Significant large-scale chromosome territory movement occurs as a result of mitosis, but not during interphase

To investigate large-scale relative movement (position change) of interphase chromosome territories (ICT), as indicated by the separation of chromosome derivatives following exposure to ionizing radiation.

A simple experiment was conducted to investigate large-scale movement of ICT, using whole chromosome 18 painting to measure the frequency of fluorescent ICT in irradiated lymphocytes, cultured over 9 days (seven cell cycles). After chromosome 18 painting, derivative chromosome territory separation was indicated by the observation of three fluorescent ICT in aberrant cells compared with the presence of two fluorescent ICT in normal cells. The frequencies of interphase nuclei containing three fluorescent chromosome territories for unirradiated resting lymphocytes and for lymphocytes acutely irradiated with 2.25 or 5.5 Gy 137Cs gamma-rays were measured for each culture time point of 0, 1, 2, 3, 4, 7 and 9 days.

No significant difference was observed in the frequency of three ICT between the average of the controls and irradiated cells cultured for 0, 1 and 2 days. However, irradiated cells cultured for >or=3 days showed a significant increase in the frequency of three fluorescent ICT over those cultured for

The finding that significant large-scale movement was not observed within the first 48 h of cell culture, but was seen in cultures after 48 h, suggests that ICT do not undergo large-scale movement relative to each other until lymphocytes go through mitosis.