Chromosome-specific paints from a high-resolution flow karyotype of the dog

Satellite DNA Sequences in Canidae and Their Chromosome Distribution in Dog and Red Fox

Satellite DNA is a characteristic component of mammalian centromeric heterochromatin, and a comparative analysis of its evolutionary dynamics can be used for phylogenetic studies. We analysed satellite and satellite-like DNA sequences available in NCBI for 4 species of the family Canidae (red fox, Vulpes vulpes, VVU; domestic dog, Canis familiaris, CFA; arctic fox, Vulpes lagopus, VLA; raccoon dog, Nyctereutes procyonoides procyonoides, NPR) by comparative sequence analysis, which revealed 86-90% intraspecies and 76-79% interspecies similarity. Comparative fluorescence in situ hybridisation in the red fox and dog showed signals of the red fox satellite probe in canine and vulpine autosomal centromeres, on VVUY, B chromosomes, and in the distal parts of VVU9q and VVU10p which were shown to contain nucleolus organiser regions. The CFA satellite probe stained autosomal centromeres only in the dog. The CFA satellite-like DNA did not show any significant sequence similarity with the satellite DNA of any species analysed and was localised to the centromeres of 9 canine chromosome pairs. No significant heterochromatin block was detected on the B chromosomes of the red fox. Our results show extensive heterogeneity of satellite sequences among Canidae and prove close evolutionary relationships between the red and arctic fox.

Afrotheria genome; overestimation of genome size and distinct chromosome GC content revealed by flow karyotyping

Afrotheria genome size is reported to be over 50% larger than that of human, but we show that this is a gross overestimate. Although genome sequencing in Afrotheria is not complete, extensive homology with human has been revealed by chromosome painting. We provide new data on chromosome size and GC content in four Afrotherian species using flow karyotyping. Genome sizes are 4.13 Gb in aardvark, 4.01 Gb in African elephant, 3.69 Gb in golden mole and 3.31 Gb in manatee, whereas published results show a mean of 5.18 Gb for Afrotheria. Genome GC content shows a negative correlation with size, indicating that this is due to differences in the amount of AT-rich sequences. Low genome GC content and small variance in chromosome GC content are characteristic of aardvark and elephant and may be associated with the high degree of conserved synteny, suggesting that these are features of the Afrotherian ancestral genome.

The bat genome: GC-biased small chromosomes associated with reduction in genome size

Bats are distinct from other mammals in their small genome size as well as their high metabolic rate, possibly related to flight ability. Although the genome sequence has been published in two species, the data lack cytogenetic information. In this study, the size and GC content of each chromosome are measured from the flow karyotype of the mouse-eared bat, Myotis myotis (MMY). The smaller chromosomes are GC-rich compared to the larger chromosomes, and the relative proportions of homologous segments between MMY and human differ among the MMY chromosomes. The MMY genome size calculated from the sum of the chromosome sizes is 2.25 Gb, and the total GC content is 42.3%, compared to human and dog with 41.0 and 41.2%, respectively. The GC-rich small MMY genome is characterised by GC-biased smaller chromosomes resulting from preferential loss of AT-rich sequences. Although the association between GC-rich small chromosomes and small genome size has been reported only in birds so far, we show in this paper, for the first time, that the same phenomenon is observed in at least one group of mammals, implying that this may be a mechanism common to genome evolution in general.

Chromosomes in the flow to simplify genome analysis

Nuclear genomes of human, animals, and plants are organized into subunits called chromosomes. When isolated into aqueous suspension, mitotic chromosomes can be classified using flow cytometry according to light scatter and fluorescence parameters. Chromosomes of interest can be purified by flow sorting if they can be resolved from other chromosomes in a karyotype. The analysis and sorting are carried out at rates of 10(2)-10(4) chromosomes per second, and for complex genomes such as wheat the flow sorting technology has been ground-breaking in reducing genome complexity for genome sequencing. The high sample rate provides an attractive approach for karyotype analysis (flow karyotyping) and the purification of chromosomes in large numbers. In characterizing the chromosome complement of an organism, the high number that can be studied using flow cytometry allows for a statistically accurate analysis. Chromosome sorting plays a particularly important role in the analysis of nuclear genome structure and the analysis of particular and aberrant chromosomes. Other attractive but not well-explored features include the analysis of chromosomal proteins, chromosome ultrastructure, and high-resolution mapping using FISH. Recent results demonstrate that chromosome flow sorting can be coupled seamlessly with DNA array and next-generation sequencing technologies for high-throughput analyses. The main advantages are targeting the analysis to a genome region of interest and a significant reduction in sample complexity. As flow sorters can also sort single copies of chromosomes, shotgun sequencing DNA amplified from them enables the production of haplotype-resolved genome sequences. This review explains the principles of flow cytometric chromosome analysis and sorting (flow cytogenetics), discusses the major uses of this technology in genome analysis, and outlines future directions.

Comparative analysis of a plant pseudoautosomal region (PAR) in Silene latifolia with the corresponding S. vulgaris autosome

Background

The sex chromosomes of Silene latifolia are heteromorphic as in mammals, with females being homogametic (XX) and males heterogametic (XY). While recombination occurs along the entire X chromosome in females, recombination between the X and Y chromosomes in males is restricted to the pseudoautosomal region (PAR). In the few mammals so far studied, PARs are often characterized by elevated recombination and mutation rates and high GC content compared with the rest of the genome. However, PARs have not been studied in plants until now. In this paper we report the construction of a BAC library for S. latifolia and the first analysis of a > 100 kb fragment of a S. latifolia PAR that we compare to the homologous autosomal region in the closely related gynodioecious species S. vulgaris.

Results

Six new sex-linked genes were identified in the S. latifolia PAR, together with numerous transposable elements. The same genes were found on the S. vulgaris autosomal segment, with no enlargement of the predicted coding sequences in S. latifolia. Intergenic regions were on average 1.6 times longer in S. latifolia than in S. vulgaris, mainly as a consequence of the insertion of transposable elements. The GC content did not differ significantly between the PAR region in S. latifolia and the corresponding autosomal region in S. vulgaris.

Conclusions

Our results demonstrate the usefulness of the BAC library developed here for the analysis of plant sex chromosomes and indicate that the PAR in the evolutionarily young S. latifolia sex chromosomes has diverged from the corresponding autosomal region in the gynodioecious S. vulgaris mainly with respect to the insertion of transposable elements. Gene order between the PAR and autosomal region investigated is conserved, and the PAR does not have the high GC content observed in evolutionarily much older mammalian sex chromosomes.

The dog as a possible animal model for human non-Hodgkin lymphoma: a review

Lymphoma represents the most frequent hematopoietic cancer in dogs, and it shows significant overlap with the human disease. Several environmental factors have been associated with canine lymphoma, suggesting that they may contribute to lymphomagenesis. Canine lymphoma often presents in advanced stage (III-V) at diagnosis and, most commonly, has an aggressive clinical course requiring prompt treatment, which relies on the use of polychemotherapy. In this review, we will summarize the state-of-the-art of canine lymphoma epidemiology, pathobiology, diagnostic work-up and therapy, and will highlight the links to the corresponding human disease, providing evidence for the use of dog as an animal model of spontaneous disease.

Reassessment of genome size in turtle and crocodile based on chromosome measurement by flow karyotyping: close similarity to chicken

The genome size in turtles and crocodiles is thought to be much larger than the 1.2 Gb of the chicken (Gallus gallus domesticus, GGA), according to the animal genome size database. However, GGA macrochromosomes show extensive homology in the karyotypes of the red eared slider (Trachemys scripta elegans, TSC) and the Nile crocodile (Crocodylus niloticus, CNI), and bird and reptile genomes have been highly conserved during evolution. In this study, size and GC content of all chromosomes are measured from the flow karyotypes of GGA, TSC and CNI. Genome sizes estimated from the total chromosome size demonstrate that TSC and CNI are 1.21 Gb and 1.29 Gb, respectively. This refines previous overestimations and reveals similar genome sizes in chicken, turtle and crocodile. Analysis of chromosome GC content in each of these three species shows a higher GC content in smaller chromosomes than in larger chromosomes. This contrasts with mammals and squamates in which GC content does not correlate with chromosome size. These data suggest that a common ancestor of birds, turtles and crocodiles had a small genome size and a chromosomal size-dependent GC bias, distinct from the squamate lineage.

Genome sequence of an Australian kangaroo, Macropus eugenii, provides insight into the evolution of mammalian reproduction and development

BACKGROUND

We present the genome sequence of the tammar wallaby, Macropus eugenii, which is a member of the kangaroo family and the first representative of the iconic hopping mammals that symbolize Australia to be sequenced. The tammar has many unusual biological characteristics, including the longest period of embryonic diapause of any mammal, extremely synchronized seasonal breeding and prolonged and sophisticated lactation within a well-defined pouch. Like other marsupials, it gives birth to highly altricial young, and has a small number of very large chromosomes, making it a valuable model for genomics, reproduction and development.

RESULTS

The genome has been sequenced to 2 × coverage using Sanger sequencing, enhanced with additional next generation sequencing and the integration of extensive physical and linkage maps to build the genome assembly. We also sequenced the tammar transcriptome across many tissues and developmental time points. Our analyses of these data shed light on mammalian reproduction, development and genome evolution: there is innovation in reproductive and lactational genes, rapid evolution of germ cell genes, and incomplete, locus-specific X inactivation. We also observe novel retrotransposons and a highly rearranged major histocompatibility complex, with many class I genes located outside the complex. Novel microRNAs in the tammar HOX clusters uncover new potential mammalian HOX regulatory elements.

CONCLUSIONS

Analyses of these resources enhance our understanding of marsupial gene evolution, identify marsupial-specific conserved non-coding elements and critical genes across a range of biological systems, including reproduction, development and immunity, and provide new insight into marsupial and mammalian biology and genome evolution.

A first-generation integrated tammar wallaby map and its use in creating a tammar wallaby first-generation virtual genome map

BACKGROUND

The limited (2X) coverage of the tammar wallaby (Macropus eugenii) genome sequence dataset currently presents a challenge for assembly and anchoring onto chromosomes. To provide a framework for this assembly, it would be a great advantage to have a dense map of the tammar wallaby genome. However, only limited mapping data are available for this non-model species, comprising a physical map and a linkage map.

RESULTS

We combined all available tammar wallaby mapping data to create a tammar wallaby integrated map, using the Location DataBase (LDB) strategy. This first-generation integrated map combines all available information from the second-generation tammar wallaby linkage map with 148 loci, and extensive FISH mapping data for 492 loci, especially for genes likely to be located at the ends of wallaby chromosomes or at evolutionary breakpoints inferred from comparative information. For loci whose positions are only approximately known, their location in the integrated map was refined on the basis of comparative information from opossum (Monodelphis domestica) and human. Interpolation of segments from the opossum and human assemblies into the integrated map enabled the subsequent construction of a tammar wallaby first-generation virtual genome map, which comprises 14336 markers, including 13783 genes recruited from opossum and human assemblies. Both maps are freely available at http://compldb.angis.org.au.

CONCLUSIONS

The first-generation integrated map and the first-generation virtual genome map provide a backbone for the chromosome assembly of the tammar wallaby genome sequence. For example, 78% of the 10257 gene-scaffolds in the Ensembl annotation of the tammar wallaby genome sequence (including 10522 protein-coding genes) can now be given a chromosome location in the tammar wallaby virtual genome map.

Flow analysis and sorting of plant chromosomes

The use of flow cytometry for evaluation of plant chromosomes requires some specialized attention to preparation and instrumentation. This unit deals exclusively with plant cytogenetics and presents an outline of this area as well as methods for accumulation of cells in metaphase, preparation of chromosome suspensions, flow analysis and sorting of chromosomes, and processing of the sorted chromosomes. Each method is described in tremendous detail because in many aspects dealing with plant cells is quite different from dealing with mammalian cells. Supporting histograms are presented as well as a range of special hints on dealing with plant material and a discussion of the utility of sorted chromosomes for plant genome mapping.

Canine cytogenetics--from band to basepair

Humans and dogs have coexisted for thousands of years, during which time we have developed a unique bond, centered on companionship. Along the way, we have developed purebred dog breeds in a manner that has resulted unfortunately in many of them being affected by serious genetic disorders, including cancers. With serendipity and irony the unique genetic architecture of the 21st century genome of Man's best friend may ultimately provide many of the keys to unlock some of nature's most intriguing biological puzzles. Canine cytogenetics has advanced significantly over the past 10 years, spurred on largely by the surge of interest in the dog as a biomedical model for genetic disease and the availability of advanced genomics resources. As such the role of canine cytogenetics has moved rapidly from one that served initially to define the gross genomic organization of the canine genome and provide a reliable means to determine the chromosomal location of individual genes, to one that enabled the assembled sequence of the canine genome to be anchored to the karyotype. Canine cytogenetics now presents the biomedical research community with a means to assist in our search for a greater understanding of how genome architectures altered during speciation and in our search for genes associated with cancers that affect both dogs and humans. The cytogenetics 'toolbox' for the dog is now loaded. This review aims to provide a summary of some of the recent advancements in canine cytogenetics.

Definition of the zebrafish genome using flow cytometry and cytogenetic mapping

BACKGROUND

The zebrafish (Danio rerio) is an important vertebrate model organism system for biomedical research. The syntenic conservation between the zebrafish and human genome allows one to investigate the function of human genes using the zebrafish model. To facilitate analysis of the zebrafish genome, genetic maps have been constructed and sequence annotation of a reference zebrafish genome is ongoing. However, the duplicative nature of teleost genomes, including the zebrafish, complicates accurate assembly and annotation of a representative genome sequence. Cytogenetic approaches provide "anchors" that can be integrated with accumulating genomic data.

RESULTS

Here, we cytogenetically define the zebrafish genome by first estimating the size of each linkage group (LG) chromosome using flow cytometry, followed by the cytogenetic mapping of 575 bacterial artificial chromosome (BAC) clones onto metaphase chromosomes. Of the 575 BAC clones, 544 clones localized to apparently unique chromosomal locations. 93.8% of these clones were assigned to a specific LG chromosome location using fluorescence in situ hybridization (FISH) and compared to the LG chromosome assignment reported in the zebrafish genome databases. Thirty-one BAC clones localized to multiple chromosomal locations in several different hybridization patterns. From these data, a refined second generation probe panel for each LG chromosome was also constructed.

CONCLUSION

The chromosomal mapping of the 575 large-insert DNA clones allows for these clones to be integrated into existing zebrafish mapping data. An accurately annotated zebrafish reference genome serves as a valuable resource for investigating the molecular basis of human diseases using zebrafish mutant models.

The dog: A powerful model for studying genotype-phenotype relationships

Within the last two years, series of studies have focused on the structure of the dog genome (Canis familiaris) and the characteristics of the dog population as it evolved since being domesticated from wolves about 14,000 years ago. In this review, we explain why the dog is a unique and promising model for determining genotype/phenotype relationships and why it should be easier with this model to identify the genes responsible for many genetic diseases. We also revisit the last ten years of developments in canine molecular genetics that culminated in the release of the entire genome sequence.

Extensive coloured identification of dog chromosomes to support karyotype studies: the colour code

The identification of individual dog chromosomes is problematic because the 38 pairs of autosomes are small and acrocentric. Here we describe the design and application of a FISH tool that enables definitive identification of each dog autosome in a normal karyotype, without relying on subjective interpretation of DAPI banding patterns. From a high-resolution physical map of the canine genome, we have chosen a panel of 80 canine chromosome-specific BAC clones. DNA from each clone is labeled with one of five different fluorochrome-conjugated nucleotides. By selecting one to three spatially separated BACs per chromosome, and labelling them with a distinctive combination of colours, each autosome can be identified objectively and orientated accurately, irrespective of the quality of DAPI chromosome banding. This tool, or part of it, can be used for any purpose where accurate identification of canine autosomes in a normal karyotype is essential. In this study, we demonstrate use of the 'colour code' for chromosome identification following CGH analysis of unbalanced genomic aberrations in a canine brain tumour. Our method is an improvement of an earlier procedure, featuring chromosome-specific BACs and sequential FISH hybridisations, as it enables simultaneous identification of all chromosomes in a single hybridisation.

Canine genomics and genetics: running with the pack

The domestication of the dog from its wolf ancestors is perhaps the most complex genetic experiment in history, and certainly the most extensive. Beginning with the wolf, man has created dog breeds that are hunters or herders, big or small, lean or squat, and independent or loyal. Most breeds were established in the 1800s by dog fanciers, using a small number of founders that featured traits of particular interest. Popular sire effects, population bottlenecks, and strict breeding programs designed to expand populations with desirable traits led to the development of what are now closed breeding populations, with limited phenotypic and genetic heterogeneity, but which are ideal for genetic dissection of complex traits. In this review, we first discuss the advances in mapping and sequencing that accelerated the field in recent years. We then highlight findings of interest related to disease gene mapping and population structure. Finally, we summarize novel results on the genetics of morphologic variation.

Dog star rising: the canine genetic system

Purebred dogs are providing invaluable information about morphology, behaviour and complex diseases, both of themselves and humans, by supplying tractable populations in which to map genes that control those processes. The diversification of dog breeds has led to the development of breeds enriched for particular genetic disorders, the mapping and cloning of which have been facilitated by the availability of the canine genome map and sequence. These tools have aided our understanding of canine population genetics, linkage disequilibrium and haplotype sharing in the dog, and have informed ongoing efforts of the need to identify quantitative trait loci that are important in complex traits.

Karyotype of canine soft tissue sarcomas: a multi-colour, multi-species approach to canine chromosome painting

Many canine tumour types represent useful models for tumours also found in humans. Studies of chromosomal abnormalities in canine tumours have been impeded by the complexity of the canine karyotype (2n = 78), which has made accurate identification of rearranged chromosomes difficult and laborious. To overcome this difficulty we have developed a seven-colour paint system for canine chromosomes, with six sets of chromosome paints covering all chromosomes except Y. Several pairs of canine autosomes co-locate in the flow karyotype. To distinguish these autosomes from each other, paint sets were supplemented with chromosomes of red fox and Japanese raccoon dog. Paints were used in fluorescence in-situ hybridization to analyse karyotypes in fourteen canine soft tissue sarcomas. Rearranged karyotypes were observed in seven tumours, but there was evidence for loss of rearrangement during tissue culture. Five tumours had rearrangements involving four chromosomes or fewer; one, a chondrosarcoma, had lost seven chromosomes whilst the last, a spindle cell sarcoma, had rearrangements involving eighteen chromosome pairs. The paint sets described here facilitate the complete cytogenetic analysis of balanced translocations and other inter-chromosomal rearrangements in canine tumours. We believe that this is the first canine tumour series to be subjected to this level of analysis.

Chromosome aberrations in canine multicentric lymphomas detected with comparative genomic hybridisation and a panel of single locus probes

Recurrent chromosome aberrations are frequently observed in human neoplastic cells and often correlate with other clinical and histopathological parameters of a given tumour type. The clinical presentation, histology and biology of many canine cancers closely parallels those of human malignancies. Since humans and dogs demonstrate extensive genome homology and share the same environment, it is expected that many canine cancers will also be associated with recurrent chromosome aberrations. To investigate this, we have performed molecular cytogenetic analyses on 25 cases of canine multicentric lymphoma. Comparative genomic hybridisation analysis demonstrated between one and 12 separate regions of chromosomal gain or loss within each case, involving 32 of the 38 canine autosomes. Genomic gains were almost twice as common as losses. Gain of dog chromosome (CFA) 13 was the most common aberration observed (12 of 25 cases), followed by gain of CFA 31 (eight cases) and loss of CFA 14 (five cases). Cytogenetic and histopathological data for each case are presented, and cytogenetic similarities with human non-Hodgkin's lymphoma are discussed. We have also assembled a panel of 41 canine chromosome-specific BAC probes that may be used for accurate and efficient chromosome identification in future studies of this nature.

A 1-Mb resolution radiation hybrid map of the canine genome

The purebred dog population consists of >300 partially inbred genetic isolates or breeds. Restriction of gene flow between breeds, together with strong selection for traits, has led to the establishment of a unique resource for dissecting the genetic basis of simple and complex mammalian traits. Toward this end, we present a comprehensive radiation hybrid map of the canine genome composed of 3,270 markers including 1,596 microsatellite-based markers, 900 cloned gene sequences and ESTs, 668 canine-specific bacterial artificial chromosome (BAC) ends, and 106 sequence-tagged sites. The map was constructed by using the RHDF5000-2 whole-genome radiation hybrid panel and computed by using MULTIMAP and TSP/CONCORDE. The 3,270 markers map to 3,021 unique positions and define an average intermarker distance corresponding to 1 Mb. We also define a minimal screening set of 325 highly informative well spaced markers, to be used in the initiation of genome-wide scans. The well defined synteny between the dog and human genomes, established in part as a function of this work by the identification of 85 conserved fragments, will allow follow-up of initial findings of linkage by selection of candidate genes from the human genome sequence. This work continues to define the canine system as the method of choice in the pursuit of the genes causing mammalian variation and disease.

Use of fluorescent sequence-specific polyamides to discriminate human chromosomes by microscopy and flow cytometry

In this paper, we demonstrate the use of synthetic polyamide probes to fluorescently label heterochromatic regions on human chromosomes for discrimination in cytogenetic preparations and by flow cytometry. Polyamides bind to the minor groove of DNA in a sequence-specific manner. Unlike conventional sequence-specific DNA or RNA probes, polyamides can recognize their target sequence without the need to subject chromosomes to harsh denaturing conditions. For this study, we designed and synthesized a polyamide to target the TTCCA-motif repeated in the heterochromatic regions of chromosome 9, Y and 1. We demonstrate that the fluorescently labeled polyamide binds to its target sequence in both conventional cytogenetic preparations of metaphase chromosomes and suspended chromosomes without denaturation. Chromosomes 9 and Y can be discriminated and purified by flow sorting on the basis of polyamide binding and Hoechst 33258 staining. We generate chromosome 9- and Y-specific 'paints' from the sorted fractions. We demonstrate the utility of this technology by characterizing the sequence of an olfactory receptor gene that is duplicated on multiple chromosomes. By separating chromosome 9 from chromosomes 10-12 on the basis of polyamide fluorescence, we determine and differentiate the haplotypes of the highly similar copies of this gene on chromosomes 9 and 11.

Molecular cytogenetic analysis of a novel high-grade canine T-lymphoblastic lymphoma demonstrating co-expression of CD3 and CD79a cell markers

We present the molecular cytogenetic analysis of a novel case of canine lymphoma, in a nine-year-old entire male collie cross retriever dog that presented with an enlarged prescapular lymph node. A diagnosis of high-grade lymphoblastic lymphoma was made by histological evaluation of fixed lymph node biopsy sections, whilst immunohistochemical analyses demonstrated co-expression of B- and T-cell antigens (CD79a and CD3) by 95% of lymphomatous cells. Comparative genomic hybridisation (CGH) analysis detected loss of dog chromosomes 11, 30 and 38 and gain of chromosome 36 within the lymphoma biopsy specimen. These findings correlated with direct cytogenetic analysis of tumour metaphases using whole chromosome paint probes representing each of these four chromosomes. This study represents the first report of the combined application of both direct and indirect cytogenetic techniques for the analysis of recurrent chromosome aberrations in canine cancer.

Chromosome-specific single-locus FISH probes allow anchorage of an 1800-marker integrated radiation-hybrid/linkage map of the domestic dog genome to all chromosomes

We present here the first fully integrated, comprehensive map of the canine genome, incorporating detailed cytogenetic, radiation hybrid (RH), and meiotic information. We have mapped a collection of 266 chromosome-specific cosmid clones, each containing a microsatellite marker, to all 38 canine autosomes by fluorescence in situ hybridization (FISH). A 1500-marker RH map, comprising 1078 microsatellites, 320 dog gene markers, and 102 chromosome-specific markers, has been constructed using the RHDF5000-2 whole-genome radiation hybrid panel. Meiotic linkage analysis was performed, with at least one microsatellite marker from each dog autosome on a panel of reference families, allowing one meiotic linkage group to be anchored to all 38 dog autosomes. We present a karyotype in which each chromosome is identified by one meiotic linkage group and one or more RH groups. This updated integrated map, containing a total of 1800 markers, covers >90% of the dog genome. Positional selection of anchor clones enabled us, for the first time, to orientate nearly all of the integrated groups on each chromosome and to evaluate the extent of individual chromosome coverage in the integrated genome map. Finally, the inclusion of 320 dog genes into this integrated map enhances existing comparative mapping data between human and dog, and the 1000 mapped microsatellite markers constitute an invaluable tool with which to perform genome scanning studies on pedigrees of interest.

Chromosome painting in farm, pet and wild animal species

Among the advanced karyotype analysis approaches embraced by animal cytogenetics during the past decade, chromosome painting has had the greatest impact. Generation of chromosome specific paints is considered pivotal to his development. Additionally, ability to use these paints across species (referred to as Zoo-FISH or comparative painting) is undisputedly the most important breakthrough that has contributed to our ability to compare karyotypes of a wide range of evolutionarily highly diverged chromosome painting, and makes them aware of the tools/resources available to carry out this research in a variety of animal species. An overview of the current status of comparative chromosome painting results across closely as well as distantly related species is presented. Findings from different studies show how some segmental syntenies are more conserved as compared to others. The comparisons provide insight into the likely constitution of a vertebrate/mammalian ancestral karyotype and help understand some of the intricacies about karyotype evolution. Importance of comparative painting in setting the stage for rapid development of gene maps in a number of economically important species is elaborated.

A comparative chromosome map of the Arctic fox, red fox and dog defined by chromosome painting and high resolution G-banding

A complete set of paint probes, with each probe specific for a single type of dog chromosome, was generated by DOP-PCR amplification of flow-sorted chromosomes. These probes have been assigned to high-resolution G-banded chromosomes of the dog and Arctic fox by fluorescence in-situ hybridization. On the basis of these results we propose improved nomenclature for the G-banded karyotypes of the dog and Artic fox. A comparative map between the Arctic fox, red fox and dog has been established based on results from chromosome painting and high-resolution G-banding. This map demonstrates that the euchromatic complements of these three canid species consists of 42 conserved segments. Thirty-four of these 42 segments are each represented by a single dog chromosome with dog chromosomes 1, 13, 18 and 19 each retaining two segments, respectively. The autosomes of the Arctic fox and red fox could be reconstructed from these 42 blocks in different combinations through chromosomal fusions. Our findings suggest that chromosome fusion has been the principal mechanism of karyotype evolution occuring during speciation in canids.

Use of flow-sorted canine chromosomes in the assignment of canine linkage, radiation hybrid, and syntenic groups to chromosomes: refinement and verification of the comparative chromosome map for dog and human

The mapping of the canine genome has recently been accelerated by the availability of chromosome-specific reagents and publication of radiation hybrid (RH), genetic linkage, and dog/human comparative maps, but the assignment of mapping groups to chromosomes is incomplete. To assign published radiation hybrid, linkage, and "syntenic" groups to chromosomes, individual markers found within each group have been amplified from canine and vulpine flow-sorted, chromosome-specific DNAs as templates. Here a further 102 type I genetic markers (previously mapped in human) and 21 further type II markers are assigned to canine chromosomes using marker-specific PCR. We have assigned all linkage, RH, and syntenic groups in the two most recently published canine genome maps to chromosomes. This demonstrates directly that there is at least one published mapping group for each of the 38 canine autosomes and thus that the coverage of the canine chromosome map is approaching completion. The dog/human comparative map is one of the most complex so far described, with 90 separate segments of chromosomal homology previously seen in dog-on-human cross-species chromosome-painting studies. The total of 142 type I markers now placed on canine chromosomes using this method of marker mapping has allowed us to confirm the placement of the great majority (83) of the 90 homologous segments. The positions of the remaining homologous segments were confirmed in new cross-species chromosome-painting experiments (dog-on-human, fox-on-human).

Chromosome identification and assignment of DNA clones in the dog using a red fox and dog comparative map

We have developed a novel method for identifying dog chromosomes and unambiguously mapping specific clones onto canine chromosomes. This method uses a previously established red fox/dog comparative chromosome map to guide the FISH mapping of cloned canine DNA. Mixing metaphase preparations of the red fox and dog enabled a single hybridization to be performed on both species. We used this approach to map the chromosomal locations of twenty-six canine cosmids. Each cosmid contains highly polymorphic microsatellite markers currently used by the DogMap project to compile the canine linkage map. All but two cosmids were successfully assigned to subchromosomal regions on red fox and dog chromosomes. For eight cosmids previously mapped on dog chromosomes, we confirmed and refined the canine chromosomal assignments of seven cosmids and corrected an erroneous assignment regarding cosmid CanBern1. These results demonstrate that the red fox and dog comparative chromosome map can greatly improve the accuracy and efficiency of chromosomal assignments of canine genetic markers by FISH.

Comparative genomic hybridization (CGH) in dogs--application to the study of a canine glial tumour cell line

Recurrent chromosome aberrations are associated with many human cancers. Detailed cytogenetic analysis of tumors has benefited enormously from the development of molecular cytogenetic techniques based on fluorescence in situ hybridization (FISH). Comparative genomic hybridization (CGH) is a recently developed FISH technique that allows a rapid and comprehensive identification of imbalanced genomic material in tumour DNA. Comparative genomic hybridisation has been used widely in human medicine to evaluate losses and gains of tumour DNA isolated from a variety of sources, including fresh samples, cell-culture material and archival specimens, and has been instrumental in identifying sites in the human genome which contain genies involved in tumour development and progression. This report describes the first application of CGH in the dog, illustrated by the analysis of DNA isolated from a canine glial tumour cell line.

Canine genetics comes of age

The dog, as human's favored companion, is unique among animal species in providing new insights into human genetic disease. In this review, we will discuss both the breed and the population structure of dogs and why that makes canines amenable to genetic studies. We will review the current state of the map and discuss the particular disease states in which canines stand to make the greatest contribution to medical genetics.

A complete comparative chromosome map for the dog, red fox, and human and its integration with canine genetic maps

Cross-species reciprocal chromosome painting was used to delineate homologous chromosomal segments between domestic dog, red fox, and human. Whole sets of chromosome-specific painting probes for the red fox and dog were made by PCR amplification of flow-sorted chromosomes from established cell cultures. Based on their hybridization patterns, a complete comparative chromosome map of the three species has been built. Thirty-nine of the 44 synteny groups from the published radiation hybrid map and 33 of the 40 linkage groups in the linkage map of the dog have been assigned to specific chromosomes by fluorescence in situ hybridization and PCR-based genotyping. Each canine chromosome has at least one DNA marker assigned to it. The human-canid map shows that the canid karyotypes are among the most extensively rearranged karyotypes in mammals. Twenty-two human autosomal paints delineated 73 homologous regions on 38 canine autosomes, while paints from 38 dog autosomes detected 90 homologous segments in the human genome. Of the 22 human autosomes, only the syntenies of three chromosomes (14, 20, and 21) have been maintained intact in the canid genome. The dog-fox map and DAPI banding comparison demonstrate that the remarkable karyotype differences between fox (2n = 34 + 0-8 Bs) and dog (2n = 78) are due to 26 chromosomal fusion events and 4 fission events. It is proposed that the more easily karyotyped fox chromosomes can be used as a common reference and control system for future gene mapping in the DogMap project and CGH analysis of canine tumor DNA.

Flow karyotyping and sorting of mitotic chromosomes of barley (Hordeum vulgare L.)

A high-yield method for isolation of barley chromosomes in suspension, their analysis and sorting using flow cytometry is described. To accumulate meristem root tip cells at metaphase, actively growing roots were subjected to subsequent treatment with 2 mmol/L hydroxyurea for 18 h, 2.5 micromol/L amiprophos methyl for 2 h, and ice water (overnight). This treatment resulted in metaphase indices exceeding 50%. Synchronized root tips were fixed in 2% formaldehyde for 20 min and chromosomes were released into a lysis buffer by mechanical homogenization, producing, on average, 5 x 10(5) chromosomes from 50 root tips. The isolated chromosomes were morphologically intact and suitable for flow cytometric analysis and sorting. While it was possible to discriminate and sort only one chromosome from a barley cultivar with standard karyotype, up to three chromosomes could be sorted in translocation lines with morphologically distinct chromosomes. The purity of chromosome fractions, estimated after PRINS with primers specific for GAA microsatellites, reached 97%. PCR with chromosome-specific primers confirmed the purity and suitability of flow-sorted chromosomes for physical mapping of DNA sequences.

Karyotype relationships between four distantly related marsupials revealed by reciprocal chromosome painting

Marsupial karyotypes have shown extensive conservation even between distantly related groups with a high diversity of life forms and reproductive biology. Banding analysis has been the main test for assessing their homologies and chromosome rearrangements. More recently, cross-species reciprocal chromosome painting has been developed and applied to several mammalian species and has shown homologies and rearrangements not revealed by banding analysis. Karyotype relationships between four marsupial species, Sminthopsis crassicaudata, Potorous tridactylus, Trichosurus vulpecula and Macropus eugenii, which are from different families in two orders, were investigated and presented in the form of comparative chromosome maps. These show that only a limited number of chromosomal rearrangements have occurred during their evolution. A karyotype phylogeny of the four marsupials was derived from these maps. A comparison between published gene location and the comparative chromosome maps for these species is presented and inconsistencies with previous gene mapping data indicated.

Reciprocal chromosome painting reveals detailed regions of conserved synteny between the karyotypes of the domestic dog (Canis familiaris) and human

The domestic dog is increasingly being recognized as a useful model for human disease. The aim of this study was to conduct the first detailed whole-genome comparison of human and dog using bidirectional heterologous chromosome painting (reciprocal Zoo-FISH) analysis. We used whole-chromosome paint probes produced from degenerate oligonucleotide-primed PCR amplification of high-resolution bivariate flow-sorted human and dog chromosomes. No fewer than 68 evolutionarily conserved segments were identified between the dog and the human karyotypes. The use of elongated metaphase chromosomes for both species allowed the boundaries of each evolutionarily conserved segment to be determined to subband resolution. The distribution of conserved segments is discussed, as are the applications of these data in refining the current status of the dog genome map.

The DAPI banded karyotype of the domestic dog (Canis familiaris) generated using chromosome-specific paint probes

The domestic dog (Canis familiaris) is widely used as a model in the study of human disease. However, many of the 78 chromosomes comprising the canine karyotype are extremely difficult to identify reliably by classical cytogenetics. This has been a major hindrance to molecular cytogenetic studies of this species. The Animal Health Trust and the Sanger Centre have developed a set of canine whole chromosome-specific fluorescence in situ hybridisation (FISH) probes (chromosome paints). We have used these chromosome paints to identify unequivocally each chromosome in a metaphase spread. An increasing number of laboratories are making use of cooled CCD cameras and sophisticated software for FISH mapping. Consequently, there is a major trend towards the use of DAPI banding for concurrent chromosome identification during FISH analyses in a range of species. Here we present, for the first time, a complete DAPI banded karyotype of the dog in which each chromosome has been accurately placed, together with a 460-band DAPI ideogram. These data will facilitate the accurate assignment of FISH-mapped loci to all chromosomes comprising the karyotype and form the basis for an agreed standard of the dog karyotype.

Localization and characterization of nucleotide sequences from the canine Y chromosome

We previously reported the identification of a male-specific 658-bp DNA sequence in dogs. We used a specific primer pair designed for PCR amplification of this fragment with DNA samples from 238 dogs, 6 dingoes and 12 wolves. All 133 male samples amplified the 658-bp sequence, whereas all female samples did not. The sequence was not amplified from male DNA samples representing other wild canids (jackals, coyotes, foxes). A lambda phage was isolated from a canine male genomic library that contained an insert of approximately 15 kb of canine genomic DNA, including the male-specific 658-bp sequence. This lambda phage was used in fluorescence in-situ hybridization experiments. It hybridized to the canine Y chromosome together with a lambda clone containing a segment of the SRY gene and a cosmid clone containing a portion of the pseudoautosomal region. The male-specific 658-bp sequence was located at the end opposite to the pseudoautosomal region while the SRY gene sequence hybridized near the centromere. Additionally, two (CA)-repeat sequences were identified in the lambda clone that contained the 658-bp sequence. Specific primer pairs were designed to amplify each of the repeats. Primer pair MS34 amplified three different alleles from 13 unrelated canine male DNA samples with a PIC value of 0.40. Primer pair MS41 amplified five alleles with a PIC value of 0.71. These microsatellites are the first reported polymorphic sequences in the dog located in the non-recombining portion of the Y chromosome.

Molecular analysis of a spontaneous dystrophin 'knockout' dog

We have determined the molecular basis for skeletal myopathy and dilated cardiomyopathy in two male German short-haired pointer (GSHP) littermates. Analysis of skeletal muscle demonstrated a complete absence of dystrophin on Western blot analysis. PCR analysis of genomic DNA revealed a deletion encompassing the entire dystrophin gene. Molecular cytogenetic analysis of lymphocytes from the dam and both dystrophic pups confirmed a visible deletion in the p21 region of the affected canine X chromosome. Utrophin is up-regulated in the skeletal muscle, but does not appear to ameliorate the dystrophic canine phenotype. This new canine model should further our understanding of the physiological and biochemical processes in Duchenne muscular dystrophy.

Construction and characterization of an eightfold redundant dog genomic bacterial artificial chromosome library

A large insert canine genomic bacterial artificial chromosome (BAC) library was built from a Doberman pinscher. Approximately 166,000 clones were gridded on nine high-density hybridization filters. Insert analysis of randomly selected clones indicated a mean insert size of 155 kb and predicted 8.1 coverage of the canine genome. Two percent of the clones were nonrecombinant. Chromosomal fluorescence in situ hybridization studies of 60 BAC clones indicated no chimerism. The library was hybridized with dog PCR products representing eight genes (ADA, TNFA, GCA, MYB, HOXA, GUSB, THY1, and TOP1). The resulting positive clones were characterized and shown to be compatible with an eightfold redundant library.

A whole-genome radiation hybrid map of the dog genome

A whole genome radiation hybrid (RH) map of the canine genome was constructed by typing 400 markers, including 218 genes and 182 microsatellites, on a panel of 126 radiation hybrid cell lines. Fifty-seven RH groups have been determined with lod scores greater than 6, and 180 framework landmarks were ordered with odds greater than 1000:1. Average spacing between adjacent markers is 23 cR5000, an estimated physical distance of 3.8 Mb. Fourteen groups have been assigned to 9 of the canine chromosomes, and a comparison of RH and genetic groups allowed the successful bridging of both types of data on one map composed of 31 RH and 13 syntenic RH groups. Comparison of canine, human, mouse, and pig maps underlined regions of conserved synteny. This integrated map, covering an estimated 80% of the dog genome, should prove a powerful tool for localizing and identifiying genes implicated in pathological and phenotypical traits.

A linkage map of the canine genome

A genetic linkage map of the canine genome has been developed by typing 150 microsatellite markers using 17 three-generation pedigrees, composed of 163 F2 individuals. One hundred and thirty-nine markers were linked to at least one other marker with a lod score > or = 3.0, identifying 30 linkage groups. The largest chromosome had 9 markers spanning 106.1 cM. The average distance between markers was 14.03 cM, and the map covers an estimated 2073 cM. Eleven markers were informative on the mapping panel, but were unlinked to any other marker. These likely represent single markers located on small, distinct canine chromosomes. This map will be the initial resource for mapping canine traits of interest and serve as a foundation for development of a comprehensive canine genetic map.

Construction of a panel of canine-rodent hybrid cell lines for use in partitioning of the canine genome

We have constructed a collection of canine-rodent microcell hybrid cell lines by fusion of canine fibroblast microcell donors with immortalized rodent recipient cells. Characterization of the hybrid cell lines using a combination of fluorescence in situ hybridization and PCR analysis of canine microsatellite repeat sequences allowed selection of a panel of hybrids in which most canine chromosomes are represented. Approximately 90% of genetic markers and genes that were tested could be assigned to 1 of 31 anonymous canine chromosome groups, based on common patterns of retention in the hybrid set. Many of these putative chromosome groups have now been validated by linkage analysis. This panel of cell lines provides a tool for development of genetic, physical, and comparative maps of the canine genome.

Isolation of chromosome-specific paints from high-resolution flow karyotypes of the sheep (Ovis aries)

High-resolution bivariate flow karyotypes were obtained using fibroblast cell lines from a sheep with a normal karyotype (2n = 54), from sheep carrying Robertsonian translocation chromosomes and from sheep-hamster somatic cell hybrids. By taking advantage of the presence of chromosome polymorphisms, translocation chromosomes and sheep-hamster somatic cell hybrids, all sheep chromosomes were isolated by flow sorting. Chromosome-specific paints were generated from each sorted peak using degenerate oligonucleotide-primed polymerase chain reaction (DOP-PCR). The sheep chromosome present in each peak was identified by chromosome-specific microsatellite analysis of the DOP-PCR products and fluorescence in situ hybridization (FISH) onto DAPI-banded sheep metaphase chromosomes. The chromosome-specific DNA obtained in this study can be used for the production of genomic libraries and as a resource for mapping randomly cloned DNA sequences that will greatly aid the construction of genetic and physical maps in the sheep. The chromosome-specific paints will facilitate chromosome identification and contribute to the study of karyotype evolution in the sheep and related species.

Flow cytometric analysis of the chromosomes and stability of a wheat cell-culture line

A rapidly growing, long-term suspension culture derived from Triticum aestivum L. (wheat) was synchronized using hydroxyurea and colchicine, and a chromosome suspension with 2-3 x 10(6) chromosomes ml(-1) was made. After staining with the DNA-specific fluorochromes Hoechst 33258 and Chromomycin A(3), univariate and bivariate flow-cytometry histograms showed 15 clearly resolved peaks corresponding to individual chromosome types or groups of chromosomes with similar DNA contents. The flow karyotype was closely similar to a histogram of DNA content measurements of Feulgen-stained chromosomes made by microdensitometry. We were able to show the stability of the flow karyotype of the cell line over a year, while a parallel subculture had a slightly different, stable, karyotype following different growth conditions. The data indicate that flow cytometric analysis of plant karyotypes enables accurate, statistically precise chromosome classification and karyotyping of cereals. There was little overlap between individual flow-histogram peaks, so the method is useful for flow sorting and the construction of chromosome specific-recombinant DNA libraries. Using bivariate analysis, the AT:GC ratio of all the chromosomes was remarkably similar, in striking contrast to mammalian flow karyotypes. We speculate about a fundamental difference in organization and homogenization of DNA sequences between chromosomes within mammalian and plant genomes.