Development of in-vitro-fertilized primate embryos into blastocysts in a chemically defined, protein-free culture medium.

The formulation of chemically defined culture media that support primate embryo development would facilitate studies on primate preimplantation embryogenesis. The specific aims of this study were (i) to evaluate the development of the macaque embryos in a simple, chemically defined, protein-free medium developed for a rodent embryo model, and (ii) to determine if a two-step progressive culture system could enhance blastocyst development and zona escape. In experiment 1, in-vitro-fertilized pronucleate-stage embryos (n = 81) from nine monkeys were randomly allocated to one of three treatments: (a) hamster embryo culture medium-6 (HECM-6; chemically defined, protein-free medium), (b) CMRL-BCS medium (modified CMRL-1066 medium containing 20% bovine calf serum; BCS), and (c) a two-step culture procedure (HECM-6 through to the 8- to 12-cell stage, and CMRL-BCS medium beyond that stage). Optimal development was attained equally (P > or = 0.05) with embryos cultured in CMRL-BCS medium or the two-step procedure (48 and 61%), but not to the blastocysts respectively). HECM-6 alone supported development to the morula stage (72%) equally as well as CMRL-BCS medium (80%) or the two-step procedure (69%), but not to the blastocyst stage (22 versus 48 and 61% respectively). Hatching of the blastocysts was essentially limited to the serum-containing media (CMRL-BCS medium, 31%; two-step procedure, 44%). In experiment 2, in-vitro-fertilized pronucleate-stage embryos (n = 87) from nine monkeys were randomly placed in each of four two-step treatments: (a) HECM-6 through to the 8- to 12-cell stage and CMRL-BCS medium beyond that stage, (b) HECM-6 through the 8- to 12-cell stage and HECM-6-BCS beyond that stage, (c) HECM-6 through to the morula stage and CMRL-BCS medium beyond that stage, and (d) HECM-6 through to the morula stage and HECM-6-BCS beyond that stage. Greater (P < or = 0.05) percentages of embryos developed into blastocysts, expanded blastocysts and hatched blastocysts when switched at the 8- to 12-cell versus the morula stage in the second step medium. When transferred into BCS-containing medium at either the 8- to 12-cell or morula stage, embryos underwent blastulation and expansion equally well in CMRL-BCS medium versus HECM-6-BCS. However, when embryos were switched to the second step medium at the 8- to 12-cell stage, hatched blastocysts were obtained more (P < or = 0.05) frequently in CMRL-BCS medium (50.9%) than in HECM-6-BCS (37%). This work is the first to produce in-vitro-fertilized primate blastocysts cultured from the pronucleate stage in chemically defined, protein-free medium, and demonstrates that while primate embryos can form morulae in such a medium, their requirements for blastocoel formation and zona escape appear to be more demanding, and may be acquired as early as the 8-cell stage.