An automatic system for detecting and counting sister chromatid exchanges in human chromosomes has been developed. Metaphase chromosomes from lymphocytes which had incorporated 5-bromodeoxyuridine for two replication cycles were treated with the dye 33258 Hoechst and photodegraded so that the sister chromatids exhibited differential Giemsa staining. A computer-controlled television-microscope system was used to acquire digitized metaphase spread images by direct scanning of microscope slides. Individual objects in the images were identified by a thresholding procedure. The probability that each object was a single, separate chromosome was estimated from size and shape measurements. An analysis of the spatial relationships of the dark-chromatid regions of each object yielded a set of possible exchange locations and estimated probabilities that such locations corresponded to sister chromatid exchanges. A normalized estimate of the sister chromatid exchange frequency was obtained by summing the joint probabilities that a location contained an exchange within a single, separate chromosome over the set of chromosomes from one or more cells and dividing by the expected value of the total chromosome area analyzed. Comparison with manual scoring of exchanges showed satisfactory agreement up to levels of approximately 30 sister chromatid exchanges/cell, or slightly more than twice control levels. The processing time for this automated sister chromatid exchange detection system was comparable to that of manual scoring.

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Fetal nucleated cells within maternal blood represent a potential source of fetal genes obtainable by venipuncture. We used monoclonal antibody against the transferrin receptor (TfR) to identify nucleated erythrocytes in the peripheral blood of pregnant women. Candidate fetal cells from 19 pregnancies were isolated by flow sorting at 121/-17 weeks gestation. The DNA in these cells was amplified for a 222-base-pair (bp) sequence present on the short arm of the Y chromosome as proof that the cells were derived from the fetus. The amplified DNA was compared with standardized DNA concentrations; 0.1-1 ng offetal DNA was obtained in the 20-ml maternal samples. In 7/19 cases, a 222-bp band of amplified DNA was detected, consistent with the presence of male DNA in the isolated cells; 6/7 of these were confirmed as male pregnancies by karyotyping amniocytes. In the case of the female fetus, DNA prepared from samples at 32 weeks of gestation and cord blood at delivery also showed the presence of the Y chromosomal sequence, suggesting Y sequence mosaicism or translocation. In 10/12 cases where the 222-bp band was absent, the fetuses were female. Thus, we were successful in detecting the Y chromosomal sequence in 75% of the male-bearing pregnancies, demonstrating that it is possible to isolate fetal gene sequences from cells in maternal blood. Further rermement in methodology should increase sensitivity and facilitate noninvasive screening for fetal gene mutations.

Many Prader-Willi syndrome (PWS) and Angelman syndrome (AS) patients have a cytogenetic deletion of 15q11q13. While AS and PWS share a similar cytogenetic anomaly, they have very different clinical phenotypes. DNAs from 4 AS patients were examined using 5 chromosome 15q11q13-specific cloned DNA segments. With the present level of resolution, the molecular deletions between AS and those previously reported for PWS did not appear to differ. However, in contrast to the paternal inheritance of the deleted chromosome 15 observed in the majority of PWS patients, maternal inheritance of the deleted chromosome 15 was demonstrated in the AS patients by restriction fragment length polymorphisms (RFLPs).

DNA replication in eukaryotic organisms is semiconservative (1), initiating at discontinuous foci (2) and terminating in a temporal sequence characteristic of the location of the DNA segment in metaphase chromosomes (3). Biochemical and cytological studies have correlated late DNA replication with both genetic inactivity and the persistence of chromosome condensation throughout most of the cell cycle (4, 5). Regions with these properties are termed heterochromatic and have been shown to correspond to regions of metaphase chromosomes staining intensely either with quinacrine or quinacrine mustard, or with Giemsa mixtures after any of a variety of pretreatments (6, 7). However, previous correlation of late DNA replication with banded regions of metaphase chromosomes has been limited by the resolution usually realized of the autoradiographic techniques used, and the chromosomebanding stains do not effectively differentiate the facultative heterochromatic X chromosome from its active homologue. More precise correlation of DNA replication with chromosome location in individual metaphases could be achieved were it possible to detect DNA synthesis at the level of resolution of optical techniques.Direct light-microscopic visualization of DNA replication might use DNA base analogues with distinctive absorptive or fluorescent properties. However, available base analogues do not, at present, make such an approach practical. As ai alternative method, one might use an indirect phenomenon, Abbreviation: Hepes, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid. Address reprint requests to author at: Children's Hospital Medical Center, 300 Longwood Ave., Boston, Mass. 02115. 3395 such as the environmental sensitivity of fluorescent chromosome stains, using them to report the incorporation of nucleotide analogues containing substituents, such as heavy atoms (8), perturbing dye luminescence.Towards this purpose, we have examined several dyes, including the compound 33258 Hoechst [2-[2-(4-hydroxyphenyl)-6-benzimidazolyl]-6-(1-methyl4-piperazyl)-benzimidazol * 3 HClJ, which has previously been used to demonstrate constitutive heterochromatin in rodent metaphase chromosomes (9). We observed that the fluorescence of a sample of 33258 Hoechst, kindly supplied by Dr. H. Loewe, Hoechst, is much less efficient when the dye is bound to poly(dA-BrdU) than when bound to poly(dA-dT). This paper introduces a method based on this observation. Reduction in the fluorescence intensity of 33258 Hoechst bound to chromatin, upon incorporation of BrdU, has been used to follow DNA synthesis in interphase nuclei and metaphase chromosomes. MATERIALS AND METHODSCell Growth. Peripheral human leukocytes were cultured in Eagle's minimal essential medium (MBA) with 2 mM Lglutamine and 20% fetal-calf serum (GIBCO), to which crude phytohemagglutinin was added. BrdU and thymidine, added to cultures grown at 370, as described in the figure legends, were obtained from Sigma and their tritiated derivatives from New England Nuclear Corp. Uridine was also obt...

Human factor VIII--von Willebrand factor (vWF) is a large, multimeric glycoprotein that plays a central role in the blood coagulation system, serving both as a carrier for factor VIIIC (antihemophilic factor) and as a major mediator of platelet-vessel wall interaction. Diminished or abnormal vWF activity results in von Willebrand's disease (vWD), a common and complex hereditary bleeding disorder. Overlapping vWF cDNA clones that span 8.2 kilobases of the vWF messenger RNA have been obtained. vWF accounts for approximately 0.3 percent of endothelial cell messenger RNA and was undetectable in several other tissues examined. A large single copy gene for vWF is located on the short arm of chromosome 12 (12p12----12pter). No gross gene rearrangement or deletion was detected in the DNA of two patients with severe vWD.

Absorption, fluroescence and circular dichroism measrements on 33258 Hoechst-deoxyribonucleic acid (DNA) complexes are consistent with the existence of two types of dye-binding interactions. One type, which persists at elevated solution ionic strength, is highly specific for adenine-thymine-rich DNA. Dye bound under this condition exhibits efficient fluorescence and strong optical activity. A less specific, largely electrostatic interaction is associated with less intense fluorescence and weaker optical activity. The fluorescence of 33258 Hoechst and several other bisbenzimidazole dyes is less when bound to poly(deoxyadenylate-5-bromodeoxyuridylate) than when bound to poly(deoxyadenlyate-deoxythymidylate). Quenching of 33258 Hoechst fluorescence can also be used to detect biosynthetic incorporation of 5-bromodeoxyuridine into the DNA of living cells. This property of 33258 Hoechst should allow fluorescence-activated cell and chromosome sorting according to the extent of DNA synthesis, providing a bridge between biochemical and cytologic analyses of processes related to DNA replication.

A method that allows the specific cloning of DNA fragments absent from patients homozygous or hemizygous for chromosomal deletions is described. The method involves phenol-accelerated competitive DNA reassociation and subsequent molecular cloning of appropriately reassociated molecules. The deletion DNA sample utilized in the competition was isolated from a patient with a minute interstitial deletion in the short arm of the X chromosome. Sheared DNA isolated from a male child, who was diagnosed as having Duchenne muscular dystrophy, chronic granulomatous disease, and retinitis pigmentosa, was combined in a 200-fold excess with Mbo I-cleaved DNA isolated from a 49,XXXXY human lymphoid cell line, and the mixture was subjected to a phenol-enhanced reassociation technique. Analysis of 81 unique segments derived from cloned reassociated DNA molecules has led to the identification of 4 (5%) human DNA fragments that are absent from the male patient's DNA. The 4 clones were localized, on the basis of hybridization with restriction nuclease-digested genomic DNA from a panel of human and human-rodent hybrid cell lines, into three regions surrounding band 21 of the short arm of the normal human X chromosome. These clones are potential linkage markers for the diseases affecting this boy. Each clone, as well as others obtainable by this approach, may also serve as a starting point in the eventual cloning of these three X-linked-disease loci. Extension of this approach to other loci, including human tumors potentially homozygous for small deletions, should also be possible.