The rationale for adding GM-CSF to culture media
To validate the rationale for adding GM-CSF to culture media, it is necessary to demonstrate its secretion into the reproductive tract. Also, it is necessary to demonstrate the presence of GM-CSF receptors on embryos and the dependence of embryo development and viability upon GM-CSF.
In this respect, GM-CSF has been shown to be produced and secreted from the human oviductal and endometrial epithelium.3,4 Levels of GM-CSF reach a peak during the secretory phase of the menstrual cycle4,5, which coincides with the time of conception and implantation.
The GM-CSF receptor is a dimer comprised of a cytokine-specific alpha subunit (GM-Rα) and a signal transducing beta subunit (βc), βc forming a high-affinity complex with ligand-coupled GM-Rα.6 However, GM-Rα can also act alone, for example, to mediate the effect of GM-CSF on glucose transport via a kinase-independent pathway.7 Indeed, GM-CSF has been shown to promote glucose transport in the embryo, which expresses the GM-Rα receptor throughout preimplantation development.8,9