ATP levels in clone mouse embryos

The transfer of a somatic cell nucleus into an oocyte results in a dramatic change of the transcriptional profile. Although the underlying process of chromatin remodeling after nuclear transfer so far has not been defined at the molecular level, adenosine triphosphate (ATP) is considered a crucial component. In our study, clones were cultured in six media (M16, CZB, KSOM(aa), alpha-MEM, D-MEM, G1/G2) and energy levels compared to fertilized embryos. Our data indicate that nuclear transfer into an oocyte does not cause a significant change of ATP content subsequent to chromatin remodeling and pronucleus-like nucleus formation. During cleavage, while ATP levels of normal embryos were kept within narrow limits, they were less restricted in clones. ATP variability was eminent until the clones reached the blastocyst stage. This profile is consistent with the emerging representation of cleavage-stage clone embryos as mosaics, whereby intra-embryo variations compound inter-embryo variations. The issue of energy in embryos remains a complex one. The existence of multiple and integrated pathways governing the physiology, metabolism and consequently the ATP level of a cell contrasts the single gene readout situation exemplified by Oct4. Such principal differences may explain why Oct4 is a prognostic marker for clones whereas ATP is not. Copyright (C) 2004 S. Karger AG, Basel.