Akiko Takizawa

Generation of Knockout Rats with X-Linked Severe Combined Immunodeficiency (X-SCID) Using Zinc-Finger Nucleases

Background Although the rat is extensively used as a laboratory model, the inability to utilize germ line-competent rat embryonic stem (ES) cells has been a major drawback for studies that aim to elucidate gene functions. Recently, zinc-finger nucleases (ZFNs) were successfully used to create genome-specific double-stranded breaks and thereby induce targeted gene mutations in a wide variety of organisms including plants, drosophila, zebrafish, etc. Methodology/Principal Findings We report here on ZFN-induced gene targeting of the rat interleukin 2 receptor gamma (Il2rg) locus, where orthologous human and mouse mutations cause X-linked severe combined immune deficiency (X-SCID). Co-injection of mRNAs encoding custom-designed ZFNs into the pronucleus of fertilized oocytes yielded genetically modified offspring at rates greater than 20%, which possessed a wide variety of deletion/insertion mutations. ZFN-modified founders faithfully transmitted their genetic changes to the next generation along with the severe combined immune deficiency phenotype. Conclusions and Significance The efficient and rapid generation of gene knockout rats shows that using ZFN technology is a new strategy for creating gene-targeted rat models of human diseases. In addition, the X-SCID rats that were established in this study will be valuable in vivo tools for evaluating drug treatment or gene therapy as well as model systems for examining the treatment of xenotransplanted malignancies.

Viable Piglets Generated from Porcine Oocytes Matured In Vitro and Fertilized by Intracytoplasmic Sperm Head Injection

Abstract Intracytoplasmic sperm injection (ICSI) of a nonmotile cell into the ooplasm for assisted fertilization is a highly specialized procedure for producing the next generation. The production of piglets by ICSI has succeeded when in vivo-matured oocytes have been used as recipients. Our objective was to generate viable piglets by using porcine oocytes matured in vitro and fertilized by ICSI after evaluating the efficacy of using donor spermatozoa in which the acrosome had been artificially removed by treatment with calcium ionophore A23187 (Ca-I). The rate of acrosomal loss in spermatozoa was increased significantly as the duration of treatment with 10 μM Ca-I was prolonged for 30–120 min (Ca-I treated; 55.6–78.6%), whereas the rate was not different as the duration of incubation without Ca-I was prolonged for 30–120 min (control; 45.3–58.4%). On the sixth day of in vitro culture after injection of the sperm head and subsequent stimulation with an electrical pulse, the rates of blastocyst formation were not significantly different between the two groups: the rates for oocytes injected with Ca-I-treated sperm heads (incubated for 120 min) and for those injected with control sperm heads were 8.6% and 4.0%, respectively. The mean cell numbers of the blastocysts were not significantly different between the two groups (25.6 and 22.7, respectively). Within 2 h after the stimulation, the injected oocytes were transferred to estrous-synchronized recipients. The three recipients that received oocytes injected with Ca-I-treated sperm heads (77–150 oocytes per recipient) were not pregnant, whereas two of the four recipients given oocytes injected with control sperm heads (55–100 oocytes per recipient) were pregnant. One of these farrowed three (a male and two female) healthy piglets. The results demonstrate clearly that in vitro-matured oocytes injected with sperm heads are developmentally competent and can produce viable piglets. They also suggest that removal of the acrosome from the spermatozoon before injection does not affect the development of the blastocyst in vitro. This might not also improve the production of piglets in vivo.

An ENU-induced mutant archive for gene targeting in rats

To the editor: Although the laboratory rat is increasingly being used as a mammalian model in biomedical research, no technology exists thus far for the production of in vivo genetically engineered mutations equivalent to knockout or knock-in mice because of the lack of development of functional embryonic stem cells in this species. Rat spermatogonial stem cells may possibly have greater potential use for genetic engineering to produce gene-targeted rats1,2. The use of somatic cell nuclear transfer to develop cloned rats as an alternative to using embryonic stem cells has also been reported3, but it seems to be a very difficult technique to perform. At present, N-ethyl-Nnitrosourea (ENU) mutagenesis followed by a screening method to detect single-nucleotide substitutions within the targeted gene seems to be the most promising technology in rats, as previously reported by several groups4,5,6. The screening protocol, however, either a yeastbased screening assay4,5 or a highthroughput resequencing-based screening technique7, is expensive. In addition, gene-driven ENU mutagenesis approaches in rats are not a very efficient use of resources because most of the rats generated are usually discarded within a few weeks or months after the targeted genes have been screened owing to a lack of reliable sperm conservation and rederivation technologies. We have developed a new, efficient approach that combines two methods: a high-throughput, lowa b

A Missense Mutation of the Gene Encoding Voltage-Dependent Sodium Channel (Nav1.1) Confers Susceptibility to Febrile Seizures in Rats

Although febrile seizures (FSs) are the most common convulsive syndrome in infants and childhood, the etiology of FSs has remained unclarified. Several missense mutations of the Nav1.1 channel (SCN1A), which alter channel properties, have been reported in a familial syndrome of GEFS+ (generalized epilepsy with febrile seizures plus). Here, we generated Scn1a-targeted rats carrying a missense mutation (N1417H) in the third pore region of the sodium channel by gene-driven ENU (N-ethyl-N-nitrosourea) mutagenesis. Despite their normal appearance under ordinary circumstances, Scn1a mutant rats exhibited remarkably high susceptibility to hyperthermia-induced seizures, which involve generalized clonic and/or tonic–clonic convulsions with paroxysmal epileptiform discharges. Whole-cell patch-clamp recordings from HEK cells expressing N1417H mutant channels and from hippocampal GABAergic interneurons of N1417H mutant rats revealed a significant shift of the inactivation curve in the hyperpolarizing direction. In addition, clamp recordings clearly showed the reduction in action potential amplitude in the hippocampal interneurons of these rats. These findings suggest that a missense mutation (N1417H) of the Nav1.1 channel confers susceptibility to FS and the impaired biophysical properties of inhibitory GABAergic neurons underlie one of the mechanisms of FS.

Effects of chelating agents during freeze-drying of boar spermatozoa on DNA fragmentation and on developmental ability in vitro and in vivo after intracytoplasmic sperm head injection.

Successful offspring production after intracytoplasmic injection of freeze-dried sperm has been reported in laboratory animals but not in domesticated livestock, including pigs. The integrity of the DNA in the freeze-dried sperm is reported to affect embryogenesis. Release of endonucleases from the sperm is one of the causes of induction of sperm DNA fragmentation. We examined the effects of chelating agents, which inhibit the activation of such enzymes, on DNA fragmentation in freeze-dried sperm and on the in vitro and in vivo developmental ability of porcine oocytes following boar sperm head injection. Boar ejaculated sperm were sonicated, suspended in buffer supplemented with (1) 50 mM EGTA, (2) 50 mM EDTA, (3) 10 mM EDTA, or (4) no chelating agent and freeze-dried. A fertilization medium (Pig-FM) was used as a control. The rehydrated spermatozoa in each group were then incubated in Pig-FM at room temperature. The rate of DNA fragmentation in the control group, as assessed by the TUNEL method, increased gradually as time after rehydration elapsed (2.8% at 0 min to 12.2% at 180 min). However, the rates in all experimental groups (1-4) did not increase, even at 180 min (0.7-4.1%), which were all significantly lower (p < 0.05) than that of the control group. The rate of blastocyst formation after the injection in the control group (6.0%) was significantly lower (p < 0.05) than those in the 50 mM EGTA (23.1%) and 10 mM EDTA (22.6%) groups incubated for 120-180 min. The average number of blastocyst cells in the 50 mM EGTA group (33.1 cells) was significantly higher (p < 0.05) than that in the 10 mM EDTA group (17.8 cells). Finally, we transferred oocytes from 50 mM EGTA or control groups incubated for 0-60 min into estrous-synchronized recipients. The two recipients of the control oocytes became pregnant and one miscarried two fetuses on day 39. The results suggested that fragmentation of DNA in freeze-dried boar sperm is one of the causes of decreased in vitro developmental ability of injected oocytes to the blastocyst stage. Supplementation with EGTA in a freeze-drying buffer improves this ability.

Enhanced colitis-associated colon carcinogenesis in a novel Apc mutant rat

To establish an efficient rat model for colitis‐associated colorectal cancer, azoxymethane and dextran sodium sulfate (AOM/DSS)‐induced colon carcinogenesis was applied to a novel adenomatous polyposis coli (Apc) mutant, the Kyoto Apc Delta (KAD) rat. The KAD rat was derived from ethylnitrosourea mutagenesis and harbors a nonsense mutation in the Apc gene (S2523X). The truncated APC of the KAD rat was deduced to lack part of the basic domain, an EB1‐binding domain, and a PDZ domain, but retained an intact β‐catenin binding region. KAD rats, homozygous for the Apc mutation on a genetic background of the F344 rat, showed no spontaneous tumors in the gastrointestinal tract. At 5 weeks of age, male KAD rats were given a single subcutaneous administration of AOM (20 mg/kg, bodyweight). One week later, they were given DSS (2% in drinking water) for 1 week. At week 15, the incidence and multiplicity of colon tumors developed in the KAD rat were remarkably severe compared with those in the F344 rat: 100 versus 50% in incidence and 10.7 ± 3.5 versus 0.8 ± 1.0 in multiplicity. KAD tumors were dominantly distributed in the rectum and distal colon, resembling human colorectal cancer. Accumulation of β‐catenin protein and frequent β‐catenin mutations were prominent features of KAD colon tumors. To our knowledge, AOM/DSS‐induced colon carcinogenesis using the KAD rat is the most efficient to induce colon tumors in the rat, and therefore would be available as an excellent model for human colitis‐associated CRC.

A rat model for LGI1-related epilepsies

Mutations of the leucine-rich glioma-inactivated 1 (LGI1) gene cause an autosomal dominant partial epilepsy with auditory features also known as autosomal-dominant lateral temporal lobe epilepsy. LGI1 is also the main antigen present in sera and cerebrospinal fluids of patients with limbic encephalitis and seizures, highlighting its importance in a spectrum of epileptic disorders. LGI1 encodes a neuronal secreted protein, whose brain function is still poorly understood. Here, we generated, by ENU (N-ethyl-N-nitrosourea) mutagenesis, Lgi1-mutant rats carrying a missense mutation (L385R). We found that the L385R mutation prevents the secretion of Lgi1 protein by COS7 transfected cells. However, the L385R-Lgi1 protein was found at low levels in the brains and cultured neurons of Lgi1-mutant rats, suggesting that mutant protein may be destabilized in vivo. Studies on the behavioral phenotype and intracranial electroencephalographic signals from Lgi1-mutant rats recalled several features of the human genetic disorder. We show that homozygous Lgi1-mutant rats (Lgi1(L385R/L385R)) generated early-onset spontaneous epileptic seizures from P10 and died prematurely. Heterozygous Lgi1-mutant rats (Lgi1(+/L385R)) were more susceptible to sound-induced, generalized tonic-clonic seizures than control rats. Audiogenic seizures were suppressed by antiepileptic drugs such as carbamazepine, phenytoin and levetiracetam, which are commonly used to treat partial seizures, but not by the prototypic absence seizure drug, ethosuximide. Our findings provide the first rat model with a missense mutation in Lgi1 gene, an original model complementary to knockout mice. This study revealed that LGI1 disease-causing missense mutations might cause a depletion of the protein in neurons, and not only a failure of Lgi1 secretion.

Molecular characteristics of horse phospholipase C zeta (PLCζ).

A sperm-specific phospholipase C (PLC), PLCzeta (PLCζ), is thought to underlie the initiation of calcium ([Ca(2+) ]i ) oscillations that induce egg activation in mammals. In large domestic species, only bovine, porcine and recently equine PLCζ have been cloned, and the physiological functions of these molecules have not been fully characterized. Here, we evaluated the physiological functions of equine PLCζ (ePLCζ) in mouse oocytes. ePLCζ was cloned from testis using RT-PCR. The expression of ePLCζ messenger RNA was confirmed in testis but not in other tissues. Microinjection of ePLCζ complementary RNA (cRNA) into mouse oocytes induced long-lasting [Ca(2+) ]i oscillations, and most of the injected oocytes formed pronuclei (PN). The injection of cRNAs encoding horse, mouse, human and cow PLCζ into mouse oocytes showed that ePLCζ had the highest [Ca(2+) ]i oscillation-inducing activity among the species tested. Mutation of D202R, which renders the protein inactive, abrogated the activity of ePLCζ. The nuclear translocation ability of ePLCζ was defective when expressed in mouse oocytes. Taken together, our findings show for the first time that ePLCζ has highest activity of the mammalian species studied to date. Our findings will be useful for the improvement of reproductive technologies in the horse.

Kcna1-mutant rats dominantly display myokymia, neuromyotonia and spontaneous epileptic seizures

Mutations in the KCNA1 gene, which encodes for the α subunit of the voltage-gated potassium channel Kv1.1, cause episodic ataxia type 1 (EA1). EA1 is a dominant human neurological disorder characterized by variable phenotypes of brief episodes of ataxia, myokymia, neuromyotonia, and associated epilepsy. Animal models for EA1 include Kcna1-deficient mice, which recessively display severe seizures and die prematurely, and V408A-knock-in mice, which dominantly exhibit stress-induced loss of motor coordination. In the present study, we have identified an N-ethyl-N-nitrosourea-mutagenized rat, named autosomal dominant myokymia and seizures (ADMS), with a missense mutation (S309T) in the voltage-sensor domain, S4, of the Kcna1 gene. ADMS rats dominantly exhibited myokymia, neuromyotonia and generalized tonic-clonic seizures. They also showed cold stress-induced tremor, neuromyotonia, and motor incoordination. Expression studies of homomeric and heteromeric Kv1.1 channels in HEK cells and Xenopus oocytes, showed that, although S309T channels are transferred to the cell membrane surface, they remained non-functional in terms of their biophysical properties, suggesting a dominant-negative effect of the S309T mutation on potassium channel function. ADMS rats provide a new model, distinct from previously reported mouse models, for studying the diverse functions of Kv1.1 in vivo, as well as for understanding the pathology of EA1.

Offspring Derived from Intracytoplasmic Injection of Sonicated Rat Sperm Heads

ABSTRACT The present study investigated the effect of separation of spermatozoa by sonication or Piezo-pulse on in vitro development of oocytes injected with sperm heads in the rat. We also examined development to term of rat oocytes injected with sperm heads. Rat frozen-thawed spermatozoa were separated into heads and tails by sonication for 10 sec or Piezo-pulse in KRB medium, and each treated sperm head was injected into an ooplasm. The oocytes were observed for formation of two pronuclei and development to 2-cell embryos. The percentages of formation of two pronuclei and development to the 2-cell stage did not significantly (P>0.05) differ between the two groups. Oocytes injected with sonicated sperm heads that reached the pronuclear stage at 10 h after injection of sperm heads were transferred into 7 recipients. Five recipients became pregnant, and 8 living pups were obtained. The results indicate that rat oocytes injected with sonicated sperm heads can develop to term in vivo. Furthermore, no difference was observed in the development in vitro between rat oocytes injected with sperm heads separated by sonication or by Piezo-pulse.