Heterochromatin (chromosome dots and chromocentres): key to planarian regeneration?

Regenerating planaria were treated with colchicine dissolved in planarian saline solution in order to harvest metaphase chromosomes. Slides containing such chromosomes were incubated in phosphate buffer at high temperature for 2h and stained with Giemsa solution in order to view heterochromatic dots in chromosomes. The chromosomes were found to contain massive regions of dense heterochromatin. In addition, most interphase cells exhibited numerous densely staining chromocentres. Heterochromatin has been postulated to reduce the duration and enhance the speed of the cell cycle, and previous work has implicated heterochromatin in cells undergoing rapid division. These findings imply that the profound regenerative potential of planarians may be due to their high cellular levels of heterochromatin.