Protein alterations associated with N‐methyl‐N‐nitrosourea exposure of preimplantation mouse embryos transferred to surrogate mothers

Mouse preimplantation embryo functions have been shown to be disrupted by in vitro exposure to N‐methyl‐N‐nitrosourea (MNU) with subsequent transfer to the uteri of pseudopregnant surrogate mothers. Increased gross malformations and decreased fetal body lengths in the midgestational period have been previously documented. Protein extracts were isolated from day 12 mouse fetuses developed from MNU‐ or solvent‐exposed blastocysts and analyzed by two‐dimensional electrophoresis. The electrophoretic patterns reveal six protein alterations in day 12 fetal tissue induced by MNU treatment at the blastocyst stage. Five of these alterations involve shifts in isoelectric point (pI) and the other alteration involves a quantitative increase in a protein. The possibility that two of the proteins which exhibit a shift in pI following MNU exposure represent the cell adhesion molecules, N‐CAM and L‐CAM (based on similar M_r values), was investigated by Western blot analysis. No pI alteration in L‐CAM or N‐CAM expression is seen after MNU exposure. These results demonstrate that in vitro MNU exposure of preimplantation embryos results in protein alterations in midgestational fetuses. Thus, the effects of MNU exposure on preimplantation embryos may be manifest long after exposure, and subtle, non‐lethal mutations may play a role in poor fetal outcome after early chemical exposure.