Expression and localization of creatine kinase in the preimplantation embryo

Creatine Kinase (CK) catalyses the "creatine shuttle," the reversible conversion of creatine phosphate to creatine with the liberation of ATP. This article examines the potential role of the creatine shuttle in the provision of ATP during mouse preimplantation embryo development. Using quantitative PCR, transcripts of four subunit isoforms of CK--CKM, CKB, CKMT1, and CKMT2--were detectable at all developmental stages, from the presumptive zygote to late blastocyst, but there was no obvious pattern in gene expression. By contrast, total CK biochemical activity, measured by a novel method, was relatively constant from the 2- to 8-cell stage, before exhibiting a significant decrease in activity at the blastocyst stage. Immunocytochemical studies revealed a marked association of CKB with the mitotic spindle in 2- and 4-cell mouse embryos, consistent with the proposition that the creatine shuttle plays a key role in local delivery of ATP during cytokinesis. Endogenous creatine was detected in the blastocyst at a level of 0.53 pmol/embryo. In conclusion, we believe that creatine phosphate can now be added to the list of potential sources of ATP during preimplantation development.