Embryonic stem cell-derived cardiomyocytes (ESC-CMs) have applications in understanding cardiac disease pathophysiology, pharmacology and toxicology. However, a comprehensive characterisation of their basic physiological and pharmacological properties is critical in determining their suitability as models of cardiac activity.Initially, video microscopy and motion analysis software were used to investigate the responses of mouse ESC-derived beating bodies (BBs) to isoprenaline (Iso) and the cardio-active peptides angiotensin II (Ang II) and endothelin-1 (ET-1). Whilst all of these agonists mediated changes in contraction amplitude, indicating the presence of functional ß-adrenoceptor, ETA, AT1 and AT2 receptors, the BBs could be divided on the basis of their contraction frequency responses to the peptide agonists, Ang II and ET-1. This indicated functional heterogeneity amongst the pacemaker cells within the differentiated CM population.An Nkx2.5-eGFP ESC reporter cell line was used to facilitate the isolation of pacemaker cells of the cardiac lineage through live single cell high acquisition rate calcium imaging. Multiple kinetically distinct, previously unreported intracellular Ca2+ ([Ca2+]i) waveforms were observed, most of which were markedly sensitive to reactive oxygen species generation during confocal imaging. By modifying the imaging medium to contain an anti-oxidant cocktail, the activities of six distinct [Ca2+]i waveforms were preserved. On the basis of their kinetics and immunocytochemical profiles, the single cells exhibiting these distinct [Ca2+]i waveforms could be crudely localised to specific regions of the secondary cardiac conduction system. Through investigation of [Ca2+]i handling mechanisms, as well as responsiveness to various cardio-active agonists, this study has demonstrated that automaticity in different spontaneously active Nkx2.5-eGFP+ pacemaker-like populations is governed by varying mechanisms and each population exhibits distinct agonist response profiles.Through collaboration with David Elliott at the Monash Immunology and Stem Cell Laboratories, the pharmacological modulation and [Ca2+]i handling properties of NKX2.5-GFP+ human ESC-BBs was investigated. Only a maximum of 60% of BBs responded to Iso, carbachol, Ang II and ET-1. Investigation of second messenger signalling activation indicated that this was due to ineffective receptor-second messenger coupling during early differentiation stages. Furthermore, confocal calcium imaging on sorted, spontaneously active NKX2.5-GFP+ hESC-cardiac cells indicated the presence of a single, homogeneous pacemaker-like population within these BBs. Unlike the mESC-derived cardiac system, the human BBs were differentiated using a defined exogenous growth factor induced approach which may have biased the differentiation of a particular cardiac conduction system cell type. The signalling cues required for the differentiation of these distinct cardiac subpopulations is under continued investigation.Due to the technical challenges of their investigation from in vivo sources, little is known regarding the function of secondary cardiac conduction system cells, particularly with respect to the mechanisms by which arrhythmias manifest themselves. The ability to isolate and characterise distinct populations of the cardiac conduction system is, therefore, highly clinically relevant. The results from this thesis provide strong support for the potential use of ESCs in conduction system disease modelling, as well as drug discovery and screening platforms.

Since the first successful isolation and cultivation of human embryonic stem cells at the University of Wisconsin, Madison in 1998, there has been high levels of both interest and controversy in this area of research. This book provides a concise overview of an exciting field, covering the characteristics of both human embryonic stem cells and pluripotent stem cells from other human cell lineages. The following chapters describe state-of-the-art differentiation and characterization of specific ectoderm, mesoderm and endoderm-derived lineages from human embryonic stem cells, emphasizing how these can be used to study human developmental mechanisms. A further chapter discusses genetic manipulation of human ES cells. The concluding section covers therapeutic applications of human ES cells, as well as addressing the ethical and legal issues that this research have raised.

This volume covers all aspects of embryonic stem cell differentiation, including mouse embryonic stem cells, mouse embryonic germ cells, monkey and human embryonic stem cells, and gene discovery.* Early commitment steps and generation of chimeric mice* Differentiation to mesoderm derivatives* Gene discovery by manipulation of mouse embryonic stem cells