Unusual compartmentalization of CTCF and other transcription factors in the course of terminal erythroid differentiation

Abstract

It is demonstrated that in chicken embryonic and mature erythrocyte nuclei the distribution of a versatile transcription factor CTCF differs drastically from its distribution in nuclei of proliferating erythroid and non-erythroid cells. In the latter case CTCF was distributed throughout the whole nucleus volume, being concentrated in many small compartments (punctuate nuclear staining). In contrast, in embryonic and mature erythrocytes CTCF was concentrated in a limited number of large compartments. These large CTCF-containing compartments were not observed in other cells. Occasionally, but not in all cells, some of these compartments were localized close to nucleoli but did not colocalize with them. In mature erythrocytes a clear exclusion of CTCF-containing compartments from the chromatin domain was observed. This exclusion correlated with a tight association of CTCF with the nuclear matrix. Concentration in relatively large compartments and exclusion from the chromatin domain in nuclei of mature erythrocytes were also observed for RNA polymerase II and several transcription factors. The data are discussed in the context of a hypothesis postulating that relocalization of different components of the transcriptional machinery from the chromatin domain into the interchromatin compartment is an important step of the terminal inactivation of chicken erythrocyte nuclei.

Chromatin loops, illegitimate recombination, and genome evolution

“…As discussed in the previous sections, the incorrect joining of cleaved DNA chains is likely to be the main cause of translocations occurring in cells treated with topoisomerase II poisons 51, 64–66. It seems obvious that broken DNA chains of different chromosomes can be incorrectly joined only when they are close to each other.…”

Reorganisation of chromatin during erythroid differentiation

“…Исчезновение регуляторных петлевых взаимодействий не может быть объяснено остановкой транскрипционной активности и, соответственно, продвижения комплекса ассоциированных с транскрипцией белков, поскольку в ядрах сперматозоидов, также транскрипционно неактивных, доменная организация сохранялась. Возможно, подобная картина объясняется перемещением белков когезинового комплекса и CTCF, ответственных за данный тип взаимодействий, с ДНК в интерхроматиновое пространство, так как в ядрах активно делящихся эритробластов белок равномерно распределен по всему объему клеточного ядра, а в ядрах зрелых эритроцитов курицы CTCF диссоциирует с ДНК и находится большей своей частью на периферии ядра (Kantidze et al, 2007). Таким образом, отсутствие активного процесса протягивания петель, вероятно, позволяет установиться равновесному состоянию со строго разделенными зонами хроматина разного типа в ядрах терминально дифференцированных эритроидных клеток.…”

Compartmentalization of the cell nucleus and spatial organization of the genome

“…In fact, many nuclear proteins display a focal (nonuni form) distribution in the nucleus at least in some cells [152][153][154][155]. The most important compartments (PML bodies, Cajal bodies, speckles, and some others) are quite large and were identified by light or electron microscopy long before the advent of immunostaining (for more detail, see [2,4,93]).…”