Showing papers on "Chromosome 22 published in 1994"

Evidence for the complete inactivation of the NF2 gene in the majority of sporadic meningiomas

Abstract: Meningiomas are common central nervous system tumours which present usually in the 4th and 5th decades of life. Loss of constitutional heterozygosity on chromosome 22 in 60% of sporadic meningiomas has implied the involvement of a tumour suppressor gene. The neurofibromatosis type 2 gene (NF2), a prime candidate for involvement in meningioma, was screened for point mutations. After examining eight of the 16 known NF2 exons in 151 meningiomas, 24 inactivating mutations were characterized. Significantly, these aberrations were exclusively detected in tumours which lost the other chromosome 22 allele. These results provide strong evidence that the suppressor gene on chromosome 22, frequently inactivated in meningioma, is the NF2 gene, and suggest that another gene is involved in the development of 40% of meningiomas.

Complete Dna-Sequence Of Yeast Chromosome-Xi

Abstract: The complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome XI has been determined. In addition to a compact arrangement of potential protein coding sequences, the 666,448-base-pair sequence has revealed general chromosome patterns; in particular, alternating regional variations in average base composition correlate with variations in local gene density along the chromosome. Significant discrepancies with the previously published genetic map demonstrate the need for using independent physical mapping criteria.

Identification of the TCL1 gene involved in T-cell malignancies.

Abstract: The TCL1 locus on chromosome 14q32.1 is frequently involved in chromosomal translocations and inversions with one of the T-cell receptor loci in human T-cell leukemias and lymphomas. The chromosome 14 region translocated or rearranged involves approximately 350 kb of DNA at chromosome band 14q32.1. Within this region we have identified a gene coding for a 1.3-kb transcript, expressed only in restricted subsets of cells within the lymphoid lineage and expressed at high levels in leukemic cells carrying a t(14;14)(q11;q32) chromosome translocation or a inv(14)(q11;q32) chromosome inversion. The cognate cDNA sequence reveals an open reading frame of 342 nt encoding a protein of 14 kDa. The TCL1 gene sequence, which, to our knowledge, shows no sequence homology with other human genes, is preferentially expressed early in T- and B-lymphocyte differentiation.

Complete DNA sequence of yeast chromosome II

Abstract: In the framework of the EU genome-sequencing programmes, the complete DNA sequence of the yeast Saccharomyces cerevisiae chromosome II (807 188 bp) has been determined. At present, this is the largest eukaryotic chromosome entirely sequenced. A total of 410 open reading frames (ORFs) were identified, covering 72% of the sequence. Similarity searches revealed that 124 ORFs (30%) correspond to genes of known function, 51 ORFs (12.5%) appear to be homologues of genes whose functions are known, 52 others (12.5%) have homologues the functions of which are not well defined and another 33 of the novel putative genes (8%) exhibit a degree of similarity which is insufficient to confidently assign function. Of the genes on chromosome II, 37-45% are thus of unpredicted function. Among the novel putative genes, we found several that are related to genes that perform differentiated functions in multicellular organisms of are involved in malignancy. In addition to a compact arrangement of potential protein coding sequences, the analysis of this chromosome confirmed general chromosome patterns but also revealed particular novel features of chromosomal organization. Alternating regional variations in average base composition correlate with variations in local gene density along chromosome II, as observed in chromosomes XI and III. We propose that functional ARS elements are preferably located in the AT-rich regions that have a spacing of approximately 110 kb. Similarly, the 13 tRNA genes and the three Ty elements of chromosome II are found in AT-rich regions. In chromosome II, the distribution of coding sequences between the two strands is biased, with a ratio of 1.3:1. An interesting aspect regarding the evolution of the eukaryotic genome is the finding that chromosome II has a high degree of internal genetic redundancy, amounting to 16% of the coding capacity.

Clinical and molecular studies in a large Dutch family with Noonan syndrome

Abstract: We describe the largest Noonan syndrome (NS) family reported to date. The manifestations of the affected relatives are discussed. In the absence of a biochemical marker NS is still a clinical diagnosis. The diagnostic criteria that were used are presented compared with other published criteria for diagnosing NS. The large size of this family enabled us to test the possible involvement of candidate regions by multipoint linkage analysis. Both the region surrounding the NF1 locus on chromosome 17 and the proximal part of chromosome 22 could be excluded. Since NS may well be heterogeneous, the use of such a large family in linkage studies of NS should prove indispensable.

A Cis-Acting Locus That Promotes Crossing over between X Chromosomes in Caenorhabditis Elegans

Abstract: This study reports the characterization of a cis-acting locus on the Caenorhabditis elegans X chromosome that is crucial for promoting normal levels of crossing over specifically between the X homologs and for ensuring their proper disjunction at meiosis I. The function of this locus is disrupted by the mutation me8, which maps to the extreme left end of the X chromosome within the region previously implicated by studies of X; A translocations and X duplications to contain a meiotic pairing site. Hermaphrodites homozygous for a deletion of the locus (Df/Df) or heterozygous for a deletion and the me8 mutation (me8/Df) exhibit extremely high level of X chromosome nondisjunction at the reductional division; this is correlated with a sharp decrease in crossing over between the X homologs as evidenced both by reductions in genetic map distances and by the presence of achiasmate chromosomes in cytological preparations of oocyte nuclei. Duplications of the wild-type region that are unlinked to the X chromosome cannot complement the recombination and disjunction defects in trans, indicating that this region must be present in cis to the X chromosome to ensure normal levels of crossing over and proper homolog disjunction. me8 homozygotes exhibit an altered distribution of crossovers along the X chromosome that suggests a defect in processivity along the X chromosome of an event that initiates at the chromosome end. Models are discussed in which the cis-acting locus deleted by the Dfs functions as a meiotic pairing center that recruits trans-acting factors onto the chromosomes to nucleate assembly of a crossover-competent complex between the X homologs. This pairing center might function in the process of homolog recognition, or in the initiation of homologous synapsis.

EWS-erg and EWS-Fli1 fusion transcripts in Ewing's sarcoma and primitive neuroectodermal tumors with variant translocations.

Abstract: We have determined the frequency of EWS fusion transcripts in a series of primary Ewing's sarcomas and peripheral primitive neuroectodermal tumors and cells lines. Type 1 and 2 EWS-Fli1 fusions were demonstrated in 8 cell lines and 14 patient samples. Five patients with cytogenetically characterized rearrangements of chromosome 22 that did not involve chromosome 11 were included in these studies. A novel EWS-Fli1 in-frame isoform fusing EWS to exon 8 of Fli1 was isolated from a tumor with a variant t(12;22;22)(q14;p1;q12) translocation. Three in-frame isoforms of a novel hybrid transcript derived from the fusion of EWS with the ETS domain of the human erg gene were identified in patient samples and a cell line with cytogenetically unidentified or cryptic translocations involving chromosomes 21 and 22. Interphase analysis by fluorescent in situ suppression hybridization using two overlapping erg yeast artificial chromosome clones demonstrated disruption of the erg gene on chromosome 21 in a patient sample with monosomy 22. Our results provide new information about the involvement of EWS in small round cell tumors involving exchange of its putative RNA-binding domain with DNA-binding domains derived from different members of the ETS family of transcription factors. These studies emphasize the utility of reverse transcriptase PCR analysis and fluorescent in situ hybridization as additional diagnostic tools for differential diagnosis among small round cell tumors.

Molecular and phenotypic mapping of the short arm of chromosome 5: sublocalization of the critical region for the cri-du-chat syndrome

Abstract: Forty-nine individuals have been identified with deletions or translocations involving the short arm of chromosome 5. While most display the classical phenotype of the cri-du-chat syndrome, several of the patients do not have the syndrome or have only a subset of the clinical features. Somatic cell hybrids containing the deleted chromosome 5 were derived from each patient. Each somatic cell hybrid was analyzed at the DNA level using 136 chromosome 5p-specific DNA fragments. It was possible to unambiguously order most of the chromosomal breakpoints present in the somatic cell hybrids based on the hybridization patterns of Southern blots. Further comparisons between the deletions present in the patients and their clinical features identified several chromosomal regions that were involved in specific clinical features. A critical chromosomal region involved the high-pitched cry mapped to 5p15.3, while the chromosomal region involved in the remaining features of the cri-du-chat syndrome mapped to a small region within 5p15.2. Deletions that did not include these two chromosomal regions presented varying clinical phenotypes from severe mental retardation and microcephaly to a clinically normal phenotype. These results demonstrate the need for careful characterization of a 5p deletion in prenatal cases before clinical predictions are made.

Frequent NF2 gene transcript mutations in sporadic meningiomas and vestibular schwannomas

Abstract: The gene for the hereditary disorder neurofibromatosis type 2 (NF2), which predisposes for benign CNS tumors such as vestibular schwannomas and meningiomas, has been assigned to chromosome 22 and recently has been isolated Mutations in the NF2 gene were found in both sporadic meningiomas and vestibular schwannomas However, so far only 6 of the 16 exons of the gene have been analyzed In order to extend the analysis of an involvement of the NF2 gene in the sporadic counterparts of these NF2-related tumors, we have used reverse transcriptase-PCR amplification followed by SSCP and DNA sequence analysis to screen for mutations in the coding region of the NF2 gene Analysis of the NF2 gene transcript in 53 unrelated patients with meningiomas and vestibular schwannomas revealed mutations in 32% of the sporadic meningiomas (n = 44), in 50% of the sporadic vestibular schwannomas (n = 4), in 100% of the tumors found in NF2 patients (n = 2), and in one of three tumors from multiple-meningioma patients Of the 18 tumors in which a mutation in the NF2 gene transcript was observed and the copy number of chromosome 22 could be established, 14 also showed loss of (parts of) chromosome 22 This suggests that in sporadic meningiomas and NF2-associated tumors the NF2 gene functions as a recessive tumor-suppressor gene The mutations detected resulted mostly in frameshifts, predicting truncations starting within the N-terminal half of the putative protein

Analysis of chromosome 22 markers in nine schizophrenia pedigrees

Abstract: Previous results of a genome-wide survey for schizophrenia susceptibility genes in nine multiplex families indicated a possible region of linkage on chromosome 22. We therefore tested for linkage using ten highly polymorphic chromosome 22 DNA markers. Lod score analyses were suggestive of linkage for several markers on the distal end of the chromosome; however, no lod score exceeded 3 assuming either autosomal dominant or autosomal recessive transmission. The highest lod score was 2.09 (theta = 0.10) for marker D22S276 under autosomal recessive inheritance. Based on simulation analyses, this result is unlikely to represent a false positive. Analyses using information from affected individuals only resulted in reduced lod scores, with a maximum of 1.40 (theta = 0.05) for D22S276 assuming autosomal recessive inheritance. Two nonparametric methods, sib pair analysis and the Affected-Pedigree-Member method, also yielded suggestive but inconclusive findings; results were positive, but strict thresholds of significance were not met. Additionally, we tested one candidate gene, the Arylsulfatase A gene, located in the region of 22q13.31-qter. Results were again inconclusive, though the DNA marker available for this gene was a 2-allele RFLP with heterozygosity of 0.5, and therefore not maximally informative. Further investigation of this chromosomal region and this and other candidate genes may be warranted.

Possible origin of a B chromosome deduced from its DNA composition using double FISH technique

Abstract: Double fluorescentin situ hybridization (FISH) with two DNA probes (a 180 bp tandemly repeated DNA and ribosomal DNA) was performed in embryo cells of the grasshopperEyprepocnemis plorans. Repetitive DNA was present in most standard chromosomes (excepting 7, 8 and 10) and in the proximal two-thirds of the B chromosome, which was its major location in the complement. Ribosomal DNA was present distally on the B, and in the active nucleolar organizer regions (NORs) of the X, 9, 10 and 11 chromosomes. A small number of rRNA gene clusters was also observed in the pericentromeric regions of chromosomes 1–8. The double FISH technique showed that the B chromosome (B2 type) is mainly composed of a 180 bp tandem repeat and ribosomal DNA, the minute short arm being the only region that does not hybridize with them. The location and order of the centromere and both the DNA sequences on the B chromosome coincide only with those in the X chromosome, indicating that the B most probably derives from the X.

Deletions on chromosome 22 in sporadic meningioma

Abstract: Meningiomas are the second most common group of primary central nervous system tumors in humans. Cytogenetic and molecular studies imply that genes involved in the primary development of meningioma reside on chromosome 22. The recently characterized neurofibromatosis type 2 gene (NF2) has been shown to be mutated in two cases of sporadic meningioma, suggesting that this is the chromosome 22 gene which is involved in tumorigenesis. We have investigated a series of 170 meningiomas by deletion mapping analysis with 43 markers from chromosome 22 to ascertain if NF2 is the only gene on this autosome that is inactivated. Half of the tumors showed results consistent with monosomy for chromosome 22, whereas 13 cases showed terminal deletions of 22q, including the NF2 region. Homozygous (complete) deletions were detected in tumors from two patients. In one of them complete loss was found at the NF2 locus and cosmid contigs from the region were used to determine the extent of the deletions. The second tumor showed homozygous loss of two large genomic regions outside the NF2 region. These aberrations were confined to only one part of this large tumor, suggesting that they may be involved in the later stages of meningioma development. An additional four tumors had interstitial deletions on chromosome 22, in three of them without overlap with NF2. Our results show that NF2 is completely inactivated in sporadic meningioma but do not rule out the possibility that additional chromosome 22 loci are important in tumorigenesis.

Swedish survey on extra structurally abnormal chromosomes in 39 105 consecutive prenatal diagnoses: Prevalence and characterization by fluorescence in situ hybridization

Abstract: During 7 years (1985–1992), 39 105 consecutive prenatal diagnoses (34 908 amniocenteses and 4197 chorionic villus samples) were made at the five largest clinical genetic laboratories in Sweden. Thirty-one cases of extra structurally abnormal chromosomes (ESACs) were found, giving a total prevalence of 0·8 per 1000. Twelve ESACs were inherited, 14 were de novo and in five the parental origin was unknown. This gives an estimated prevalence of 0·3–0·4 per 1000 for familial and 0·4–0·5 per 1000 for de novo ESACs. Retrospectively, the ESACs were characterized by fluorescence in situ hybridization (FISH). In nine cases, no material was available for this analysis. In 21 of the remaining 22 cases, the chromosomal origin could be identified by FISH. Seventeen of these (81 per cent) were derived from the acrocentric chromosomes, of which 13 originated from chromosome 15 (62 per cent). The most common ESAC was the inv dup(15) (57 per cent). Two cases were derived from chromosome 22, one from chromosome 14, and one from either chromosome 13 or chromosome 21. The four remaining cases consisted to two i(18p)s and two small ring chromosomes derived from chromosomes 4 and 19, respectively.

Characterization of a new member of the human /-adaptin gene family from chromosome 22q12, a candidate meningioma gene

Abstract: A 140 kb homozygous deletion from 22q12 in one meningioma directed us towards the cloning and characterization of a new member of the human beta-adaptin gene family (named BAM22). Adaptins are essential for the formation of clathrin coated vesicles in the course of intracellular transport of receptor-ligand complexes. The BAM22 gene is totally inactivated in the tumor with homozygous deletion. Northern blot analysis of 70 sporadic meningiomas showed specific loss of expression in 8 tumors, suggesting inactivation of BAM22. Based on this, we propose BAM22 as a second chromosome 22 locus important in meningioma development, after the neurofibromatosis type 2 gene.

Comparison of genetic and physical maps of group 7 chromosomes from Triticum aestivum L.

Abstract: We present a high density physical map of homoeologous group 7 chromosomes from Triticum aestivum L using a series of 54 deletion lines, 6 random amplified polymorphic DNA (RAPD) markers and 91 cDNA or genomic DNA clones from wheat, barley and oat So far, 51 chromosome segments have been distinguished by molecular markers, and 54 homoeoloci have been allocated among chromosomes 7A, 7B and 7D The linear order of molecular markers along the chromosomes is almost identical in the A- B- and D-genome of wheat In addition, there is colinearity between the physical and genetic maps of chromosomes 7A, 7B and 7D from T aestivum, indicating gene synteny among the Triticeae However, comparison of the physical map of chromosome 7D from T aestivum with the genetic map from Triticum tauschii some markers have been shown to be physically allocated with distortion in more distal chromosome regions The integration of genetic and physical maps could assist in estimating the frequency and distribution of recombination in defined regions along the chromosome Physical distance did not correlate with genetic distance A dense map facilitates the detection of multiple rearrangements We present the first evidence for an interstitial inversion either on chromosome arm 7AS or 7DS of Chinese Spring Molecularly tagged chromosome regions (MTCRs) provide landmarks for long-range mapping of DNA fragments

Mapping of two genes encoding members of a distinct subfamily of MAX interacting proteins: MAD to human chromosome 2 and mouse chromosome 6, and MXI1 to human chromosome 10 and mouse chromosome 19.

Abstract: Both the MAD and the MXI1 genes encode basic-helix-loop-helix-leucine zipper (bHLH-Zip) transcription factors which bind Max in vitro, forming a sequence-specific DNA-binding complex similar to the Myc-Max heterodimer. Mad and Myc compete for binding to Max. In addition, Mad has been shown to act as a transcriptional repressor while Myc appears to function as an activator. Mxi1 also appears to lack a transcriptional activation domain. Therefore, Mxi1 and Mad might antagonize Myc function and are candidate tumor suppressor genes. We report here the mapping of the MAD and MXI1 genes in human and mouse by fluorescence in situ hybridization (FISH) and by recombination mapping. The MAD gene was mapped to human chromosome 2 at band p13 by FISH and to mouse chromosome 6 by meiotic mapping. The MXI1 gene was mapped to human chromosome 10 at band q25 and on mouse chromosome 19 at region D by FISH. There was a second site of hybridization on mouse chromosome 2 at region C, which may represent a pseudogene or a related sequence. The mapping results confirm regions of conservation between human chromosome 2p13 and mouse chromosome 6 and between chromosome 10q25 and mouse chromosome 19D. Human chromosomes 2p13 and 10q25 have been involved in specific tumors where the role of Mad and Mxi1 can now be investigated.

Chromosomal deletions in anaplastic meningiomas suggest multiple regions outside chromosome 22 as important in tumor progression

Abstract: Meningioma is a common, usually benign, sporadic and solitary tumor of the meninges covering the central nervous system. Meningiomas can become malignant, and such anaplastic tumors are associated with a high rate of recurrence and death from the disease. We analyzed 16 sporadic, anaplastic meningiomas for loss of alleles on the majority of chromosomal arms, in order to define regions in the genome which may be important for tumor progression. Loss of genetic material was observed on all but 2 chromosomes studied. While loss of heterozygozity (LOH) from chromosome 22 was the most frequent finding, LOH from the short arm of chromosome I was the second most common lesion occurring preferentially in tumors from men, and at a frequency almost as high as for LOH on chromosome 22. This suggests the existence of a tumor-suppressor locus on Ip involved in meningioma carcinogenesis. Three tumor samples from one large, anaplastic tumor, each with distinct histopathological characteristics, were studied. All 3 samples showed deletions on 22q and Ip. However, only one tumor sample, with the most malignant histopathological phenotype, displayed, in addition to 22q and Ip, deletions on 9q and 17p. This case suggests that the latter 2 chromosomal regions may harbor genes which contribute to the progression of meningioma.

Somatic NF2 gene mutations in familial and non-familial vestibular schwannoma

Abstract: Vestibular schwannoma occurs both as a sporadic tumour and in the dominantly inherited familial cancer syndrome neurofibromatosis type 2 (NF2). The gene for NF2 has recently been isolated on chromosome 22, and the demonstration of inactivating germline mutations in NF2 patients and NF2 associated tumours suggests that it act as a tumour suppressor. We have investigated 85 sporadic and 2 NF2 associated vestibular schwannomas, and one vagal schwannoma for chromosome 22 allele loss and NF2 gene mutations. A further 7 vestibular schwannomas were investigated for NF2 mutations only. Chromosome 22 allele loss was detected in 34 of 87 vestibular schwannomas and in the vagal nerve schwannoma. Six exons of the NF2 gene were investigated by SSCP analysis in all 95 tumours. Somatic NF2 gene mutations were detected in 13 non-familial vestibular schwannomas and in one of the NF2 vestibular schwannomas. Seven non-familial tumours with an NF2 gene mutation also displayed a chromosome 22 allele loss. Thirteen of the mutations were predicted to produce truncation of the NF2 protein. These results suggest that somatic mutations of the NF2 tumour suppressor gene are a critical step in the pathogenesis of both familial and non-familial vestibular schwannoma and that the mechanism of tumourigenesis complies with a 'two-hit' mutation model.

Chromosome 2-specific DNA clones from flow-sorted chromosomes of tomato.

Abstract: We obtained DNA clones specific to tomato chromosome 2 from a small number of chromosomes collected by flow sorting. Suspensions of metaphase chromosomes were prepared from 3-month-old tomato cell cultures of Lycopersicon pennellii. Isolated chromosomes stained with chromomycin A3 and Hoechst 33258 were analyzed on an EPICS 753 flow cytometer using a UV laser to excite Hoechst fluorescence and a 458 nm laser to excite chromomycin A3 fluorescence. Chromosomes from well-resolved peaks on a bivariate flow karyotype were sorted directly onto membrane filters for spot-blot analysis. The filters were processed and hybridized with chromosome-specific repetitive DNA probes. In this way tomato chromosome 1 and chromosome 2 were assigned to peaks in the bivariate flow karyotypes. One thousand copies of the putative chromosome 2 were flow-sorted directly into microfuge tubes. DNA specific to chromosome 2 was amplified by a polymerase chain reaction (PCR) technique using universal 22mer degenerate oligonucleotide primers (DOP) sequences. DOP-PCR yields a smear of fragments of various sizes from 250 to 1600 bp. Amplified products were cloned into the Bluescript plasmid vector. Approximately 11 of the clones contained sequences with highly repetitive elements, and 85% contained only low-copy-number sequences. Eleven clones containing low-copy-number sequences that detect restriction fragment length polymorphisms were placed on the molecular linkage map of tomato. All showed linkage to chromosome 2.

Search for a schizophrenia susceptibility locus on human chromosome 22

Abstract: We used 10 highly informative DNA polymorphic markers and genetic linkage analysis to examine whether a gene locus predisposing to schizophrenia is located on chromosome 22, in 105 families with schizophrenia and schizoaffective disorder. The LOD score method, including analysis for heterogeneity, provided no conclusive evidence of linkage under a dominant, recessive, or penetrance free model of inheritance. Affected sib-pair analysis was inconclusive. Affected pedigree member analysis gave only suggestive evidence for linkage. Multipoint APM analysis, using 4 adjacent loci including D22S281 and IL2RB, a region of interest from the APM analysis, gave non-significant results for the three different weighting functions.

Tetrasomy 15q: two marker chromosomes with no detectable alpha-satellite DNA.

Abstract: Two patients with specific and similar phenotypes were both found to have an unusual marker chromosome present in 70%-80% of their lymphocytes at routine cytogenetic examination. The marker chromosomes were isolated by flow sorting and were amplified by degenerate oligonucleotide-primed PCR. These libraries and a cosmid probe located at 15q26 were used to characterize the marker chromosomes by FISH. Both marker chromosomes were found to consist of duplicated chromosome material from the distal part of chromosome 15q and were identified as inv dup(15) (qter-->q23::q23-->qter) and inv dup(15) (qter-->q24::q24-->qter), respectively. Hence, the markers did not include any known centromere region, and no alpha-satellite DNA could be detected at the site of the primary constriction. Tetrasomy 15q may be a new syndrome, associated with a specific type of marker chromosome. In addition, further analyses of this type of marker chromosome might give new insight into the structure and function of the mammalian centromere.

A small (2.4 Mb) Bacillus cereus chromosome corresponds to a conserved region of a larger (5.3 Mb) Bacillus cereus chromosome

Abstract: Summary We have determined the sizes of the chromosomes of six Bacillus cereus strains (range 2.4–4.3 Mb) and constructed a physical map of the smallest B. cereus chromosome (2.4 Mb). This map was compared to those of the chromosomes of four B. cereus strains and one B. thuringiensis strain previously determined to be 5.4-6.3 Mb. Of more than 50 probes, 30 were localized to the same half of the larger B. cereus and B. thuringiensis chromosomes. All 30 were also present on the small chromosome. Twenty of the probes present on the other half of the larger chromosomes were either present on extrachromosomal DNA, or absent from the B. cereus strain carrying the small chromosome. We propose that the genome of B. cereus and B. thuringiensis has one constant part and another less stable part which is more easily mobilized into other genetic elements. This part of the genome is localized to one region of the chromosome and may be subject to deletions or more frequent relocations between the chromosome and episomal elements of varying sizes up to the order of megabases.

Philadelphia-negative chronic myeloid leukaemia: detection by FISH of BCR-ABL fusion gene localized either to chromosome 9 or chromosome 22.

Abstract: Dual-colour FISH has been used to study two patients with chronic myeloid leukaemia (CML) associated with a normal karyotype. Co-localization of signals from BCR and ABL cosmids was observed in interphase nuclei from both patients. In one patient, analysis of metaphase spreads showed that the 3' region of the ABL gene was deleted from one chromosome 9 and inserted into chromosome 22. In a second patient 5' BCR sequences were missing from one copy of chromosome 22, and co-localized with 3' ABL sequences on chromosome 9. These results demonstrate the molecular heterogeneity of Ph-negative CML. In addition, they illustrate the potential usefulness of dual-colour FISH on interphase nuclei for monitoring the response to treatment of patients with Ph-negative CML.

Long-range cis preference in DNA homology search over the length of a Drosophila chromosome.

Abstract: P element-induced chromosome breakage on the X chromosome of Drosophila melanogaster was repaired six times more frequently when a homologous template was located anywhere on the X chromosome rather than on an autosome. Cis-trans comparisons confirmed that recombinational repair was more frequent when the interacting sequences were physically connected. These results suggest that the search for homology between the broken ends and a matching template sequence occurs preferentially in the cis configuration. This cis advantage operates over more than 15 megabases of DNA.

Interchromosomal exchange of a large subtelomeric segment in a Plasmodium falciparum cross.

Abstract: Duplications and interchromosomal transpositions of chromosome segments are implicated in the genetic variability of Plasmodium falciparum malaria parasites. One parasite clone, HB3, was shown to lack a subtelomeric region of chromosome 13 that normally carries a PfHRPIII gene. We show here that the chromosome 13 segment carrying PfHRPIII was replaced in HB3 by a duplicated terminal segment from chromosome 11. Mapping results indicate that the segment includes at least 100-200 kb of subtelomeric DNA and contains duplicated copies of the Pf332 and RESA-2 genes. We followed inheritance of this duplication in a genetic cross between the HB3 and another P.falciparum clone, Dd2, that is euploid for the Pf332, RESA-2 and PfHRPIII genes. Three types of progeny from the cross showed expected inheritance forms: a Dd2 euploid parent type, an HB3 aneuploid parent type, and a recombinant euploid type that carried PfHRPIII from Dd2 chromosome 13 and Pf332 from HB3 chromosome 11. However, a fourth euploid progeny type was also observed, in which the chromosome 13 segment from HB3 was transposed back to replace the terminus of chromosome 11. Three of 14 individual progeny were of this type. These findings suggest a mechanism of recombination from subtelomeric pairing and exchange between non-homologous chromosomes in meiosis.

A molecular analysis of the origin of the Crepis capillaris B chromosome

Abstract: The origin of the B chromosome of Crepis capillaris has been studied by using in situ hybridization with different DNA probes. Genomic in situ hybridization (GISH) with DNA from plants with and without Bs as probes indicates that the B chromosome has many DNA sequences in common with A chromosomes, showing no region rich in B-specific sequences. Six additional DNA probes were used to test the possible origin of this B from the standard NOR chromosome (chromosome 3). In the short arm of the NOR chromosome, we detected not only 18 S + 25 S rDNA, but also 5 S rDNA and a specific repetitive sequence from the NOR chromosome (pCcH32); in the heterochromatic bands of the long arm, we found two different repetitive sequences (pCcE9 and pCcD29). In the B chromosome, however, only the 18 S + 25 S rDNA and the telomeric sequences from Arabidopsis thaliana were observed. Our in situ hybridization data with telomeric repeats indicate that the two telomeres of the B are larger than those of the A chromosomes, confirming the isochromosomal nature of this B. Hybridizations of 18 S + 25 S rDNA and telomeric repeats to blots of DNA from plants with and without Bs reveal a high homology between A and B 18 S + 25 S rDNA genes, but some sequence dissimilarities between A and B telomeres. Taken as a whole, these data indicate that the entire B of C. capillaris, although possibly having originated from the standard genome, did not derive directly from the NOR chromosome.