Spatial localization of chromosome nuclear envelope interaction sites

In interphase, nuclear chromosomes are tightly associated with the nuclear envelope (NE) through special granular chromatin particles termed anchoroso mes. It remains unclear whether anchorosomes represent constant nuclear str uctures, persisting throughout the cell cycle, or they appear only in inter phase during the formation of contacts between the chromosomes and the NE, in other words, whether specific NE interaction sires do exist in chromosom es or any chromatin region can form anchorosome? In this work, we used micronucleated PK cells, in which almost every micron ucleus (MN) is formed by a single chromosome. The spatial distribution and quantitative characteristics of the anchorosomal layer in MN was studied us ing stereological analysis and three-dimensional computer reconstruction. I t was shown that, ill cells with about 30 MN, the total surface area of the NE reaches about 355 mu(2). whereas in normal mononuclear cells, it is 110 mu(2). Hence, the NE surface are increases 3-fold during MN formation. In contrast to normal cells, only 80% of the NE surface in MN is covered with anchorosomes, i.e., the total surface area of the anchorosomal layer increa ses by a factor of 2.5. The 3D-reconstruction has demonstrated highly rando m distribution of anchorosome-free zones, the distribution pattens varying in individual MN. These finding are thought to be an evidence for existence of a limited numb er of specific chromosomal sites potentially capable of forming contacts wi th the NE.