Generation of mice derived from embryonic stem cells using blastocysts of different developmental ages

Simultaneous visualization of RNA transcripts and proteins in whole-mount mouse preimplantation embryos using single-molecule fluorescence in situ hybridization and immunofluorescence microscopy

Whole-mount single-molecule RNA fluorescence in situ hybridization (smRNA FISH) in combination with immunofluorescence (IF) offers great potential to study long non-coding RNAs (lncRNAs): their subcellular localization, their interactions with proteins, and their function. Here, we describe a step-by-step, optimized, and robust protocol that allows detection of multiple RNA transcripts and protein molecules in whole-mount preimplantation mouse embryos. Moreover, to simultaneously detect protein and enable RNA probe penetration for the combined IF/smRNA FISH technique, we performed IF before smRNA FISH. We removed the zona pellucida, used Triton X-100 to permeabilize the embryos, and did not use a proteinase digestion step so as to preserve the antigens. In addition, we modified the IF technique by using RNase-free reagents to prevent RNA degradation during the IF procedure. Using this modified sequential IF/smRNA FISH technique, we have simultaneously detected protein, lncRNA, and mRNA in whole-mount preimplantation embryos. This reliable and robust protocol will contribute to the developmental biology and RNA biology fields by providing information regarding 3D expression patterns of RNA transcripts and proteins, shedding light on their biological function.

Contributions of Mammalian Chimeras to Pluripotent Stem Cell Research

Chimeras are widely acknowledged as the gold standard for assessing stem cell pluripotency, based on their capacity to test donor cell lineage potential in the context of an organized, normally developing tissue. Experimental chimeras provide key insights into mammalian developmental mechanisms and offer a resource for interrogating the fate potential of various pluripotent stem cell states. We highlight the applications and current limitations presented by intra- and inter-species chimeras and consider their future contribution to the stem cell field. Despite the technical and ethical demands of experimental chimeras, including human-interspecies chimeras, they are a provocative resource for achieving regenerative medicine goals.

Improved derivation efficiency and pluripotency of stem cells from the refractory inbred C57BL/6 mouse strain by small molecules

The ability of small molecules to maintain self-renewal and to inhibit differentiation of pluripotent stem cells has been well-demonstrated. Two widely used molecules are PD 98059 (PD), an inhibitor of extracellular-signal-regulated kinase 1 (ERK), and SC1 (Pluripotin), which inhibits the RasGAP and ERK pathways. However, no studies have been conducted to compare their effects on the pluripotency and derivation of embryonic stem (ES) cells from inbred mice C57BL/6, an important mouse strain frequently used to model behavior, cognitive functions, immune system, and metabolic disorders in humans and also the first mouse strain chosen to be sequenced for its entire genome. We found significantly increased derivation efficiency of ES cells from in vivo fertilized embryos (fES) of C57BL/6 with the use of PD (71.4% over the control of 35.3%). Because fES and ES from cloned embryos (ntES) are not distinguishable in transcription or translation profiles, we used ntES cells to compare the effect of small molecules on their in vitro characteristics, in vitro differentiation ability, and the ability to generate full-term ntES-4N pups by tetraploid complementation. NtES cells exhibited typical ES characteristics and up-regulated Sox2 expression in media with either small-molecule. Higher rates of full term ntES-4N pup were generated by the supplementation of PD or SC1. We obtained the highest efficiency of ntES-4N pup generation ever reported from this strain by supplementing ES medium with SC1. Lastly, we compared the pluripotency of fES, ntES and induced pluripotent stem (iPS) cells of C57BL/6 background using the tetraploid complementation assay. A significant increase in implantation sites and the number of full-term pups were obtained when fES, ntES, and iPS cells were cultured with SC1 compared to the control ES medium. In conclusion, supplementing ES cell culture medium with PD and SC1 increases the derivation efficiency and pluripotency, respectively, of stem cells derived from the refractory inbred C57BL/6 strain.

Genetically engineered mouse models for drug development and preclinical trials

Drug development and preclinical trials are challenging processes and more than 80% to 90% of drug candidates fail to gain approval from the United States Food and Drug Administration. Predictive and efficient tools are required to discover high quality targets and increase the probability of success in the process of new drug development. One such solution to the challenges faced in the development of new drugs and combination therapies is the use of low-cost and experimentally manageable in vivo animal models. Since the 1980's, scientists have been able to genetically modify the mouse genome by removing or replacing a specific gene, which has improved the identification and validation of target genes of interest. Now genetically engineered mouse models (GEMMs) are widely used and have proved to be a powerful tool in drug discovery processes. This review particularly covers recent fascinating technologies for drug discovery and preclinical trials, targeted transgenesis and RNAi mouse, including application and combination of inducible system. Improvements in technologies and the development of new GEMMs are expected to guide future applications of these models to drug discovery and preclinical trials.

Stem cell potency and the ability to contribute to chimeric organisms

Mouse embryonic chimeras are a well-established tool for studying cell lineage commitment and pluripotency. Experimental chimeras were successfully produced by combining two or more preimplantation embryos or by introducing into host embryo cultured pluripotent embryonic stem cells (ESCs). Chimera production using genetically modified ESCs became the method of choice for the generation of knockout or knockin mice. Although the derivation of ESCs or ESC-like cells has been reported for other species, only mouse and rat pluripotent stem cells have been shown to contribute to germline-competent chimeras, which is the defining feature of ESCs. Herein, we describe different approaches employed for the generation of embryonic chimeras, define chimera-competent cell types, and describe cases of spontaneous chimerism in humans. We also review the current state of derivation of pluripotent stem cells in several species and discuss outcomes of various chimera studies when such cells are used.

Valproic acid treatment from the 4-cell stage improves Oct4 expression and nuclear distribution of histone H3K27me3 in mouse cloned blastocysts

We examined effects of treatment with valproic acid (0, 0.2, 1 or 2 mM, VPA), an inhibitor of class I and IIa histone deacetylases (HDACs), of mouse somatic cell nuclear transfer (SCNT) embryos for 24 h from 48 h (4-cell stage), 24 h (2-cell stage) or immediately after oocyte activation on blastocyst formation rates and qualities of the resultant blastocysts. Blastocyst formation rates (33.4–37.0%) were not improved by VPA treatments compared with the untreated control (35.1–36.4%). However, immunofluorescence staining revealed that Oct4 expression levels, evaluated from percentages of embryos expressing Oct4 strongly and having more than 10 Oct4-positive cells, in blastocysts from SCNT embryos treated with 1 mM VPA for 24 h from the 4-cell stage (VPA-4C) were highest among all the groups and that the proportion of cells with a normal nuclear distribution of histone H3 trimethylated at lysine 27 (H3K27me3), a marker of the state of X-chromosome inactivation, significantly increased in the VPA-4C group (36.6%) compared with the control group (12.4%, P<0.05). Treatments with scriptaid and sodium butyrate, inhibitors of class I and IIa/b HDACs, for 24 h from the 4-cell stage also had beneficial effects on SCNT blastocysts. These findings indicate that treatment with 1 mM VPA from the 4-cell stage improves the Oct4 expression and nuclear distribution of H3K27me3 in mouse SCNT blastocysts and suggest that the inhibition of class I and IIa HDACs from the 4-cell stage plays an important role in these effects.

Ability of tetraploid rat blastocysts to support fetal development after complementation with embryonic stem cells

This study was undertaken to generate rat offspring via tetraploid blastocyst complementation with embryonic stem (ES) cells. Tetraploid blastocysts were prepared by electrofusion of blastomeres from two-cell stage embryos, and subsequent in vivo culture for 4 days. Microinjection into the tetraploid blastocoel of an inner cell mass isolated by immunosurgery resulted in the generation of rat offspring, suggesting the successful contribution of tetraploid blastocysts to their placenta. Tetraploid blastocyst complementation was attempted with a total of 4 ES cell lines (2 lines of female karyotype and 2 lines of male karyotype). In the rESWIv-3i-5 (XX) cell line, normal-sized fetuses with heartbeats were harvested on E11.5 (12.1%), E12.5 (9.5%), and E13.5 (9.1%), but no viable fetuses were detected on E14.5. Similarly, use of the rESWIv-3i-1 (XX) cell line resulted in no viable fetus production on E14.5. Using the rESBLK2i-1 (XY) cell line, viable fetuses were harvested not only on E11.5-E13.5 (2.6-5.5%), but also on E14.5 (3.0%). The transfer of a total of 487 tetraploid blastocysts complemented with rESBLK2i-1 cells resulted in 256 implantation sites (52.6%) on E21.5, but no viable offspring was detected. Use of the rESBLK2i-1/huKO (XY) cell line also resulted in no viable offspring production on E21.5. Analyses of the methylation pattern in differentially methylated regions and transcript level of genes that are imprinted in mice (H19, Meg3, Igf2r, Peg5, and Peg10) in the E14.5 conceptuses indicated a marked difference between the ES cell-derived and control normal fetuses, but not between the tetraploid and control diploid placenta.

Chimeric primates: embryonic stem cells need not apply

In this issue, Tachibana et al. report the generation of the first chimeras from a nonhuman primate, the rhesus monkey. Unlike mice, rhesus chimeras fail to form when embryonic stem cells are injected into blastocysts. Instead, chimera formation is achieved by aggregation of several four-cell embryos.

Generation of chimeric rhesus monkeys

Totipotent cells in early embryos are progenitors of all stem cells and are capable of developing into a whole organism, including extraembryonic tissues such as placenta. Pluripotent cells in the inner cell mass (ICM) are the descendants of totipotent cells and can differentiate into any cell type of a body except extraembryonic tissues. The ability to contribute to chimeric animals upon reintroduction into host embryos is the key feature of murine totipotent and pluripotent cells. Here, we demonstrate that rhesus monkey embryonic stem cells (ESCs) and isolated ICMs fail to incorporate into host embryos and develop into chimeras. However, chimeric offspring were produced following aggregation of totipotent cells of the four-cell embryos. These results provide insights into the species-specific nature of primate embryos and suggest that a chimera assay using pluripotent cells may not be feasible.

Acceptance of embryonic stem cells by a wide developmental range of mouse tetraploid embryos

Tetraploid (4N) complementation assay is regard as the most stringent characterization test for the pluripotency of embryonic stem (ES) cells. The technology can generate mice fully derived from the injected ES cell (ES-4N) with 4N placentas. However, it remains a very inefficient procedure owing to a lack of information on the optimal conditions for ES incorporation into the 4N embryos. In the present study, we injected ES cells from embryos of natural fertilization (fES) and somatic cell nuclear transfer (ntES) into 4N embryos at various stages of development to determine the optimal stage of ES cells integration by comparing the efficiency of full-term ES-4N mouse generation. Our results demonstrate that fES/ntES cells can be incorporated into 4N embryos at 2-cell, 4-cell and blastocyst stages and full-term mice can be generated. Interestingly, ntES cells injected into the 4-cell group resulted in the lowest efficiency (5.6%) compared to the 2-cell (13.8%, P > 0.05) and blastocyst (16.7%, P < 0.05) stages. Because 4N embryos start to form compacted morulae at the 4-cell stage, we investigated whether the lower efficiency at this stage was due to early compaction by injecting ntES cells into artificially de-compacted embryos treated with calcium free medium. Although the treatment changed the embryonic morphology, it did not increase the efficiency of ES-4N mice generation. Immunochemistry of the cytoskeleton displayed microtubule and microfilament polarization at the late 4-cell stage in 4N embryos, which suggests that de-compaction treatment cannot reverse the polarization process. Taken together, we show here that a wide developmental range of 4N embryos can be used for 4N complementation and embryo polarization and compaction may restrict incorporation of ES cells into 4N embryos.

Germline competence of mouse ES and iPS cell lines: Chimera technologies and genetic background

In mice, gene targeting by homologous recombination continues to play an essential role in the understanding of functional genomics. This strategy allows precise location of the site of transgene integration and is most commonly used to ablate gene expression ("knock-out"), or to introduce mutant or modified alleles at the locus of interest ("knock-in"). The efficacy of producing live, transgenic mice challenges our understanding of this complex process, and of the factors which influence germline competence of embryonic stem cell lines. Increasingly, evidence indicates that culture conditions and in vitro manipulation can affect the germline-competence of Embryonic Stem cell (ES cell) lines by accumulation of chromosome abnormalities and/or epigenetic alterations of the ES cell genome. The effectiveness of ES cell derivation is greatly strain-dependent and it may also influence the germline transmission capability. Recent technical improvements in the production of germline chimeras have been focused on means of generating ES cells lines with a higher germline potential. There are a number of options for generating chimeras from ES cells (ES chimera mice); however, each method has its advantages and disadvantages. Recent developments in induced pluripotent stem (iPS) cell technology have opened new avenues for generation of animals from genetically modified somatic cells by means of chimera technologies. The aim of this review is to give a brief account of how the factors mentioned above are influencing the germline transmission capacity and the developmental potential of mouse pluripotent stem cell lines. The most recent methods for generating specifically ES and iPS chimera mice, including the advantages and disadvantages of each method are also discussed.

Male germline and embryonic stem cell lines from NOD mice: efficient derivation of GS cells from a nonpermissive strain for ES cell derivation

The nonobese diabetic (NOD) mouse is a valuable model for human type 1 diabetes and the development of humanized mice. Although the importance of this mouse strain is widely recognized, its usefulness is constrained by the absence of NOD embryonic stem (ES) lines with adequate germline transmission competence. In the present study, we established two germline transmission-competent types of cell lines from NOD mice; these cell lines, male germline stem (GS) cells and ES cells, were derived from NOD spermatogonia and blastocysts, respectively. NOD-GS cells proliferated in vitro and differentiated into mature sperm after transplantation into testis. NOD-ES cell lines were effectively established from NOD blastocysts using culture medium containing inhibitors for fibroblast growth receptor, MEK, and GSK3. Both the NOD-GS and NOD-ES cell lines transmitted their haplotypes to progeny, revealing a novel strategy for gene modification in a pure NOD genetic background. Our results also suggest that the establishment of GS cells is an effective procedure in nonpermissive mouse strains or other species for ES cell derivation.

Detrimental effects of microgravity on mouse preimplantation development in vitro

Sustaining life beyond Earth either on space stations or on other planets will require a clear understanding of how the space environment affects key phases of mammalian reproduction. However, because of the difficulty of doing such experiments in mammals, most studies of reproduction in space have been carried out with other taxa, such as sea urchins, fish, amphibians or birds. Here, we studied the possibility of mammalian fertilization and preimplantation development under microgravity (microG) conditions using a three-dimensional (3D) clinostat, which faithfully simulates 10(-3) G using 3D rotation. Fertilization occurred normally in vitro under microG. However, although we obtained 75 healthy offspring from microG-fertilized and -cultured embryos after transfer to recipient females, the birth rate was lower than among the 1G controls. Immunostaining demonstrated that in vitro culture under microG caused slower development and fewer trophectoderm cells than in 1G controls but did not affect polarization of the blastocyst. These results suggest for the first time that fertilization can occur normally under microG environment in a mammal, but normal preimplantation embryo development might require 1G.