Production of genome-edited mice by visualization of nucleases introduced into the embryos using electroporation

Importance of nuclear localization signal-fused Cas9 in the production of genome-edited mice via embryo electroporation

Previously, to generate genome-edited animals by introducing CRISPR-associated protein 9 (Cas9) into embryos, we developed the Technique for Animal Knockout system by Electroporation (TAKE). Additionally, by fluorescently labeling Cas9, we successfully visualized the Cas9 introduced into the pronuclei of embryos; however, whether Cas9 was introduced directly into the pronuclei by electric pulse or transferred from the cytoplasm by nuclear localization signal (NLS) remained unknown. Herein, we evaluated the localization of Cas9 with (Cas9-NLS) or without NLS (Cas9-noNLS) in mice embryos following electroporation by fusing them with GFP. Furthermore, we visually studied their effects on genome-editing rates in offspring by targeting tyrosinase gene. Fluorescence intensity in pronuclei of Cas9-NLS-electroporated embryos and genome-editing rates of offspring were significantly higher than those of Cas9-noNLS-electroporated embryos. Furthermore, fluorescence in Cas9-NLS-electroporated embryos in which pronuclei had not yet appeared 2.5 h after insemination was observed in the pronuclei of embryos appearing 3.5 h after electroporation. We demonstrated the effective transportation of Cas9 from the cytoplasm to pronuclei by the NLS following TAKE, which resulted in increased genome-editing rates in offspring. The TAKE along with fluorescently labeled nucleases can be used to verify nuclease delivery into individual embryos prior to embryo transfer for efficiently producing genome-edited animals.

Novel dicarbonyl metabolic pathway via mitochondrial ES1 possessing glyoxalase III activity

Glycation, caused by reactive dicarbonyls, plays a role in various diseases by forming advanced glycation end products. In live cells, reactive dicarbonyls such as glyoxal (GO) and methylglyoxal (MGO) are produced during cell metabolism, and these should be removed consistently. However, the dicarbonyl metabolic system in the mitochondria remains unclear. It has been speculated that the mammalian mitochondrial protein ES1 is a homolog of bacterial elbB possessing glyoxalase III (GLO3) activity. Therefore, in this study, to investigate ES1 functions and GLO3 activity, we generated ES1-knockout (KO) mice and recombinant mouse ES1 protein and investigated the biochemical and histological analyses. In the mitochondrial fraction obtained from ES1-KO mouse brains, the GO metabolism and cytochrome c oxidase activity were significantly lower than those in the mitochondrial fraction obtained from wildtype (WT) mouse brains. However, the morphological features of the mitochondria did not change noticeably in the ES1-KO mouse brains compared with those in the WT mouse brains. The mitochondrial proteome analysis showed that the MGO degradation III pathway and oxidative phosphorylation-related proteins were increased. These should be the response to the reduced GO metabolism caused by ES1 deletion to compensate for the dicarbonyl metabolism and damaged cytochrome c oxidase by elevated GO. Recombinant mouse ES1 protein exhibited catalytic activity of converting GO to glycolic acid. These results indicate that ES1 possesses GLO3 activity and modulates the metabolism of GO in the mitochondria. To our knowledge, this is the first study to show a novel metabolic pathway for reactive dicarbonyls in mitochondria.

Full-length human dystrophin on human artificial chromosome compensates for mouse dystrophin deficiency in a Duchenne muscular dystrophy mouse model

Dystrophin maintains membrane integrity as a sarcolemmal protein. Dystrophin mutations lead to Duchenne muscular dystrophy, an X-linked recessive disorder. Since dystrophin is one of the largest genes consisting of 79 exons in the human genome, delivering a full-length dystrophin using virus vectors is challenging for gene therapy. Human artificial chromosome is a vector that can load megabase-sized genome without any interference from the host chromosome. Chimeric mice carrying a 2.4-Mb human dystrophin gene-loaded human artificial chromosome (DYS-HAC) was previously generated, and dystrophin expression from DYS-HAC was confirmed in skeletal muscles. Here we investigated whether human dystrophin expression from DYS-HAC rescues the muscle phenotypes seen in dystrophin-deficient mice. Human dystrophin was normally expressed in the sarcolemma of skeletal muscle and heart at expected molecular weights, and it ameliorated histological and functional alterations in dystrophin-deficient mice. These results indicate that the 2.4-Mb gene is enough for dystrophin to be correctly transcribed and translated, improving muscular dystrophy. Therefore, this technique using HAC gives insight into developing new treatments and novel humanized Duchenne muscular dystrophy mouse models with human dystrophin gene mutations.

Genome Editing of Rat

Many genetically engineered rat strains have been produced by the development of genome editing technology, although it used to be technical difficulty and low production efficiency. Knockout and knock-in strains can be simple and quick produced using zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), or clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9. Presently, genome edited strains have been produced by microinjection and a new electroporation method named technique for animal knockout system by electroporation (TAKE). This chapter presents the latest protocols for producing genome edited rats.

Genome Editing in Mouse and Rat by Electroporation

Many genome-edited mouse and rat strains have been produced using engineered endonucleases, including zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), or clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9. Especially, CRISPR-Cas9 is powerful tool that can be easy, rapid, and high-efficiency-produced new genome-edited strains. Furthermore, new technique, Technique for Animal Knockout system by Electroporation (TAKE), efficiently accelerate production of new strains by direct nuclease introduction into intact embryos using electroporation. This chapter presents a latest technical information in the production of genome-edited mouse and rat by TAKE method.

The iodide transporter Slc26a7 impacts thyroid function more strongly than Slc26a4 in mice

SLC26A4 is a known iodide transporter, and is localized at the apical membrane of thyrocytes. Previously, we reported that SLC26A7 is also involved in iodide transport and that Slc26a7 is a novel causative gene for congenital hypothyroidism. However, its detailed role in vivo remains to be elucidated. We generated mice that were deficient in Slc26a7 and Slc26a4 to delineate differences and associations in their roles in iodide transport. Slc26a7^-/- mice showed goitrous congenital hypothyroidism and mild growth failure on a normal diet. Slc26a7^-/- mice with a low iodine environment showed marked growth failure. In contrast, Slc26a4^-/- mice showed no growth failure and hypothyroidism in the same low iodine environment. Double-deficient mice showed more severe growth failure than Slc26a7^-/- mice. RNA-seq analysis revealed that the number of differentially expressed genes (DEGs) in Slc26a7^-/- mice was significantly higher than that in Slc26a4^-/- mice. These indicate that SLC26A7 is more strongly involved in iodide transport and the maintenance of thyroid function than SLC26A4.

Survivability and subsequent development of vitrified early-stage mouse embryos after warming at different temperatures

Cryopreservation of embryos is a useful method for stably preserving various strains for a long time, and the cryopreserved embryos can be used at any time by simple warming. However, the viability of cryopreserved embryos, particularly vitrification at an early stage, is low compared to that of fresh embryos. As the warming process during vitrification is known to affect the survivability and subsequent development of embryos, the present study aimed to examine the viability and subsequent development of vitrified early-stage mouse embryos after warming at different temperatures. The survival rate of pronuclear and 2-cell stage embryos warmed at 60 °C (97% and 88%, respectively) was significantly higher than that of the embryos warmed at 37 °C (46% and 48%, respectively). The pronuclear and 2-cell stage embryos warmed at 60 °C (86% and 100%) showed better development to the blastocyst stage than the embryos warmed at 37 °C (72% and 84%, respectively). The development of offspring of the surviving embryos was similar at both the warming temperatures. These results showed that the survivability and subsequent development of vitrified early-stage mouse embryos were obviously increased upon rapid warming. This improved warming process could be helpful for the maintenance and reproduction of genetic resources.

Successful pseudopregnancy of rats by short period artificial stimulation using sonic vibration

Psuedopregnancy for embryo transfer (ET) is usually induced in rats by mating with vasectomized males. Previously, we successfully induced pseudopregnancy using sonic vibration instead (Easy-ET method). The transferred embryos developed normally. Conventionally, stimulation is performed 7 × 30 s with 5 min intervals at the day before ET. However, this protocol is time-consuming because it imitates natural mating behavior. Here, we investigated pseudopregnancy induction with shorter stimulation times. Stimulation was performed 2 × 30 s, with 30 s intervals at the proestrus stage at the day before ET. Of the transferred pronuclear or two-cell embryos, 43% or 62% developed normally, respectively. Furthermore, 67% or 68% of transferred pronuclear or two-cell embryos in rats at estrus stage stimulated on the day of ET developed normally, respectively. Pseudopregnancy was successfully induced with shorter stimulation. Furthermore, this protocol may be used to perform a single-day stimulation and ET operation at the estrus stage.