One-step versus two-step culture of mouse preimplantation embryos: is there a difference?

BACKGROUND: A comparison has been made of the development of mouse zygotes in either one-step or two-step culture systems. METHODS: Embryo culture, blastocyst cell counts and embryo transfer were done. RESULTS: No significant differences were observed in the proportions of blastocysts, rates of hatching, numbers of cells in the inner cell mass (ICM) and trophectoderm (TE) that developed in protocols: one-step culture in potassium-enriched simplex optimized medium supplemented with glucose and amino acids (KSOMgAA), two-step culture in KSOMgAA/KSOMgAA, and two-step culture in G1.2/G2.2. No gross abnormalities were observed in the fetuses that developed from zygotes in the one-step protocol using KSOMgAA and a two-step protocol using G1.2/G2.2. The body weights of these two groups of fetuses were not significantly different and no developmental abnormalities were observed. No significant differences were observed in the proportions of blastocysts, rates of hatching, numbers of cells in the ICM and TE that developed in protocols: one-step culture in KSOMgAA, two-step culture in KSOMgAA/KSOMgAA, and two-step culture in DM2/DM1. EDTA is not toxic to the initial cleavage stages of development at a concentration of 0.01 mmol/l in KSOMgAA. CONCLUSIONS: Two-step culture protocols are sufficient for the support of preimplantation mouse development in vitro but they are not necessary.