Modifications in the techniques for the induction of mammalian somatic cell hybridization by polyethylene glycol (PEG) have led to procedures that are rapid, simple, and effective. The basic improvements, for both monolayer and suspension fusions, are a short exposure to PEG and a rapid dilution of PEG following treatment. There is a marked effect of PEG concentration on cell hybridization, and there seem to be inherent differences between cells in terms of the extent of cell fusion induced by PEG.

No abstract

Sister chromatid exchanges, which may reflect chromosome repair in response to certain types of DNA damage, provide a means of investigating the increased chromosome fragility characteristic of Fanconi's anemia. By a recently developed technique using 33258 Hoechst and 5-bromodeoxyuridine, it was observed that the baseline frequency of sister chromatid exchanges in phytohemagglutinin-stimulated lymphocytes from four males with Fanconi's anemia differed little from that of normal lymphocytes. However, addition of the bifunctional alkylating agent mitomycin C (0.01 or 0.03 ;Ig/ml) to the Fanconi's anemia cells during culture induces less than half of the increase in exchanges found in identically treated normal lymphocytes. This reduced increment in exchanges is accompanied by a partial suppression of mitosis and a marked increase in chromatid breaks and rearrangements. Many of these events occur at sites of incomplete chromatid interchange. The increase in sister chromatid exchanges induced in Fanconi's anemia lymphocytes by the monofunctional alkylating agent ethylmethane sulfonate (0.25 mg/ml) was slightly less than that in normal cells. Lymphocytes from two sets of parents of the patients with Fanconi's anemia exhibited a normal response to alkylating agents, while dermal fibroblasts from two different patients with Fanconi's anemia reacted to mitomycin C with an increase in chromatid breaks, but a nearly normal increment of sister chromatid exchanges. The results suggest that chromosomal breaks and rearrangements in Fanconi's anemia lymphocytes may result from a defect in a form of repair of DNA damage. Fanconi's anemia is a hereditary disease characterized by pancytopenia, congenital malformations, and patches of increased skin pigmentation (1). Chromosomes from affected individuals exhibit structural lability (2, 3), and there is a strong predisposition for the development of neoplasia (4, 5). Because of the high frequency of chromosomal abnormalities, predominantly breaks, it has been suggested that an error in DNA repair exists in Fanconi's anemia (5).Bifunctional alkylating agents such as mitomycin C (6), as well as y-rays (7), are unusually effective in inducing breaks in chromosomes of peripheral lymphocytes from individuals with Fanconi's anemia. Similarly, mitomycin C has been reported to be highly lethal to fibroblasts cultured from patients with Fanconi's anemia (8). Monofunctional alkylating agents exhibit less selective toxicity to Fanconi's anemia cells than do their bifunctional counterparts (6,8). One recent study has suggested that Fanconi's anemia fibroblasts may also have a reduced ability to excise thymine dimers (9).The observation that alkylating agents are able to induce large numbers of sister chromatid exchanges in chromosomes from normal cells (10-12) provides a new approach for investigating Fanconi's anemia. Since MATERIALS AND METHODSSister chromatid exchanges in human lymphocyte chromosomes were detected by fluorescence microscopy after staining with the dye 33258 Hoec...