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PubMed2000

Mapping of X chromosome inversion breakpoints [inv(X)(q11q28)] associated with FG syndrome: a second FG locus [FGS2]?

FG syndrome is an X-linked condition comprising mental retardation, congenital hypotonia, macrocephaly, distinctive facial changes, and constipation or anal malformations. In a linkage analysis, we mapped a major FG syndrome locus [FGS1] to Xq13, between loci DXS135 and DXS1066. The same data, however, clearly demonstrated genetic heterogeneity. Recently, we studied a French family in which an inversion [inv(X)(q12q28)] segregates with clinical symptoms of FG syndrome. This suggests that one of the breakpoints corresponds to a second FG syndrome locus [FGS2]. We report the results of fluorescence in situ hybridization analysis performed in this family using YACs and cosmids encompassing the Xq11q12 and Xq28 regions. Two YACs, one positive for the DXS1 locus at Xq11.2 and one positive for the color vision pigment genes and G6PD loci at Xq28, were found to cross the breakpoints, respectively. We postulate that a gene might be disrupted by one of the breakpoints.

Abnormalities, Multiple↗
PubMed2006

TCR variable gene involvement in chromosome inversion between 14q11 and 14q24 in adult T-cell leukemia.

Chromosomal translocations in T-cell malignancies frequently involve the T-cell receptor (TCR)alpha/delta locus at chromosome 14q11. Although 14q11 abnormalities are found in about 10% of adult T-cell leukemia (ATL) cases, until now there has been no direct evidence showing involvement of the TCR locus in ATL-a malignancy closely associated with HTLV-1 infection. The breakpoints of T-cell malignancies most commonly occur within the Jalpha or Jdelta region of the TCR locus. In ATL, however, despite extensive searching no breakpoint has yet been found in that region. Using fluorescence in situ hybridization with a panel of cosmid and bacterial artificial chromosome probes derived from chromosome 14, including the variable region of the TCRalpha locus, comprehensive analysis of an ATL patient carrying inv(14)(q11q32) revealed that the TCR locus was indeed involved in this inversion. Molecular cloning of the breakpoint revealed the juxtaposition of TCR Valpha to the 14q24 region as a result of two consecutive inversions: inv(14)(q11q32) and inv(14)(q11q24). We also found a gene near the breakpoint at the 14q24 region that is downregulated in this ATL patient and is assigned in the database as a pseudogene of ADAM21 (a disintegrin and metalloproteinase domain 21). Our expression analysis, however, showed that this pseudogene was actually expressed and was capable of encoding a protein similar to ADAM21; thus we have named this gene ADAM21-like (ADAM21-L).

ADAM Proteins↗
PubMed1988

Effects of chromosomal inversion on cell fitness in Escherichia coli K-12.

In an effort to learn what factors might mitigate the establishment of Escherichia coli variants bearing major chromosomal rearrangements, we have examined the effects on cell growth of two inversions between rRNA operons. One of these inversions, IN(rrnD-rrnE), had been propagated in a commonly used subline of E. coli K-12 for approximately 30 yr before its discovery, a fact that illustrates the absence of obvious detrimental effects associated with the inversion. We found that culturing under conditions requiring repeated transition from stationary phase to rapid growth led to the replacement of IN(rrnD-rrnE) cells by cells that had undergone either of two types of additional chromosomal inversion: one type fully restored the wild-type order, while the other partially restored it. The partial reinversion was also between rrn operons, but it left a small transposition. The tendency for overgrowth by these revertants persisted through several rounds of periodic selection. In contrast, the other inversion, IN(rrnG-rrnE), was associated with severe, detrimental effects. The effects of IN(rrnG-rrnE) were also alleviated by full or partial reinversion. The probable relationship between the severity of the effects caused by the inversions and the degree of displacement of the replication origin is discussed. Spontaneous inversion events between rrn operons separated by 18% of the chromosome were estimated to occur at a frequency of roughly 10(-5). If extended to natural situations, the growth disadvantage together with the relatively high frequency of reinversion suggest that clones of cells with an inversion between these rrn operons would be readily overgrown by revertants.

Chromosome Inversion↗
PubMedDate not supplied

Genomic distribution of P elements in Drosophila willistoni and a search for their relationship with chromosomal inversions.

According to the recent-invasion hypothesis, Drosophila melanogaster may have acquired its P elements in a fairly recent process of horizontal transmission between species. Drosophila willistoni has been identified as the potential donor species in that transfer process. A most remarkable feature of D. willistoni is its extensive chromosomal polymorphism due to inversions-the adaptiveness of which has been the subject of many classical studies on evolutionary genetics. In this article, we further extend the study of P elements in D. willistoni, focusing on the possible role they may play in the generation of chromosomal inversions. Our results may be summarized as follows. P-homologous sequences were detected in South American populations of D. willistoni. In two of them, a recently collected wild population and an old laboratory stock, the P insertion sites were located in the polytene chromosomes. Several hybridization sites were mapped in all major chromosome arms of the natural population, which was also chromosomally polymorphic; in the laboratory population, nearly devoid of inversions, hybridization sites were found to be confined to the chromocenter. In the wild population, 10 of the 24 P hybridized sites coincided with several inversions break points and another five sites located themselves very close to those points. The results are discussed within the context of evolutionary hypotheses.

Animals↗
PubMed1995

Distribution of genetic diversity in relation to chromosomal inversions in the malaria mosquito Anopheles gambiae.

The epidemiology of malaria in Africa is complicated by the fact that its principal vector, the mosquito Anopheles gambiae, constitutes a complex of six sibling species. Each species is characterized by a unique array of paracentric inversions, as deduced by karyotypic analysis. In addition, most of the species carry a number of polymorphic inversions. In order to develop an understanding of the evolutionary histories of different parts of the genome, we compared the genetic variation of areas inside and outside inversions in two distinct inversion karyotypes of A. gambiae. Thirty-five cDNA clones were mapped on the five arms of the A. gambiae chromosomes with divisional probes. Sixteen of these clones, localized both inside and outside inversions of chromosome 2, were used as probes in order to determine the nucleotide diversity of different parts of the genome in the two inversion karyotypes. We observed that the sequence diversity inside the inversion is more than three-fold lower than in areas outside the inversion and that the degree of divergence increases gradually at loci at increasing distance from the inversion. To interpret the data we present a selectionist and a stochastic model, both of which point to a relatively recent origin of the studied inversion and may suggest differences between the evolutionary history of inversions in Anopheles and Drosophila species.

Animals↗
PubMed1993

Latitudinal differences in sex chromosome inversions, sex linked allozymes, and mitochondrial DNA variation in Drosophila subobscura.

Mitochondrial DNA, sex linked allozymes, and chromosome A gene arrangement data, from eight European natural populations of Drosophila subobscura, were analyzed to determine the existence of latitudinal clines. Strong north-south correlations with latitude were found for gene arrangements and for the Hbdh and 6Pgdh allozymes. Gametic associations between the A2 gene arrangement, the Hbdh96 and the 6Pgdh96 alleles, point out some kind of epistatic interaction. At mtDNA level, the Hae III, A variant did not show a previously found north-south clinal variation.

Alleles↗
PubMed1997

Large chromosomal inversions occur in Pseudomonas aeruginosa clone C strains isolated from cystic fibrosis patients.

An analysis of the chromosomal structure of 21 Pseudomonas aeruginosa clone C genotypes of various origins was carried out. The circular chromosomes showed various insertions and deletions which did not alter the gene order in 6 environmental and one ear isolate in comparison with strain PAO and strain C. However, the chromosome structure differed by at least one large inversion in 50% of the genotypes (7/14) isolated from cystic fibrosis patients. Recombination endpoints were scattered throughout the chromosome. All but one inversion included the terminus of replication which was displaced by the recombination events. The rearrangements shifted the positions of the rrn operons with respect to the origin of replication, but the transcription of the rrn operons remained in the same direction as replication. The exclusive detection of inversions in isolates from cystic fibrosis lungs, which represent an atypical habitat for P. aeruginosa, supports the theory that peculiar features of this new ecological niche may select, cause or tolerate genomic changes.

Chromosome Inversion↗
PubMed2004

Colour polymorphism in Drosophila mediopunctata: genetic (chromosomal) analysis and nonrandom association with chromosome inversions.

The presence of three dark spots on the abdomen is typical of the tripunctata group of Drosophila, which is the second largest Neotropical group, with 56 species. In some species, such as D. mediopunctata, the colour pattern varies considerably: ranging from flies showing no spots up to flies with three dark spots. In this paper, we present a genetic (chromosomal) analysis of this character showing that this colour polymorphism is genetically determined mainly by the second chromosome. Since this chromosome is the most polymorphic for inversions in this species, we also examined the influence of the inversions on this character. We used strains in which different second chromosomes were placed on the same genetic background and the offspring between them. We found a nonrandom association between the number of spots and the inversions PA0 and PC0. Thus, our results are consistent with the idea that the factors or genes determining a conspicuous polymorphism are likely to be associated, forming a supergene, and this association would be most efficiently accomplished through a chromosome inversion. Moreover, this is the first time that an association between a conspicuous morphological polymorphism and chromosome inversions has been described.

Analysis of Variance↗
PubMed1979

Tn10 mediated integration of the plasmid R100.1 into the bacterial chromosome: inverse transposition.

Upon integration into the bacterial chromosome the drug resistance plasmid R100.1 often loses its tetracycline resistance character. We have analyzed an Hfr strain formed by such an integration and an R-prime plasmid derived from it. We find that integration took place within the Tn10 transposon, that the two IS10 sequences were retained, but that at least 80% of the transposon segment located between them, and carrying the tetracycline resistance genes, had been lost. We suggest that integration of R100.1 was mediated by an inverse transposition using the IS10 sequences.

Chromosomes, Bacterial↗
PubMedDate not supplied

Double heterozygosity of chromosomal inversion in mice: a key to speciation.

Inversion can be very efficient as a reproductive barrier when the same chromosomes are involved in two different rearrangements leading to a double loop during the pachytene stage. The consequence can be a strongly reduced fertility of the double heterozygotes, leading to an irreversible dichotomy.

Animals↗
PubMed2000

Resistance to dieldrin + fipronil assorts with chromosome inversion 2La in the malaria vector Anopheles gambiae.

Cyclodiene insecticide resistance in malaria vector mosquitoes of the Anopheles gambiae species complex (Diptera: Culicidae) has been reported previously from several parts of Africa. We report resistance to dieldrin, a cyclodiene, in two laboratory strains of An. gambiae Giles sensu stricto code-named Ian P20 from Nigeria (1979) and CIG from Cote d'Ivoire (1997). Dieldrin resistance levels were high in adult female mosquitoes (40-75% survived exposure to 4% dieldrin for 1 h) and was closely linked with chromosomal paracentric inversion 2La. This inversion did not occur in Hardy-Weinberg proportions, but showed an excess of heterozygotes in both strains, which may account for the high levels of resistance. This linkage also suggests that dieldrin resistance in Ian P20 is dominant. After subsamples of strain Ian P20 were exposed for 1 h to dieldrin 4% or fipronil 2% (discriminating concentrations), the resultant mortality-rates (61% and 65%) were not significantly different. Most survivors after fipronil treatment also survived subsequent exposure to dieldrin (46/50=92%). This apparent cross-resistance between insecticides of two classes (cyclodiene and phenyl pyrazole) has implications for the management of insecticide resistance in wild populations of the An. gambiae complex.

Animals↗
PubMed2005

Chromosomal inversion polymorphism leads to extensive genetic structure: a multilocus survey in Drosophila subobscura.

The adaptive character of inversion polymorphism in Drosophila subobscura is well established. The O(ST) and O(3+4) chromosomal arrangements of this species differ by two overlapping inversions that arose independently on O(3) chromosomes. Nucleotide variation in eight gene regions distributed along inversion O(3) was analyzed in 14 O(ST) and 14 O(3+4) lines. Levels of variation within arrangements were quite similar along the inversion. In addition, we detected (i) extensive genetic differentiation between arrangements in all regions, regardless of their distance to the inversion breakpoints; (ii) strong association between nucleotide variants and chromosomal arrangements; and (iii) high levels of linkage disequilibrium in intralocus and also in interlocus comparisons, extending over distances as great as approximately 4 Mb. These results are not consistent with the higher genetic exchange between chromosomal arrangements expected in the central part of an inversion from double-crossover events. Hence, double crossovers were not produced or, alternatively, recombinant chromosomes were eliminated by natural selection to maintain coadapted gene complexes. If the strong genetic differentiation detected along O(3) extends to other inversions, nucleotide variation would be highly structured not only in D. subobscura, but also in the genome of other species with a rich chromosomal polymorphism.

Animals↗
PubMed1998

A natural large chromosomal inversion in Lactococcus lactis is mediated by homologous recombination between two insertion sequences.

Comparative analysis of chromosomal macrorestriction polymorphism of the two closely related Lactococcus lactis subsp. cremoris strains MG1363 and NCDO763 revealed the presence of a large inversion covering half of the genome. To determine what kind of genetic element could be implicated in this rearrangement, the two inversion junctions of MG1363 and NCDO763 chromosomes were cloned and characterized. Nucleotide sequence analysis showed the presence of one copy of the lactococcal IS905 element in each junction. Each copy of this element contained the same nucleotide mutation that inactivates the putative transposase. Comparison of the sequences surrounding the insertion sequence demonstrated that the large inversion arose from a single-step homologous recombination event between the two defective copies of the IS905 element. The large inversion presumably conferred no selective disadvantage on strain NCDO763 because this rearrangement did not alter the oriC-terC symmetry of the chromosome and the local genetic environment.

Base Sequence↗
PubMed2005

Chromosome inversions, local adaptation and speciation.

We study the evolution of inversions that capture locally adapted alleles when two populations are exchanging migrants or hybridizing. By suppressing recombination between the loci, a new inversion can spread. Neither drift nor coadaptation between the alleles (epistasis) is needed, so this local adaptation mechanism may apply to a broader range of genetic and demographic situations than alternative hypotheses that have been widely discussed. The mechanism can explain many features observed in inversion systems. It will drive an inversion to high frequency if there is no countervailing force, which could explain fixed differences observed between populations and species. An inversion can be stabilized at an intermediate frequency if it also happens to capture one or more deleterious recessive mutations, which could explain polymorphisms that are common in some species. This polymorphism can cycle in frequency with the changing selective advantage of the locally favored alleles. The mechanism can establish underdominant inversions that decrease heterokaryotype fitness by several percent if the cause of fitness loss is structural, while if the cause is genic there is no limit to the strength of underdominance that can result. The mechanism is expected to cause loci responsible for adaptive species-specific differences to map to inversions, as seen in recent QTL studies. We discuss data that support the hypothesis, review other mechanisms for inversion evolution, and suggest possible tests.

Adaptation, Physiological↗
PubMed1988

[X-chromosome inversion in Drosophila melanogaster accompanied by a mosaic-type position effect: an analysis using cloned DNA fragments].

DNA fragments carrying the genes affected by position effect variegation in the In(1LR)pn2a chromosome were revealed. In situ hybridizations demonstrate preservation of specific DNA sequences in the polytene chromosome regions containing the inactivated genes. It was shown that both euchromatic-heterochromatic boundaries in the In(1LR)pn2a chromosome contain the mobile element B104 (roo).

Animals↗
PubMed2003

A novel chromosomal inversion at 11q23 in infant acute myeloid leukemia fuses MLL to CALM, a gene that encodes a clathrin assembly protein.

Rearrangements involving the MLL gene at chromosome band 11q23 are common in infant acute myeloid leukemias (AMLs). We recently encountered an infant patient with rapidly progressive AML whose leukemic cells harbored a previously undescribed MLL rearrangement involving an inversion of 11q [inv(11)(q14q23)]. We used panhandle PCR to determine that this rearrangement juxtaposed the MLL (Mixed-Lineage Leukemia) gene to the CALM (Clathrin Assembly Lymphoid Myeloid leukemia) gene at 11q14-q21. The CALM protein participates in recruitment of clathrin to internal membrane surfaces, thereby regulating vesicle formation in both endocytosis and intracellular protein transport. Intriguingly, CALM has been identified in other cases of AML as a translocation partner for the AF10 gene, which has independently been found to be an MLL partner in AML. We identified the MLL-CALM fusion transcript (but not the reciprocal CALM-MLL transcript) in leukemia cell RNA by RT-PCR. The predicted 1803 amino acid MLL-CALM fusion protein includes amino-terminal MLL domains involved in transcriptional repression, and carboxy-terminal CALM-derived clathrin-binding domains. The genomic breakpoint in MLL is in the 7th intron (within the breakpoint cluster region); the corresponding CALM breakpoint is in the 7th CALM intron. In contrast, breakpoints in CALM-AF10 translocations lie in the 17th-19th CALM introns (30 kb downstream); also, in these translocations, CALM provides the 5' end of the fusion transcript. Together with its previously recognized association with AF10 in AML, the identification of CALM as an MLL fusion partner suggests that interference with clathrin-mediated trafficking pathways may be an underappreciated mechanism in leukemogenesis.

Acute Disease↗