DIFFERENTIAL GROWTH OF THE MOUSE PREIMPLANTATION EMBRYO IN CHEMICALLY-DEFINED MEDIA

We have recently reported the use of sequential simplex optimization m ethods to design a medium (SOM) that overcomes the block to developmen t beyond two cells which occurs in vitro in embryos from an outbred st rain of mouse. We have examined this medium and several others for the ir ability to foster development of CFl female x BGD2Fl male mouse emb ryos through the blastocyst stage. A modification of medium SOM, desig nated KSOM, with an increased concentration of K+ (2.5 mM), also suppo rts growth beyond the two-cell block; compared to other media tested i t produces a higher rate of compaction (100%), provides a larger yield of blastocysts (88%), and stimulates an increased rate of cell divisi on of the trophoblast cells. The total cell number of KSOM-cultured bl astocysts (44 +/- 12; n = 30) indicates that 5-6 cell divisions are po ssible when embryos are cultured for 36 h from pronuclear zygotes. Thi s is a significant improvement in performance over that of other defin ed media for the culture of zygotes to blastocysts.