In this study, we tested the role of colony-stimulating factor 2 (CSF2) as one of the regulatory molecules that mediate maternal effects on embryonic development during the preimplantation period. Our objective was to verify effects of CSF2 on blastocyst yield, determine posttransfer survival, and evaluate properties of the blastocyst formed after CSF2 treatment. In vitro, CSF2 increased the percentage of oocytes that became morulae and blastocysts. Blastocysts that were treated with CSF2 tended to have a greater number of inner cell mass cells and had a higher ratio of inner cell mass to trophectoderm cells. There was no effect of CSF2 on the incidence of apoptosis. Treatment with CSF2 from d 5 to 7 after insemination increased embryonic survival as indicated by improved pregnancy rate at d 30-35 of gestation. Moreover, treatment with CSF2 from either d 1-7 or 5-7 after insemination reduced pregnancy loss after d 30-35. Results indicate that treatment with CSF2 can affect embryonic development and enhance embryo competence for posttransfer survival. The fact that treatment with CSF2 during such a narrow window of development altered embryonic function much later in pregnancy suggests that CSF2 may exert epigenetic effects on the developing embryo that result in persistent changes in function during the embryonic and fetal periods of development.

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Embryo cryopreservation has been a useful tool for embryology since the early 1970s. It has become an essential part of assisted reproductive technologies, allowing long term storage of valuable embryos from lab animals, livestock, endangered species and humans. Initially, work was done with conventional slow cooling technologies, using cryoprotectants, such as glycerol or ethylene glycol and sucrose. More recently, however, greater advances have been made with vitrification, a procedure that bypasses ice crystal formation and places the embryo in a glass-like state. This technology is receiving greater attention as it is simpler, faster and less expensive, and provides the embryo with greater protection from cryoinjury. Successful cryopreservation requires a good understanding of the proper use of cryoprotectants, sugars, and macromolecules in order to allow the highest survival rates and ultimately pregnancy and live offspring following embryo transfer. Although this technology has been in existence for over three decades, it still yields variable results. It is clear now that success is dependent upon many variables, including embryo stage and quality, embryo species and derivation, cooling and warming rates and culture conditions, to name a few. Efforts to optimize these conditions will further enhance survival and future developmental potential of the embryo. This review will briefly summarize the current understanding of embryo cryopreservation technologies, including key areas of concern and strategies to achieve the greatest successes, as well as possible future directions for this field.

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