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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

Here, we present a modified method for cryopreservation of one-cell embryos as well as a protocol that couples the use of freeze-thawed embryos and electroporation for the efficient generation of genetically modified mice.

Abstract

The use of genetically modified (GM) mice has become crucial for understanding gene function and deciphering the underlying mechanisms of human diseases. The CRISPR/Cas9 system allows researchers to modify the genome with unprecedented efficiency, fidelity, and simplicity. Harnessing this technology, researchers are seeking a rapid, efficient, and easy protocol for generating GM mice. Here we introduce an improved method for cryopreservation of one-cell embryos that leads to a higher developmental rate of the freeze-thawed embryos. By combining it with optimized electroporation conditions, this protocol allows for the generation of knockout and knock-in mice with high efficiency and low mosaic rates within a short time. Furthermore, we show a step-by-step explanation of our optimized protocol, covering CRISPR reagent preparation, in vitro fertilization, cryopreservation and thawing of one-cell embryos, electroporation of CRISPR reagents, mouse generation, and genotyping of the founders. Using this protocol, researchers should be able to prepare GM mice with unparalleled ease, speed, and efficiency.

Introduction

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system is a scientific breakthrough that provides unprecedented targeted modification in the genome1. The CRISPR/Cas9 system is comprised of Cas9 protein and guide RNA (gRNA) with two molecular components: a target-specific CRISPR RNA (crRNA) and a trans-activating CRISPR RNA (tracrRNA)2 . A gRNA directs the Cas9 protein to the specific locus in the genome, 20 nucleotides complementary to crRNA, and adjacent to the protospacer adjacent motif (PAM). The Cas9 protein binds to the target sequence and induces double-stra....

Protocol

All animal care and procedures performed in this study were undertaken according to the rules and regulations of the Guide for the Care and Use of Laboratory Animals. The experimental protocol was approved by the Animal Care Committee of Laboratory Animals of University of Toyama, University of Tokyo, Jichi University, and Max Planck Florida Institute for Neuroscience. Information about all reagents is showed in the Table of Materials.

1. CRISPR reagents design

  1. crR.......

Representative Results

Our modified method for cryopreservation of one-cell embryos, including incubation in HTF containing 20% FBS for 10 min followed by cryopreservation in 1 M DMSO and DAP213 solution, improved the developmental rate of the freeze-thawed embryos into the two-cell stage (Figure 1, p = 0.009, Student’s t-test).The freeze-thawed embryos were used for the production of GM mice and electroporation conditions were optimized: five repeats of 25 V with 3 ms pulses and 97 ms intervals using an ele.......

Discussion

The described protocol allows for the generation of GM mice with high efficiency and low mosaic rates (Table 1). It enables researchers without advanced embryo manipulation skills to create mutant mice easily because it takes advantage of the latest and most useful advances in both reproductive engineering and genome editing technologies: CRISPR/Cas9 ribonucleoprotein (RNP) and electroporation into freeze-thawed embryos. These advances facilitated and expedited the generation of the GM mice. As described.......

Acknowledgements

We wish to thank Hitomi Sawada and Elizabeth Garcia for animal care. This work was supported by KAKENHI (15K20134, 17K11222, 16H06276 and 16K01946) and Hokugin Research Grant (to H.N.), and Jichi Medical University Young Investigator Award (to H.U.). The Otsuka Toshimi Scholarship Foundation supported M.D.

....

Materials

NameCompanyCatalog NumberComments
0.25 M SucroseARK Resource Co., Ltd. (Kumamoto, Japan)SUCROSE
1 M DMSOARK Resource Co., Ltd. (Kumamoto, Japan)1M DMSO
ButorphanolMeiji Seika Pharma Co., Ltd. (Tokyo, Japan)Vetorphale 5mg
Cas9 protein: Alt-R® S.p. HiFi Cas9 Nuclease 3NLSIntegrated DNA Technologies, Inc. (Coralville, IA)1081060
C57BL/6J miceJapan SLC (Hamamatsu, Japan)N/A
DAP213ARK Resource Co., Ltd. (Kumamoto, Japan)DAP213
FBSSigma-Aldrich, Inc. (St. Louis, MO)ES-009-C
hCGMOCHIDA PHARMACEUTICAL CO., LTD (Tokyo, Japan)HCG Mochida 3000
HTFARK Resource Co., Ltd. (Kumamoto, Japan)HTF
ICR miceJapan SLC (Hamamatsu, Japan)N/A
IsofluranePetterson Vet Supply, Inc. (Greeley, CO)07-893-1389
KSOMARK Resource Co., Ltd. (Kumamoto, Japan)KSOM
LN2 TankChart Industries (Ball Ground, GA)XC 34/18
M2ARK Resource Co., Ltd. (Kumamoto, Japan)M2
MedetomidineNippon Zenyaku Kogyo Co.,Ltd. (Koriyama, Japan)1124401A1060
MicroscopeNikon Co. (Tokyo, Japan)SMZ745T
MidazolamSandoz K.K. (Tokyo, Japan)1124401A1060
Nuclease free bufferIntegrated DNA Technologies, Inc. (Coralville, IA)1072570
Nucleospin DNA extraction kitTakara Bio Inc (Kusatsu, Japan)740952 .5
One-hole slide glassMatsunami Glass Ind., Ltd. (Kishiwada, Japan)S339929
One-step type ElectroporatorBEX Co., Ltd. (Tokyo, Japan)CUY21EDIT II
Paraffin LiquidNACALAI TESQUE Inc. (Kyoto, Japan)SP 26137-85
Platinum plate electrodeBEX Co., Ltd. (Tokyo, Japan)LF501PT1-10, GE-101
PMSGASKA Animal Health Co., Ltd (Tokyo, Japan)SEROTROPIN 1000
Povidone iodideProfessional Disposables International, Inc. (Orangeburg, NY)C12400
Reduced-Serum Minimal Essential Medium: OptiMEM ISigma-Aldrich, Inc. (St. Louis, MO)22600134
Two-step type ElectroporatorNepa Gene Co., Ltd. (Ichikawa, Japan)NEPA21

References

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Genetically Modified MiceFreeze thawed EmbryosIn Vitro FertilizationSuper OvulationSperm CapacitationCryopreservationEmbryo ElectroporationHigh efficiencyLow Mosaic RateProtocol

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