Chromatin position in human HepG2 cells: Although being non-random, significantly changed in daughter cells

Abstract

Mammalian chromosomes occupy chromosome territories within nuclear space the positions of which are generally accepted as non-random. However, it is still controversial whether position of chromosome territories/chromatin is maintained in daughter cells. We addressed this issue and investigated maintenance of various chromatin regions of unknown composition as well as nucleolus-associated chromatin, a significant part of which is composed of nucleolus organizer region-bearing chromosomes. The photoconvertible histone H4-Dendra2 was used to label such regions in transfected HepG2 cells, and its position was followed up to next interphase. The distribution of labeled chromatin in daughter cells exhibited a non-random character. However, its distribution in a vast majority of daughter cells extensively differed from the original ones and the labeled nucleolus-associated chromatin differently located into the vicinity of different nucleoli. Therefore, our results were not consistent with a concept of preservation chromatin position. This conclusion was supported by the finding that the numbers of nucleoli significantly differed between the two daughter cells. Our results support a view that while the transfected daughter HepG2 cells maintain some features of the parental cell chromosome organization, there is also a significant stochastic component associated with reassortment of chromosome territories/chromatin that results in their positional rearrangements.

4D Chromatin dynamics in cycling cells

“…6F, lower). In line with previous studies, 14,16 however, this finding argues against a complete randomization of CT proximity patterns present in the mother nucleus already after a single mitotic event. In such a case we would have expected scattering of fluorescent chromatin patches throughout the entire nuclear space in all experiments where we activated paGFP-H4 in a half or a quarter of the nuclear area.…”

“…Several groups have studied this problem in living cells taking advantage of cell lines, which express core histones tagged with fluorescent proteins. [14][15][16] Lasermicroirradiation was used to produce fluorescent chromatin patterns, which were then followed through interphase and mitosis. Gerlich et al 15 concluded that global chromosome positions are maintained in cycling mammalian cells and proposed a mechanism acting at anaphase to restore the loss of order.…”

“…Thomson et al 18 tracked specific human loci after exit from mitosis and concluded that the organization of chromatin in the nucleus is not passed down precisely from one cell to its descendants but is more plastic and becomes refined during early G 1 . Cvacková et al 14 demonstrated major changes of chromatin arrangements between mother and daughter nuclei, but noted that the CT order present in the mother nucleus was not entirely randomized despite a significant stochastic component associated with reassortment of chromosome territories/chromatin. A partial maintenance of order could happen by chance and would not require a special mitotic mechanism.…”

Chromosome Territories

“…This allowed following up fluorescently labeled chromatin through mitosis into the next interphase. Present evidence argues for the stability of a given CT neighborhood arrangement once established at the onset of interphase until the next prophase, whereas chromosome movements during prometaphase necessary to establish the metaphase plate can lead to major changes of side-by-side chromosome arrangements in the metaphase plate compared with the side-by-side arrangements of the respective CTs during the preceding interphase (Walter et al 2003;Cvackova et al 2009). …”

Chromosome Territory Organization within the Nucleus

“…The subsequent cultivation of these cells for three or more additional cell cycles resulted in the formation of nuclei with a few in vivo-labeled CTs that were separated by nonlabeled CTs [34][35][36][37]. Eventually, tests of Boveri's hypotheses II-IV in living cells became possible using cell lines that expressed core histones tagged with fluorescent proteins [8, 36,38]. In this way, by using laser microirradiation, distinct fluorescent chromatin patterns could be established in interphase nuclei or on mitotic chromosomes, and tracked through interphase and mitosis.…”