RESUMEN
Uterine leiomyoma is a common tumor of smooth muscle cell origin often characterized by the presence of a balanced t(12;14)(q13-15;q24.1) chromosomal translocation. This breakpoint on chromosome 14 had previously been placed between the markers SPTB and D14S77, a region estimated to span 7 cM. In this study we have used a meiotic breakpoint mapping panel to construct a high resolution genetic map of this interval. Markers that mapped within this interval were used to analyze DNA from a somatic cell hybrid containing the t(12;14) translocated chromosome. The results of this analysis localize the t(12;14) breakpoint on chromosome 14 between D14S298 and D14S540, between which no meiotic recombination was detected. This sets the stage for identifying the gene(s) disrupted by the chromosomal translocation by defining the markers that flank the translocation breakpoint.
Asunto(s)
Cromosomas Humanos Par 12 , Cromosomas Humanos Par 14 , Leiomioma/genética , Translocación Genética , Neoplasias Uterinas/genética , Secuencia de Bases , Mapeo Cromosómico , Cartilla de ADN , Femenino , Marcadores Genéticos , Haplotipos , Humanos , Meiosis , Datos de Secuencia Molecular , Sondas de Oligonucleótidos , Reacción en Cadena de la Polimerasa , Recombinación GenéticaRESUMEN
A recurrent reciprocal chromosomal translocation, t(12;14)(q15;q24) is frequently observed in uterine leiomyoma. Chromosome 12 breakpoints have been shown to occur in a region of approximately 150 kb that contains the gene for a high mobility group protein (HMGI-C). The breakpoint region on chromosome 14 has not been precisely defined. We have generated a contig of overlapping yeast artificial chromosome (YAC) clones approximately 3 Mb in size. Fluorescence in situ hybridization (FISH) analysis showed that this contig spanned the t(12;14) breakpoints in three uterine leiomyomas and that the breakpoints in these tumors occurred within a 1 Mb region. A 30 kb cosmid spanning one of the breakpoints was isolated to set the stage for identifying regions on chromosome 14 that may cause this region to be a preferential site for chromosomal translocation.
Asunto(s)
Cromosomas Humanos Par 14/genética , ADN de Neoplasias/genética , Leiomioma/genética , Translocación Genética/genética , Neoplasias Uterinas/genética , Cromosomas Artificiales de Levadura/genética , Cromosomas Humanos Par 12/genética , Clonación Molecular , Femenino , Marcadores Genéticos , Humanos , Cariotipificación , Reacción en Cadena de la PolimerasaRESUMEN
Mycoplasma pulmonis is a murine pathogen that causes chronic respiratory disease in laboratory rats and mice. Several examples of high-frequency phenotypic switching have been reported for M. pulmonis, the molecular basis of which is unknown. We report here that during growth the M. pulmonis chromosome undergoes DNA rearrangements at a high frequency. Some of the rearrangements we examined correlated with changes in the susceptibility of the cells to mycoplasma virus P1, an example of phenotypic switching involving changes in surface antigen structure. Other rearrangements, unrelated to phenotypic switching, involved a DNA element present in the chromosome in multiple copies. The high level of DNA recombination that occurred in M. pulmonis indicates that this may be one of the most variable genomes studied to date. High levels of DNA recombination may contribute to the unusually high rate of evolution that mycoplasmas are thought to be undergoing. Understanding the molecular basis for this phenomenon may provide an insight into the chronic nature of many mycoplasmal infections.
Asunto(s)
Variación Antigénica/genética , Cromosomas Bacterianos , Mycoplasma/genética , Recombinación Genética , Bacteriófagos/fisiología , Clonación Molecular , ADN Bacteriano , Fenotipo , Polimorfismo de Longitud del Fragmento de Restricción , Secuencias Repetitivas de Ácidos NucleicosRESUMEN
Insertion sequence (IS) elements are mobile genetic elements found in prokaryotes. We have identified a repetitive element from Mycoplasma pulmonis, a murine pathogen, that is similar to eubacterial IS elements. By subcloning a single strain of M. pulmonis, we isolated a variant clone in which the IS element had undergone an apparent transposition event. The nucleotide sequences of the element, designated IS1138, and the target site into which it inserted were determined. IS1138 consists of 1288 bp with 18 bp perfect terminal inverted repeats. Sequence analysis of the target site before and after insertion of IS1138 identified a 3 bp duplication of target DNA flanking the element. The predicted amino acids encoded by the major open reading frame of IS1138 share significant similarity with the transposases of the IS3 family. Southern hybridization analysis indicates that repetitive sequences similar to IS1138 are present in most, if not all, strains of M. pulmonis, but IS1138-like sequences were not detected in other mycoplasmal species.
Asunto(s)
Elementos Transponibles de ADN/genética , Mycoplasma/genética , Secuencia de Aminoácidos , Secuencia de Bases , Clonación Molecular , Secuencia de Consenso , Datos de Secuencia Molecular , Familia de Multigenes/genética , Mycoplasma/enzimología , Nucleotidiltransferasas/genética , Sistemas de Lectura Abierta/genética , Reacción en Cadena de la Polimerasa , Polimorfismo de Longitud del Fragmento de Restricción , Secuencias Repetitivas de Ácidos Nucleicos/genética , Homología de Secuencia de Aminoácido , Especificidad de la Especie , TransposasasRESUMEN
The chromosome of the murine pathogen Mycoplasma pulmonis undergoes rearrangements at a high frequency. We show that some of these rearrangements regulate the phase-variable expression of a cluster of genes (the vsa locus) that encode the variable V-1 surface antigens. Only one vsa gene is associated with an expression site; the other vsa genes are transcriptionally silent. The silent genes lack the 5' end region (promoter and ribosome-binding site) that is present in the expressed gene, and DNA rearrangements regulate gene expression by reassorting the 5' end region from an expressed gene with the 3' end region from a previously silent gene. All vsa rearrangements identified so far are site-specific DNA inversions that occur between copies of a specific 34 bp sequence that is conserved in each vsa gene. Interestingly, DNA inversions within the vsa locus apparently occur in concert with inversion of the hsd1 element, which regulates restriction and modification activity in M. pulmonis.
Asunto(s)
Variación Antigénica/genética , Antígenos de Superficie/genética , Inversión Cromosómica , Reordenamiento Génico , Mycoplasma/genética , Mycoplasma/inmunología , Secuencia de Aminoácidos , Antígenos de Superficie/química , Proteínas Bacterianas/genética , Northern Blotting , Western Blotting , Mapeo Cromosómico , Clonación Molecular , Regulación Bacteriana de la Expresión Génica , Genes Bacterianos , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Sistemas de Lectura Abierta , Regiones Promotoras Genéticas , Recombinación Genética , Secuencias Repetitivas de Ácidos Nucleicos , Transcripción GenéticaRESUMEN
A translocation involving chromosomes 12 and 14 [t(12;14)(q15;24.1)] is commonly seen in benign smooth muscle tumor as uterine leiomyoma (UL). A contig of P1-derived artificial chromosome and bacterial artificial chromosome clones on chromosome 14, encompassing a t(12;14) breakpoint cluster region (BCR) in UL, was generated principally using the recently developed HAPPY map of chromosome 14 as a framework (P. H. Dear et al., 1998, Genomics 48: 232-241). Three UL t(12;14) breakpoints have been localized within this contig, showing that a BCR of at least 400 kb exists on chromosome 14. Other studies of tumors with t(12;14) rearrangements similarly show breakpoints within a 475-kb multiple aberration region on chromosome 12. Thus t(12;14) is an example of a translocation in which the breakpoints are located within a BCR on both chromosome 12 and chromosome 14, justifying the identification of expressed sequences that are altered in these BCR regions. A total of four expressed sequences were identified in the BCR on chromosome 14. Two of these were novel cDNAs (D14S1460E and D14S1461E). The chromosome 14 cDNAs were expressed in multiple adult tissues. The identification of a large breakpoint cluster region on chromosome 14 suggests that translocations in this region mediate their effects at a distance and also that elements that predispose this region to recurrent chromosomal translocation may be widely distributed.