Little is known of molecular requirements for specification of human germ cells. However, it is likely that they are specified through the action of sequentially expressed genes just as in model organisms. We sought to determine whether human embryonic stem (ES) cell lines, like those of mice, might be capable of forming germ cells in vitro. We compared transcriptional profiles of three pluripotent human ES cells to those of isolated inner cell mass (ICM) cells. We found that ICM cells expressed NANOS1, STELLAR and OCT4, whereas undifferentiated human ES cells expressed these genes along with the germ cell-specific gene, DAZL. Upon ES cell differentiation into embryoid bodies (EBs), we observed a shift in expression from RNA and protein markers of immature germ cells to those indicative of mature germ cells, including expression of VASA, BOL, SCP1, SCP3, GDF9 and TEKT1. Although ability to test the function of these putative VASA positive germ cells is limited, these results demonstrate that differentiation of human ES cells into EBs in vitro results in formation of cells that express markers specific to gonocytes.
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The authors thank Christa Heyting for the SCP3 antisera, Joanna Gonsalves for assistance with SCP3 and MLH1 staining, Juanito Menses for isolation of ICM cells, and Robert Taylor, Richard Weiner, Joanna Gonsalves, Frederick Moore, Joyce Tung and Eugene Xu for helpful comments on the manuscript. We are indebted to Dr Marcelle I. Cedars for her expertise and provision of tissue samples from patients, with informed consent. This work was supported by National Institutes of Health grants from the National Institute of Child Health and Human Development (Grant RO1-HD37095) and the Sandler Family Foundation to RARP.