Induction of premature chromatid separation (PCS) in individuals with PCS trait and in normal controls

Cultured peripheral blood lymphocytes from ten normal individuals, treated with 0.075 M KCl at 37 degrees C for 20 min, showed 0-2% cells in premature chromatid separation (PCS), a configuration with split centromeres and chromatids of most or all chromosomes. When treated for 30 min, they increased to 19% in the average, and at 45 min to 63%. Similar and significant effects of temperature and duration of hypotonic treatment on the frequencies of PCSs were found also in mitotic lymphocytes from patients with homozygous PCS trait, a cancer-prone disorder with >50% lymphocytes in PCS, mosaic variegated aneuploidy, and a variety of clinical manifestations; and from their heterozygous carrier parents. B lymphoblastoid cells from two infants with the homozygous PCS trait did not show PCSs when processed without hypotonic treatment. The frequencies of their PCSs increased with increasing temperature and duration of hypotonic treatment, attaining more than 65% after 20 min treatment and 90% after 45 min at 37 degrees C. PCS is thus likely to be induced largely by hypotonic treatment. Treatment at 37 degrees C for 20 min was found to be most suitable for the count of PCSs, in which the frequency of PCSs becomes almost zero in cells from normal individuals, and the difference in frequency of PCSs was most remarkable between the patients and heterozygous carriers, and between the heterozygous carriers and normal individuals. Chromosomes from the patients with the homozygous PCS trait tended to be long, and their PCSs tended to have a large number of widely separated sister chromatids. Chromosomes from normal individuals tended to be short, and the sister chromatids in their PCSs were set close to each other.