RESUMO
A female patient with a structurally abnormal idic(Y) (p11.32) chromosome was studied using fluorescence in situ hybridization and PCR to define the precise position of the breakpoint. The patient had a complex mosaic karyotype with eight cell lines and at least two morphologically distinct derivatives from the Y chromosome. The rearrangement was a result of a meiosis I exchange between sister chromatids at the pseudoautosomal region, followed by centromere misdivision at meiosis II. Due to instability of the dicentric Y chromosome, new cell lines later arose because of mitotic errors occurring during embryonic development. Physical examination revealed a normal female phenotype without genital ambiguity, a normal uterus and rudimentary gonads which were surgically removed.
Assuntos
Quebra Cromossômica/genética , Cromossomos Humanos Y , Mosaicismo , Síndrome de Turner/diagnóstico , Sequência de Bases , Pré-Escolar , Feminino , Humanos , Hibridização in Situ Fluorescente , Cariotipagem , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , Análise de Sequência de DNA , Síndrome de Turner/genética , Síndrome de Turner/cirurgiaRESUMO
We report on a clinical and molecular cytogenetic study of a patient who presents a complex chromosomal rearrangement with two different cell lines. Using high-resolution GTG banding and fluorescence in situ hybridization (FISH) with several probes, including bacterial artificial chromosomes (BACs), the karyotype was defined as 46,XX,del(9)(p23)[54]/46,XX,der(9)t(1;9)(q41;p23)[46], indicating the presence of monosomy 9p23 in all cells and trisomy 1q41 in approximately 50% of the cells. The patient studied presents most of the manifestations of the 9p deletion and 1q duplication syndromes. The breakpoint was mapped at 9p23 with a loss of approximately 13.9-Mb of DNA. The duplicated segment consists of approximately 35 Mb from 1q41-qter region. We also suggest that a mechanism for telomere capture and interstitial telomeric sequences (ITs) is involved in a neo-telomere formation in one of the cell lines. This study highlights the importance of combining high-resolution chromosome and FISH with BACs in order to make genotype-phenotype correlations and to understand the mechanisms involved chromosomal aberrations.
Assuntos
Aberrações Cromossômicas , Cromossomos Humanos Par 1/genética , Cromossomos Humanos Par 9/genética , Mosaicismo , Telômero/genética , Criança , Bandeamento Cromossômico , Quebra Cromossômica/genética , Deleção Cromossômica , Feminino , Humanos , Hibridização in Situ Fluorescente , Cariotipagem , Modelos Genéticos , Monossomia , Translocação Genética , TrissomiaRESUMO
A female patient with a structurally abnormal idic(Y) (p11.32) chromosome was studied using fluorescence in situ hybridization and PCR to define the precise position of the breakpoint. The patient had a complex mosaic karyotype with eight cell lines and at least two morphologically distinct derivatives from the Y chromosome. The rearrangement was a result of a meiosis I exchange between sister chromatids at the pseudoautosomal region, followed by centromere misdivision at meiosis II. Due to instability of the dicentric Y chromosome, new cell lines later arose because of mitotic errors occurring during embryonic development. Physical examination revealed a normal female phenotype without genital ambiguity, a normal uterus and rudimentary gonads which were surgically removed.
Assuntos
Humanos , Feminino , Pré-Escolar , Cromossomos Humanos Y , Mosaicismo , Quebra Cromossômica/genética , Síndrome de Turner/diagnóstico , Hibridização in Situ Fluorescente , Análise de Sequência de DNA , Cariotipagem , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , Sequência de Bases , Síndrome de Turner/genética , Síndrome de Turner/cirurgiaRESUMO
Although large deletions from the coagulation factor VIII gene, F8, are responsible for 5% of severe hemophilia A (seHA), few of them have been fully characterised. A detailed description of a large partial deletion of the F8 caused by unequal recombination between homeologous AluSx-derived sequences is presented. The proband, a case of isolated hemophilia A with a high inhibitor titre (5700 BU), showed a consistent absence of PCR-amplification of exons 4 to 10, EX4_EX10del. Two approaches were used to narrow down the deletion breakpoints: a direct physical analysis based on PCR (that additionally permits carrier detection in the family); and, under the hypothesis that the mutation resulted from homologous recombination, sequence alignments of F8 intron 3 and 10. Both approaches indicate an unequal crossing over (CO) between two Alu-related sequences. Both elements involved were derived from the AluSx-subfamily consensus and demonstrate 86% sequence identity (with only single-base mismatches), with three gaps (of 2, 3 and 14-bases) and two main tracts of perfectly homologous sequence (28 and 24-bp). The short stretch of intron 10 embedded into intron 3 sequence, linked to the CO, represents a typical hallmark of homologous recombination (double-strand break repair model). A detailed description of EX4_EX10del mutation is c.[338+3485delins1687+2223_1687+2225; 338+3551_1687+2291 del]. The common involvement of unequal homologous recombination mediated by repetitive elements allowed us to suggest that our experimental design (based on intron sequence alignments) may be successfully applied to rearrangements involved in other X-linked inherited diseases. Like other Alu-rich genes throughout the human genome, Alu-mediated homologous recombination in F8 may be an important cause of hemophilia by promoting large DNA deletions.
Assuntos
Elementos Alu/genética , Hemofilia A/genética , Recombinação Genética/genética , Homologia de Sequência do Ácido Nucleico , Sequência de Bases , Quebra Cromossômica/genética , Deleção Cromossômica , Sequência Consenso/genética , Análise Mutacional de DNA , Éxons/genética , Genômica , Humanos , Íntrons/genética , Modelos Genéticos , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , Deleção de Sequência/genéticaRESUMO
In a Brazilian population of the neotropical rodent Akodon montensis we found five sex-reversed XY females. These animals were cytogenetically analyzed by chromosome painting using species-specific DNA probes from the Y chromosome, generated by chromosomal microdissection and subsequent use of the degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR). The results showed a chromosome complement with an apparently normal Y chromosome and an X chromosome carrying a translocation that encompasses a large portion of the Y chromosome (seemingly the entire Y). Ovarian histology suggested that these females are fertile. Amplification of the SRY HMG box sequence by PCR shows that at least one copy of the Sry gene is present in the A. montensis XY females. Based on our findings, we suggest that the breakpoint of the X;Y translocation probably altered an X-linked sex-determining locus (or loci), blocking testicular organogenesis in the XY females. Further studies are necessary to determine the precise location and role of this putative sex-determining chromosomal region. Genetic mechanisms of XY sex reversal in A. montensis populations are discussed.
Assuntos
Coloração Cromossômica , Fertilidade/genética , Muridae/genética , Proteínas Nucleares , Fatores de Transcrição , Translocação Genética/genética , Cromossomo X/genética , Cromossomo Y/genética , Motivos de Aminoácidos , Animais , Brasil , Bandeamento Cromossômico , Quebra Cromossômica/genética , Sondas de DNA/genética , Proteínas de Ligação a DNA/química , Proteínas de Ligação a DNA/genética , Diploide , Transtornos do Desenvolvimento Sexual , Feminino , Dosagem de Genes , Heterocromatina/genética , Cariotipagem , Masculino , Ovário/patologia , Reação em Cadeia da Polimerase , Processos de Determinação Sexual , Proteína da Região Y Determinante do SexoRESUMO
The kinetics of micronucleated polychromatic erythrocytes (MN-PCE) induction by methylnitrosourea (MNU) was determined in mice with the purpose of discerning whether or not the kinetics reflects the mechanism of chromosome break induction. A very long latency period (LP) was observed which is not compatible with an agent that does not require metabolic activation or incorporation to DNA for acting, but this is consistent with the mechanism demonstrated earlier that MNU causes chromosome breaks throughout the repair of mismatches induced by the alkylation of bases in a previous division. This is also supported by the presence of two rates of MN-PCE induction with respect to dose, which suggests that MN-PCE are induced by two mechanisms, an efficient one induced with the lower dose, and another less efficient one induced with higher doses. A similar behavior was observed in the curve of LP vs. dose, the lower dose causes 8 h of LP and higher doses increase LP but not proportionally to dose. The lower dose did not cause a reduction in the proportion of polychromatic erythrocytes, suggesting that this dose did not produce an important cytotoxic effect that could explain the long LP.
Assuntos
Quebra Cromossômica/genética , Metilnitrosoureia/toxicidade , Mutagênicos/toxicidade , Animais , Relação Dose-Resposta a Droga , Eritrócitos/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Testes para Micronúcleos , Fatores de TempoRESUMO
Restriction endonucleases and ionizing radiations have been extensively used to study the origin of chromosomal aberrations. Although a non-random distribution of chromosome breakpoints induced by these agents has been claimed by several authors, the significance of the chromatin structure and nuclear architecture in the localization of breakpoints is still not well understood. Breakpoint patterns produced by endonucleases targeted to specific genome sequences or by ionizing radiations could provide additional evidence to clarify this point. Results obtained from the localization of breakpoints induced by AluI, BamHI or DNase I as well as by neutrons or gamma-rays in G-banded Chinese hamster ovary (CHO) chromosomes are presented. AluI and BamHI were electroporated into CHO cells either during the G1 or S-phase of the cell cycle. A co-localization of breakpoints was found with a preferential occurrence in G-light bands independent of the cell cycle stage in which aberration production took place. Since AluI and BamHI recognition sequences are partitioned in the housekeeping and tissue-specific subgenomes respectively, we postulated that nuclease sensitive sites in active chromatin could be the main targets for the induction of breakpoints by these endonucleases. This assumption is supported by the finding that DNase I-induced breakpoint patterns in CHO cells are similar to those produced by AluI and BamHI. Digestion of fixed CHO chromosomes with these endonucleases induced G-banding suggesting a higher sensitivity of G-light chromatin. For comparison purposes, CHO cells were irradiated with neutrons or gamma-rays and breakpoints localized in G-banded chromosome aberrations. A higher occurrence of breakpoints in G-light bands was also observed. We detected seven breakage-prone G-light bands that were preferentially damaged by the three endonucleases and by both types of radiation. These results emphasize the possible implication of the chromatin structure and the nuclear architecture in the localization of chromosome breakpoints induced by endonucleases, neutrons and gamma-rays.
Assuntos
Cromatina/química , Quebra Cromossômica/genética , Cromossomos/metabolismo , Animais , Células CHO , Ciclo Celular/fisiologia , Núcleo Celular/fisiologia , Bandeamento Cromossômico , Cricetinae , Eletroporação , Endonucleases/metabolismo , Raios gama , NêutronsRESUMO
It has been suggested that genetic predisposition to cancer might be related to spontaneous chromosome instability or to fragile site expression. Therefore, spontaneous breakage and fragile sites were analyzed in nine untreated chronic lymphocytic leukemia (CLL) patients to determine their relation to cancer rearrangements. Five cases presented spontaneous gaps and breaks with a random distribution of breakpoints. In cultures treated with fluorodeoxyuridine or aphidicolin, 29 specific bands could be defined as fragile sites. A significant clustering of these sites was found with known common fragile sites (c-fra) and cancer breakpoints described in the literature. Most of these cancer breakpoints were involved in structural abnormalities associated with CLL (p < 0.00001). These data suggest that the expression of specific fragile sites might be related to structural chromosomal aberrations in CLL.