The specific aims of our research grant # RC1-00137 entitled “Human Oocyte Development for Genetic, Pharmacological and Reprogramming Applications” are as follows: Aim 1) Assess and compare the potential of multiple nonfederal hESC lines to contribute to the germ cell lineage. Aim 2) Differentiate hESCs to oocytes. Aim 3) Assay the ability of differentiated germ cells to reprogram a somatic nucleus. Historically, it has not been possible to examine the differentiation of human germ cells (the cells that give rise to mature eggs and sperm); however, with the derivation of hESC lines, we sought to determine whether hESCs might provide a system to differentiate human germ cells. Our proposed research plan is based on our initial studies indicating that hESCs provide a useful system. However, it was not clear whether hESC lines differed from each other in terms of differentiation at both the quantitative and qualitative levels. In addition, although a number of labs have reported the differentiation of both mouse and human germ cells, in general only immature germ cells were produced. Finally, we note that a common problem in IVF (in vitro fertilization), is the retrieval of immature oocytes and an inability to mature these oocytes in the clinic. Against this backdrop, in the last funding cycle, we have succeeded in extending our analysis of hESC lines and differentiation of the germ cell lineage to eight independently-derived lines, we have demonstrated that we can modulate germ cell differentiation in vitro to increase numbers of germ cells formed via external and internal cell-based induction, we have succeeded in differentiating germ cells that enter and progress through meiosis (a critical step in the production of mature eggs and sperm), and we have developed the methods to mature human oocytes in vitro and derive hESC lines from single blastomeres. A subset of these findings has been submitted for publication (or is in press) and additional publications are in preparation. These results will shed light on human development and the cell-based decisions to form germ cells versus other cell types of the body (somatic cells) and will potentially contribute to alleviating a common health problem that afflicts 10-15% of couples in California (infertility), as well as forming a foundation for understanding reprogramming in early human development (a process required for normal development that is a basis for development of novel strategies to produce pluripotent stem cell lines).