Birth of mice from vitrified/warmed 2-cell embryos transported at a cold temperature

A novel technique for large-fragment knock-in animal production without ex vivo handling of zygotes

CRISPR/Cas-based genome editing has dramatically improved genetic modification technology. In situ electroporation called genome editing via oviductal nucleic acid delivery (GONAD), which eliminates the need for ex vivo embryo handling, is technically the simplest method for gene transfer and can be performed in laboratories without developmental engineering expertise including micromanipulation techniques. However, the use of this method remains challenging in the case of large-fragment knock-in, such as gene expression cassettes. Adeno-associated viruses (AAV) act as donor DNA for homologous recombination in infected cells, including rodent embryos. In this study, we demonstrated simultaneous electroporation of AAV donors and CRISPR/Cas9 components into embryos to create knock-in animals, and successfully generated knock-in rats carrying a gene cassette with a length of 3.0 kb using a small number of animals and in situ electroporation. These findings indicate that this technique is an efficient high-throughput strategy for producing genetically modified rodents and may be applicable to other animal species.

Optimised CO2-containing medium for in vitro culture and transportation of mouse preimplantation embryos without CO2 incubator

Conventional in vitro culture and manipulation of mouse embryos require a CO₂ incubator, which not only increases the cost of performing experiments but also hampers the transport of embryos to the other laboratories. In this study, we established and tested a new CO₂ incubator-free embryo culture system and transported embryos using this system. Using an Anaero pouch, which is a CO₂ gas-generating agent, to increase the CO₂ partial pressure of CZB medium to 4%–5%, 2-cell embryos were cultured to the blastocyst stage in a sealed tube without a CO₂ incubator at 37°C. Further, the developmental rate to blastocyst and full-term development after embryo transfer were comparable with those of usual culture method using a CO₂ incubator (blastocyst rate: 97% versus 95%, respectively; offspring rate: 30% versus 35%, respectively). Furthermore, using a thermal bottle, embryos were reliably cultured using this system for up to 2 days at room temperature, and live offspring were obtained from embryos transported in this simple and very low-cost manner without reducing the offspring rate (thermal bottle: 26.2% versus CO₂ incubator: 34.3%). This study demonstrates that CO₂ incubators are not essential for embryo culture and transportation and that this system provides a useful, low-cost alternative for mouse embryo culture and manipulation.

Simple transport and cryopreservation of cold-stored mouse embryos

The cold storage of two-cell embryos is a useful technique for transporting genetically engineered mice without the shipment of live animals. However, the developmental ability of cold-stored embryos decreases with prolonged storage periods. Therefore, the transported embryos must be readily transferred to recipient mice upon arrival. The cryopreservation of cold-transported embryos may improve the flexibility of the schedule of embryo transfer. In this paper, we examined the viability and developmental ability of vitrified-warmed mouse embryos at the two-cell stage after cold storage in refrigerated temperatures for 0, 24, 48, 72, or 96 h. The viability of vitrified-warmed embryos after cold storage was comparable to vitrified-warmed embryos without cold storage. Vitrified-warmed embryos after cold storage also developed normally to pups by embryo transfer. In addition, live pups were obtained from vitrified-warmed embryos after cold-transportation from Asahikawa Medical University. In summary, cold-stored embryos can be used for the transportation and archive of genetically engineered mice.

Cryopreservation of mouse resources

The cryopreservation of sperm and embryos is useful to efficiently archive valuable resources of genetically engineered mice. Till date, more than 60,000 strains of genetically engineered mice have been archived in mouse banks worldwide. Researchers can request for the archived mouse strains for their research projects. The research infrastructure of mouse banks improves the availability of mouse resources, the productivity of research projects, and the reproducibility of animal experiments. Our research team manages the mouse bank at the Center for Animal Resources and Development in Kumamoto University and continuously develops new techniques in mouse reproductive technology to efficiently improve the system of mouse banking. In this review, we introduce the activities of mouse banks and the latest techniques used in mouse reproductive technology.

Basic mouse reproductive techniques developed and modified at the Center for Animal Resources and Development (CARD), Kumamoto University

The Center for Animal Resources and Development (CARD), Kumamoto University was established in 1998. We provide advanced research support services for the mouse-based biomedical research community via an official and a premium mouse bank system. To efficiently manage these mouse banks, we have actively developed and modified basic mouse reproductive techniques. We shall introduce these techniques in this paper.

Production of F0 mice from embryonic stem cells injected eight-cell stage embryos which stored at refrigeration temperature

At refrigeration temperature, mouse embryos can retain their developmental ability for a couple of days. Previous research reports have focused on the effect of cool temperature on the development of 2-cell stage embryos, morulae or blastocysts and determined that the embryo still has the ability to produce offspring after about 48 h storage at refrigeration temperature. Here we examined whether refrigeration temperature affects the development of the eight-cell stage and if the stored eight-cell stage embryo can still be used as a host embryo for ES cell injection. Our results show that eight-cell stage embryos can develop into blastocysts and yield pups after cold storage for 24 and 48 h. After ES cell injection, stored eight-cell stage embryos can support ES cells developing to F0 pups. In summary, cool storage can preserve the developmental ability of eight-cell stage embryos for at least 48 h, allowing transportation of the embryos at refrigeration temperature between different labs and their subsequent use as host embryos for ES cell injection.

Minimum volume Spatula MVD vitrification method improves embryo survival compared to traditional slow freezing, both for in vivo and in vitro produced mice embryos

This study was conducted to compare the effect of minimum volume Spatula MVD vitrification (VIT) versus traditional slow freezing (SLF) of mouse embryos. A total of 2,617 8-cell in vivo derived and 2-cell in vitro produced B6D2 mouse embryos were subjected to freezing/thawing or vitrification/warming, while fresh embryos were used as control group. Embryo recovery, survival and development rate, pregnancy rate and offspring production were analyzed. In Experiment 1, 8-cell in vivo derived embryos were subjected to in vitro culture, resulting in greater survival and development rates at 3.5 days post coitum stage in VIT than in SLF group (P < 0.05). Although both methods reached an acceptable hatching rate (41.0% and 49.7% for VIT and SLF, respectively; P=NS), it was significantly lower respect to the control group (67.8%, P < 0.01). In Experiment 2, 2-cell in vitro produced mouse embryos showed a similar recovery rate from the device after freezing/thawing or vitrification/warming (∼84%), however survival rate was significantly higher for vitrified/warmed (94.7%) than frozen/thawed embryos (85.1%; P < 0.01). Vitrified/warmed and control fresh embryos were transferred to surrogate mothers, revealing no differences both in pregnancy and offspring production rates. Our data demonstrate that minimum volume Spatula MVD method is a simple home-made useful technique for vitrification of 2-cell and 8-cell mouse embryos produced either in vitro or in vivo.

Shipment of Live Preimplantation-Stage Mouse Embryos

Sharing genetically modified mouse models is a very important part of collaboration between researchers. Shipping live animals around the world is inconvenient, expensive, and cumbersome because of the variety of international regulations and paperwork. The issue of health status differences between animal facilities is of great importance; traditionally, imported animals are quarantined to determine their health status and avoid the introduction of undesirable pathogens. The shipment of preimplantation-stage embryos for immediate transfer into pseudopregnant recipients upon arrival is a commonly used method for transportation. Time coordination on both sides is critical in this case, but the shipment can be done by any courier and the container does not need to be returned. This protocol has been used since the early 1990s to rederive dozens of mouse strains.

Impact of Storage at -80°C on Encapsulated Liver Spheroids After Liquid Nitrogen Storage

For many bioengineered tissues to have practical clinical application, cryopreservation for use on demand is essential. This study examined different thermal histories on warming and short holding periods at different subzero temperatures on subsequent functional recoveries of alginate encapsulated liver spheroids (ELS) for use in a bioartificial liver device. This mimicked transport at liquid nitrogen (−196°C) or dry ice (∼−80°C) temperatures. Holding at −80°C on warming after −196°C storage resulted in ELS expressing significant (p < 0.001) damage compared with direct thaw from liquid nitrogen, with viable cell number falling from 74.0 ± 8.4 million viable cells/mL without −80°C storage to 1.9 ± 0.6 million viable cells/mL 72 h post-thaw after 8 days storage at −80°C. Even 1 day at −80°C after −196°C storage resulted in lower viability (down 21% 24 h post-thaw), viable cell count (down 29% 24 h post-thaw), glucose, and alpha-1-fetoprotein production (reduced by 59% and 95% 24 h from 1 day post-thaw, respectively). Storage at −80°C was determined to be harmful only during the warming cycle. Chemical measurements of the alginate component of ELS were unchanged by cryogenic exposure in either condition.

Superovulation using the combined administration of inhibin antiserum and equine chorionic gonadotropin increases the number of ovulated oocytes in C57BL/6 female mice

Superovulation is a reproductive technique generally used to produce genetically engineered mice. Superovulation in mice involves the administration of equine chorionic gonadotropin (eCG) to promote follicle growth and then that of human chorionic gonadotropin (hCG) to induce ovulation. Previously, some published studies reported that inhibin antiserum (IAS) increased the number of ovulated oocytes in ddY and wild-derived strains of mice. However, the effect of IAS on the C57BL/6 strain, which is the most widely used inbred strain for the production of genetically engineered mice, has not been investigated. In addition, the combined effect of IAS and eCG (IASe) on the number of ovulated oocytes in superovulation treatment has not been examined. In this study, we examined the effect of IAS and eCG on the number of ovulated oocytes in immature female mice of the C57BL/6 strain in superovulation treatment. Furthermore, we evaluated the quality of obtained oocytes produced by superovulation using IASe by in vitro fertilization (IVF) with sperm from C57BL/6 or genetically engineered mice. The developmental ability of fresh or cryopreserved embryos was examined by embryo transfer. The administration of IAS or eCG had a similar effect on the number of ovulated oocytes in C57BL/6 female mice. The number of ovulated oocytes increased to about 3-fold by the administration of IASe than by the administration of IAS or eCG alone. Oocytes derived from superovulation using IASe normally developed into 2-cell embryos by IVF using sperm from C57BL/6 mice. Fresh or cryopreserved 2-cell embryos produced by IVF between oocytes of C57BL/6 mice and sperm from genetically engineered mice normally developed into live pups following embryo transfer. In summary, a novel technique of superovulation using IASe is extremely useful for producing a great number of oocytes and offspring from genetically engineered mice.

The thymic cortical epithelium determines the TCR repertoire of IL-17-producing γδT cells

The thymus provides a specialized microenvironment in which distinct subsets of thymic epithelial cells (TECs) support T-cell development. Here, we describe the significance of cortical TECs (cTECs) in T-cell development, using a newly established mouse model of cTEC deficiency. The deficiency of mature cTECs caused a massive loss of thymic cellularity and impaired the development of αβT cells and invariant natural killer T cells. Unexpectedly, the differentiation of certain γδT-cell subpopulations-interleukin-17-producing Vγ4 and Vγ6 cells-was strongly dysregulated, resulting in the perturbation of γδT-mediated inflammatory responses in peripheral tissues. These findings show that cTECs contribute to the shaping of the TCR repertoire, not only of "conventional" αβT cells but also of inflammatory "innate" γδT cells.

Statin treatment rescues FGFR3 skeletal dysplasia phenotypes

Gain-of-function mutations in the fibroblast growth factor receptor 3 gene (FGFR3) result in skeletal dysplasias, such as thanatophoric dysplasia and achondroplasia (ACH). The lack of disease models using human cells has hampered the identification of a clinically effective treatment for these diseases. Here we show that statin treatment can rescue patient-specific induced pluripotent stem cell (iPSC) models and a mouse model of FGFR3 skeletal dysplasia. We converted fibroblasts from thanatophoric dysplasia type I (TD1) and ACH patients into iPSCs. The chondrogenic differentiation of TD1 iPSCs and ACH iPSCs resulted in the formation of degraded cartilage. We found that statins could correct the degraded cartilage in both chondrogenically differentiated TD1 and ACH iPSCs. Treatment of ACH model mice with statin led to a significant recovery of bone growth. These results suggest that statins could represent a medical treatment for infants and children with TD1 and ACH.

Transporting mouse embryos and germplasm as frozen or unfrozen materials

The 21st century has seen a huge proliferation in the availability of genetically altered mice. The availability of these resources has been accompanied by ever greater opportunities for international collaborations between laboratories involving the exchange of mouse strains. This exchange can involve significant costs in terms of animal welfare and transportation expenses. In an attempt to mitigate some of these costs, the mouse community has developed a battery of techniques that can be used to avoid transporting live mice. Transporting frozen embryos and sperm at liquid nitrogen (LN2 ) temperatures using dry shippers has been common practice for some time. However, current advances in this field have refined transportation procedures and introduced new techniques for disseminating embryos and sperm: for example, shipping frozen sperm on dry ice, exchanging unfrozen epididymides from which sperm can be extracted, and transporting frozen/thawed embryos in isotonic media. This article discusses some of the current practices used by laboratories to transport mouse strains around the world without having to exchange live mice.

Investigations of motility and fertilization potential in thawed cryopreserved mouse sperm from cold-stored epididymides

Cold transport of epididymides from genetically modified mice is an efficient alternative to the shipment of live animals between research facilities. Mouse sperm from epididymides cold-stored for short periods can maintain viability. We previously reported that cold storage of mouse epididymides in Lifor® perfusion medium prolonged sperm motility and fertilization potential and that the sperm efficiently fertilized oocytes when reduced glutathione was added to the fertilization medium. Cryopreservation usually results in decreased sperm viability; an optimized protocol for cold storage of epididymides plus sperm cryopreservation has yet to be established. Here, we examined the motility and fertilization potential of cryopreserved, thawed (frozen-thawed) sperm from previously cold-stored mouse epididymides. We also examined the protective effect of sphingosine-1-phosphate (S1P) on sperm viability when S1P was added to the preservation medium during cold storage. We assessed viability of frozen-thawed sperm from mouse epididymides that had been cold-transported domestically or internationally and investigated whether embryos fertilized in vitro with these sperm developed normally when implanted in pseudo-pregnant mice. Our results indicate that frozen-thawed sperm from epididymides cold-stored for up to 48 h maintained high fertilization potential. Fertilization potential was reduced after cold storage for 72 h, but not if S1P was included in the cold storage medium. Live pups were born normally to recipients after in vitro fertilization using frozen-thawed sperm from cold-transported epididymides. In summary, we demonstrate an improved protocol for cold-storage of epididymides that can facilitate transport of genetically engineered-mice and preserve sperm viability after cryopreservation.

Short-term storage of tripronucleated human embryos

PURPOSE

To determine the survival and subsequent in vitro development of human cleavage stage embryos and hatched blastocysts following varying periods of short-term storage at 4 °C, using tripronucleated human embryos (TPN) as a model.

METHODS

TPN cleavage embryos and hatched blastocysts short-term stored at 4 °C for 0 h (control), 24 h and 48 h. The main outcome measures were: survival rates (SR) and in vitro developmental ability (blastocyst rate and blastocyst-re-expansion rate) in each of the groups after storage.

RESULTS

Cleavage-stage TPN survived at comparable rates to controls, regardless of storage time (average: 97.3 %). The in vitro development of cleavage-stage TPN stored for 24 h was comparable to that of controls (average 64.7 %), but was significantly impaired when storage lasted 48-h (20.8 %). After artificial shrinkage, SR was comparable in 24-h-stored and non-stored hatched blastocysts (85.7 %; p > 0.05), but was significantly impaired in the 48-h-stored group (20.0 %). Following 24-h storage, the re-expansion rate of hatched blastocysts was similar to that of controls (average: 57.1 %; p > 0.05), but was higher than that of the 48-h-stored group (15.0 %; p < 0.05).

CONCLUSIONS

TPN human cleavage embryos and blastocysts can be successfully stored short-term for up to 24 h at 4 °C without using cryoprotectants without any significant negative impact on survival or subsequent in vitro development.

Centralized mouse repositories

Because the mouse is used so widely for biomedical research and the number of mouse models being generated is increasing rapidly, centralized repositories are essential if the valuable mouse strains and models that have been developed are to be securely preserved and fully exploited. Ensuring the ongoing availability of these mouse strains preserves the investment made in creating and characterizing them and creates a global resource of enormous value. The establishment of centralized mouse repositories around the world for distributing and archiving these resources has provided critical access to and preservation of these strains. This article describes the common and specialized activities provided by major mouse repositories around the world.

Overview of new developments in and the future of cryopreservation in the laboratory mouse

The large-scale mutagenesis programmes underway around the world are generating thousands of novel GA mouse strains that need to be securely archived. In parallel with advances in mutagenesis, the procedures used to cryopreserve mouse stocks are being continually refined in order to keep pace with demand. Moreover, the construction of extensive research infrastructures for systematic phenotyping is fuelling demand for these novel strains of mice and new approaches to the distribution of frozen and unfrozen embryos and gametes are being developed in order to reduce the dependency on the transportation of live mice. This article highlights some contemporary techniques used to archive, rederive, and transport mouse strains around the world.

In vitro and in vivo development of mice morulae after storage in non-frozen conditions

BACKGROUND

Interchange of genetically modified (GM) mice between laboratories using embryos provides several advantages. Not only is transport stress avoided, but also the health status of the recipient colony is not compromised. Embryos do not need to be shipped in frozen stage, which requires expensive packaging in addition to a certain degree of expertise in order to freeze and thaw them correctly. The aim of this study was to examine different storage conditions and their effect on embryo viability in order to establish the feasibility of practical, non-frozen conditions for embryo shipment.

METHODS

Mouse morulae developed in vivo (collected from donors 2.5d post coitum) or in vitro (zygotes cultured until morulae stage) were stored, combining two different media (KSOMeq or KSOM-H) and temperatures (4 degrees C, 15 degrees C and 37 degrees C) throughout 24 or 48 hours. After storage in vitro viability was assessed determining percentage of development to blastocyst and total cell number. In vivo viability was determined based on the number of implantations and living fetuses after embryo transfer of stored embryos. The storage effect at the molecular level was assessed by studying a gene pool involved in early development by quantitative RT-PCR.

RESULTS

In vivo-produced morulae stored for 24 hours did not show differences in development up to the blastocyst stage, regardless of the storage type. Even though a decrease in the total cell number in vivo was observed, embryo development after embryo transfer was not affected. All 24 hour storage conditions tested provided a similar number of implantations and fetuses at day 14 of pregnancy. Morulae obtained from in vitro embryo culture collected at the 1-cell stage showed a decreased ability to develop to blastocyst after 24 hours of storage at 15degrees C both in KSOMeq and KSOM-H. Concomitantly, a significant decrease of embryo implantation rates after transfer to recipients was also found. In order to further characterize the effect of non-frozen storage combining a molecular approach with the ordinary in vitro culture evaluation, embryos collected at the morula stage were submitted to the same storage conditions described throughout 48 hours. In vitro culture of those embryos showed a significant decrease in their developmental rate to blastocyst in both KSOMeq and KSOM-H at 15degrees C, which also affected the total number of cells. Gene transcription studies confirmed significant alterations in retrotransposons (Erv4 and Iap) after 48 h of storage at 15degrees C.

CONCLUSIONS

Our results show that both KSOMeq and KSOM-H can be equally used, and that several temperature conditions allow good survival rates in vitro and in vivo. Some of these storage conditions can substitute freezing in order to maintain embryo viability for 24-48 hours, providing a reliable and less demanding technical alternative for embryo interchanges.