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Biomedical subjects

J German

Publications and source records attributed to J German.

At least 55 records · Page 3Linked to original sources
PubMed1990

Molecular evidence that homologous recombination occurs in proliferating human somatic cells.

A strategy has been developed to detect and characterize certain heritable genomic alterations that occur as cells proliferate in vitro. Multiple subclones of cells were isolated from two clonal lymphoblastoid cell lines--one from a boy with Bloom's syndrome (BS), a cancer-predisposing condition known to feature excessive somatic mutation, the other from a normal man. The DNAs from the cell lines were hybridized to a panel of probes that can detect restriction fragment length polymorphisms, and the patterns of polymorphism in the primary clones were compared with that in each of the secondary clones. In one of the BS secondary clones three loci, positioned distally on the long arm of chromosome 3 and that are heterozygous in the donor and all other cell lines derived from the primary clone, had lost heterozygosity and apparently had become homozygous; in contrast, heterozygous loci more proximal on 3q had retained their heterozygosity, as had those on 3p. Taking into account the pattern of chromosome instability uniquely characteristic of BS, the most plausible explanation for the alterations in the altered clone is that somatic recombination had occurred in vitro, via homologous chromatid interchange. Such spontaneous recombinational events in nonneoplastic, nonmutagenized cells may contribute to the high cancer incidence in BS and, by analogy, to cancer that arises in the general population.

Cell Division↗
PubMed1989

Frequency of variant erythrocytes at the glycophorin-A locus in two Bloom's syndrome patients.

Blood type MN is determined by a glycoprotein termed glycophorin A (GPA) which exists on the surface of erythrocytes, and the difference between the M and N types is derived from the presence of 2 different amino acids in the amino-terminal portion (Furthmayer, 1978). Using a pair of fluorescence-labeled monoclonal antibodies specific to each GPA, somatic mutations in erythrocytes of MN heterozygotes at the GPA-M and -N alleles can be quantitatively determined using a flow sorter (Langlois et al., 1986). Our results for 2 Bloom's syndrome (BS) patients showed that variants either lost expression of one allele (simple gene inactivation or loss) or expressed only one allele at twice the normal level (most probably somatic recombination) occurring at a frequency of about 1-3 per 10(3) erythrocytes. The flow cytometric patterns of erythrocytes from the BS patients showed a typical smear of variants bearing intermediate levels of expression of one GPA allele, indicating that the real variant frequency is even greater than that measured. On the other hand, the parents heterozygous for the BS gene showed variant frequencies (1-8 x 10(-5)) within the normal range. These data strongly support the hypothesis that the cancer proneness of BS patients is due to their increased frequency of spontaneous mutations and somatic recombination.

Alleles↗
PubMed1989

Evidence for increased in vivo mutation and somatic recombination in Bloom's syndrome.

The glycophorin A assay was used to estimate the frequency of mutations that accumulate in vivo in somatic cells of persons with Bloom's syndrome (BS). This assay measures the frequency in persons of blood type MN of variant erythrocytes that lack the expression of one allelic form of glycophorin A, presumably due to mutational or recombinational events in erythroid precursor cells. Samples of blood from persons with BS showed dramatic 50- to 100-fold increases in the frequency of variants of three types, those with a hemizygous phenotype, those with a homozygous phenotype, and those with what appears to be partial loss of the expression of one locus. The high frequency of homozygous variants, genetic evidence for altered allelic segregation of a specific biochemical locus, provides evidence for increased somatic crossing-over in vivo in BS. An increased generation of functional hemizygosity and homozygosity in their somatic cells may play an important role in the extreme cancer risk of persons with BS.

Adolescent↗
PubMed1989

Bloom's syndrome. XII. Report from the Registry for 1987.

Bloom's syndrome has been known as a clinical entity for 34 years. Careful records of cases diagnosed throughout the world have been maintained since its recognition as an entity, and most instances of cytologically verified Bloom's syndrome have been accessioned to what has been referred to as the Bloom's Syndrome Registry since the mid-1960s. Presented here is the fourth in a series of progress reports from the Registry of information accumulated during this long-term surveillance of affected families, along with mention of selected recent advances that have been made in the understanding of the syndrome. 130 persons had been accessioned to the Registry by the end of 1987; 96 of these were alive, their mean age being 18.9 years. Although a number of clinical complications occur in Bloom's syndrome, the most important is malignant neoplasia. In the 130 persons in the Registry, 57 malignant neoplasms had been detected, the mean age at diagnosis being 24.8 years. Neoplasia in Bloom's syndrome is noteworthy not only because of its frequency and exceptionally early age of emergence but for its variety of histological types and sites of origin.

Adolescent↗
PubMed1989

Bloom's syndrome. XIV. The disorder in Japan.

Fourteen persons have been diagnosed Bloom's syndrome in Japan, with cytological verification in 11. Widely separated birthplaces throughout Honshu, Shikoku, and Kyushu and a parental consanguinity incidence greater than in the general population suggest that the Bloom's syndrome mutation, although very rare, is distributed widely throughout the Japanese population. The locus mutated is the same as in Jews and persons of Western European extraction. The phenotype differs somewhat from most cases recognized elsewhere, in that dolichocephaly is a less constant feature, the facial skin lesion is less prominent, and life-threatening infections are less common. The characteristic predisposition to neoplasia exists, however, as probably does that to diabetes mellitus.

Adolescent↗
PubMed1988

Gonadal dimorphism explained as a dosage effect of a locus on the sex chromosomes, the gonad-differentiation locus (GDL).

In human somatic cells bearing two X chromosomes, one X is genetically inactivated throughout most of its length, whereas in cells with one X and one Y both sex chromosomes are active (with the exception of the constitutive heterochromatin of the Y that is inert). The vast base of information concerning normal and abnormal human sexual development that has accumulated since the advent of human cytogenetics 3 decades ago can be integrated by the following hypothesis: Homologous gonad-differentiation loci (GDLs) exist on the X and Y. The GDLs are strictly sex-linked; that is, normally they do not recombine during spermatogenesis, so that considerable divergence in DNA sequence doubtless has occurred between the locus on the X and the locus on the Y. The abundance of their evolutionarily conserved product--a substance still to be identified--determines the path of differentiation that the indifferent gonadal anlage of the early embryo will take: if only one GDL is transcribed, the case when two X chromosomes are present, ovary will develop; if two GDLs are transcribed, the case when a Y is present along with an X, testis will develop. By implication, facultative X inactivation is an integral and essential component of the system adopted in mammalian evolution for accomplishing gonadal--viz., sexual--dimorphism.

Chromosome Mapping↗
PubMed1987

Different mutations are responsible for the elevated sister-chromatid exchange frequencies characteristic of Bloom's syndrome and hamster EM9 cells.

Experimental hybridization of cultured cells was employed to determine whether the strikingly elevated rates of sister-chromatid exchange (SCE) exhibited by Bloom's syndrome (BS) and hamster cell line EM9 have the same or different bases. Seventeen cell lines were developed from polyethylene glycol-treated mixtures of BS and EM9 cells. Cytogenetic analysis proved the hybrid nature of 12 of the lines; 9 of those 12 exhibited low (normal) numbers of SCEs, signifying complementation. The parental BS and EM9 cells, although resembling each other in exhibiting very high SCE frequencies in BrdUrd-containing medium, differ from one another with respect to their proliferative abilities in such medium, the EM9 cells but not the BS cells being exquisitely hypersensitive to BrdUrd. In the low-SCE hybrid lines, hypersensitivity to growth in BrdUrd-containing medium was restored to normal whereas the hypersensitivity was retained by the high-SCE hybrids. It is concluded, first, that the mutations in BS and EM9 cells are different and, second, that both the elevated SCE frequency and the excessive BrdUrd hypersensitivity of EM9 cells are due to the same mutation.

Animals↗
PubMed1987

A test for Fanconi's anemia.

A simple and reliable cytogenetic test for Fanconi's anemia (FA) that is based on the hypersensitivity of FA cells to mitomycin C (MC) is described. Equal volumes of whole blood from a patient in whom the diagnosis of FA is suspected and from a normal person of the opposite sex are co-cultured in phytohemagglutinin-containing medium in the presence and absence of MC. After five days' co-cultivation, 100 quinacrine-stained metaphases from both the MC-containing and the MC-free cultures are examined for the presence of a Y chromosome using fluorescence microscopy. In all bona fide FA patients in whom testing was successful, hypersensitivity to MC was readily demonstrated by the striking deficiency of FA metaphases (0.9% to 14.9%) in the MC-containing co-cultures. In contrast, none of the three patients with Diamond-Blackfan anemia and none of the five with undiagnosed conditions reminiscent of FA exhibited hypersensitivity to MC; cells from them, from parents of FA patients, and from several normal laboratory personnel constituted approximately half of the metaphases (40.4% to 71.2%) of MC-containing co-cultures, as would be expected in the absence of hypersensitivity to MC.

Anemia, Aplastic↗
PubMed1986

The heat-shock response in vivo: experimental induction during mammalian organogenesis.

According to the embryonic stress hypothesis of teratogenesis, anatomical malformation can be the consequence of the induction of a heat-shock response (HSR) in the embryo at some critical stage during the determination or differentiation of organs. This hypothesis states that a teratogen is any agent that is capable of inducing a HSR and that can reach the developing embryo. As a first step in determining whether the hypothesis is tenable, it was necessary to determine whether the embryo in fact is capable of making the HSR during the period of organogenesis. Pregnant mice were treated with two classical inducers of the HSR, one a physical and the other a chemical agent--namely, hyperthermia and sodium arsenite. The embryos, while still in the living mouse, responded with heat-shock protein induction, as did control bone marrow.

Abnormalities, Drug-Induced↗
PubMed1986

Bloom's syndrome. XIII. DNA-polymerase activity of cultured lymphoblastoid cells.

The biochemical defect in Bloom's syndrome (BS) remains unknown, but two characteristic features of BS cells point to a disturbance of DNA replication, namely, an excessive number of sister-chromatid exchanges (SCEs) in bromodeoxyuridine (BrdU)-substituted cells and an abnormally slow rate of replicon elongation. The hypothesis of an abnormal DNA polymerase as the explanation for these observations was tested using an in situ assay system for DNA polymerase activity and to estimate molecular weights in cellular extracts of cultured BS cells. DNA polymerase subunits in cellular extracts from the BS cells when separated electrophoretically on polyacrylamide gels showed the same mobilities (i.e., molecular weights) as the controls and were equally effective at promoting the incorporation of isotopically labeled nucleosides. It is concluded that the genetic defect in BS has no direct effect on either DNA-polymerase activity or the amounts and molecular weights of the different forms of the enzyme.

Autoradiography↗
PubMed1985

Evidence for chromosome instability in vivo in Bloom syndrome: increased numbers of micronuclei in exfoliated cells.

The incidence of exfoliated epithelial cells containing micronuclei was determined in two small human populations, one homozygous and the other heterozygous for the Bloom syndrome gene (bl). The objectives of the study were two: to learn whether the chromosome instability featured so prominently by Bloom syndrome (BS) cells proliferating in vitro also occurs in vivo, and as part of a broad survey of various cancer-prone populations, to determine whether estimating micronucleus frequencies in exfoliated cell samples might be useful for identifying individuals with genetically determined chromosome instability. Eight individuals homozygous (bl/bl) for the BS gene, i.e., persons with the clinical syndrome, were examined, along with 11 obligate heterozygotes (bl/+), parents of affected persons. Exfoliated cells were obtained from two sites, the oral cavity and the urinary tract. Striking and statistically highly significant elevations in the frequencies of cells with micronuclei were observed in cells from both sites in bl/bl individuals compared to that in bl/+ (P less than 0.001) and in a control population, indicating that chromosome instability occurs in vivo in BS. In contrast, micronucleus frequencies at either site did not differ significantly between bl/+ individuals and the control population. This survey, in combination with similar earlier ones of populations predisposed to cancer not on a genetic basis but because of exposure to some environmental carcinogen, suggests that the exfoliated cell micronucleus test identifies individuals whose somatic genetic material has, for either genetic or environmental reasons, been damaged in a way that produces chromosome breakage and rearrangement.

Adult↗
PubMed1985

Hybridization with human cells corrects the elevated SCE frequency and BrdU hypersensitivity of hamster cell line EM9.

Cells of the Chinese hamster line EM9 exhibit an elevated SCE frequency and a decreased proliferative response in bromodeoxyuridine (BrdU)-containing medium. Here, these phenotypic features were examined experimentally using polyethylene glycol fusion of EM9 and normal human cells. EM9/human hybrids exhibited both normal SCE frequencies and normal proliferative responses in BrdU-containing medium, suggesting that SCE elevation and BrdU hypersensitivity in EM9 have a common molecular basis.

Animals↗
PubMed1984

Bloom's syndrome and EM9 cells in BrdU-containing medium exhibit similarly elevated frequencies of sister chromatid exchange but dissimilar amounts of cellular proliferation and chromosome disruption.

Bloom's syndrome (BS) and EM9 cells both display elevated frequencies of sister chromatid exchange (SCE) following growth for two rounds of DNA replication in bromodeoxyuridine (BrdU)-containing medium. To learn whether hyperresponsiveness to BrdU itself might play a role in causing the SCE elevation, the effects of BrdU on two other parameters, cellular proliferation and chromosome disruption, were examined, comparing the responses of BS and normal lymphoblastoid cells and of EM9 and CHO cells. BS and normal cells responded similarly with respect to growth for 4 days in BrdU-containing medium (0, 1, 3, and 5 micrograms/ml). Chromosome aberrations were increased only slightly in the BS and normal cells after 2 days in BrdU. CHO cells responded to growth in BrdU-containing medium like BS and normal cells; however, little growth of EM9 was detected at any of the BrdU concentrations employed. CHO and EM9 cells also exhibited strikingly different amounts of chromosome damage following growth in BrdU. After 2 days in 1, 3, and 5 micrograms/ml BrdU 21%, 46%, and 50%, respectively, of the CHO cells had chromosome aberrations in contrast to 92%, 96%, and 98% of the EM9 cells. Most of the aberrations in the BrdU-treated CHO cells consisted of what appeared to be polycentric and ring chromosomes or chromosomes exhibiting telemere association. Acentric fragments were absent from most cells with polycentric and ring chromosomes, indicating either that the abnormal chromosomes were formed during an earlier cell cycle or that the abnormal chromosomes represent a form of association in which the telomeres are apposed so tightly that the juncture between chromosomes cannot be identified microscopically.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Embryonic stress hypothesis of teratogenesis.

Cells and tissues of essentially all eukaryotes respond uniformly to a variety of stressful situations. Immediately following the onset of several types of environmental insult (e.g., hyperthermia), genes for the so-called heat-shock proteins become unusually active; simultaneously, other genetic loci that were engaged in transcription at the onset of the insult become relatively less active. The biologic significance of the heat-shock response is unknown, as is its role, if any, in maintaining human health. In fact, the heat-shock response seems not to have been invoked previously to explain any aspect of human health or disease. Herein, the proposal is made that induction of the heat-shock response in the mammalian embryo during the critical period of organogenesis can alter the established program of activation and inactivation of genetic loci essential for normal intrauterine development, the result being anatomic malformation. By this hypothesis, induction of the heat-shock response provides a common pathway by which diverse environmental agents can result in any of a variety of developmental abnormalities, the precise period during gestation when the response is induced determining the nature of the abnormalities.

Animals↗
PubMed1984

Bloom's syndrome XI. Progress report for 1983.

During the 30 years since its description as a clinical entity, Bloom's syndrome has been diagnosed in more than 100 persons. It is believed that most of these have been accessioned to the Bloom's Syndrome Registry, which now includes 103 persons. Of those 103, 80 are alive, with a mean age of 18.2 years. Twenty-eight malignant neoplasms have been detected, at a mean age of 20.7 years. Periodically, progress reports are being made in this journal of the long-term surveillance of affected families.

Adolescent↗