Successful development of viable blastocysts from enhanced green fluorescent protein transgene-microinjected mouse embryos: comparison of culture media

Successful Derivation of an Induced Pluripotent Stem Cell Line from a Genetically Nonpermissive Enhanced Green Fluorescent Protein-Transgenic FVB/N Mouse Strain

The embryonic stem cell line derivation from nonpermissive mouse strains is a challenging and highly inefficient process. The cellular reprogramming strategy provides an alternative route for generating pluripotent stem cell (PSC) lines from such strains. In this study, we successfully derived an enhanced green fluorescent protein (EGFP)-transgenic "N9" induced pluripotent stem cell (iPS cell, iPSC) line from the FVB/N strain-derived mouse embryonic fibroblasts (MEFs). The exposure of MEFs to human OCT4, SOX2, KLF4, and c-MYC (OSKM) transgenes via lentiviral transduction resulted in complete reprogramming. The N9 iPS cell line demonstrated all the criteria of a typical mouse PSC line, including normal colony morphology and karyotype (40,XY), high replication and propagation efficiencies, expression of the pluripotency-associated genes, spontaneous differentiation to three germ lineage-derived cell types, and robust potential of chimeric blastocyst formation. Taken together, using human OSKM genes for transduction, we report, for the first time, the successful derivation of an EGFP-expressing iPS cell line from a genetically nonpermissive transgenic FVB/N mouse. This cell line could provide opportunities for designing protocols for efficient derivation of PSC lines from other nonpermissive strains and developing mouse models of human diseases.

Embryo-endometrial expression of leukemia inhibitory factor in the golden hamster (Mesocricetus auratus): increased expression during proestrous and window of implantation stages

Leukemia inhibitory factor (LIF) is a pleiotropic IL-6 family cytokine and its maternal uterine expression is critical for mouse blastocyst implantation. In the golden hamster (Mesocricetus auratus), although the blastocyst hatching phenomenon is quite interesting and LIF is shown to regulate hatching, information is not available on the embryonic and uterine expression of LIF and hormonal regulation of LIF expression during the peri-implantation period. The present investigation is aimed at studying embryonic and uterine expression of LIF during preimplantation hamster development. We observed embryonic expression of LIF mRNA and protein in the 8-cell, morula and blastocyst stages. In cycling females, uterine LIF mRNA expression was maximal during the oestrogen-dominant phase of the oestrous cycle, i.e. proestrous stage. Interestingly, during pregnancy, both LIF mRNA and protein were highly upregulated on Days 3.5 and 4 (‘window of implantation’), implying a role for this cytokine in blastocyst hatching and implantation. Cell type-specific localisation of LIF mRNA and protein was observed predominantly in luminal epithelium and uterine glands with faint staining being detected in the stroma. The hamster uterus encoded a ~4.2 kb LIF transcript whose coding region, when cloned and sequenced, showed a high degree of identity to the murine cDNA counterpart. These data demonstrate that: (1) hamster preimplantation embryos show LIF mRNA and protein expression; (2) uterine expression of LIF mRNA and protein was dependent on elevated levels of circulating oestrogen, and (3) there is a possible functional association of LIF with the peri-implantation development in the golden hamster.

Strain Differences in Superovulatory Response, Embryo Development and Efficiency of Transgenic Rat Production

The differences between rat strains in superovulation response, in vitro and in vivo development of preimplantation embryos and overall transgenic efficiency was studied. The protocols for induction of superovulation using single injections of pregnant mare's serum gonadotropin (PMSG) or minipumps with follicle stimulating hormone (FSH) were compared in Lewis (LEW), Wistar-Kyoto (WKY), and stroke-prone spontaneously hypertensive rats (SHRSP) or Sprague-Dawley (SD) and Wistar rats as representative inbred or outbred strains, respectively. The percentage of mated animals with positive superovulatory response was similar in all strains (60.0-100%). The mean number of ova per donor was not dependent on the kind of hormonal treatment used within each rat strain. In general, females from outbred SD and Wistar rats were more responsive to hormonal treatments than animals from inbred rat strains. In addition, SD female rats produced a significantly higher number of embryos per female in response to PMSG-treatment compared to all other strains. Between the inbred strains, SHRSP was the most effective for superovulation. In vitro development of intact zygotes to the blastocyst stage was not different between SD, Wistar and SHRSP rats. In contrast, in vitro development of WKY zygotes was significantly less efficient than in other strains. However, 2-cell stage embryos in vivo produced from SD, SD x Wistar and WKY animals showed no difference in competence to develop to blastocyst stage in vitro. The proportion of offspring developing after oviduct transfer of intact zygotes was similar in all strains (44.0-56.4%) with the exception of WKY rats (35.9%). We also compared the survival rate after injection, ability of manipulated zygotes to develop to term and overall transgenic efficiency in various rat strains. SD and SHRSP zygotes survived after microinjection better than the WKY and Lewis zygotes. No differences were found in the efficiency of transgene integration per newborn in different strains ranging from 5.7 to 16.7%. The results of this study demonstrate that different rat strains have varying responses to superovulation, sensitivity to microinjection, capability to develop in vitro until blastocyst stage or in vivo to term after transfer to foster mothers. Despite these differences all studied strains can be used for efficient transgenic rat production.

Human embryonic stem cell methyl cycle enzyme expression: modelling epigenetic programming in assisted reproduction?

To investigate a possible mechanism for inducing epigenetic defects in the preimplantation embryo, a human embryonic stem cell model was developed, and gene expression of the key methyl cycle enzymes, MAT2A, MAT2B, GNMT, SAHH, CBS, CGL, MTR, MTRR, BHMT, BHMT2, mSHMT, cSHMT and MTHFR was demonstrated, while MAT1 was barely detectable. Several potential acceptors of cycle-generated methyl groups, the DNA methyltransferases (DNMT1, DNMT3A, DNMT3B and DNMT3L), glycine methyltransferase and the polyamine biosynthetic enzymes, SAM decarboxylase and ornithine decarboxylase, were also expressed. Expression of folate receptor alpha suggests a propensity for folate metabolism. Methotrexate-induced depletion of folate resulted in elevated intracellular homocysteine concentration after 7 days in culture and a concomitant increase in cysteine and glutathione, indicating clearance of homocysteine through the transulphuration pathway. These studies indicate that altered methyl group metabolism provides a potential mechanism for inducing epigenetic changes in the preimplantation embryo.

Impact of embryonic expression of enhanced green fluorescent protein on early mouse development

The impact of embryonic enhanced green fluorescent protein (EGFP)-expression on development is not clear. In this study, we comprehensively assessed EGFP-expression pattern and its effect on early mouse development, following pronuclear-microinjection of the EGFP-transgene, containing chicken-beta-actin promoter and cytomegalovirus enhancer. Preimplantation embryos exhibited differential EGFP-expression patterns. While blastocyst development of non-expressing embryos was 77.3+/-1.8%, that of expressing embryos was only 43.9+/-1.6% (P<0.0001). Developmental competence of embryos negatively correlated (r=-0.99) with the levels of EGFP-expression. Faint-, moderate-, and intense-expressing embryos developed to 83.1+/-5.3%, 50+/-5%, and 9.5+/-3.9% blastocysts, respectively (P<0.002). Interestingly, blastocysts expressing faint-moderate levels of EGFP were developmentally competent through the post-implantation period and delivered viable transgenic 'green' mice, following embryo transfer. These results indicate that hyper-expression of EGFP affects preimplantation development and faint-moderate level of its expression is compatible with normal embryogenesis in the mouse.

Embryo culture-based generation of enhanced green fluorescent protein-transgenic mice

One of the limitations of transgenesis is low efficiency. In this study, we generated transgenic mice harboring the enhanced green fluorescent protein (EGFP) gene, under the control of chicken-beta-actin promoter and cytomegalovirus enhancer, using two approaches and compared their efficiencies. One involved culture of EGFP-injected embryos developing through EGFP-expressing "green" blastocysts, followed by their transfer to uterus. The second was oviductal-transfer of EGFP-injected-eggs. Embryo culture-based-transgenesis (ECBT) produced 100% transgenic mice, unlike the second approach. Moreover, ECBT required reduced number of recipients and markedly increased pregnancy rates. Of the nine founders, seven exhibited ubiquitous EGFP-expression, one (GU1) was a mosaic and the other (G18) was non-expressing. The molecular basis for this was attributed to repeat-induced gene silencing, since the G18 had a high copy number (approximately 99/genome) of the non-mutated and non-rearranged EGFP-transgene integrated at a single site. Our results show the superiority of ECBT over the conventional oviductal approach for generating transgenic "green" mice.