electroporation and targeting of GFP to the pro-sensory area of the auditory organ was confirmed by RNA in situ hybridization. The method paper also provides an optimized protocol for the use of the thymidine analog EdU to analyze cell proliferation; an example of an EdU based cell proliferation assay that combines immuno-labeling and click EdU chemistry is provided.

Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation

The auditory organ mediates hearing. Here we present a modified in ovo micro-electroporation method optimized for studying auditory progenitor cell proliferation and differentiation in the developing chicken auditory organ.

Chicken embryos are ideal model systems for studying embryonic development as manipulations of gene function can be conducted with relative ease in ovo. ...

Microinjection for Transgenesis and Genome Editing in Threespine Sticklebacks

The threespine stickleback fish has emerged as a powerful system to study the genetic basis of a wide variety of morphological, physiological, and behavioral phenotypes. The remarkably diverse phenotypes that have evolved as marine populations adapt to countless freshwater environments, combined with the ability to cross marine and freshwater forms, provide a rare vertebrate system in which genetics can be used to map genomic regions controlling evolved traits. Excellent genomic resources are now available, facilitating molecular genetic dissection of evolved changes. While mapping experiments generate lists of interesting candidate genes, functional genetic manipulations are required to test the roles of these genes. Gene regulation can be studied with transgenic reporter plasmids and BACs integrated into the genome using the Tol2 transposase system. Functions of specific candidate genes and cis-regulatory elements can be assessed by inducing targeted mutations with TALEN and CRISPR/Cas9 genome editing reagents. All methods require introducing nucleic acids into fertilized one-cell stickleback embryos, a task made challenging by the thick chorion of stickleback embryos and the relatively small and thin blastomere. Here, a detailed protocol for microinjection of nucleic acids into stickleback embryos is described for transgenic and genome editing applications to study gene expression and function, as well as techniques to assess the success of transgenesis and recover stable lines.

Transgenic manipulations and genome editing are critical for functionally testing the roles of genes and cis-regulatory elements. Here a detailed microinjection protocol for the generation of genomic modifications (including Tol2-mediated fluorescent reporter transgene constructs, TALENs, and CRISPRs) is presented for the emergent model fish, the threespine stickleback.

The threespine stickleback fish has emerged as a powerful system to study the genetic basis of a wide variety of morphological, physiological, and ...

CRISPR-mediated Loss of Function Analysis in Cerebellar Granule Cells Using In Utero Electroporation-based Gene Transfer

Brain malformation is often caused by genetic mutations. Deciphering the mutations in patient-derived tissues has identified potential causative factors of the diseases. To validate the contribution of a dysfunction of the mutated genes to disease development, the generation of animal models carrying the mutations is one obvious approach. While germline genetically engineered mouse models (GEMMs) are popular biological tools and exhibit reproducible results, it is restricted by time and costs. Meanwhile, non-germline GEMMs often enable exploring gene function in a more feasible manner. Since some brain diseases (e.g., brain tumors) appear to result from somatic but not germline mutations, non-germline chimeric mouse models, in which normal and abnormal cells coexist, could be helpful for disease-relevant analysis. In this study, we report a method for the induction of CRISPR-mediated somatic mutations in the cerebellum. Specifically, we utilized conditional knock-in mice, in which Cas9 and GFP are chronically activated by the CAG (CMV enhancer/chicken &#223;-actin) promoter after Cre-mediated recombination of the genome. The self-designed single-guide RNAs (sgRNAs) and the Cre recombinase sequence, both encoded in a single plasmid construct, were delivered into cerebellar stem/progenitor cells at an embryonic stage using in utero electroporation. Consequently, transfected cells and their daughter cells were labeled with green fluorescent protein (GFP), thus facilitating further phenotypic analyses. Hence, this method is not only showing electroporation-based gene delivery into embryonic cerebellar cells but also proposing a novel quantitative approach to assess CRISPR-mediated loss-of-function phenotypes.

CRISPR-mediated Loss of Function Analysis in Cerebellar Granule Cells Using In Utero Electroporation-based Gene Transfer

Conventional loss-of-function studies of genes using knockout animals have often been costly and time-consuming. Electroporation-based CRISPR-mediated somatic mutagenesis is a powerful tool to understand gene functions in vivo. Here, we report a method to analyze knockout phenotypes in proliferating cells of the cerebellum.

Brain malformation is often caused by genetic mutations. Deciphering the mutations in patient-derived tissues has identified potential causative factors ...

An Efficient Strategy for Generating Tissue-specific Binary Transcription Systems in Drosophila by Genome Editing

Binary transcription systems are powerful genetic tools widely used for visualizing and manipulating cell fate and gene expression in specific groups of cells or tissues in model organisms. These systems contain two components as separate transgenic lines. A driver line expresses a transcriptional activator under the control of tissue-specific promoters/enhancers, and a reporter/effector line harbors a target gene placed downstream to the binding site of the transcription activator. Animals harboring both components induce tissue-specific transactivation of a target gene expression. Precise spatiotemporal expression of the gene in targeted tissues is critical for unbiased interpretation of cell/gene activity. Therefore, developing a method for generating exclusive cell/tissue-specific driver lines is essential. Here we present a method to generate highly tissue-specific targeted expression system by employing a &#34;Clustered Regularly Interspaced Short Palindromic Repeat/CRISPR-associated&#34; (CRISPR/Cas)-based genome editing technique. In this method, the endonuclease Cas9 is targeted by two chimeric guide RNAs (gRNA) to specific sites in the first coding exon of a gene in the Drosophila genome to create double-strand breaks (DSB). Subsequently, using an exogenous donor plasmid containing the transactivator sequence, the cell-autonomous repair machinery enables homology-directed repair (HDR) of the DSB, resulting in precise deletion and replacement of the exon with the transactivator sequence. The knocked-in transactivator is expressed exclusively in cells where the cis-regulatory elements of the replaced gene are functional. The detailed step-by-step protocol presented here for generating a binary transcriptional driver expressed in Drosophila fgf/branchless-producing epithelial/neuronal cells can be adopted for any gene- or tissue-specific expression.

An Efficient Strategy for Generating Tissue-specific Binary Transcription Systems in Drosophila by Genome Editing

Here, we present a method for generating tissue-specific binary transcription systems in Drosophila by replacing the first coding exon of genes with transcription drivers. The CRISPR/Cas9-based method places a transactivator sequence under the endogenous regulation of a replaced gene, and consequently facilitates transctivator expression exclusively in gene-specific spatiotemporal patterns.

Binary transcription systems are powerful genetic tools widely used for visualizing and manipulating cell fate and gene expression in specific groups of ...

Fast and Efficient Expression of Multiple Proteins in Avian Embryos Using mRNA Electroporation

We report that mRNA electroporation permits fluorescent proteins to label cells in living quail embryos more quickly and broadly than DNA electroporation. The high transfection efficiency permits at least 4 distinct mRNAs to be co-transfected with ~87% efficiency. Most of the electroporated mRNAs are degraded during the first 2 h post-electroporation, permitting time-sensitive experiments to be carried out in the developing embryo. Finally, we describe how to dynamically image live embryos electroporated with mRNAs that encode various subcellular targeted fluorescent proteins.

We report messenger RNA (mRNA) electroporation as a method that permits fast and efficient expression of multiple proteins in the quail embryo model system. This method can be used to fluorescently label cells and record their in vivo movements by time-lapse microscopy shortly after electroporation.

We report that mRNA electroporation permits fluorescent proteins to label cells in living quail embryos more quickly and broadly than DNA electroporation. ...

Egg Microinjection and Efficient Mating for Genome Editing in the Firebrat Thermobia domestica

The firebrat Thermobia domestica is an ametabolous, wingless species that is suitable for studying the developmental mechanisms of insects that led to their successful evolutionary radiation on the earth. The application of genetic tools such as genome editing is the key to understanding genetic changes that are responsible for evolutionary transitions in an Evo-Devo approach. In this article, we describe our current protocol for generating and maintaining mutant strains of T. domestica. We report a dry injection method, as an alternative to the reported wet injection method, that allows us to obtain stably high survival rates in injected embryos. We also report an optimized environment setting to mate adults and obtain subsequent generations with high efficiency. Our method underlines the importance of taking each species&#8217; unique biology into account for the successful application of genome editing methods to non-traditional model organisms. We predict that these genome editing protocols will help in implementing T. domestica as a laboratory model and to further accelerate the development and application of useful genetic tools in this species.

Egg Microinjection and Efficient Mating for Genome Editing in the Firebrat Thermobia domestica

We provide a detailed protocol for rearing, microinjection of eggs and for efficient mating of the firebrat Thermobia domestica to generate and maintain mutant strains after genome editing.

The firebrat Thermobia domestica is an ametabolous, wingless species that is suitable for studying the developmental mechanisms of insects that led to ...

Methods Article

Efficient Genome Editing of Mice by CRISPR Electroporation of Zygotes