REDISTRIBUTION OF NUCLEAR ANTIGENS LINKED TO CELL-PROLIFERATION AND RNA PROCESSING IN MOUSE OOCYTES AND EARLY EMBRYOS

We have systematically analyzed by indirect immunofluorescence the sub cellular distribution of nuclear antigens in relation to developmental stages of maturing mouse oocytes and developing embryos. Antigens wer e of two types: (1) a protein whose nuclear localization in interphase somatic cells depends on their proliferative state protein recognized by a monoclonal antibody 43B1N, and (2) snRNP polypeptides recognized by autoimmune sera of anti-Sm and anti-RNP type. The protein recogniz ed by 43B1N was present in the germinal vesicle of oocytes from antral follicles, but absent from the nuclei during the first hours of embry onic life up to the middle to late 2-cell stage. Starting from this st age, it was always found in nuclei of interphase blastomeres, where it s ''speckles'' co-localized with the speckles containing high concentr ations of snRNP polypeptides. SnRNP polypeptides recognized by anti-Sm and anti-RNP sera were in turn found in nuclei of all developmental s tages. When embryos were treated with aphidicolin or cytochalasin D to arrest cell division, the 43B1N reacting protein was again localized in the pronuclei at 42 hr post-hCG, i.e., slightly later than the onse t of transcriptional activity. These results suggest a progressive bui lding up of nuclei during embryonic development, which could influence gene expression. (C) 1994 Wiley-Liss, Inc.