Reduction in chromosome mobility accompanies nuclear organization during early embryogenesis in Caenorhabditis elegans.
Arai R, Sugawara T, Sato Y, Minakuchi Y, Toyoda A, Nabeshima K, Kimura H, Kimura A.
Scientific Reports, 7, 3631 (2017). DOI:10.1038/s41598-017-03483-5
Many of us may imagine the DNA inside our cells as a jumble of noodles. However, DNA is more organized than this inside the nucleus, with chromosomes occupying distinct nuclear territories, for example. It is unclear though whether this organization is always present or whether it appears at some point during development after fertilization of the egg. We studied chromosome organization by observing the mobility of chromosomes inside in the nucleus in developing nematode embryos from the 2-cell to the 48-cell stage. We found that chromosome mobility decreases in 8-cell embryos, suggesting the initiation of chromosome organization at this point. Chromosome organization in the nucleus is important for gene expression and may have other purposes as well. For example, we found that in nematodes, the timing of chromosome organization coincides with the appearance of epigenetic marks, which regulate gene expression, and of a nuclear domain called the nucleolus. Now that we have identified the timeline of nuclear chromosome organization in nematodes, we will be able to conduct future studies to determine the factors responsible for initiating this organization.
Figure. [Left images] Examples of the tracking (lines) of specific chromosomal loci (white dots) at indicated stages. The yellow dot reveals the center of the nucleus (not shown for the 48-cell stage). [Right graph] MSCD (mean squared change in distance) analyses of mobility: MSCD of the loci was plotted against the time interval (τ) for each stage. Some of the panels are identical as the panels in the paper (Arai et al., 2017)