Nucleomorphin: a nucleolar calmodulin binding protein that regulates nuclear number

核仁是细胞核中的一个特殊区域，是正常细胞和癌细胞分裂的中心控制元件。最初被认为只是一个核糖体工厂，现在已知它还有许多其他关键功能。它参与细胞周期、生命周期、病毒复制、分子隔离和应激反应等活动。我们已经发现并研究了盘基网柄菌中一种名为核仁蛋白(NumA1)的核仁蛋白。网柄网柄菌是细胞和发育生物学研究的模式生物。NumA1现在是网柄基菌中研究最充分的核仁蛋白。像人类的核仁蛋白一样，NumA1具有核仁和核定位信号以及广泛的酸性氨基酸(谷氨酸/天冬氨酸)。当这种酸性氨基酸序列被移除时，细胞变得高度多核。细胞通常只有一个核，这表明NumA1参与了核数量的调节。NumA1通过这种酸性延伸与钙结合蛋白(CBP4a)以钙依赖的方式结合，表明它也参与了NumA1的功能。我们将敲除CBP4a的基因，以了解它在调节核数量和其他细胞功能中的作用。在其他物种中，核仁蛋白在核仁、核质和细胞质之间来回移动，但这一过程的确切控制方式仍然难以捉摸。我们将研究NumA1的磷酸化以及它的核仁和核定位信号，以确定这是否是控制这种易位的原因。与相关实验一起，这项工作将在两种核仁蛋白在细胞功能中的作用以及如何调节核数方面取得重大进展。从长远来看，我们相信这将为利用网柄基底菌作为研究所有生物体中核仁结构和功能的模型系统奠定基础。

The nucleolus is a special compartment in the cell nucleus that is a central controlling element in cell division of normal and cancer cells. Originally considered simply a ribosome factory it now is known to have many other critical functions. It is involved in the cell cycle, life span, viral replication, molecular sequestering, and stress responses, among other activities. We have discovered and have studied a nucleolar protein called nucleomorphin (NumA1) in Dictyostelium discoideum. Dictyostelium is recognized as a model organism for the study of cell and developmental biology. NumA1 now represents the most well studied nucleolar protein in Dictyostelium. Like nucleolar proteins in humans, NumA1 has nucleolar and nuclear localization signals plus an extensive stretch of acidic amino acids (glutamic acid/aspartic acid). When this acidic amino acid sequence is removed, the cells become highly multinucleated. Cells typically have a single nucleus suggesting NumA1 is involved in the regulation of nuclear number. NumA1 binds to calcium binding protein (CBP4a) in a calcium-dependent manner via this acidic stretch of acids suggesting it too is involved in NumA1 function. We will knockout the gene for CBP4a to learn what its role is in regulating nuclear number and in other cell functions. In other species, nucleolar proteins move back and forth between the nucleolus, nucleoplasm and cytoplasm but exactly how this is controlled remains elusive. We will study the phosphorylation of NumA1 as well as its nucleolar and nuclear localization signals to determine if this is what controls this translocation. Along with related experiments, this work will provide major advances into the roles of two nucleolar proteins in cell function and in how nuclear number is regulated. In the long term, we believe it will set the stage for using Dictyostelium as a model system for the study of nucleolar structure and function in all organisms.