Development and application of whole-chromosome painting of chromosomes 7A and 8A of Arachis duranensis based on chromosome-specific single-copy oligonucleotides.

For peanut, the lack of stable cytological markers is a barrier to tracking specific chromosomes, elucidating the genetic relationships between genomes and identifying chromosomal variations. Chromosome mapping using single-copy oligonucleotide (oligo) probe libraries has unique advantages for identifying homologous chromosomes and chromosomal rearrangements. In this study, we developed two whole-chromosome single-copy oligo probe libraries, LS-7A and LS-8A, based on the reference genome sequences of chromosomes 7A and 8A of Arachis duranensis. Fluorescence in situ hybridization (FISH) analysis confirmed that the libraries could specifically paint chromosomes 7 and 8. In addition, sequential FISH and electronic localization of LS-7A and LS-8A in A. duranensis (AA) and A. ipaensis (BB) showed that chromosomes 7A and 8A contained translocations and inversions relative to chromosomes 7B and 8B. Analysis of the chromosomes of wild Arachis species using LS-8A confirmed that this library could accurately and effectively identify A genome species. Finally, LS-7A and LS-8A were used to paint the chromosomes of interspecific hybrids and their progenies, which verified the authenticity of the interspecific hybrids and identified a disomic addition line. This study provides a model for developing specific oligo probes to identify the structural variations of other chromosomes in Arachis and demonstrates the practical utility of LS-7A and LS-8A.

Chromosome Painting Using Chromosome-Specific BAC Clones.

Chromosome painting (CP) refers to visualization of large chromosome regions, chromosome arms or entire chromosomes via fluorescence in situ hybridization (FISH) of chromosome-specific DNA sequences. For CP in crucifers (Brassicaceae), typically contigs of chromosome-specific bacterial artificial chromosomes (BAC) from Arabidopsis thaliana are applied as painting probes on chromosomes of A. thaliana or other species (comparative chromosome painting, CCP). CP/CCP enables to identify and trace particular chromosome regions and/or chromosomes throughout all mitotic and meiotic stages as well as corresponding interphase chromosome territories. However, extended pachytene chromosomes provide the highest resolution of CP/CCP. Fine-scale chromosome structure, structural chromosome rearrangements (such as inversions, translocations, centromere repositioning), and chromosome breakpoints can be investigated by CP/CCP. BAC DNA probes can be accompanied by other types of DNA probes, such as repetitive DNA, genomic DNA, or synthetic oligonucleotide probes. Here, we describe a robust step-by-step protocol of CP and CCP which proved to be efficient across the family Brassicaceae, but which is also applicable to other angiosperm families.

Bulked Oligo-FISH for Chromosome Painting and Chromosome Barcoding.

Recently developed bulked oligo-FISH is a highly versatile method, which is applicable in any plant species with an assembled genome sequence. This technique allows in situ identification of individual chromosomes, large chromosomal rearrangements, comparative karyotype analysis, or even the reconstruction of the three-dimensional organization of the genome. The method is based on the identification of thousands of short oligonucleotides, unique to specific genome regions, which are synthesized in parallel, fluorescently labeled and used as probes for FISH. In this chapter, we propose a detailed protocol for amplification and labeling of single-stranded oligo-based painting probes from so-called MYtags immortal libraries, the preparation of mitotic metaphase and meiotic pachytene chromosome spreads, and a protocol for the fluorescence in situ hybridization procedure using the synthetic oligo probes. The proposed protocols are demonstrated for banana (Musa spp.).

Chromosome painting and phylogenetic analysis suggest that the genus Lophostoma (Chiroptera, Phyllostomidae) is paraphyletic.

The subfamily Phyllostominae (Chiroptera, Phyllostomidae) comprises 10 genera of Microchiroptera bats from the Neotropics. The taxonomy of this group is controversial due to incongruities in the phylogenetic relationships evident from different datasets. The genus Lophostoma currently includes eight species whose phylogenetic relationships have not been resolved. Integrative analyzes including morphological, molecular and chromosomal data are powerful tools to investigate the phylogenetics of organisms, particularly if obtained by chromosomal painting. In the present work we performed comparative genomic mapping of three species of Lophostoma (L. brasiliense 2n = 30, L. carrikeri 2n = 26 and L. schulzi 2n = 26), by chromosome painting using whole chromosome probes from Phyllostomus hastatus and Carollia brevicauda; this included mapping interstitial telomeric sites. The karyotype of L. schulzi (LSC) is a new cytotype. The species L. brasiliense and L. carrikeri showed interstitial telomeric sequences that probably resulted from expansions of repetitive sequences near pericentromeric regions. The addition of chromosomal painting data from other species of Phyllostominae allowed phylogeny construction by maximum parsimony, and the determination that the genera of this subfamily are monophyletic, and that the genus Lophostoma is paraphyletic. Additionally, a review of the taxonomic status of LSC is suggested to determine if this species should be reclassified as part of the genus Tonatia.

Chromosomal painting in Charadrius collaris Vieillot, 1818 and Vanellus chilensis Molina, 1782 and an analysis of chromosomal signatures in Charadriiformes.

Charadriiformes represent one of the largest orders of birds; members of this order are diverse in morphology, behavior and reproduction, making them an excellent model for studying evolution. It is accepted that the avian putative ancestral karyotype, with 2n = 80, remains conserved for about 100 million years. So far, only a few species of Charadriiformes have been studied using molecular cytogenetics. Here, we performed chromosome painting on metphase chromosomes of two species of Charadriidae, Charadrius collaris and Vanellus chilensis, with whole chromosome paint probes from Burhinus oedicnemus. Charadrius collaris has a diploid number of 76, with both sex chromosomes being submetacentric. In V. chilensi a diploid number of 78 was identified, and the Z chromosome is submetacentric. Chromosome painting suggests that chromosome conservation is a characteristic common to the family Charadriidae. The results allowed a comparative analysis between the three suborders of Charadriiformes and the order Gruiformes using chromosome rearrangements to understand phylogenetic relationships between species and karyotypic evolution. However, the comparative analysis between the Charadriiformes suborders so far has not revealed any shared rearrangements, indicating that each suborder follows an independent evolutionary path, as previously proposed. Likewise, although the orders Charadriiformes and Gruiformes are placed on sister branches, they do not share any signature chromosomal rearrangements.

Comparative chromosome maps between the stone curlew and three ciconiiform species (the grey heron, little egret and crested ibis).

BACKGROUND: Previous cytogenetic studies show that the karyotypes of species in Ciconiiformes vary considerably, from 2n = 52 to 78. Their karyotypes include different numbers of small to minute bi-armed chromosomes that have evolved probably by fusions of two ancestral microchromosomes, besides macrochromosomes and dot-like microchromosomes. However, it is impossible to define the inter-species homologies of such small-sized bi-armed chromosomes based on chromosome morphology and banding characteristics. Although painting probes from the chicken (Gallus gallus, GGA) chromosomes 1-9 and Z have been widely used to investigate avian chromosome homologies, GGA microchromosome probes are rarely used in these studies because most GGA microchromosome probes generated by flow sorting often contain multiple GGA microchromosomes. In contrast, the stone curlew (Burhinus oedicnemus, BOE, Charadriiformes) has an atypical low diploid chromosome number (42) karyotype and only 4 pairs of dot-like microchromosomes; a set of chromosome-specific painting probes that cover all BOE chromosomes has been generated. To get a genome-wide view of evolutionary chromosomal rearrangements in different lineages of Ciconiiformes, we used BOE painting probes instead of GGA painting probes to analyze the karyotypes of three ciconiiform species belonging to two different families: the eastern grey heron (Ardea cinerea, ACI, 2n = 64, Ardeidae), the little egret (Egretta garzetta, EGA, 2n = 64, Ardeidae) and the crested ibis (Nipponia nippon, NNI, 2n = 68, Threskiornithidae). RESULTS: BOE painting probes display the same hybridization pattern on chromosomes of ACI and EGA, while a different hybridization pattern is observed on chromosomes of NNI. BOE autosome probes detected 21 conserved homologous segments and 5 fusions on the sixteen pairs of recognizable chromosomes of ACI and EGA, while 16 conserved homologous segments and 4 fusions were found on the twelve pairs of recognizable chromosomes of NNI. Only a portion of smaller bi-armed chromosomes in the karyotypes of the ciconiiform species could have evolved from fusions of ancestral microchromosomes. In particular BOE 5, which is the result of a fusion between two segments homologous to GGA 7 and 8 respectively, was retained also as either a single chromosome in ACI (ACI 5) and EGA (EGA 5) or had fused with a part of the BOE 10 equivalent in NNI (NNI 5). CONCLUSION: Our painting results indicate that different chromosome rearrangements occur in different ciconiiform lineages. Some of the small-sized bi-armed chromosomes in ACI, EGA and NNI are derived from the fusions of two microchromosomes, indicating that microchromosome fusions play an important role in ciconiiform chromosome evolution. The fusion segment homologous to GGA 7 and 8 is a potential cytogenetic signature that unites Ardeidae and Threskiornithidae.

Chromosome-specific painting unveils chromosomal fusions and distinct allopolyploid species in the Saccharum complex.

Karyotypes provide key cytogenetic information on the phylogenetic relationships and evolutionary origins in related eukaryotic species. Despite our knowledge of the chromosome numbers of sugarcane and its wild relatives, the chromosome composition and evolution among the species in the Saccharum complex have been elusive owing to the complex polyploidy and the large numbers of chromosomes of these species. Oligonucleotide-based chromosome painting has become a powerful tool of cytogenetic studies especially for plant species with large numbers of chromosomes. We developed oligo-based chromosome painting probes for all 10 chromosomes in Saccharum officinarum (2n = 8x = 80). The 10 painting probes generated robust fluorescence in situ hybridization signals in all plant species within the Saccharum complex, including species in the genera Saccharum, Miscanthus, Narenga and Erianthus. We conducted comparative chromosome analysis using the same set of probes among species from four different genera within the Saccharum complex. Excitingly, we discovered several novel cytotypes and chromosome rearrangements in these species. We discovered that fusion from two different chromosomes is a common type of chromosome rearrangement associated with the species in the Saccharum complex. Such fusion events changed the basic chromosome number and resulted in distinct allopolyploids in the Saccharum complex.

PaintSHOP enables the interactive design of transcriptome- and genome-scale oligonucleotide FISH experiments.

Fluorescence in situ hybridization (FISH) allows researchers to visualize the spatial position and quantity of nucleic acids in fixed samples. Recently, considerable progress has been made in developing oligonucleotide (oligo)-based FISH methods that have enabled researchers to study the three-dimensional organization of the genome at super-resolution and visualize the spatial patterns of gene expression for thousands of genes in individual cells. However, there are few existing computational tools to support the bioinformatics workflows necessary to carry out these experiments using oligo FISH probes. Here, we introduce paint server and homology optimization pipeline (PaintSHOP), an interactive platform for the design of oligo FISH experiments. PaintSHOP enables researchers to identify probes for their experimental targets efficiently, to incorporate additional necessary sequences such as primer pairs and to easily generate files documenting library design. PaintSHOP democratizes and standardizes the process of designing complex probe sets for the oligo FISH community.

Reconstruction of ancestral karyotype illuminates chromosome evolution in the genus Cucumis.

Karyotype dynamics driven by complex chromosome rearrangements constitute a fundamental issue in evolutionary genetics. The evolutionary events underlying karyotype diversity within plant genera, however, have rarely been reconstructed from a computed ancestral progenitor. Here, we developed a method to rapidly and accurately represent extant karyotypes with the genus, Cucumis, using highly customizable comparative oligo-painting (COP) allowing visualization of fine-scale genome structures of eight Cucumis species from both African-origin and Asian-origin clades. Based on COP data, an evolutionary framework containing a genus-level ancestral karyotype was reconstructed, allowing elucidation of the evolutionary events that account for the origin of these diverse genomes within Cucumis. Our results characterize the cryptic rearrangement hotspots on ancestral chromosomes, and demonstrate that the ancestral Cucumis karyotype (n = 12) evolved to extant Cucumis genomes by hybridizations and frequent lineage- and species-specific genome reshuffling. Relative to the African species, the Asian species, including melon (Cucumis melo, n = 12), Cucumis hystrix (n = 12) and cucumber (Cucumis sativus, n = 7), had highly shuffled genomes caused by large-scale inversions, centromere repositioning and chromothripsis-like rearrangement. The deduced reconstructed ancestral karyotype for the genus allowed us to propose evolutionary trajectories and specific events underlying the origin of these Cucumis species. Our findings highlight that the partitioned evolutionary plasticity of Cucumis karyotype is primarily located in the centromere-proximal regions marked by rearrangement hotspots, which can potentially serve as a reservoir for chromosome evolution due to their fragility.

Multicolor-FISH Characterization of a Prenatal Mosaicism for a Chromosomal Rearrangement Undetected by Molecular Cytogenetics.

Fetal mosaicism for chromosomal rearrangements remains a challenge to diagnose, even in the era of whole-genome sequencing. We present here a case of fetal mosaicism for a chromosomal rearrangement explored in amniocytes and fetal muscle, consisting of a major cell population (95%) with partial monosomy 4q and a minor population (5%) with additional material replacing the 4qter deleted segment. Molecular techniques (MLPA, array-CGH) failed to assess the origin of this material. Only multicolor-FISH identified the additional segment on chromosome 4 as derived from chromosome 17. Due to the poor prognosis, the couple chose to terminate the pregnancy. Because of low-level mosaicism, chromosomal microarray analysis (CMA), now considered as first-tier prenatal genetic analysis, did not allow the identification of the minor cell line. In case of large CNVs (>5 Mb) detected by CMA, karyotyping may be considered to elucidate the mechanism of the underlying rearrangement and eliminate mosaicism.

A Chromosome-Painting-Based Pipeline to Infer Local Ancestry under Limited Source Availability.

Contemporary individuals are the combination of genetic fragments inherited from ancestors belonging to multiple populations, as the result of migration and admixture. Isolating and characterizing these layers are crucial to the understanding of the genetic history of a given population. Ancestry deconvolution approaches make use of a large amount of source individuals, therefore constraining the performance of Local Ancestry Inferences when only few genomes are available from a given population. Here we present WINC, a local ancestry framework derived from the combination of ChromoPainter and NNLS approaches, as a method to retrieve local genetic assignments when only a few reference individuals are available. The framework is aided by a score assignment based on source differentiation to maximize the amount of sequences retrieved and is capable of retrieving accurate ancestry assignments when only two individuals for source populations are used.

Mapping of Chromosome Territories by 3D-Chromosome Painting During Early Mouse Development.

Following fertilization in mammals, the chromatin landscape inherited from the two parental genomes and the nuclear organization are extensively reprogrammed. A tight regulation of nuclear organization is important for developmental success. One main nuclear feature is the organization of the chromosomes in discrete and individual nuclear spaces known as chromosome territories (CTs). In culture cells, their arrangements can be constrained depending on their genomic content (e.g., gene density or repeats) or by specific nuclear constrains such as the periphery or the nucleolus. However, during the early steps of mouse embryonic development, much less is known, specifically regarding how and when the two parental genomes intermingle. Here, we describe a three-dimensional fluorescence in situ hybridization (3D-FISH) for chromosome painting (3D-ChromoPaint) optimized to gain understanding in nuclear organization of specific CTs following fertilization. Our approach preserves the nuclear structure, and the acquired images allow full spatial analysis of interphase chromosome positioning and morphology across the cell cycle and during early development. This method will be useful in understanding the dynamics of chromosome repositioning during development as well as the alteration of chromosome territories upon changes in transcriptional status during key developmental steps. This protocol can be adapted to any other species or organoids in culture.

An efficient Oligo-FISH painting system for revealing chromosome rearrangements and polyploidization in Triticeae.

A chromosome-specific painting technique has been developed which combines the most recent approaches of the companion disciplines of molecular cytogenetics and genome research. We developed seven oligonucleotide (oligo) pools derivd from single-copy sequences on chromosomes 1 to 7 of barley (Hordeum vulgare L.) and corresponding collinear regions of wheat (Triticum aestivum L.). The seven groups of pooled oligos comprised between 10 986 and 12 496 45-bp monomers, and these then produced stable fluorescence in situ hybridization (FISH) signals on chromosomes of each linkage group of wheat and barley. The pooled oligo probes were applied to high-throughput karyotyping of the chromosomes of other Triticeae species in the genera Secale, Aegilops, Thinopyrum, and Dasypyrum, and the study also extended to some wheat-alien amphiploids and derived lines. We demonstrated that a complete set of whole-chromosome oligo painting probes facilitated the study of inter-species chromosome homologous relationships and visualized non-homologous chromosomal rearrangements in Triticeae species and some wheat-alien species derivatives. When combined with other non-denaturing FISH procedures using tandem-repeat oligos, the newly developed oligo painting techniques provide an efficient tool for the study of chromosome structure, organization, and evolution among any wild Triticeae species with non-sequenced genomes.

Chromosome Painting in Cultivated Bananas and Their Wild Relatives (Musa spp.) Reveals Differences in Chromosome Structure.

Edible banana cultivars are diploid, triploid, or tetraploid hybrids, which originated by natural cross hybridization between subspecies of diploid Musa acuminata, or between M. acuminata and diploid Musa balbisiana. The participation of two other wild diploid species Musa schizocarpa and Musa textilis was also indicated by molecular studies. The fusion of gametes with structurally different chromosome sets may give rise to progenies with structural chromosome heterozygosity and reduced fertility due to aberrant chromosome pairing and unbalanced chromosome segregation. Only a few translocations have been classified on the genomic level so far, and a comprehensive molecular cytogenetic characterization of cultivars and species of the family Musaceae is still lacking. Fluorescence in situ hybridization (FISH) with chromosome-arm-specific oligo painting probes was used for comparative karyotype analysis in a set of wild Musa species and edible banana clones. The results revealed large differences in chromosome structure, discriminating individual accessions. These results permitted the identification of putative progenitors of cultivated clones and clarified the genomic constitution and evolution of aneuploid banana clones, which seem to be common among the polyploid banana accessions. New insights into the chromosome organization and structural chromosome changes will be a valuable asset in breeding programs, particularly in the selection of appropriate parents for cross hybridization.

Revisiting the Karyotype Evolution of Neotropical Boid Snakes: A Puzzle Mediated by Chromosomal Fissions.

The Boidae family is an ancient group of snakes widely distributed across the Neotropical region, where several biogeographic events contributed towards shaping their evolution and diversification. Most species of this family have a diploid number composed of 2n = 36; however, among Booidea families, the Boidae stands out by presenting the greatest chromosomal diversity, with 2n ranging between 36 and 44 chromosomes and an undifferentiated XY sex chromosome system. Here, we applied a comparative chromosome analysis using cross-species chromosome paintings in five species representing four Boidae genera, to decipher the evolutionary dynamics of some chromosomes in these Neotropical snakes. Our study included all diploid numbers (2n = 36, 40, and 44) known for this family and our comparative chromosomal mappings point to a strong evolutionary relationship among the genera Boa, Corallus, Eunectes, and Epicrates. The results also allowed us to propose the cytogenomic diversification that had occurred in this family: a process mediated by centric fissions, including fission events of the putative and undifferentiated XY sex chromosome system in the 2n = 44 karyotype, which is critical in solving the puzzle of the karyotype evolution of boid snakes.

Karyotypic Evolution of Sauropsid Vertebrates Illuminated by Optical and Physical Mapping of the Painted Turtle and Slider Turtle Genomes.

Recent sequencing and software enhancements have advanced our understanding of the evolution of genomic structure and function, especially addressing novel evolutionary biology questions. Yet fragmentary turtle genome assemblies remain a challenge to fully decipher the genetic architecture of adaptive evolution. Here, we use optical mapping to improve the contiguity of the painted turtle (Chrysemys picta) genome assembly and use de novo fluorescent in situ hybridization (FISH) of bacterial artificial chromosome (BAC) clones, BAC-FISH, to physically map the genomes of the painted and slider turtles (Trachemys scripta elegans). Optical mapping increased C. picta's N50 by ~242% compared to the previous assembly. Physical mapping permitted anchoring ~45% of the genome assembly, spanning 5544 genes (including 20 genes related to the sex determination network of turtles and vertebrates). BAC-FISH data revealed assembly errors in C. picta and T. s. elegans assemblies, highlighting the importance of molecular cytogenetic data to complement bioinformatic approaches. We also compared C. picta's anchored scaffolds to the genomes of other chelonians, chicken, lizards, and snake. Results revealed a mostly one-to-one correspondence between chromosomes of painted and slider turtles, and high homology among large syntenic blocks shared with other turtles and sauropsids. Yet, numerous chromosomal rearrangements were also evident across chelonians, between turtles and squamates, and between avian and non-avian reptiles.

3D mapping and accelerated super-resolution imaging of the human genome using in situ sequencing.

There is a need for methods that can image chromosomes with genome-wide coverage, as well as greater genomic and optical resolution. We introduce OligoFISSEQ, a suite of three methods that leverage fluorescence in situ sequencing (FISSEQ) of barcoded Oligopaint probes to enable the rapid visualization of many targeted genomic regions. Applying OligoFISSEQ to human diploid fibroblast cells, we show how four rounds of sequencing are sufficient to produce 3D maps of 36 genomic targets across six chromosomes in hundreds to thousands of cells, implying a potential to image thousands of targets in only five to eight rounds of sequencing. We also use OligoFISSEQ to trace chromosomes at finer resolution, following the path of the X chromosome through 46 regions, with separate studies showing compatibility of OligoFISSEQ with immunocytochemistry. Finally, we combined OligoFISSEQ with OligoSTORM, laying the foundation for accelerated single-molecule super-resolution imaging of large swaths of, if not entire, human genomes.

A Comprehensive Cytogenetic Analysis of Several Members of the Family Columbidae (Aves, Columbiformes).

The Columbidae species (Aves, Columbiformes) show considerable variation in their diploid numbers (2n = 68-86), but there is limited understanding of the events that shaped the extant karyotypes. Hence, we performed whole chromosome painting (wcp) for paints GGA1-10 and bacterial artificial chromosome (BAC) probes for chromosomes GGA11-28 for Columbina passerina, Columbina talpacoti, Patagioenas cayennensis, Geotrygon violacea and Geotrygon montana. Streptopelia decaocto was only investigated with paints because BACs for GGA10-28 had been previously analyzed. We also performed phylogenetic analyses in order to trace the evolutionary history of this family in light of chromosomal changes using our wcp data with chicken probes and from Zenaida auriculata, Columbina picui, Columba livia and Leptotila verreauxi, previously published. G-banding was performed on all these species. Comparative chromosome paint and G-banding results suggested that at least one interchromosomal and many intrachromosomal rearrangements had occurred in the diversification of Columbidae species. On the other hand, a high degree of conservation of microchromosome organization was observed in these species. Our cladistic analysis, considering all the chromosome rearrangements detected, provided strong support for L. verreauxi and P. cayennensis, G. montana and G. violacea, C. passerina and C. talpacoti having sister taxa relationships, as well as for all Columbidae species analyzed herein. Additionally, the chromosome characters were mapped in a consensus phylogenetic topology previously proposed, revealing a pericentric inversion in the chromosome homologous to GGA4 in a chromosomal signature unique to small New World ground doves.

Fluorescent In Situ Hybridization Using Oligonucleotide-Based Probes.

Efficient and consistent chromosome identification is the foundation for successful cytogenetic studies. Fluorescent in situ hybridization (FISH) has been the most popular technique for chromosome identification in plants. Large insert genomic DNA clones, such as bacterial artificial chromosome (BAC) clones, and repetitive DNA sequences have been the most commonly used DNA probes for FISH. However, most of such traditional probes can only be used to identify a single chromosome or are too polymorphic to consistently identify the same chromosome in the target species. In contrast, FISH using oligonucleotide (oligo)-based probes is highly versatile. In this procedure, a large number of oligos specific to a chromosomal region, to an entire chromosome, or to multiple chromosomes are computationally identified, synthesized in parallel, and labeled as probes. In addition, each oligo probe can be used for thousands of FISH experiments and represents an infinite resource. In this chapter we describe a detailed protocol for amplification and labeling of oligo-based probes, relevant chromosome preparation, and FISH procedures.