Nuclear Actin in Development and Transcriptional Reprogramming.

Shinji Misu,Kei Miyamoto,Marina Takebayashi

doi:10.3389/fgene.2017.00027

Abstract

Actin is a highly abundant protein in eukaryotic cells and dynamically changes its polymerized states with the help of actin-binding proteins. Its critical function as a constituent of cytoskeleton has been well-documented. Growing evidence demonstrates that actin is also present in nuclei, referred to as nuclear actin, and is involved in a number of nuclear processes, including transcriptional regulation and chromatin remodeling. The contribution of nuclear actin to transcriptional regulation can be explained by its direct interaction with transcription machineries and chromatin remodeling factors and by controlling the activities of transcription factors. In both cases, polymerized states of nuclear actin affect the transcriptional outcome. Nuclear actin also plays an important role in activating strongly silenced genes in somatic cells for transcriptional reprogramming. When these nuclear functions of actin are considered, it is plausible to speculate that nuclear actin is also implicated in embryonic development, in which numerous genes need to be activated in a well-coordinated manner. In this review, we especially focus on nuclear actin’s roles in transcriptional activation, reprogramming and development, including stem cell differentiation and we discuss how nuclear actin can be an important player in development and cell differentiation.

Highlights

Eukaryotic cells have a globular, multifunctional protein called actin
Nuclear actin has attracted a lot of attention, its function has often been regarded as a controversial topic due to the technical difficulties of discriminating nuclear actin from cytoplasmic actin, which is highly abundant in cells
Using the oil germinal vesicle (GV) system, we have shown that perturbation of polymerized states of nuclear actin affects transcriptional reprogramming of Oct4, a key pluripotency gene; namely decreased actin polymerization results in failed activation of Oct4 and increased actin polymerization is associated with enhanced Oct4 expression (Miyamoto et al, 2011)

Summary

Introduction

Eukaryotic cells have a globular, multifunctional protein called actin. Actin plays key roles in the cytoplasm by controlling a dynamic equilibrium between the monomeric and filamentous states for a variety of cellular processes, such as cell motility and adhesion. In addition to these functions of actin to support fundamental nuclear processes, nuclear actin influences cellular phenotypes through transcriptional regulation and chromatin alternation, exemplified by transcriptional activation of the osteogenic genes in differentiating mesenchymal stem cells (MSCs; Sen et al, 2015) or by reorganization of heterochromatin during lineage commitment of epidermal stem cells (Le et al, 2016) (Figure 2).

Results

Conclusion