The F-act's of nuclear actin.

The presence and state of actin in the nucleus has long been controversial. This is poised to change. Over the past two years, the regulation of nuclear actin and its polymerization have begun to be characterized. The transport of actin into and out of the nucleus has been defined and the importance of nuclear actin polymerization in the retention of the serum response factor coactivator MRTF-A is now quite clear. Moreover, serum-starved fibroblasts that are stimulated with serum rapidly form long actin bundles that can be visualized using the F-actin binding drug phalloidin. This provides the first compelling direct evidence that actin polymerizes in the nucleus and provides the foundation for a serious investigation of the function(s) of nuclear polymeric actin. [ABSTRACT FROM AUTHOR]