Nuclear size plays pivotal roles in gene expression, embryo development, and disease. A central hypothesis in organisms ranging from yeast to vertebrates is that nuclear size scales to cell size. This implies that nuclei may reach steady-state sizes set by limiting cytoplasmic pools of size-regulating components. By monitoring nuclear dynamics in early sea urchin embryos, we found that nuclei undergo substantial growth in each interphase, reaching a maximal size prior to mitosis that declined steadily over the course of development. Manipulations of cytoplasmic volume through multiple chemical and physical means ruled out cell size as a major determinant of nuclear size and growth. Rather, our data suggest that the perinuclear endoplasmic reticulum, accumulated through dynein activity, serves as a limiting membrane pool that sets nuclear surface growth rate. Partitioning of this local pool at each cell division modulates nuclear growth kinetics and dictates size scaling throughout early development.

核大小在基因表达、胚胎发育和疾病中起着关键作用。从酵母到脊椎动物，生物体的一个中心假设是细胞核大小与细胞大小成比例。这意味着细胞核可以通过限制大小调节成分的细胞质池达到稳态大小。通过监测早期海胆胚胎的核动力学，我们发现细胞核在每个间期都经历了大量增长，在有丝分裂之前达到最大尺寸，在发育过程中稳步下降。通过多种化学和物理手段操纵细胞质体积排除了细胞大小作为核大小和生长的主要决定因素。相反，我们的数据表明，通过动力蛋白活动积累的核周内质网，用作设置核表面生长速率的限制性膜池。在每次细胞分裂时划分这个局部池会调节核生长动力学，并决定整个早期发育过程中的大小缩放。