Andrew J. French

Simplified technique for differential staining of inner cell mass and trophectoderm cells of mouse and bovine blastocysts.

Histological staining and counting of blastocyst inner cell mass (ICM) and trophectoderm (TE) cells differentially with chromatin-specific dyes is a more accurate indicator of cultured blastocyst quality and normality than total cell number assessment. The aim of this study was to test the effectiveness of a simplified method of chemically-defined differential blastocyst staining. The TE of cultured mouse and bovine blastocysts of different developmental stages was stained when blastocysts were treated with a permeabilizing solution containing the ionic detergent Triton X-100 and the fluorochrome propidium iodide. Blastocysts were then incubated in a second solution containing 100% ethanol (for fixation) and the secondary fluorochrome bisbenzimide. Fixed and stained whole blastocysts were mounted and assessed for cell number using ultraviolet fluorescent microscopy. Using this method, in-vitro cultured mouse blastocysts (day 4.5) were shown to have an ICM:TE ratio of 1:2.63 with an average total cell count of 75.3 +/- 3. While day 7 and 8 in-vitro produced bovine blastocysts were shown to have an ICM:TE ratio of 1:3.42 and 1:3.36 with an average total cell count of 151.3 +/- 5.48 and 217.8 +/- 8.75 respectively. Blastocyst staining patterns indicate that this modified technique represents a simple and reliable alternative to current bichromatic blastocyst staining techniques for the differential assessment of cell numbers and may be useful for the assessment of blastocysts derived from in-vitro maturation, novel culture systems and advanced reproductive technologies such as cloning.

Development of Human Cloned Blastocysts Following Somatic Cell Nuclear Transfer with Adult Fibroblasts

Nuclear transfer stem cells hold considerable promise in the field of regenerative medicine and cell‐based drug discovery. In this study, a total of 29 oocytes were obtained from three young (20–24 years old) reproductive egg donors who had been successful in previous cycles. These oocytes, deemed by intended parents to be in excess of their reproductive needs, were donated for research without financial compensation by both the egg donor and intended parents after receiving informed consent. All intended parents successfully achieved ongoing pregnancies with the oocytes retained for reproductive purposes. Mature oocytes, obtained within 2 hours following transvaginal aspiration, were enucleated using one of two methods, extrusion or aspiration, after 45 minutes of incubation in cytochalasin B. Rates of oocyte lysis or degeneration did not differ between the two methods. Somatic cell nuclear transfer (SCNT) embryos were constructed using two established adult male fibroblast lines of normal karyotype. High rates of pronuclear formation (66%), early cleavage (47%), and blastocyst (23%) development were observed following incubation in standard in vitro fertilization culture media. One cloned blastocyst was confirmed by DNA and mitochondrial DNA fingerprinting analyses, and DNA fingerprinting of two other cloned blastocysts indicated that they were also generated by SCNT. Blastocysts were also obtained from a limited number of parthenogenetically activated oocytes. This study demonstrates, for the first time, that SCNT can produce human blastocyst‐stage embryos using nuclei obtained from differentiated adult cells and provides new information on methods that may be needed for a higher level of efficiency for human nuclear transfer.

Characterization of a CD46 transgenic pig and protection of transgenic kidneys against hyperacute rejection in non-immunosuppressed baboons

Abstract:  Human membrane cofactor protein (CD46) controls complement activation and when expressed sufficiently as a transgene protects xenografts against complement‐mediated rejection, as shown here using non‐immunosuppressed baboons and heterotopic CD46 transgenic pig kidney xenografts. This report is of a carefully engineered transgene that enables high‐level CD46 expression. A novel CD46 minigene was validated by transfection and production of a transgenic pig line. Pig lymphocytes were tested for resistance to antibody and complement‐mediated lysis, transgenic tissues were characterized for CD46 expression, and kidneys were transplanted to baboons without immunosuppression. Absorption of anti‐Galα(1,3)Gal epitope (anti‐GAL) serum antibodies was measured. Transgenic pigs expressed high levels of CD46 in all tissues, especially vascular endothelium, with stable expression through three generations that was readily monitored by flow cytometry of transgenic peripheral blood mononuclear cells (PBMC). Transgenic PBMC pre‐sensitized with antibody were highly resistant to human complement‐mediated lysis which readily lysed normal pig PBMC. Normal pig kidneys transplanted without cold ischemia into non‐immunosuppressed adult baboons survived a median of 3.5 h (n = 7) whereas transgenic grafts (n = 9), harvested at ∼24‐h intervals, were either macroscopically normal (at 29, 48 and 68 h) or showed limited macroscopic damage (median > 50 h). Microscopic assessment of transplanted transgenic kidneys showed only focal tubular infarcts with viable renal tissue elsewhere, no endothelial swelling or polymorph adherence and infiltration by lymphocytes beginning at 3 days. Coagulopathy was not a feature of the histology in four kidneys not rejected and assessed at 48 h or later after transplantation. Baboon anti‐GAL serum antibody titers were high before transplantation and, in one extensively analyzed recipient, reduced ∼8‐fold within 5.5 h. The data demonstrate that a single CD46 transgene controls hyperacute kidney graft rejection in untreated baboons despite the presence of antibody and complement deposition. The expression levels, tissue distribution and in vitro functional tests indicate highly efficient CD46 function, controlling both classical and alternative pathway complement activation, which suggests it might be the complement regulator of choice to protect xenografts.

Analysis of Imprinted Messenger RNA Expression During Bovine Preimplantation Development

Abstract While the expression and epigenetic differences of imprinted genes have been extensively characterized in the mouse and human, little is known about imprinted genes in livestock species. In the current study, eight genes that are imprinted in the human or mouse were investigated in preimplantation bovine embryos. Amplified cDNA was created from three single metaphase II (MII) oocytes or embryos throughout preimplantation development. The imprinted genes Dlk1 and Mest (isoform 1) had no detectable transcripts during preimplantation development. Gnas and Grb10 were expressed in most embryos from the 2-cell to blastocyst stages of development. Mest (isoform 2) was expressed in all oocytes and embryos, except for one blastocyst sample. Ndn and Xist were expressed from the 8–16-cell stage (maternal-to-zygotic transition, MZT) onwards. Sgce was expressed until the MZT, and Nnat in both early (α form) and late (β form) stage embryos. The paternally imprinted genes Gnas, Grb10, and Xist were expressed in both in vitro-fertilized (IVF) and parthenogenetically activated (PA) blastocysts as expected. Of the four maternally imprinted genes expressed in the blastocyst (Mest, Ndn, Nnat, and Sgce), Nnat alone showed differential mRNA expression between IVF and PA blastocysts, suggesting imprinting by this stage of development. In conclusion, seven of the eight genes investigated showed mRNA expression during preimplantation development, indicating a potential role during early development. Also significant is the observation that Nnat is imprinted by the blastocyst stage of development although the other genes are not, indicating a temporal imprinting program.

Comparison of two approaches to nuclear transfer in the bovine : hand-made cloning with modifications and the conventional nuclear transfer technique

The aim of the present study was to compare the in vitro and in vivo developmental competence of hand-made cloning (HMC) embryos with the conventional nuclear transfer (NT) method using five somatic cell lines and in vitro-fertilised (IVF; control) embryos. Modifications to the HMC procedure included fusion efficiency optimisation, effect of cytoplasmic volume and cloned embryo aggregation. The developmental competence of blastocysts from each of the treatment groups and cell lines used was assessed following transfer to 345 recipients. Vitrification was also used to enable management of recipient resources and to assess the susceptibility of membranes to cryopreservation following zona removal. Increasing cytoplasmic volume to 150% or aggregating two embryos improved the blastocyst development rate and increased the total cell number. Although HMC embryo transfers established a significantly higher pregnancy rate on Day 30 than fresh IVF or NT embryo transfers, the overall outcome in terms of cloned live births derived from either fresh or vitrified/thawed HMC or NT embryo transfers across the five cell lines did not differ. The birth and continued survival of clones produced with HMC technology with equivalent efficiency to NT shows that it can be used as an alternative method for the generation of cloned offspring in the bovine.

Mitochondrial DNA transmission and transcription after somatic cell fusion to one or more cytoplasts.

Following fertilization, mitochondrial DNA is inherited from the oocyte and transmitted homoplasmically. However, following nuclear transfer, mitochondrial DNA can be transmitted from both the donor cell and recipient oocyte, resulting in a state of heteroplasmy. To determine whether the genetic diversity between donor cell and recipient cytoplast mitochondrial DNA influences development, we generated bovine embryos by fusing a donor cell to one or more enucleated cytoplasts. Analysis of mitochondrial DNA from embryos, fetal tissues, and blood samples from offspring revealed that early preimplantation embryos from two or three cytoplasts had significantly more mitochondrial DNA variants than fetal tissues. Phylogenic analysis of embryos generated using single cytoplasts divided the mitochondrial DNA sequence variants into three separate groups with various amounts of genetic divergence from the donor cell line. In heteroplasmic tissue and blood samples, the predominant mitochondrial DNA population was significantly more divergent from the donor cell than the less frequent allele. Furthermore, analysis of the mitochondrially encoded cytochrome B gene showed that two heteroplasmic alleles encoded for different amino acids, and the ratios of mitochondrial DNA/mRNA for each allele differed significantly between tissues. The degree of evolutionary distance between the donor cell and the cytoplast and the variability in heteroplasmy between tissues may have an impact on more divergent intergeneric nuclear transfer and the use of this approach for the generation of embryonic stem cells.

Stereomicroscopic and histological examination of bovine embryos following extended in vitro culture.

Attempts to support survival of mammalian embryos after hatching have met with limited success, although some mouse studies have reported growth at the post-implantation stage. The aim of the present research was to establish and characterise an in vitro culture system that could support extended growth and differentiation of bovine embryos. Abattoir-derived oocytes were matured and fertilised in vitro. Presumptive zygotes were cultured in modified synthetic oviduct fluid (SOFaaci) medium supplemented with 5% cow serum (CS). On Day 9, single hatched blastocysts (n = 160) were randomly allocated to SOFaaci supplemented with either 5% bovine serum albumin, 5% CS, 5% fetal calf serum (FCS) or SOF only and cultured on a collagen gel substrate for up to 45 days. Embryos were evaluated at various time-points until complete disaggregation or the total disappearance of embryonic cells. Blastocyst viability post hatching was severely compromised in protein-free SOFaaci medium. Addition of FCS generated increased embryonic growth for the longest time period (Day 45) when compared to the other groups. Long-term survival of embryonic cells was observed stereomicroscopically by the proliferation and development of three-dimensional tubular structures to 85% confluence in culture. Haematoxylin and eosin staining of morphological structures obtained from all treatment groups revealed embryos displaying trophoblast, inner cell mass and hypoblast development to varying degrees. Regardless of treatment, extended in vitro culture did not result in development comparable with that described for in vivo embryos. In the present work, however, there was evidence of extended culture of bovine embryos beyond that achieved previously. However, further research is required to identify the exact requirements for extended in vitro culture for bovine embryos.

Analysis of the expression of putatively imprinted genes in bovine peri-implantation embryos.

The application of assisted reproductive technologies (ART) has been shown to induce changes in the methylation of the embryonic genome, leading to aberrant gene expression, including that of imprinted genes. Aberrant methylation and gene expression has been linked to the large offspring syndrome (LOS) in bovine embryos resulting in increased embryonic morbidity and mortality. In the bovine, limited numbers of imprinted genes have been studied and studies have primarily been restricted to pre-implantation stages. This study reports original data on the expression pattern of 8 putatively imprinted genes (Ata3, Dlk1, Gnas, Grb10, Magel2, Mest-1, Ndn and Sgce) in bovine peri-implantation embryos. Two embryonic developmental stages were examined, Day 14 and Day 21. The gene expression pattern of single embryos was recorded for in vivo, in vitro produced (IVP) and parthenogenetic embryos. The IVP embryos allow us to estimate the effect of in vitro procedures and the analysis of parthenogenetic embryos provides provisional information on maternal genomic imprinting. Among the 8 genes investigated, only Mest-1 showed differential expression in Day 21 parthenogenetic embryos compared to in vivo and IVP counterparts, indicating maternal imprinting of this gene. In addition, our expression analysis of single embryos revealed a more heterogeneous gene expression in IVP than in in vivo developed embryos, adding further to the hypothesis of transcriptional dysregulation induced by in vitro procedures, either by in vitro maturation, fertilization or culture. In conclusion, effects of genomic imprinting and of in vitro procedures for embryo production may influence the success of bovine embryo implantation.

Developmental disparity between in vitro-produced and somatic cell nuclear transfer bovine days 14 and 21 embryos: implications for embryonic loss.

In ruminants, the greatest period of embryonic loss coincides with the period of elongation when the embryonic disc is formed and gastrulation occurs prior to implantation. The impact of early embryonic mortality is not only a major obstacle to the cattle breeding industry but also impedes the application of new reproductive technologies such as somatic cell nuclear transfer (SCNT). In the present study, days 14 and 21 bovine embryos, generated by either in vitro-production (IVP) or SCNT, performed by either subzonal injection (SUZI) or handmade cloning (HMC), were compared by stereomicroscopy, immunohistochemistry, and transmission electron microscopy to establish in vivo developmental milestones. Following morphological examination, samples were characterized for the presence of epiblast (POU5F1), mesoderm (VIM), and neuroectoderm (TUBB3). On D14, only 25, 15, and 7% of IVP, SUZI, and HMC embryos were recovered from the embryos transferred respectively, and similar low recovery rates were noted on D21, suggesting that most of the embryonic loss had already occurred by D14. A number of D14 IVP, SUZI, and HMC embryos lacked an epiblast, but presented trophectoderm and hypoblast. When the epiblast was present, POU5F1 staining was limited to this compartment in all types of embryos. At the ultrastructural level, SCNT embryos displayed abundant secondary lysosomes and vacuoles, had fewer mitochondria, polyribosomes, tight junctions, desmosomes, and tonofilaments than their IVP counterparts. The staining of VIM and TUBB3 was less distinct in SCNT embryos when compared with IVP embryos, indicating slower or compromised development. In conclusion, SCNT and to some degree, IVP embryos displayed a high rate of embryonic mortality before D14 and surviving embryos displayed reduced quality with respect to ultrastructural features and differentiation markers.

Putative imprinted gene expression in uniparental bovine embryo models

Altered patterns of gene expression and the imprinted status of genes have a profound effect on cell physiology and can markedly alter embryonic and fetal development. Failure to maintain correct imprinting patterns can lead to abnormal growth and behavioural problems, or to early pregnancy loss. Recently, it has been reported that the Igf2R and Grb10 genes are biallelically expressed in sheep blastocysts, but monoallelically expressed at Day 21 of development. The present study investigated the imprinting status of 17 genes in in vivo, parthenogenetic and androgenetic bovine blastocysts in order to determine the prevalence of this unique phenomenon. Specifically, the putatively imprinted genes Ata3, Impact, L3Mbtl, Magel2, Mkrn3, Peg3, Snrpn, Ube3a and Zac1 were investigated for the first time in bovine in vitro fertilised embryos. Ata3 was the only gene not detected. The results of the present study revealed that all genes, except Xist, failed to display monoallelic expression patterns in bovine embryos and support recent results reported for ovine embryos. Collectively, the data suggest that monoallelic expression may not be required for most imprinted genes during preimplantation development, especially in ruminants. The research also suggests that monoallelic expression of genes may develop in a gene- and time-dependent manner.