Newly established F1 hybrid Embryonic Stem cells allow the production of ES cell-derived animals at a high enough efficiency to directly make ES cell based genetics feasible. An F1 hybrid ES cell line, G4 was used to generate transgenic over-expressing cell lines. The consequence of the expression of a panel of transgenes was assessed directly from ES cell-derived embryos produced by the tetraploid complementation assay. The generation of ES cell-derived embryos/animals was very efficient. A sufficient number of mutants for initial phenotypic analyses was derived only a few weeks after the establishment of the cell lines. The genes used in the study had either angiogenic/vasculogenic, anti-angiogenic or unknown properties. Of these transgenic mouse lines VEGF-A and Flt-Fc were used to further elucidate the effects of altered VEGF signaling on cell fate decisions in embryonic development and ES differentiation in two experimental systems. A. Early but transient Flk-1 activation led to enhanced generation of blood progenitors, whereas continuous activation of Flk-1 abolished this effect and enhanced endothelial cell generation. Ex vivo analysis of cells derived from E7.5 embryos demonstrated that sFlt-1-mediated control of Flk-1 activity also impacted the fate of hematopoietic and endothelial cells. The Flt-1-Fc transgenic mouse model was used to alter Flk-1 activation in vivo and show the relevance of the in vitro observations. These results demonstrate that sFlt-1 regulates Flk-1 activation in an oxygen responsive manner. Inhibition of Flk-1 activation by sFlt-1 increases the specification of hemangioblasts to blood cells consistent with a VEGF-independent default mechanism. B. Ubiquitous over-expression of VEGF164 isoform led to E8.75 embryonic lethality. The primary cause of lethality was the failure to form an organized cardiovascular system, which was manifested in three ways: the absence of yolk sac blood vessels, the lack of embryonic-maternal circulation due to the failure of allantochorionic fusion and improper cardiac function. The described phenotypes suggest that VEGF does not inhibit embryonic or extra-embryonic mesoderm formation at gastrulation but perturbs the balance amongst the mesodermal components.

Newly established F1 hybrid Embryonic Stem cells allow the production of ES cell-derived animals at a high enough efficiency to directly make ES cell based genetics feasible. An F1 hybrid ES cell line, G4 was used to generate transgenic over-expressing cell lines. The consequence of the expression of a panel of transgenes was assessed directly from ES cell-derived embryos produced by the tetraploid complementation assay. The generation of ES cell-derived embryos/animals was very efficient. A sufficient number of mutants for initial phenotypic analyses was derived only a few weeks after the establishment of the cell lines. The genes used in the study had either angiogenic/vasculogenic, anti-angiogenic or unknown properties. Of these transgenic mouse lines VEGF-A and Flt-Fc were used to further elucidate the effects of altered VEGF signaling on cell fate decisions in embryonic development and ES differentiation in two experimental systems. A. Early but transient Flk-1 activation led to enhanced generation of blood progenitors, whereas continuous activation of Flk-1 abolished this effect and enhanced endothelial cell generation. Ex vivo analysis of cells derived from E7.5 embryos demonstrated that sFlt-1-mediated control of Flk-1 activity also impacted the fate of hematopoietic and endothelial cells. The Flt-1-Fc transgenic mouse model was used to alter Flk-1 activation in vivo and show the relevance of the in vitro observations. These results demonstrate that sFlt-1 regulates Flk-1 activation in an oxygen responsive manner. Inhibition of Flk-1 activation by sFlt-1 increases the specification of hemangioblasts to blood cells consistent with a VEGF-independent default mechanism. B. Ubiquitous over-expression of VEGF164 isoform led to E8.75 embryonic lethality. The primary cause of lethality was the failure to form an organized cardiovascular system, which was manifested in three ways: the absence of yolk sac blood vessels, the lack of embryonic-maternal circulation due to the failure of allantochorionic fusion and improper cardiac function. The described phenotypes suggest that VEGF does not inhibit embryonic or extra-embryonic mesoderm formation at gastrulation but perturbs the balance amongst the mesodermal components.

Source: Masters Abstracts International, Volume: 47-02, page: 0981. Adviser: Luisa Franzini. Includes bibliographical references.

The basis of developmental biology lies in the idea of when and how cells decide to divide or to differentiate. Previous studies have established several signaling pathways that determine cell fate decisions, including Notch, Wingless, Hedgehog, Bone morphogenetic protein, and Fibroblast growth factor. Signaling converges on transcriptional factors that regulate gene expression. In mouse embryonic stem cells, I explored how pluripotency and differentiation are regulated through opposing actions of beta-catenin-mediated canonical Wnt signaling, and the mechanisms underlying Sonic hedgehog signaling in generating progenitor cells in the ventral neural tube.

The loss of regenerative capacity of bone, from fetal to adult to aged animals, has been attributed not only to a decline in the function of cells involved in bone formation but also to alterations in the bone microenvironment that occur through development and aging, including extracellular matrix (ECM) composition and growth/trophic factor content. In the development of novel treatments for bone repair, one potential therapeutic goal is the restoration of a more regenerative microenvironment, as found during embryonic development. One approach to creating such a microenvironment is through the use of stem cells. In addition to serving as a differentiated cell source, pluripotent stem cells, such as embryonic stem cells (ESCs), may possess the unique potential to modulate tissue environments via local production of ECM and growth factors. ESC-produced factors may be harnessed and delivered to promote functional tissue regeneration. Such an approach to generate a naturally derived, acelluar therapy has been employed successfully to deliver osteoinductive factors found within adult bone, in the form of demineralized bone matrix (DBM), but the development of treatments derived instead from developing, more regenerative tissues or cells remains attractive. Furthermore, the derivation of regenerative materials from an ESC source also presents the added benefit of eliminating donor to donor variability of adult, cadaveric tissue derived materials, such as DBM. Thus, the objective of this project was to examine the osteoinductive potential harbored within the embryonic microenvironment, in vitro and in vivo. The osteogenic differentiation of mouse ESCs as embryoid bodies (EBs) was evaluated in response to phosphate treatment, in vitro, including osteoinductive growth factor production. The osteoinductivity of EB-derived material (EBM) was then compared to that of adult tissue-derived DBM, in vivo. Phosphate treatment enhanced osteogenic differentiation of EBs. EBM derived from phosphate treated EBs retained bioactive, osteoinductive factors and induced new bone formation, demonstrating that the microenvironment within osteogenic EBs can be harnessed in an acellular material to yield in vivo osteoinductivity. This work not only provides new insights into the dynamic microenvironments of differentiating stem cells but also establishes an approach for the development of an ESC-derived, tissue specific therapy.

Embryonic stem cells (ESCs) are being considered as a cell source for cardiac regeneration because of their potency and availability. We studied the electrophysiological implications using co-cultures of ESCs and neonatal rat ventricular myocytes (NRVM) grown on a multi-electrode array (MEA). To mimic expected engraftment rates 5% mouse ESCs were co-cultured with NRVMs. Comparing cultures without and with 5% ESCs at 4 days, the mean bipolar field potential duration (FPD) of NRVMs increased from 26.3 ± 2.2 ms (n=10) to 44.3 ± 6.2 ms (n=9; p < 0.05), the interspike interval (ISI) increased from 358.3 ± 62.8 ms (n=10) to 947.8 ± 214.6 ms (n=7; p < 0.01), and conduction velocity (CV) decreased from 14.2 ± 1.3 cm/s (n=8) to 4.6 ± 1.2 cm/s (n=5; p < 0.01). To evaluate whether ESC were having direct or paracrine effects on NRVMs, media conditioned by 3x106 ESCs for 24 hr was diluted 1:1 with fresh media and then introduced to NRVM cultures on the day of plating. Conditioned media was changed daily and altered mean FPD, ISI, and CV to 46.1 ± 7.8 ms, ISI to 682.0 ± 128.5 ms, and 4.2 ± 0.4 cm/s (n=8; p < 0.01 for each measure), respectively at 4 days. However, changes were not seen in media that was incubated for 24hrs and diluted 1:1 with fresh media and introduced to NRVM cultures in a similar fashion (n=7; p > 0.05). Slowed CV is associated with increased arrhythmic risk and reports demonstrate an inverse relationship between CV and nonphosphorylated Cx43(NP-Cx43). Western blots for total Cx43 expression revealed a decrease in ratio of P-Cx43/NP-Cx43 in the 5% mouse ESCs and ESC conditioned media cultures as compared to controls (n=8; p < 0.01 for each). There was not significant increase in the total Cx43 expression (n=6; p > 0.05). Culturing ESCs with NRVMs resulted in a decreased ISI, prolonged FPD, and slowed CV of the co-cultures as compared to controls leading to pro-arrhythmic conditions. Similar effects on NRVMs were observed when applying media conditioned by ESCs, suggesting that the electrophysiological changes were mediated by soluble factors. The increase in NP-Cx43 leads to gap junction uncoupling being a potential mechanism for these arrhythmogenic substrates. Further research into preventing NP-Cx43 in cultures is currently underway.

Thesis (Ph. D.)--Cornell University, May, 2007. / Vita. Includes bibliographical references.

There is growing knowledge that neuronal circuitry undergoes alteration throughout development. Experience plays a key role in the reorganization of neuronal circuitry through the various mechanisms of learning. For example, when an animal is deprived of sensory input such as light in one or both sides of the eye, it can result in blindness on that side. In a study of rats placed in either isolated or enriched environments, those placed in enriched environments performed better on learning tests (maze test) than those placed in isolated environment. There was increased neurogenesis, synaptogenesis, myelination and angiogenesis in rats placed in enriched environments. These were all as a result of learning, which induces neuroplasticity in the nervous system. The goals of this study were to determine how evoked movement is altered by changes in key parameters of light stimulation: intensity and period and to determine if one hour of light (optogenetic) stimulation could give rise to plastic changes in the nervous system as indicated by alterations in spontaneous motility. To ascertain how evoked motor activity influences neuronal activity through learning and experience, optogenetics was employed to evoke movement in an embryonic chick at embryonic day nine (E9) after electroporation of a channelrhodopsin variant, ChIEF, into the neural tube. I first attempted to determine the optimal intensity needed to cause neuroplasticity in an embryonic chick by varying current to a LED light to produce three different light intensities. A protocol of 5 pulses of light with a period of 2 seconds was used to illuminate the right leg of 5 embryonic chicks with each intensity. To determine the optimal period of stimulation, I varied the period to 3 s and 4 s with one animal. Stimulation for an hour with a training protocol of 1800 pulses/hour (with a period of 2 s) of blue light (470 nm) was then used to illuminate the right thigh of the embryonic chick. There were varied responses to light of all intensities used for stimulation, but high light intensity (maximum - 100%) seemed to have produced the best responses in terms of producing the largest joint angle changes and shortest latencies of movement in all joints of the leg of embryonic chick. Movements of the hip and ankle joints were the most robust. This was closely followed by those of the mid (83.33%) intensity. Therefore, it can be inferred that the greater the intensity of light, the better the response. The training protocol did not produce significant changes in embryonic activity. There were some decreases in joint angles and variable spontaneous movement duration in all animals used but there could be some changes going on at the neuronal or muscular level which were beyond the scope of this study to investigate. It is my hope that this study will provide some knowledge pertinent to the treatment or management of neurodevelopmental disorders that may result in paraplegia or Erb's palsy.

Indiana University-Purdue University Indianapolis (IUPUI) / Serotonin (5-hydroxytryptamine, 5-HT) is a monoamine neurotransmitter that is synthesized from the amino acid L-tryptophan and is reported to localize in mitochondria of embryonic stem cells. Even before its role as a neurotransmitter in mature brain was discovered, 5-HT has been shown to play an important role in regulating brain development. However, there is a lack of knowledge about the downstream target genes regulated by serotonin in embryonic stem (ES) cells. Towards this end, our study helps in understanding transcriptional regulatory mechanisms of 5-HT responsive genes in ES cells. By combining the gene expression data with motif prediction algorithms, literature validation and comparison with public domain data, gene targets specific to endogenous or exogenous 5-HT in ES cells were identified. By performing one-way ANOVA, and volcano plots using GeneSpring software, we identified 44 5-HT induced and 29 5-HT suppressed genes, likely to be transcriptionally regulated by 4 & 2 TFs respectively. Motif enrichment analysis on these target genes using MotifScanner revealed that the transcription factor TFAP2A plays a key role in regulating the expression of 5-HT responsive genes. Furthermore, by comparing our dataset with published expression profiles of ES cells, we observed a number of 5-HT responsive target genes showing enrichment in ES cells. Genes such as Nanog, Slc38a5, Hoxb1 and Eif2s1 from this analysis have been observed to be components of ‘stemness’ phenotypes reported in literature. Functional annotation of the 5-HT responsive genes identified gene ontologies such as regulation of translation in response to stress and energy derivation by oxidation, suggesting a regulatory role for 5-HT in mitochondrial functions of ES cells. Additionally, enrichment of other biological process terms such as development of various parts of nervous system, cell adhesion, and apoptosis suggests that 5-HT target genes may play an important role in ES cell differentiation. Our study implemented a new combinatorial approach for identifying gene regulatory mechanisms involved in 5-HT responsive genes and proposed potential mediatory role for serotonin in ES cell differentiation and growth. Thus, this study provides potential 5-HT target genes in ES cells for biological validation.

Thesis (DPhil (Philosophy))--University of Stellenbosch, 2007. / Should surplus embryos which are destined to be discarded be protected at all cost, to the extent that they cannot contribute to medical knowledge - knowledge which could benefit society at large? Are embryos people or merely items of property? Different moral theories address these questions in different ways. Deontologists argue that the end never justifies the means and that the right not to be killed is more fundamental than the obligation to save. Utilitarians, on the other hand, argue that certain criteria should be met before moral significance can be contributed to an entity. The question of the moral status of the embryo is, as my discussion will show, one of the most widely discussed issues in the history of bioethics. Extensive literature exists on the topic. This study holds that an Ethics of Responsibility (ER) should by applied when answering the questions posed above as it encourages one to accept responsibility for the choices or decisions made and to defend them accordingly. I have endeavoured to answer the question of the personhood and rights of the embryo within the framework of the Ethics of Responsibility. Although these concepts overlap in many ways they remain central to the debate surrounding the sanctioning or prevention of the use of human embryonic stem cells in research. After identifying the micro-issues surrounding the human embryonic stem cell debate and explaining why both the deontologist and utilitarians fail to provide any adequate answers in this respect, I turn my attention to macro-issues such as safety concerns surrounding the usages and storage of stem cells. Commercialization, power issues, accessibility and the allocation of limited resources are also examined. Living in a society such as South Africa one cannot be blind to the inequalities of our health system. On a macro level I cannot but conclude that stem cell research does not seem to be a viable exercise within the South African context. South Africa faces a health care crisis far greater than the benefits stem cell research currently has to offer. However, the need still exists for a policy to guide future lawmakers who might need to address stem cell research and to guide decisions and actions. This brings me to my final chapter, namely proposing a morally justified policy for South Africa. I propose a policy which respects and values the autonomy of the progenitors’ choices (provided they have not been coerced) and which focuses on the beneficence of the greater society. Furthermore, it is paramount that the goal of any stem cell research should be for therapeutic use ONLY. Before commencing with the extraction of the stem cells, scientists should be obligated first to present convincing evidence that they have tried alternative ways to reach the same result. Once this has been proven, a regulatory body could issue the scientist/team with a license to undertake the specific research with a specific therapy as goal in order to prevent abuse. If they are found guilty of any unethical conduct their licenses should be revoked and an investigation launched.