Cross-species cloning: influence of cytoplasmic factors on development.

It is widely accepted that the crosstalk between naive nucleus and maternal factors deposited in the egg cytoplasm before zygotic genome activation is crucial for early development. This crosstalk may also exert some influence on later development. It is interesting to clarify the relative roles of the zygotic genome and the cytoplasmic factors in development. Cross-species nuclear transfer (NT) between two distantly related species provides a unique system to study the relative role and crosstalk between egg cytoplasm and zygotic nucleus in development. In this review, we will summarize the recent progress of cross-species NT, with emphasis on the cross-species NT in fish and the influence of cytoplasmic factors on development. Finally, we conclude that the developmental process and its evolution should be interpreted in a systemic way, rather than in a way that solely focuses on the role of the nuclear genome.