GM-CSF perturbs cell identity in mouse pre-implantation embryos.

Growth factors became attractive candidates for medium supplementation to further improve the quality of embryo culture and to mimic in vivo nutrition. Granulocyte macrophage colony-stimulating factor (GM-CSF) is a cytokine influencing the maternal-fetal interface and supporting placental development in mouse and human. It is expressed in epithelial cells of the endometrium under the regulation of estrogens. The factor is already in clinical use and a large clinical trial showed that, if supplemented to an embryo culture medium, it leads to increased survival of embryos, especially in women with previous miscarriages. Animal and cell culture studies on isolated trophectoderm cells support an effect mainly on cellular expansion. Aim of this study was to investigate, if the supplementation of GM-CSF either in a human ART medium or in a mouse optimized medium, leads to a change in cell number and cell lineages in the early pre-implantation mouse embryo. Our data shows that mouse GM-CSF increased total cell numbers with increasing concentrations. This increase of cell number has not been found in embryos cultured in ART media with or without human GM-CSF (hGM-CSF) or in a mouse medium supplemented with different concentrations of hGM-CSF. The changes were caused by a marked difference in TE and primitive endoderm cell numbers but not due to a change in epiblast cell numbers. Additionally, results show an ectopic expression of NANOG among trophectoderm cells in both, human ART media (with and without GM-CSF) and at increasing concentrations in the mouse and the human GM-CSF supplemented media. In conclusion, we could show that GM-CSF has an effect on cell identity in mice, which might probably also occur in the human. Therefore, we would like to rare awareness that the use of supplements without proper research could bare risks for the embryo itself and probably also in the post-implantation phase.

The C-X-C signalling system in the rodent vs primate testis: impact on germ cell niche interaction.

In zebrafish, action of the chemokine Cxcl12 is mediated through its G-protein-coupled seven-transmembrane domain receptor Cxcr4 and the atypical receptor Cxcr7. Employing this animal model, it was revealed that this Cxcl12 signalling system plays a crucial role for directed migration of primordial germ cells (PGC) during early testicular development. Importantly, subsequent studies indicated that this regulatory mechanism is evolutionarily conserved also in mice. What is more, the functional role of the CXCL12 system does not seem to be limited to early phases of testicular development. Data from mouse studies rather demonstrate that CXCL12 and its receptors are also involved in the homing process of gonocytes into their niches at the basal membrane of the seminiferous tubules. Intriguingly, even the spermatogonial stem cells (SSCs) present in the adult mouse testis appear to maintain the ability to migrate towards a CXCL12 gradient as demonstrated by functional in vitro migration assays and in vivo germ cell transplantation assays. These findings not only indicate a role of the CXCL12 system throughout male germ cell development in mice but also suggest that this system may be evolutionarily conserved. In this review, we take into account the available literature focusing on the localization patterns of the CXCL12 system not only in rodents but also in primates, including the human. Based on these data, we discuss whether the CXCL12 system is also conserved between rodents and primates and discuss the known and potential functional consequences.