Defects in germ-cell (oocyte and sperm) development are a leading cause of infertility in men and women. Several studies have shown that germ cells can be differentiated from mouse and human embryonic stem cells, but human germ cells produced in this way generally fail to develop beyond the earliest stages and do not enter meiosis. Now a team from Stanford's Institute for Stem Cell Biology and Regenerative Medicine has developed a system in which primordial germ cells can be derived from both male and female human embryonic stem cells. By silencing and overexpressing germ-cell-specific genes, human germ-cell formation and developmental progression can be modulated. Specifically, the human DAZL gene, which is implicated in infertility, is shown to function in primordial germ-cell formation, whereas closely related family members, DAZ and BOULE, modulate later stages of meiosis and development of haploid male gametes. This system can be used to study germ-cell defects and the potential to correct them therapeutically. Defects in human germ-cell (oocyte and sperm) development are the leading cause of infertility in men and women. A germ-cell reporter is now used to quantify and isolate primordial germ cells derived from both male and female human embryonic stem cells. Human DAZL is observed to function in primordial germ-cell formation, whereas the closely related genes DAZ and BOULE promote later stages of meiosis and development of gametes. The leading cause of infertility in men and women is quantitative and qualitative defects in human germ-cell (oocyte and sperm) development. Yet, it has not been possible to examine the unique developmental genetics of human germ-cell formation and differentiation owing to inaccessibility of germ cells during fetal development. Although several studies have shown that germ cells can be differentiated from mouse and human embryonic stem cells, human germ cells differentiated in these studies generally did not develop beyond the earliest stages1,2,3,4,5,6,7,8. Here we used a germ-cell reporter to quantify and isolate primordial germ cells derived from both male and female human embryonic stem cells. By silencing and overexpressing genes that encode germ-cell-specific cytoplasmic RNA-binding proteins (not transcription factors), we modulated human germ-cell formation and developmental progression. We observed that human DAZL (deleted in azoospermia-like) functions in primordial germ-cell formation, whereas closely related genes DAZ and BOULE (also called BOLL) promote later stages of meiosis and development of haploid gametes. These results are significant to the generation of gametes for future basic science and potential clinical applications.

Historically, our understanding of molecular genetic aspects of human germ cell development has been limited, at least in part due to inaccessibility of early stages of human development to experimentation. However, the derivation of pluripotent stem cells may provide the necessary human genetic system to study germ cell development. In this study, we compared the potential of human induced pluripotent stem cells (iPSCs), derived from adult and fetal somatic cells to form primordial and meiotic germ cells, relative to human embryonic stem cells. We found that ∼5% of human iPSCs differentiated to primordial germ cells (PGCs) following induction with bone morphogenetic proteins. Furthermore, we observed that PGCs expressed green fluorescent protein from a germ cell-specific reporter and were enriched for the expression of endogenous germ cell-specific proteins and mRNAs. In response to the overexpression of intrinsic regulators, we also observed that iPSCs formed meiotic cells with extensive synaptonemal complexes and post-meiotic haploid cells with a similar pattern of ACROSIN staining as observed in human spermatids. These results indicate that human iPSCs derived from reprogramming of adult somatic cells can form germline cells. This system may provide a useful model for molecular genetic studies of human germline formation and pathology and a novel platform for clinical studies and potential therapeutical applications.

The growth factors bone morphogenetic protein-4 (BMP4), BMP7, and BMP8b are required for specification of primordial germ cells (PGCs) in mice. Disruption of the genes that encode these factors leads to a severe reduction in number, or the complete absence, of PGCs. In addition, several studies have demonstrated that human BMP4 can promote PGC differentiation from mouse embryonic stem (ES) cells and in organ cultures. Here, we sought to determine whether recombinant human BMPs could induce differentiation of germ cells from human (h) ES cells. We found that addition of recombinant human BMP4 increased the expression of the germ cell-specific markers VASA and SYCP3 during differentiation of hES cells to embryoid bodies (EBs). In addition, BMP7 and BMP8b showed additive effects on germ cell induction when added together with BMP4. Finally, we observed that addition of BMPs to differentiating ES cells also increased the percentage of cells that stained positively for VASA. We note that the effects of recombinant BMPs were modest but reproducible and suggest that addition of BMPs to differentiation media increases differentiation of human germ cells from hES cells.