CSF-1 and mouse preimplantation development in vitro.

The effects of macrophage colony stimulating factor on the development of the zygote to the blastocyst stage of an outbred strain of mouse have been studied in KSOM, an improved medium that supports a high rate of in vitro development. Macrophage colony stimulating factor accelerates the formation of the blastocyst cavity by day 4 (96 hours post-hCG). It also increases overall embryonic cell number through a differential increase in the number of trophoblast cells, with no significant effect on the number of inner cell mass cells. By day 5 of culture (120 hours post-hCG), colony stimulating factor-treated embryos have about 20 more trophoblast cells than control embryos, an increase of about 30 percent of the total number of cells in a control blastocyst. The maximum response of embryos was obtained at a concentration around 540 U ml-1 colony stimulating factor (identical to 918 Stanley units ml-1), and the cytokine can produce the same effects even if it is present in the medium for only part of the culture period. This in vitro stimulation of preimplantation development with macrophage colony stimulating factor is compatible with continued normal fetal development in vivo.