The effect of protein supplementation on single-cell mouse embryos in vitro

For determination of the effect of protein supplementation on single-cell mouse embryos in vitro, 842 single-cell embryos were cultured initially in protein-free medium for variable periods of time and then transferred to bovine serum albumin (BSA)-supplemented medium. The embryos cultured for 24 hours or longer in protein-free medium demonstrated significantly reduced growth rates. An additional 770 embryos were cultured in BSA-supplemented medium initially and then transferred to human fetal cord serum (HCS)-supplemented medium. Significantly reduced growth rates were observed when transfer from BSA to HCS occurred at 48 hours or earlier, and an increased hatching rate was seen if culture in BSA-supplemented medium continued for up to 57 hours. Another 492 embryos were cultured in HCS-supplemented medium and then transferred to BSA. Significantly reduced growth rates were observed when the transfer occurred at 24 hours or later. HCS was then separated by ultrafiltration (10,000 mol wt cutoff), and 1109 embryos were cultured in the media with BSA, whole HCS, small molecular weight fraction (SMCS), or large molecular weight fraction (LMCS) of HCS or BSA and SMCS. The embryos cultured with SMCS demonstrated a significantly reduced growth rate even if BSA was added in the medium. In summary, it appears that the type and timing of protein supplementation of the culture medium is important to embryo growth. Moreover, it seems that serum contains properties that may even be toxic to embryo survival in vitro.