Tomas Stojanov

In Vitro Fertilization Causes Epigenetic Modifications to the Onset of Gene Expression from the Zygotic Genome in Mice

Abstract The effect of in vitro fertilization (IVF) and culture of mouse preimplantation embryos in vitro on the onset of expression of insulin-like growth factor 1 (IGF-1) ligand and receptor, insulin ligand and receptor, alpha-transforming growth factor (α-TGF) ligand, PAF:acetylhydrolase 1b (Pafah1b; α1, α2, and β subunits of the enzyme), and the transcription requiring complex proteins (TRC) was examined. The IGF-1 ligand was detected in preimplantation embryos by immunofluorescence at all developmental stages tested. However, IVF and culture significantly reduced the amount of protein detected in the 8-cell embryo and blastocyst (P < 0.001), and this was due to a delayed onset of expression of the mRNA for IGF-1 ligand from the zygotic genome. The expression of the α1 subunit of Pafah1b was first detected at the 2-cell stage in fresh embryos, but expression was significantly retarded (P < 0.001) when IVF and ISF (in situ-fertilized) zygotes were cultured in vitro. In vitro fertilization or ISF did not delay the onset of expression of TRC nor mRNA for the IGF-1 receptor, insulin receptor, α2 or β subunit of Pafah1b, nor did they effect α-TGF protein synthesis. Thus, IVF causes epigenetic modification in the normal pattern of expression of some but not all genes involved in normal embryo growth and survival.

Derivation of Huntington's Disease-Affected Human Embryonic Stem Cell Lines

Huntingtons disease (HD) is an autosomal dominant neurodegenerative disease caused by an expansion of cytosine-adenine-guanine (CAG) repeats in the Huntingtin gene Htt. To facilitate research into HD, we have derived 4 human embryonic stem cell (hESC) lines containing ≥ 40 CAG repeats in exon 1 of Htt: SIVF017-HD (CAG₄₀), SIVF018-HD (CAG₄₆), SIVF020-HD (CAG₄₈), and SIVF046-HD (CAG₄₅). Additionally, we have derived a normal sibling-matched control for SIVF020-HD, cell line SIVF019. All 5 hESC lines had a normal karyotype, expressed pluripotency markers including Oct4, SSEA3, and Tra-1-81, and could be maintained in culture for multiple (>40) passages. Teratoma studies revealed that the hESC lines were capable of differentiating into cells representative of the 3 germ layers. Furthermore, in vitro neuronal differentiation experiments have confirmed that the hESC lines were able to generate MAP2-positive neuronal cells that express the Htt protein. Combined, these experiments confirm that the cell lines represent pluripotent stem cell lines. These HD-affected hESC lines will be made available to biomedical research laboratories and will provide a valuable tool to investigate the mechanisms and potential treatments for HD.

Characterization and Functional Significance of Calcium Transients in the 2-cell Mouse Embryo Induced by an Autocrine Growth Factor

Growth of preimplantation embryos is influenced by autocrine trophic factors that need to act by the 2-cell stage, but their mode of action is not yet described. This report shows that late zygote and 2-cell stage mouse embryos responded to embryo-derived platelet-activating factor (PAF) with transient increases in intracellular calcium concentration ([Ca2+] i ). [Ca2+] i transients were single global events and were specifically induced by embryo-derived PAF. They were blocked by inhibition of phospholipase C (U 73122) and an inositol trisphosphate (IP3) receptor antagonist (xestospongin C), indicating the release of calcium from IP3-sensitive intracellular stores. Transients were also inhibited by the absence of calcium from extracellular medium and partially inhibited by treatment with dihydropyridine (nifedipine, 10 μm), but not pimozide (an inhibitor of an embryonic T-type calcium channel). (±)BAY K8644 (an L-type channel agonist) induced [Ca2+] i transients, yet these were completely inhibited by nifedipine (10 μm). The complete inhibition of BAY K8644, but only partial inhibition of PAF by nifedipine shows that L-type channels were only partly responsible for the calcium influx. Depolarization of 2-cell embryos by 50 mm K+ did not inhibit PAF-induced calcium transients, showing that the influx channels were not voltage-dependent. Depletion of intracellular calcium stores by thapsigargin revealed the presence of store-operated channels. The interdependent requirement for IP3-sensitive internal calcium stores and extracellular calcium in the generation of PAF-induced transients may be explained by a requirement for capacitative calcium entry via store-operated channels. A functionally important role for the PAF-induced transients is supported by the observation that inhibition of [Ca2+] i transients by a PAF-antagonist (WEB 2086) or an intracellular calcium chelator (1,2-bis(2-aminophenoxy)-ethane-N,N,N′,N′-tetraacetic acid tetrakis-acetoxymethyl ester; BAPTA-AM) caused marked inhibition of early embryo development. Growth inhibition by BAPTA-AM was relieved by addition of exogenous PAF.

Karyotypically Normal and Abnormal Human Embryonic Stem Cell Lines Derived from PGD-Analyzed Embryos

Although a normal karyotype is generally a requirement for stem cell lines, new applications are likely to emerge for stem cells with defined chromosomal aneuploidies. We therefore investigated the use of embryos found to be aneuploid on biopsy followed by preimplantation genetic diagnosis (PGD) with fluorescent in situ hybridization (FISH), and developmentally arrested embryos for stem cell derivation. Eleven stem cell lines were obtained from 41 embryos in 36 cultures, with higher success rate achieved from PGD-analyzed, developmentally advanced embryos (45%) than from clinically unsuitable non-PGD embryos (13%). The resulting stem cell lines were karyotyped, and surprisingly, six of the nine lines from aneuploid embryos as well as both lines from non-PGD embryos were karyotypically normal. Three lines from PGD embryos were aneuploid exhibiting trisomy 5, trisomy 16, and an isochromosome 13, respectively. None of the aneuploid lines presented the same anomally as the original PGD analysis. Our study has three important implications. First, we confirm the ability to produce stem cell lines from PGD-tested embryos as well as developmentally abnormal embryos, offering specialty stem cell lines for research into the clinically important aneuploidies. Second, we observe that stem cell derivation from apparently aneuploid embryos is often thwarted by underlying mosaicism and emerging dominance of the stem cell line by karyotypically normal cells. The corollary, however, is that regular production of normal stem cell lines from developmentally abnormal embryos ordinarity discarded opens a new source of embryos for stem cells, whether for research or for eventual therapeutic use within the donating families.

Variable expressivity of the tumour suppressor protein TRP53 in cryopreserved human blastocysts

In a mouse model, in vitro fertilization or extended embryo culture leads to the increased expression of TRP53 in susceptible embryos. Ablation of the TRP53 gene improved embryo viability indicating that increased expression of TRP53 is a cause of the reduction of embryo viability resulting from in vitro fertilization or embryo culture. This study investigates the status of TRP53 expression in human embryos produced by intracytoplasmic sperm injection. Following fertilization, embryos were cultured for 96 h and then cryopreserved. Immediately upon thawing they were fixed in formaldehyde and subjected to immunostaining for TRP53. Staining was visualized by confocal microscopy. Negative controls were incubated with isotype control immunoglobulin and showed negligible staining. All embryos showed TRP53 staining above negative controls. TRP53 staining was heterogenous within and between embryos. An embryo that showed retarded development showed high levels of TRP53 expression. A blastocyst that had a collapsed blastocoel also showed high levels of TRP53 compared to morphologically normal blastocysts. Most TRP53 staining was in the region of the nucleus. Morphologically normal blastocysts tended to show little nuclear accumulation of stain. However, some cells within these embryos had high levels of nuclear TRP53 expression. The results show that embryos have varying sensitivity to the stresses of production and culture in vitro, and this resulted in variable expressivity of TRP53.

Derivation of three new human embryonic stem cell lines

Human embryonic stem cells are pluripotent cells capable of extensive self-renewal and differentiation to all cells of the embryo proper. Here, we describe the derivation and characterization of three Sydney IVF human embryonic stem cell lines not already reported elsewhere, designated SIVF001, SIVF002, and SIVF014. The cell lines display typical compact colony morphology of embryonic stem cells, have stable growth rates over more than 40 passages and are cytogenetically normal. Furthermore, the cell lines express pluripotency markers including Nanog, Oct4, SSEA3 and Tra-1-81, and are capable of generating teratoma cells derived from each of the three germ layers in immunodeficient mice. These experiments show that the cell lines constitute pluripotent stem cell lines.

Derivation of Human Embryonic Stem Cell Lines from Vitrified Human Embryos

Human embryonic stem cell lines are usually derived from human embryos that have become excess to clinical needs in assisted reproduction programs, whether because the couple in question has completed their family or because the embryo was found to be clinically unsuitable for transfer due to severe genetic condition (in case of pre-implantation genetic diagnosis, PGD). Culturing embryos to a blastocyst stage (5-6 days after IVF) before embryo transfer or cryopreservation instead of earlier commonly used 8-cell stage (3 days after IVF) calls for new methods for embryo cryopreservation and allows higher efficiencies for the actual stem cell derivation. Despite the vast advances in other fields of embryonic stem cell research, methods for derivation of new lines have not changed much over the years, mainly due to scarcity of embryos limiting experimentation. We describe here methods required to derive new embryonic stem cell lines starting from the initial cryopreservation of an embryo and finishing with a new cell line. We cover embryo cryopreservation and warming using a highly efficient vitrification method, the production of feeder cells and feeder plates, as well as embryo handling, plating and critical early passages, including earliest possible cryopreservation of putative stem cells using vitrification.

Generation of Human Embryonic Stem Cells

This unit describes generation of human embryonic stem cell lines from early human embryos. The focus is on actual handling of embryos and early embryonic outgrowths, omitting steps required for actual generation, freezing, and thawing of embryos, as well as further culture and characterization of newly derived stem cells. Hence, the initial culture of embryos to a blastocyst stage is described, followed by removal of the protective zona pellucida layer, isolation of the inner cell mass (ICM), subsequent plating of ICM or whole embryo and, finally, the first few passages of an early embryonic outgrowth. A few alternative procedures for some steps such as zona removal and inner cell mass isolation are described, to allow procedures to be modified according to circumstances.