Amino acids and preimplantation development of the mouse in protein-free potassium simplex optimized medium

Development of outbred CF1 mouse zygotes in vitro was studied in a chemical ly defined, protein-free medium both with and without amino acids. The addi tion of amino acids to protein-free potassium simplex optimized medium (KSO M) had little effect on the proportion of embryos that developed at least t o the zona-enclosed blastocyst stage. In contrast, amino acids stimulated v ery significantly, in a dilution-dependent way, the proportion of blastocys ts that at least partially or completely hatched. Amino acids also stimulat ed cell proliferation in both the trophectoderm and inner cell mass (ICM) c ells, at rates that favored proliferation of cells in the ICM; had no effec t on the incidence of cell death (oncosis or apoptosis); and improved devel opment of the basement membranes, which form on the blastocoelic surface of the trophectoderm and between the primitive endoderm and the primitive ect oderm, Thus, KSOM, supplemented with amino acids but containing no protein supplements, supports development of a newly fertilized ovum to the late bl astocyst stage, in which its normal, three-dimensional structure is preserv ed and in which the ICM has been partitioned into the primitive ectoderm an d primitive endoderm.