DNA flow histogram analysis, using 33342 Hoechst as a stain, has been used to detect the effect of the potentially bifunctional alkylating agent, mitomycin C (MMC) on dermal fibroblasts from patients with Fanconi's anemia (FA), a hereditary human disease characterized by pancytopenia, hypersensitivity to DNA-crosslinking agents, congenital abnormalities, and a predisposition for neoplasia. At 24 or 48 hr after a 2-hr exposure to 0.05 or 0.10 pg/ml MMC, 3HdT incorporation was reduced to a greater extent in FA cells than in normal cells. Cells sorted from the last half of S phase showed a slightly greater inhibition of 3HdT incorporation than did those sorted from the first half of S.Fanconi's anemia cells exhibited a marked accumulation in the Gz + M peak of flow histograms following exposure to MMC. Twenty-four hr after treatment with 0.05 pg/ ml MMC, the G2 + M fraction of FA cells (eight lines) increased to more than 0.5 from a control value of approximately 0.2. Both normals (six lines) and heterozygotes (eight lines) showed, on the average, much less of a Gz + M increment than did FA cells, even after exposure to 0.1 pg/ml MMC. Examination of cells sorted from the Gz + M peak revealed that MMC-treated FA cells were blocked prior to mitosis.To determine whether the response of FA cells was specific for a bifunctional alkylating agent, cells were also treated with ethylmethanesulfonate, a monofunctional agent. Twenty-four hours after exposure to 0.25 or 0.5 mg/ml ethylmethanesulfonate, FA and normal cells showed similar, small increases in the G2 + M peak. The results suggest the utility of flow cytometry in the diagnostic evaluation of fibroblasts from patients suspected of having Fanconi's anemia.Key terms: Fanconi's anemia, DNA crosslinking agent, mitomycin C, flow cytometry, 33342 Hoechst, Gz block, Cell cycle analysis, DNA repair Fanconi's anemia (FA), a syndrome of pancytopenia and a variable constellation of congenital anomalies (12,34,44), has been shown to be associated with chromosomal instability (8, 42, 47) and a predisposition for cancer (5,16, 43). Cells from patients with FA show increased sensitivity to agents capable of producing DNA crosslinks. This sensitivity is evident as decreased survival (51), increased chromosome breakage (3, 29,40) and a reduction in both the rate of progression through I This research was supported by grants CD-36F from the American Cancer Society and GM21121 from the National Institute of General Medical Sciences.Presented at the VIII Conference on Analytical Cytology and Cytometry, Wentworth-by-the-Sea, New Hampshire, May 19-25, 1981. the cell cycle (41) and in the proportion of mitotic cells (17, 51), following exposure to such agents.A reduction in the ability of cells from patients with Fanconi's anemia to remove DNA crosslinks, caused e.g. by mitomycin C (MMC), was observed in some studies (15) but not in others (13, 25). There are also isolated reports that cells from patients with FA exhibit other defects, such as a reduced ability to remove damage induc...

Cells from patients with Fanconi’s anemia are unusually sensitive to agents which are capable of crosslinking DNA. This increased sensitivity can be detected both by cytogenetic and flow cytometric methods. An elevated frequency of chromosome aberrations, which is further exaggerated by exposure of cells to DNA crosslinking agents, is a general feature of Fanconi’s anemia. Information about the formation of sister chromatid exchanges in this disease is less consistent. Cytogenetic analysis of cells from patients with Fanconi’s anemia can be compromised by a low mitotic index. This is reflected in an accumulation of cells in the G2 phase of the cycle, after exposure to the bifunctional alkylating agent, mitomycin C. New methods for differentiating individuals with Fanconi’s anemia from unaffected individuals should be of empirical use and might also facilitate mechanistic studies of this disease.

A lambda phage library enriched in X(7) chromosomal material has been constructed from flow sorted chromosomes isolated from mice carrying the Cattanach translocation T(X;7)1Ct. The flow sorted fraction that was cloned contained 40% X(7) chromosomes, so that the resulting lambda phage library should be more than 10-fold enriched for X chromosomal DNA. Approximately 100,000 lambda phage clones were obtained; of these, at least 80% were recombinant. Three quarters of recombinants were positive for mouse repetitive DNA as detected either by phage plaque filter hybridization or by Southern blotting. Recombinant DNA inserts were prepared from some of the remaining nonrepetitive phage fraction. The X-chromosome specificity of cloned DNA inserts was tested by hybridization to DNA from mouse-hamster somatic cell hybrids that had retained all or most of the mouse X as the only mouse chromosome and by comparison of the extent of hybridization to DNA from male and female mice. Out of nine cloned unique sequence segments successfully examined thus far, two were presumably derived from the X. Possession of phage library highly enriched for mouse X DNA should facilitate molecular studies of the control of X chromosome gene expression.