Embryoid bodies from human embryonic stem cells form a niche for male germ cell development in vitro

Determining the mechanism of human primordial germ cell (PGC) and gamete development is important for understanding the causes of infertility, effects of chemicals on reproductive development and cancer: and may eventually lead to new clinical applications. Germ cells can be derived from mouse and human embryonic stem cells (hESCs) although the proportion of cells undergoing meiosis is very low. HESCs were differentiated as embryoid bodies (EBs) in various culture media supplemented with growth factors [e.g. BMP4 retinoic acid (RA)] or conditioned with primary cells [e.g. neonatal mouse testis (NMT)]. EBs were analysed for germ cell development and culture media collected for analysis of steroid hormone secretion. Gene expression profiles (Q-PCR) revealed a consistent pattern in keeping with PGC formation and germ cell development. A small population of post-meiotic spermatid cells were identified using sperm-specific antibodies. Although gene expression of egg development and follicle-like structures was determined, oocytes with extra-cellular zona pellucida (ZP) were not detected using ZP-specific monoclonal antibody. Small. but significant levels of oestradiol (4 pg/ml) and dihydrotestosterone (30 pg/ml) were secreted into culture medium of EBs after 14 days development. We conclude that hESCs can form PGCs and post-meiotic spermatids in vitro, but there remains some doubt about egg development. The level of steroid hormones produced by EBs was significant for the quantity of cells and suggests that hESCs may create a favourable hormonal niche for spermatogenesis.