The human leukocyte test system. III. Premature chromosome condensation from chemically and x-ray induced micronuclei.

Premature chromosome condensation (PCC) was induced in human leukocytes in vitro by a bifunctional alkylating agent 2,5-bis-(methoxyethoxy)-3,6-bis-ethylene-imino-p-benzoquinone (A 139), bleomycin and X-rays. Analysis shows that PCC originates from micronuclei that have been slowed down in their cell cycles in respect to the main nuclei. The mitosing chromatin of the main nuclei induced PCC in the associated micronuclei. Morphologically the PCC was mostly of the S-phase type with the chromatin exhibiting a more or less pulverized appearance; in some experiments this was verified by incorporation of (3H) thymidine (TdR). In a few cases the PCC looked like G2-phase PCC with ladder-like chromosomes. GI-phase PCC was not found. PCC of the type described in this work may be used as an indicator of induced lagging of chromatin that can be the result of chromosomal aberrations or of nondisjunction.