Nuclear translocation of nuclear factor kappa B in early 1-cell mouse embryos.

Nuclear factor kappa B (NF-kappaB) is a transcription factor that controls the expression of a number of genes under cellular redox potential. It has recently been found that NF-kappaB plays a pivotal role in morphogenesis and embryonic development, e.g., in formation of Drosophila malanogaster ventral structures and chicken limb buds. However, the role of NF-kappaB in preimplantation development in mammals is not yet understood. In this study, we show that RelA, one of the subunits of NF-kappaB, is expressed in mouse eggs and embryos from the metaphase II (MII) oocyte to the blastocyst stage. Therefore, it is thought that RelA is maternally expressed and that it continues to be expressed during preimplantation development. Immunofluorescence analysis showed that RelA protein was mainly distributed in the cytoplasm of embryos, whereas nuclear translocation of RelA, evidence for NF-kappaB activation, was observed only at the early 1-cell stage. Finally we studied the effects of NF-kappaB inhibitors, pyrrolidine dithiocarbamate and N-acetyl-L-cysteine, on the preimplantation development of mouse embryos. When these inhibitors were added to the culture medium from the early 1-cell stage, subsequent development through the 2-cell stage was inhibited. However, little, if any, influence on the progression through the 2-cell stage was observed when the inhibitors were added at the late 1-cell or the 2-cell stage. Taken together, the results suggest that the activation of NF-kappaB at the early 1-cell stage is required for the development of mouse embryos beyond the 2-cell stage.