Nuclear Dynamics and Its Timing Regulation Revealed by Live-Cell Imaging.

Time is an important physical factor controlling all biological phenomena. Within the short period from fertilization to preimplantation, various events occur in a timely manner. A rapid replication of the genome and extensive epigenetic reprogramming occur concomitantly during the transformation from gametes to totipotent zygotes and differentiated cells. In the nuclei, large-scale changes such as genome replication and chromosome segregation progress within a short time. Simultaneously, classical epigenetic information, including histone modifications and DNA methylation patterns, is dynamically remodeled. During this period, the genome, including chromatin architecture and nuclear positioning of gene loci, is under strict control. Recently, single-cell omics analyses and high-throughput chromosome conformation capture (Hi-C) data have provided locus-level resolution of these genomic structures. These global changes inside and outside the cell nuclei occur across several species; however, differences in timing exist because of interspecies variation in developmental speed. In this chapter, we describe the history of research on these spatiotemporal changes inside and outside cell nuclei and present live-cell imaging technology as an important tool for the quantitative analysis of these phenomena.