Granulocyte-macrophage colony-stimulating factor promotes glucose transport and blastomere viability in murine preimplantation embryos

Granulocyte-macrophage colony-stimulating factor (GMCSF) secretion from epi thelial cells lining the female reproductive tract is induced during early pregnancy by ovarian steroid hormones and constituents of seminal plasma. I n this study we have investigated the influence of CM-CSF on development of preimplantation mouse embryos. Blastocyst-stage embryos were found to spec ifically bind I-125-GM-CSF and analysis of CM-CSF mRNA receptor expression by reverse transcriptase-polymerase chain reaction indicated expression of the low-affinity alpha subunit of the CM-CSF receptor, but not the affinity -converting beta subunit (beta (c)), or GM-CSF ligand. GM-CSF receptor mRNA was present in the fertilized oocyte and all subsequent stages of developm ent, and in blastocysts it was expressed in both inner cell mass and trophe ctoderm cells. In vitro culture of eight-cell embryos in recombinant CM-CSF accelerated development of blastocysts to hatching and implantation stages , with a maximum response at a concentration of 2 ng/ml (77 pM). Blastocyst s recovered from CM-CSF-null mutant (GM-/-) mice on Day 4 of natural pregna ncy or after superovulation showed retarded development, with the total cel l number reduced by 14% and 18%, respectively, compared with GM+/+ embryos. Blastocysts generated in vitro from two-cell GM-/- and GM+/+ embryos were larger when recombinant GM-CSF was added to the culture medium (20% and 24% increases in total cell numbers in GM+/+ and GM-/- blastocysts, respective ly). Incubation of blastocysts with recombinant GM-CSF elicited a 50% incre ase in the uptake of the nonmetabolizable glucose analogue, 3-O-methyl gluc ose. In conclusion, these data indicate that GM-CSF signaling through the l ow-affinity CM-CSF receptor in blastocysts is associated with increased glu cose uptake and enhanced proliferation and/or viability of blastomeres. Tog ether, the findings implicate a physiological role for maternal tract-deriv ed GM-CSF in targeting the preimplantation embryo, and suggest that defecti ve blastocyst development contributes to compromised pregnancy outcome in G M-CSF-null mutant mice.