Until recently it was widely accepted that the dynamic cytoskeletal matrix is 
exclusive to the cytoplasm of eukaryotes, evolving before the emergence of the 
cell nucleus to enable phagocytosis, cell motility and the sophisticated 
functioning of the endomembrane system within the cytosol. The discovery of the 
existence of a prokaryotic cytoskeleton has changed this picture significantly. 
As a result, the idea has taken shape that the appearance of actin occurred in 
the very first cell; therefore, the emergence of microfilaments precedes that of 
the eukaryotic cytoskeleton. The discovery of nuclear actin opened new 
perspective on the field, suggesting that the nuclear activities of actin 
reflect the functions of primordial actin-like proteins. In this paper, we 
review the recent literature to explore the evolutionary origin of nuclear 
actin. We conclude that both ancient and eukaryotic features of the actin world 
can be detected in the nucleus today, which supports the idea that the 
cytoskeleton attained significant eukaryotic innovations before the tandem 
evolution of the cytoskeleton and nucleus occurred.