In the preimplantation mouse embryo, the protein kinase C (PKC) family has been implicated in regulation of egg activation, progression of meiotic and mitotic cell cycles, embryo compaction, and blastulation, but the involvement of the individual isozymes is largely unknown. Here, using semiquantitative immunocytochemistry and confocal microscopy we analyze the relative amount and subcellular distribution of ten isozymes of PKC (a, bI, bII, g, d, 1, h, u, z, i/l) and a PKC-anchoring protein, receptor for activated C-kinase 1 (RACK1). Our results show that all of these isoforms of PKC are present between the twocell and blastocyst stages of mouse preimplantation development, and that each has a distinct, dynamic pattern and level of expression. The data suggest that different complements of the isozymes are involved in various steps of preimplantation development, and will serve as a framework for further functional studies of the individual isozymes. In particular, there was a transient increase in the nuclear concentration of several isozymes at the early four-cell stage, suggesting that some of the PKC isozymes might be involved in regulation of nuclear organization and function in the early mouse embryo.

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