Mouse chromosome-specific painting probes generated from microdissected chromosomes

Using degenerate primer amplification of chromosomes microdissected from banded cytogenetic preparations, we constructed both whole chromosome painting probes for mouse Chromosomes (Chrs) 1, 2, 3, and 11 and a centromere probe that strongly paints most mouse centromeres. We also amplified a Robertsonian translocation chromosome microdissected from unstained preparations to construct a painting probe for Chrs 9 and 19. The chromosomes probes uniformly painted the respective chromosomes of origin. We demonstrated the utility of the Chr 11 probe in aberration analysis by staining mutants that we had previously identified as containing a Chr 11 translocation, and in some mutant cell lines we observed chromosome rearrangements not previously detected in stained cytogenetic preparations. The technology of microdissection and amplification applies to all mouse chromosomes or to specific subchromosomal regions and will be useful in mouse genetics, in aberration analysis, and for chromosome identification.     

Mapping of balanced chromosome translocation breakpoints to the basepair level from microdissected chromosomes

The analysis of structural variants associated with specific phenotypic features is promising for the elucidation of the function of involved genes. There is, however, at present no approach allowing the rapid mapping of chromosomal translocation breakpoints to the basepair level from a single chromosome. Here we demonstrate that we have advanced both the microdissection and the subsequent unbiased amplification to an extent that breakpoint mapping to the basepair level has become possible. As a case in point we analysed the two breakpoints of a t(7;13) translocation observed in a patient with split hand/foot malformation (SHFM1). The amplification products of the der(7) and of the der(13) were hybridized to custom‐made arrays, enabling us to define primers at flanking breakpoint regions and thus to fine‐map the breakpoints to the basepair level. Consequently, our results will also contribute to a further delineation of causative mechanisms underlying SHFM1 which are currently unknown.     

Delineation of marker chromosomes by reverse chromosome painting using only a small number of DOP-PCR amplified microdissected chromosomes

A new procedure for determining the chromosomal origin of marker chromosomes has been carried out. The origin of marker chromosomes that were unidentifiable by standard banding techniques could be verified by reverse chromosome painting. This technique includes microdissection, followed by in vitro DNA amplification and fluorescence in situ hybridization (FISH). A number of marker chromosomes prepared from unbanded and from GTG-banded lymphocyte chromosomes were collected with microneedles and transferred to a collection drop. The chromosomal material was amplified by a degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR). The resulting PCR products were labelled by nick-translation with biotin-11-dUTP and used as probes for FISH. They were hybridized onto normal metaphase spreads in order to determine the precise regional chromosomal origin of the markers. Following this approach, we tested 2–14 marker chromosomes in order to determine how many are necessary for reverse chromosome painting. As few as two marker chromosomes provided sufficient material to paint the appropriate chromosome of origin, regardless of whether the marker contained heterochromatic or mainly euchromatic material. With this method, it was possible to identify two marker chromosomes of a healthy proband [karyotype: 48,XY, +mar₁,+mar₂] and an aberrant Y chromosome of a mentally retarded boy [karyotype: 46,X, der(Y)].     

Evolutionary breakpoints through a high-resolution comparative map between porcine chromosomes 2 and 16 and human chromosomes

This study reports a high-resolution comparative map between human chromosomes and porcine chromosomes 2 (SSC2) and 16 (SSC16), pointing out new homologies and evolutionary breakpoints. SSC2 is of particular interest because of the presence of several important QTLs. Among 226 porcine ESTs selected according to their expected localization, 151 were RH mapped and ordered on SSC2. This study confirmed the extensive conservation between SSC2 and HSA11 and HSA19 and refined the homology with HSA5 (three blocks defined). Furthermore the SSC2q pericentromeric region was shown to be homologous to another human chromosome (HSA1). A complex organization of these syntenies was demonstrated on SSC2q. Our strategy led us to improve also the SSC16 RH map by adding 45 markers. Two-color fluorescence in situ hybridization of markers representative of each synteny confirmed block order. Finally, 29 breakpoints were identified in both species, and porcine BACs containing two breakpoints were isolated.     

PCR in situ followed by microdissection allows whole chromosome painting probes to be made from single microdissected chromosomes

Whole-chromosome painting probes (WCPs) and chromosome-arm painting probes (CAPs) are an integral part of the cytogenetic analysis of chromosome abnormalities. While these are routinely made by chromosome microdissection, multiple copies of the dissected region have been necessary to achieve a library sufficiently complex to provide adequate painting. Performing multiple dissections of chromosomes or chromosome regions is time consuming and occasionally impossible, such as when working with species whose banded karyotype is not well defined. We have developed a method whereby chromosome paints can be reliably generated by dissecting single chromosomes. The technique consists of performing degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR) in situ on the chromosomes, prior to dissection. Enough amplification occurs to enable a single dissected chromosome to be used to create a painting probe sufficiently complex for use in fluorescence in situ hybridization (FISH). The amplification products remain localized on the chromosomes; this allows region-specific chromosome paints to be made. We detail this novel technique and show whole-chromosome, arm-specific, and contiguous region-specific probes for human and rat, each created from single dissected fragments of chromatin. Received: 14 January 1999 / Accepted: 28 January 1999     

Improved definition of chromosomal breakpoints using high-resolution multicolour banding

Characterisation of chromosome rearrangements using conventional banding techniques often fails to determine the localisation of breakpoints precisely. In order to improve the definition of chromosomal breakpoints, the high-resolution multicolour banding (MCB) technique was applied to identify human chromosome 5 breakpoints from 40 clinical cases previously assessed by conventional banding techniques. In 30 cases (75%), at least one breakpoint was redefined, indicating that MCB markedly improves chromosomal breakpoint localisation. The MCB pattern is highly reproducible and, in contrast to conventional banding pattern, is consistent in both short and elongated chromosomes. This might be of fundamental interest for the detection of chromosomal abnormalities, especially in tumour cells. Moreover, MCB even allows the detection of abnormalities that remain cryptic in GTG-banding analysis.     

Testing the nonrandomness of chromosomal breakpoints using highest observed breakages

To determine whether a chromosomal band is a fragile site rather than a spontaneous breakpoint, an essential step is to test the nonrandomness of breakage at the region. In this paper, the nonapplicability of the testing procedure introduced by Bohm et al. is discussed, and a new detection procedure is proposed. This new procedure considers the relations of one site with the others, and can be applied to tests of the nonrandomness of breakpoints under either the proportional probability model, or the equiprobability model. A data set for Chinese patients with colorectal carcinoma is analyzed as an illustration of the proposed method. Received: 27 August 1998 / Accepted: 18 December 1998     

Assignment of oat linkage groups to microdissected Avena strigosa chromosomes

Microdissection of metaphase chromosome preparations of diploid oat Avena strigosa (2n = 14) allowed isolation of the three individual chromosomes with distinct morphologies, numbers 2, 3 and 7. Using a PCR approach based on the DNA of microdissected chromosomes, STS derivatives of RFLP markers, genetically mapped in Avena spp. linkage maps, have been physically assigned to these three chromosomes. Based on either two or four RFLP-derived STS markers, the A. strigosa chromosomes 2 and 3 were found to be homoeologous to the oat linkage groups C and E, respectively. With the DNA of chromosome 7, four RFLP-derived STS markers located within the central part of linkage group F and two distal ends of linkage group G were amplified. Accordingly, chromosome 7 corresponds to linkage group F and, most probably, is involved in an A. strigosa-specific chromosomal translocation relative to the diploid species Avena atlantica and Avena hirtula, of which the cross progeny was used for linkage mapping of the tested RFLP clones.     

Hobo transposons causing chromosomal breakpoints.

Several laboratory surveys have shown that transposable elements (TEs) can cause chromosomal breaks and lead to inversions, as in dysgenic crosses involving P-elements. However, it is not presently clear what causes inversions in natural populations of Drosophila. The only direct molecular studies must be taken as evidence against the involvement of mobile elements. Here, in Drosophila lines transformed with the hobo transposable element, and followed for 100 generations, we show the appearance of five different inversions with hobo inserts at breakpoints. Almost all breakpoints occurred in hobo insertion sites detected in previous generations. Therefore, it can be assumed that such elements are responsible for restructuring genomes in natural populations.     

Chromosome painting using chromosome-specific probes from flow-sorted pig chromosomes.

Biotinylated chromosome-specific probes were prepared from flow-sorted pig chromosomes 1, 13, 18, X, and Y using the degenerate oligonucleotide-primed polymerase chain reaction. Probes prepared in this way can be used to confirm the identity of chromosomes in the bivariate pig flow karyotype and in pig x mouse somatic cell hybrids.     

Comparative painting of mammalian chromosomes

Comparative chromosome painting has shown that synteny has been conserved for large segments of the genome in various placental mammals. Advances such as spectral karyotyping and multicolour ‘bar coding’ lend speed and precision to comparative molecular cytogenetics. Reciprocal chromosome painting and hybridisations with probes such as yeast artificial chromosomes, cosmids, and fibre fluorescence in situ hybridisation allow subchromosomal assignments of chromosome regions and can identify breakpoints of rearranged chromosomes. Advances in molecular cytogenetics can now be used to test the hypothesis that chromosome rearrangement breakpoints in human pathology and in evolution are correlated.     

Precise detection of rearrangement breakpoints in mammalian chromosomes

Background  

Genomes undergo large structural changes that alter their organisation. The chromosomal regions affected by these rearrangements are called breakpoints, while those which have not been rearranged are called synteny blocks. We developed a method to precisely delimit rearrangement breakpoints on a genome by comparison with the genome of a related species. Contrary to current methods which search for synteny blocks and simply return what remains in the genome as breakpoints, we propose to go further and to investigate the breakpoints themselves in order to refine them.     

Localization of 11q13 loci with respect to regional chromosomal breakpoints

We have employed two strategies to map 13 markers located at 11q13. First, we used pulsed-field gel electrophoresis of DNA fragments obtained with methylation-sensitive restriction enzymes. The markers used in this study were scattered over 8.4 Mb and, for most of them, could not be linked one to another. A second mapping strategy employed hybridization to either DNA of somatic hybrids containing various parts of the long arm of chromosome 11 or metaphase chromosomes of a B-cell line containing the t(11;14)(q13;q32) translocation. We were able to sort out the centromeric from the telomeric probes with respect to translocation breakpoints taken as reference chromosomal landmarks by this approach. BCL1, which corresponds to the region where the t(11;14)(q13;q32) translocation breakpoints are clustered, appears as a boundary between two areas of human/mouse homology present in conserved syntenic regions on mouse chromosomes 7 and 19.     

Localization of translocation breakpoints in somatic metaphase chromosomes of barley

Karyotype analyses based on staining by acetocarmine followed by Giemsa N-banding of somatic metaphase chromosomes of Hordeum vulgare L. were carried out on 61 reciprocal translocations induced by X-irradiation. By means of computer-based karyotype analyses all of the 122 breakpoints could be localized to defined sites or segments distributed over the seven barley chromosomes. The pre-definition of translocations with respect to their rearranged chromosome arms from other studies rendered it possible to define the break positions even in translocations having exchanged segments equal in size and the breakpoints located distally to any Giemsa band or other cytological marker. The breakpoints were found to be non-randomly spaced along the chromosomes and their arms. All breaks but one occurred in interband regions of the chromosomes, and none of the breaks was located directly within a centromere. However, short and long chromosome arms recombined at random. An improved tester set of translocations depicting the known break positions of most distal location is presented.     

A high-resolution comparative map between pig chromosome 17 and human chromosomes 4, 8, and 20: identification of synteny breakpoints

We report on the construction of a high-resolution comparative map of porcine chromosome 17 (SSC17) focusing on evolutionary breakpoints with human chromosomes. The comparative map shows high homology with human chromosome 20 but suggests more limited homologies with other human chromosomes. SSC17 is of particular interest in studies of chromosomal organization due to the presence of QTLs that affect meat quality and carcass composition. A total of 158 pig ESTs available in databases or developed by the Sino-Danish Pig Genome Sequencing Consortium were mapped using the INRA-University of Minnesota porcine radiation hybrid panel. The high-resolution map was further anchored by fluorescence in situ hybridization. This study confirmed the extensive conservation between SSC17 and HSA20 and enabled the gene order to be determined. The homology of the SSC17 pericentromeric region was extended to other human chromosomes (HSA4, HSA8) and the chromosomal breakpoint boundaries were accurately defined. In total 15 breakpoints were identified.     

A method for the rapid sequence-independent amplification of microdissected chromosomal material

We have developed a simple, efficient method by which microdissected material can be amplified directly in the collection container in a few hours. The procedure involves two initial rounds of DNA synthesis with T7 DNA polymerase, using a primer that contains a random pentanucleotide sequence at its 3' end and a defined sequence at its 5' end, followed by PCR amplification with the defined sequence as the primer. The resulting products can be biotinylated and used for fluorescence in situ hybridization (FISH) to confirm their chromosomal location. As few as 17 dissected chromosomal regions provide sufficient material for a specific FISH signal on the appropriate band of metaphase chromosomes. We have obtained a chromosome 6q25-qter-specific painting probe in this way.     

Characterisation of repeated sequences from microdissected B chromosomes of Crepis capillaris

The B chromosome of Crepis capillaris was isolated from the standard chromosomes by microdissection, and the chromosomal DNA amplified using the degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR). The PCR product was cloned and a Bspecific library created and characterised. Southern and in situ hybridisation analyses of the DOP-PCR product from microdissected B chromosomes confirmed that the B chromosome is composed mainly of sequences also present in the A chromosomes but lacks the main repeated DNA families located in the A-chromosomal heterochromatin. From 100 clones analysed, 12% of the generated B-chromosomal library was shown to be composed of dispersed repeats located in both the A and B chromosomes. No B-specific repeated sequence was detected. One of the most abundant repeated DNAs within the library, the family B134, was further characterised. Repeating units show a sequence similarity range from 69% to 90% and are characterised by their richness in (CA)n repeats. In situ hybridisation revealed that members of this family are dispersed throughout the A and B chromosomes but are more concentrated in the pericentromeric heterochromatin of the B, indicating that the molecular organization of B heterochromatin is different from that of the A chromosomes. Compared with the A chromosomes, the Bs contain about 20,000 copies per micron more of the B134 sequence. This indicates that B134 was amplified on the B chromosome after its origin. The B134 sequences in the B chromosomes have also diverged from those on the A chromosomes. Although the DNA composition of A and B chromosomes is similar, Bs are evolving separately from A chromosomes at the molecular level.     

Human Chromosome 10 loci map to three different sheep chromosomes

The interleukin 2 receptor (IL2RA), a human Chromosome (Chr) 10p locus, was mapped to sheep Chr 13q12-q15 by in situ hybridization. Two loci from human Chr 10q, cytochrome P450 subfamily XVII (CYP17) and the tachykinin 2 receptor (TAC2R), were assigned to sheep Chrs 22q21-q23 and 25q14-q23 respectively. The assignment of IL2RA allows the provisional assignment of the previously unassigned sheep syntenic group U15 to sheep Chr 13. Sheep linkage group 5 is predicted to be located on sheep Chr 25 on the basis of the TAC2R assignment.     

Normalization of a chromosomal contact map

ABSTRACT: BACKGROUND: Chromatin organization has been increasingly studied in relation with its important influence on DNA-related metabolic processes such as replication or regulation of gene expression. Since its original design ten years ago, capture of chromosome conformation (3C) has become an essential tool to investigate the overall conformation of chromosomes. It relies on the capture of long-range trans and cis interactions of chromosomal segments whose relative proportions in the final bank reflect their frequencies of interactions, hence their average spatial proximity. The recent coupling of 3C with deep sequencing approaches now allows the generation of high resolution genome-wide chromosomal contact maps. Different protocols have been used to generate such maps in various organisms. This includes mammals, drosophila and yeast. The massive amount of raw data generated by the genomic 3C has to be carefully processed to alleviate the various biases and byproducts generated by the experiments. Our study aims at proposing a simple normalization procedure to take into account these unwanted but inevitable events. RESULTS: Careful analysis of the raw data generated previously for budding yeast Saccharomyces cerevisiae led to the identification of three main biases affecting the final datasets, including an original bias resulting from the circularization of DNA molecules exhibiting specific lengths in accordance with laws from polymer physics. We then developed a simple normalization procedure to process the data and allow the generation of a normalized, highly contrasted, chromosomal contact map for S. cerevisiae. The same method was then extended to the first human genome contact map. Using the normalized data, we revisited the preferential interactions originally described between subsets of discrete chromosomal features. Notably, the detection of preferential interactions between tRNA in yeast and CTCF, PolII binding sites in human can vary with the normalization procedure used. CONCLUSIONS: We quantitatively reanalyzed the genomic 3C data obtained for S. cerevisiae, identified some of the biases inherent to the technique and proposed a simple normalization procedure to analyze them. Such an approach can be easily generalized for genomic 3C experiments in other organisms. More experiments and analysis will be necessary to reach optimal resolution and accuracies of the maps generated through these approaches. Working with cell population presenting highest levels of homogeneity will prove useful in this regards.