While it is long known that actin is part of the nuclear proteome, its 
properties and functions as regulated, functional and dynamically assembled 
actin filaments are only recently emerging. Thus, newly uncovered roles for 
intranuclear actin filaments are opening new perspectives on how the nucleus and 
its genomic content may be organized in particular with regard to a given stage 
of the cell cycle. Here, we summarize recent studies on actin filament 
polymerization and turnover within the nuclear compartment of mammalian cells. 
We emphasize and discuss novel findings, in which transient and dynamic nuclear 
actin filaments have been visualized in physiological contexts, and focus on 
aspects of signalling mechanisms, chromatin reorganization and DNA repair. 
Further, a better understanding of the spatiotemporal control of nuclear 
actin-regulating factors in mammalian cells will ultimately provide a more 
detailed view on how the nuclear F-actin cytoskeleton contributes to genome 
organization and nuclear architecture.