Human chromatin from interphase to metaphase: A scanning electron microscopic study

Abstract

Scanning electron microscopy (SEM) was used to observe surface-spread, critical-point-dried human interphase nuclei and chromosomes from cultures of peripheral lymphocytes arrested with colchicine. The following points have been documented. 1. 1. Apparently randomly packed interphase chromatin begins to aggregate into prophasic chromosomes that contain accumulations of chromatin at complementary positions along each chromatid; such chromatin accumulations are called chromomeres. 2. 2. As prophase merges into metaphase in vitro, the chromomeres become less distinct, and eventually a classic, condensed chromosome with only tortuous, looping fibers is observed. 3. 3. Chromosomes not treated with arresting solution also maintain interchromosomal fibers, thus suggesting that their existence is not artifactual secondary to spindle poisons. 4. 4. DNase studies reveal distinct chromomeres at complementary loci in each chromatid. Interphase nuclei on the same grid show only few, parallel fibers and no chromomeres. 5. 5. Scanning electron microscopy of DNase-treated whole-mount chromosomes might allow for more detailed analyses of deletions and translocations by chromomere number and position than is possible by light microscopy banding techniques.