Department of Genetics, Davison Life Sciences Complex, University of Georgia, Athens, Georgia 30602, USA.
Cytoskeleton (Hoboken). 2010 Nov;67(11):729-43. doi: 10.1002/cm.20484.
Conventional actin has been implicated in various nuclear processes including chromatin remodeling, transcription, nuclear transport, and overall nuclear structure. Moreover, actin has been identified as a component of several chromatin remodeling complexes present in the nucleus. In animal cells, nuclear actin exists as a dynamic equilibrium of monomers and polymers. Actin-binding proteins (ABPs) such as ADF/cofilin and profilin play a role in actin import and export, respectively. However, very little is known about the localization and roles of nuclear actin in plants. In multicellular plants and animals, actin is comprised of an ancient and divergent family of protein variants. Here, we have investigated the presence and differential localization of two ancient subclasses of actin in isolated Arabidopsis nuclei. Although the subclass 1 variants ACT2 and ACT8 and subclass 2 variant ACT7 were found distributed throughout the nucleoplasm, ACT7 was often found more concentrated in nuclear speckles than subclass 1 variants. The nuclei from the act2-1/act8-2 double null mutant and the act7-5 null mutant lacked their corresponding actin variants. In addition, serial sectioning of several independent nuclei revealed that ACT7 was notably more abundant in the nucleolus than the subclass 1 actins. Profilin and ADF proteins were also found in significant levels in plant nuclei. The possible functions of differentially localized nuclear actin variants are discussed.
传统肌动蛋白参与了多种核过程，包括染色质重塑、转录、核运输和整体核结构。此外，肌动蛋白已被确定为存在于核内的几种染色质重塑复合物的组成部分。在动物细胞中，核肌动蛋白存在于单体和聚合物的动态平衡中。肌动蛋白结合蛋白（ABP），如 ADF/丝切蛋白和原肌球蛋白，分别在肌动蛋白的输入和输出中发挥作用。然而，对于植物中核肌动蛋白的定位和作用知之甚少。在多细胞植物和动物中，肌动蛋白由一个古老且分化的蛋白变体家族组成。在这里，我们研究了分离的拟南芥核中两种古老肌动蛋白亚类的存在和差异定位。尽管亚类 1 变体 ACT2 和 ACT8 和亚类 2 变体 ACT7 分布在整个核质中，但 ACT7 通常比亚类 1 变体更集中在核斑点中。来自 act2-1/act8-2 双突变体和 act7-5 突变体的核缺乏相应的肌动蛋白变体。此外，对几个独立核的连续切片显示，ACT7 在核仁中的丰度明显高于亚类 1 肌动蛋白。原肌球蛋白和 ADF 蛋白也在植物核中以相当高的水平存在。讨论了差异定位的核肌动蛋白变体的可能功能。
