[Pre-mRNA splicing factors in nuclei of two-cells murine embryos].

The distribution of pre-mRNA splicing factors (snRNPs and SR-protein SC35) was studied in the nuclei of early and late 2-cell mouse embryos using light and electron immunocytochemistry. The splicing factors were shown to be present in the nuclei before the beginning of embryonic transcription. In inactive nuclei of early 2-cell embryos, SR-protein SC35 is concentrated in clusters of intranuclear granules to be absent from the karyoplasm. After the beginning of embryonic transcription activation, concentration of splicing factors in the karyoplasm increases. The data obtained are in accordance with the idea that some particular nuclear domains may be storage sites for pre-mRNA splicing factors for constant recruiting of splicing factors to perichromatin fibrils.