Nuclear actin and transcriptional activation.

Differentiated cells do not revert to an embryonic state in normal development. However, the method called nuclear reprogramming enables these differentiated cells to be reversed to an embryonic state. One essential event in the reprogramming process is reactivation of embryonic genes such as Oct4 (also known as Pou5f1). This reprogramming of transcriptional programs can be achieved by transplantation of mammalian somatic nuclei to the giant Xenopus laevis oocyte nucleus, referred to as the germinal vesicle (GV). Factors and mechanisms responsible for this transcriptional reprogramming have not been elucidated. Recently, we have found that a polymerized form of actin is abundantly present in nuclei transplanted into the Xenopus oocyte nucleus and plays an important role in transcriptional reactivation of Oct4. This study emphasizes a significant contribution of nuclear actin in transcriptional activation. Here, we discuss possible roles of nuclear actin in Xenopus oocytes and in other cell types in the context of transcriptional activation.