Reduction in chromosome mobility accompanies nuclear organization during early embryogenesis in Caenorhabditis elegans

Hiroshi Kimura,Akatsuki Kimura,Takeshi Sugawara,Atsushi Toyoda,Ritsuko Arai,Yuko Sato,Kentaro Nabeshima,Yohei Minakuchi

doi:10.1038/s41598-017-03483-5

Abstract

In differentiated cells, chromosomes are packed inside the cell nucleus in an organised fashion. In contrast, little is known about how chromosomes are packed in undifferentiated cells and how nuclear organization changes during development. To assess changes in nuclear organization during the earliest stages of development, we quantified the mobility of a pair of homologous chromosomal loci in the interphase nuclei of Caenorhabditis elegans embryos. The distribution of distances between homologous loci was consistent with a random distribution up to the 8-cell stage but not at later stages. The mobility of the loci was significantly reduced from the 2-cell to the 48-cell stage. Nuclear foci corresponding to epigenetic marks as well as heterochromatin and the nucleolus also appeared around the 8-cell stage. We propose that the earliest global transformation in nuclear organization occurs at the 8-cell stage during C. elegans embryogenesis.

Highlights

Chromosomes are long polymers that store genetic information, consisting of DNA and various proteins
Live-cell imaging of epigenetic marks and heterochromatin provided cytological evidence that a global transformation in nuclear organization occurs around the 8-cell stage in C. elegans embryos
We provide evidence that global changes in both the physical and biochemical properties of chromosomes occur around the 8-cell stage during C. elegans embryogenesis

Summary

Introduction

Chromosomes are long polymers that store genetic information, consisting of DNA and various proteins. To characterise the state of chromosomal organization during C. elegans early embryogenesis, we designed an experiment to track the mobility of a pair of homologous chromosomal loci in live cells during interphase. For this purpose, we used a lacO–LacI system in which the bacterial operator sequence lacO is artificially inserted into a chromosome and the position of this sequence is visualised with a bacterial LacI. To detect the earliest change in global chromatin organization inside the interphase nucleus, we tracked lacO loci inserted into the C. elegans genome from the 2- to the 48-cell stage. Live-cell imaging of epigenetic marks and heterochromatin provided cytological evidence that a global transformation in nuclear organization occurs around the 8-cell stage in C. elegans embryos

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