During mouse preimplantation development, two isozymes of protein kinase C (PKC), d and 1, transiently localize to nuclei at the early four-cell stage. In order to study their functions at this stage, we altered the subcellular localization of these isozymes (ratio of nuclear to cytoplasmic concentrations) with peptides that specifically activate or inhibit translocation of each isozyme. The effects of altering nuclear concentration of each isozyme on transcription (5-bromouridine 5’-triphosphate (BrUTP) incorporation), amount and distribution of small nuclear ribonucleoproteins (snRNPs), nucleolar dynamics (immunocytochemistry for Smith antigen (Sm) protein) and the activity of embryonic alkaline phosphatase (EAP; histochemistry) were examined. We found that nuclear concentration of PKC 1 correlated with total mRNA transcription. Higher nuclear concentrations of both PKC d and 1 decreased storage of snRNPs in Cajal bodies and decreased the number of nucleoli, but did not affect the nucleoplasmic concentration of snRNPs. Inhibiting translocation of PKC d out of the nucleus at the early four-cell stage decreased cytoplasmic EAP activity, whereas inhibiting translocation of PKC 1 increased EAP activity slightly. These results indicate that translocation of PKC d and 1 in and out of nuclei at the early four-cell stage in mice can affect transcription or message processing, and that sequestration of these PKC in nuclei can also affect the activity of a cytoplasmic protein (EAP).

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