LOCALIZATION OF FIBRILLARIN AND NUCLEOLIN IN NUCLEOLI OF MOUSE PREIMPLANTATION EMBRYOS

The localization of fibrillarin and nucleolin in the nuclei of mouse t wo-cell, four-cell, and eight-cell embryos has been studied using immu nofluorescent staining with specific antibodies. In all of these cleav age stages, both antigens were associated exclusively with the periphe ral region of the nucleolus precursor bodies (NPBs). The original spec kled fluorescent staining pattern in the early two-cell stage was prog ressively changed into a continuous fluorescent-positive layer localiz ed in the cortex of the NPBs in the four-cell embryos. The compact cen tral area of NPBs was never stained. Both proteins were colocalized in the same substructures of developing nucleoli. In order to analyze th e interaction of chromatin with NPBs, DNA structures were specifically immunolabelled. At the time of resumption of nucleolar transcription (in the two-cell mouse embryo), DNA was detected at the periphery of, but not penetrating into, NPBs. Our results confirm the view that the cortical region of NPBs could represent a nucleolonemal area involved in the resumption of nucleolar transcription in the early mouse embryo . (C) 1995 Wiley-Liss, Inc.