Centromere Position Research Articles

The Unique DNA Sequences Underlying Equine Centromeres.

Centromeres are highly distinctive genetic loci whose function is specified largely by epigenetic mechanisms. Understanding the role of DNA sequences in centromere function has been a daunting task due to the highly repetitive nature of centromeres in animal chromosomes. The discovery of a centromere devoid of satellite DNA in the domestic horse consolidated observations on the epigenetic nature of centromere identity, showing that entirely natural chromosomes could function without satellite DNA cues. Horses belong to the genus Equus which exhibits a very high degree of evolutionary plasticity in centromere position and DNA sequence composition. Examination of horses has revealed that the position of the satellite-free centromere is variable among individuals. Analysis of centromere location and composition in other Equus species, including domestic donkey and zebras, confirms that the satellite-less configuration of centromeres is common in this group which has undergone particularly rapid karyotype evolution. These features have established the equids as a new mammalian system in which to investigate the molecular organization, dynamics and evolutionary behaviour of centromeres.

Critical Foundation of the Kinetochore: The Constitutive Centromere-Associated Network (CCAN).

The kinetochore is a large protein complex, which is assembled at the centromere of a chromosome to ensure faithful chromosome segregation during M-phase. The centromere in most eukaryotes is epigenetically specified by DNA sequence-independent mechanisms. The constitutive centromere-associated network (CCAN) is a subcomplex in the kinetochore that localizes to the centromere throughout the cell cycle. The CCAN has interfaces bound to the centromeric chromatin and the spindle microtubule-binding complex; therefore, it functions as a foundation of kinetochore formation. Here, we summarize recent progress in our understanding of the structure and organization of the CCAN. We also discuss an additional role of the CCAN in the maintenance of centromere position and dynamic reorganization of the CCAN.

Constitutive centromere-associated network controls centromere drift in vertebrate cells.

Centromeres are specified by sequence-independent epigenetic mechanisms, and the centromere position may drift at each cell cycle, but once this position is specified, it may not be frequently moved. Currently, it is unclear whether the centromere position is stable. To address this question, we systematically analyzed the position of nonrepetitive centromeres in 21 independent clones isolated from a laboratory stock of chicken DT40 cells using chromatin immunoprecipitation combined with massive parallel sequencing analysis with anti-CENP-A antibody. We demonstrated that the centromere position varies among the clones, suggesting that centromere drift occurs during cell proliferation. However, when we analyzed this position in the subclones obtained from one isolated clone, the position was found to be relatively stable. Interestingly, the centromere drift was shown to occur frequently in CENP-U- and CENP-S-deficient cells. Based on these results, we suggest that the centromere position can change after many cell divisions, but this drift is suppressed in short-term cultures, and the complete centromere structure contributes to the suppression of the centromere drift.

An uncommon co-localization of rDNA 5S with major rDNA clusters in Callichthyidae (Siluriformes): a report case in Corydoras carlae Nijssen & Isbrücker, 1983.

Corydoras Lacepède, 1803 is the most specious genus of Corydoradinae subfamily and many of its species are still unknown in relation to molecular cytogenetic markers. However, the diploid number and karyotypic formula were recorded for many species of this group. In current study, we provided the first cytogenetic information of Corydoras carlae Nijssen & Isbrücker, 1983, an endemic fish species from Iguassu River basin, Paraná State, Brazil. The individuals were collected in Florido River, a tributary of Iguassu River and analysed with respect to diploid number, heterochromatin distribution pattern, Ag-NORs and mapping of 5S and 18S ribosomal genes. The karyotype of this species comprises 46 chromosomes arranged in 22m+22sm+2st. The heterochromatin is distributed in centromeric and pericentromeric positions in most of the chromosomes, and also associated with NORs. The Ag-NORs were detected in the terminal position on the long arm of the metacentric pair 6. The double-FISH technique showed that 5S rDNA and 18S rDNA were co-localized in the terminal portion on the long arm of the metacentric pair 6. This condition of co-localization of ribosomal genes in Corydoras carlae seems to represent a marker for this species.

Neocentromeres Provide Chromosome Segregation Accuracy and Centromere Clustering to Multiple Loci along a Candida albicans Chromosome.

Assembly of kinetochore complexes, involving greater than one hundred proteins, is essential for chromosome segregation and genome stability. Neocentromeres, or new centromeres, occur when kinetochores assemble de novo, at DNA loci not previously associated with kinetochore proteins, and they restore chromosome segregation to chromosomes lacking a functional centromere. Neocentromeres have been observed in a number of diseases and may play an evolutionary role in adaptation or speciation. However, the consequences of neocentromere formation on chromosome missegregation rates, gene expression, and three-dimensional (3D) nuclear structure are not well understood. Here, we used Candida albicans, an organism with small, epigenetically-inherited centromeres, as a model system to study the functions of twenty different neocentromere loci along a single chromosome, chromosome 5. Comparison of neocentromere properties relative to native centromere functions revealed that all twenty neocentromeres mediated chromosome segregation, albeit to different degrees. Some neocentromeres also caused reduced levels of transcription from genes found within the neocentromere region. Furthermore, like native centromeres, neocentromeres clustered in 3D with active/functional centromeres, indicating that formation of a new centromere mediates the reorganization of 3D nuclear architecture. This demonstrates that centromere clustering depends on epigenetically defined function and not on the primary DNA sequence, and that neocentromere function is independent of its distance from the native centromere position. Together, the results show that a neocentromere can form at many loci along a chromosome and can support the assembly of a functional kinetochore that exhibits native centromere functions including chromosome segregation accuracy and centromere clustering within the nucleus.

Developing an Automated Cytogenetic Imaging System for Detection of Dicentric Chromosomes in Biological Dosimetry

Background: High-energy ionizing radiation is harmful and changes the genetic makeup of DNA, which can lead to increased risk of cancer. Thus, the exposure of radiation dose should be under control and limited. Ionizing radiation might lead to some chromosome aberrations like dicentric. There is a strong relation between the frequency of dicentric chromosome in metaphase, and the received dose. Objective: Identifying the frequency of dicentric chromosomes is an important task especially in large-scale radiation accident for making rapid clinical decision. Given this, a large number of metaphases should be investigated for an accurate estimating of dose. It is well known that non-automated (visual) scoring of chromosome aberrations such as dicentrics requires highly trained experts. On the other hand, as thousands of cells should be scored, it is time-consuming and results in fatigue that can lead to poor concentration. Methods: Biological dosimetry technique for assessing radiation dose is based on analyzing chromosome in peripheral blood lymphocyte. Our study describes a technique to speed up this procedure by automatically distinguishing abnormal chromosomes from normal ones. The most important feature of dicentric chromosomes is their two centromeres. Therefore, the main approach in our study is to design an automated system to identify the number and position of centromeres. We presented a method for classifying chromosomes into four groups in accordance with the number of centromeres in each chromosome. Results: The image dataset of 311 chromosomes of normal and dicentric chromosomes is used to test the scheme. The sensitivity about 90% and specificity more than 95% for classification of chromosomes into dicentric and non-dicentric as well as accuracy more than 90% for centromere identification, are obtained. Conclusion: If an automated system with the capability of straightening bent chromosome was applied prior to the proposed algorithm, even more accurate results would be achieved.

A Taz1- and Microtubule-Dependent Regulatory Relationship between Telomere and Centromere Positions in Bouquet Formation Secures Proper Meiotic Divisions.

During meiotic prophase, telomeres cluster, forming the bouquet chromosome arrangement, and facilitate homologous chromosome pairing. In fission yeast, bouquet formation requires switching of telomere and centromere positions. Centromeres are located at the spindle pole body (SPB) during mitotic interphase, and upon entering meiosis, telomeres cluster at the SPB, followed by centromere detachment from the SPB. Telomere clustering depends on the formation of the microtubule-organizing center at telomeres by the linker of nucleoskeleton and cytoskeleton complex (LINC), while centromere detachment depends on disassembly of kinetochores, which induces meiotic centromere formation. However, how the switching of telomere and centromere positions occurs during bouquet formation is not fully understood. Here, we show that, when impaired telomere interaction with the LINC or microtubule disruption inhibited telomere clustering, kinetochore disassembly-dependent centromere detachment and accompanying meiotic centromere formation were also inhibited. Efficient centromere detachment required telomere clustering-dependent SPB recruitment of a conserved telomere component, Taz1, and microtubules. Furthermore, when artificial SPB recruitment of Taz1 induced centromere detachment in telomere clustering-defective cells, spindle formation was impaired. Thus, detachment of centromeres from the SPB without telomere clustering causes spindle impairment. These findings establish novel regulatory mechanisms, which prevent concurrent detachment of telomeres and centromeres from the SPB during bouquet formation and secure proper meiotic divisions.

The inheritance of centromere identity

ABSTRACTCENP-A (Centromere protein A) is a histone H3 variant that epigenetically determines the centromere position, but the mechanism of its centromere inheritance is obscure. We propose that CENP-A ubiquitylation, which is inherited through dimerization between rounds of cell division, is a candidate for the epigenetic mark of centromere identity.

Karyological study on 12Centaurea(Asteraceae) species from Turkey

AbstractThe purpose of this study was to determine chromosome morphology and karyological features of 12 Centaurea L. species belonging to sections Cynaroides Boiss. ex Walp. and Phaeopappus (DC.) Boiss. from Anatolia, Turkey. The chromosome numbers were determined as 2n = 18 in all species. Karyotype analyses were made in detail for the first time for all species except Centaurea kurdica Reichardt, Centaurea fenzlii Reichardt and Centaurea amanicola Hub.-Mor. Chromosome counts of three of them (Centaurea foliosa Boiss. et Kotschy ex Boiss., Centaurea haussknechtii Boiss., Centaurea gigantea Sch. Bip. ex. Boiss.) were given for the first time. The classification of chromosomes and the lengths of long and short arm, haploid chromosome lengths, arm ratios, relative sizes and centromeric positions were represented for all species. Also, photographs of metaphase chromosomes and ideograms are given for studied Centaurea taxa. A distribution map of studied taxa is provided.

Microsatellite-centromere mapping in Japanese scallop (Patinopecten yessoensis) through half-tetrad analysis in gynogenetic diploid families

Gene-centromere mapping is an essential prerequisite for understanding the composition and structure of genomes. Half-tetrad analysis is a powerful tool for mapping genes and understanding chromosomal behavior during meiosis. The Japanese scallop (Patinopecten yessoensis), a cold-tolerant species inhabiting the northwestern Pacific coast, is a commercially important marine bivalve in Asian countries. In this study, inheritance of 32 informative microsatellite loci was examined in 70-h D-shaped larvae of three induced meiogynogenetic diploid families of P. yessoensis for centromere mapping using half-tetrad analysis. The ratio of gynogenetic diploids was proven to be 100%, 100% and 96% in the three families, respectively. Inheritance analysis in the control crosses showed that 51 of the 53 genotypic ratios observed were in accordance with Mendelian expectations at the 5% level after Bonferroni correction. Seven of the 32 microsatellite loci showed the existence of null alleles in control crosses. The second division segregation frequency (y) of the microsatellite loci ranged from 0.07 to 0.85 with a mean of 0.38, suggesting the existence of positive interference after a single chiasma formation in some chromosomes in the scallop. Microsatellite-centromere distances ranged from 4 cM to 42 cM under the assumption of complete interference. Information on the positions of centromeres in relation to the microsatellite loci will represent a contribution towards the assembly of genetic maps in the commercially important scallop species.

Chromosome Banding in Amphibia. XXXIII. Demonstration of 5-Methylcytosine-Rich Heterochromatin in Anura

An experimental approach using monoclonal anti-5-methylcytosine (5-MeC) antibodies and indirect immunofluorescence was elaborated for detecting 5-MeC-rich chromosome regions in anuran chromosomes. This technique was applied to mitotic metaphases of 6 neotropical frog species belonging to 6 genera and 4 families. The hypermethylation patterns were compared with a variety of banding patterns obtained by conventional banding techniques. The hypermethylated DNA sequences are species-specific and located exclusively in constitutive heterochromatin. They are found in centromeric, pericentromeric, telomeric, and interstitial positions of the chromosomes and adjacent to nucleolus organizer regions. 5-MeC-rich DNA sequences can be embedded both in AT- and GC-rich repetitive DNA. The experimental parameters that have major influence on the reproducibility and quality of the anti-5-MeC antibody labeling are discussed.

Application of multicolor banding combined with heterochromatic and locus-specific probes identify evolutionary conserved breakpoints in Hylobates pileatus.

BackgroundThe question what makes Homo sapiens sapiens (HSA) special among other species is one of the basic questions of mankind. A small contribution to answer this question is to study the chromosomal constitution of HSA compared to other, closely related species. In order to check the types and extent of evolutionary conserved breakpoints we studied here for the first time the chromosomes of Hylobates pileatus (HPI) compared to HSA and Hylobates lar (HLA) by means of molecular cytogenetics.ResultsOverall, 68 new evolutionary conserved breakpoints compared to HSA could be characterized in this study. Interestingly, only seven of those were different compared to HLA. However, application of heterochromatic human DNA-probes provided evidence that observed high chromosomal rearrangement rates of gibbons in HPI happened rather in these repetitive elements than in euchromatin, even though most centromeric positions were preserved in HPI compared to HSA.ConclusionUnderstanding genomes of other species and comparing them to HSA needs full karyotypic and high resolution genomic data to approach both: euchromatic and heterochromatic regions of the studied chromosome-content. This study provides full karyotypic data and previously not available data on heterochromatin-syntenies of HPI and HSA.Electronic supplementary materialThe online version of this article (doi:10.1186/s13039-016-0228-x) contains supplementary material, which is available to authorized users.

Heterologous Synapsis and Crossover Suppression in Heterozygotes for a Pericentric Inversion in the Zebra Finch

In the zebra finch, 2 alternative morphs regarding centromere position were described for chromosome 6. This polymorphism was interpreted to be the result of a pericentric inversion, but other causes of the centromere repositioning were not ruled out. We used immunofluorescence localization to examine the distribution of MLH1 foci on synaptonemal complexes to test the prediction that pericentric inversions cause synaptic irregularities and/or crossover suppression in heterozygotes. We found complete suppression of crossing over in the region involved in the rearrangement in male and female heterozygotes. In contrast, the same region showed high levels of crossing over in homozygotes for the acrocentric form of this chromosome. No inversion loops or synaptic irregularities were detected along bivalent 6 in heterozygotes suggesting that heterologous pairing is achieved during zygotene or early pachytene. Altogether these findings strongly indicate that the polymorphic chromosome 6 originated by a pericentric inversion. Since inversions are common rearrangements in karyotypic evolution in birds, it seems likely that early heterologous pairing could help to fix these rearrangements, preventing crossing overs in heterozygotes and their deleterious effects on fertility.

Mapping centromeres of microchromosomes in the zebra finch (Taeniopygia guttata) using half-tetrad analysis.

Centromeres usually consist of hundreds of kilobases of repetitive sequence which renders them difficult to assemble. As a consequence, centromeres are often missing from assembled genomes and their locations on physical chromosome maps have to be inferred from flanking sequences via fluorescence in situ hybridization (FISH). Alternatively, centromere positions can be mapped using linkage analyses in accidentally triploid individuals formed by half-tetrads (resulting from the inheritance of two chromatids from a single meiosis). The current genome assembly of the zebra finch (Taeniopygia guttata) comprises 32 chromosomes, but only for the ten largest chromosomes centromere positions have been mapped using FISH. We here map the positions of most of the remaining centromeres using half-tetrad analyses. For this purpose, we genotyped 37 zebra finches that were triploid or tetraploid due to inheritance errors (and mostly died as embryos) together with their parents at 64 microsatellite markers (at least two per chromosome). Using the information on centromere positions on the ten largest chromosomes, we were able to identify 12 cases of non-disjunction in maternal meiosis I and 10 cases of non-disjunction in maternal meiosis II. These 22 informative cases allowed us to infer centromere positions on additional 19 microchromosomes in reference to the current genome assembly. This knowledge will be valuable for studies of chromosome evolution, meiotic drive and species divergence in the avian lineage.Electronic supplementary materialThe online version of this article (doi:10.1007/s00412-015-0560-7) contains supplementary material, which is available to authorized users.

Centromere and telomere sequence alterations reflect the rapid genome evolution within the carnivorous plant genus Genlisea.

Linear chromosomes of eukaryotic organisms invariably possess centromeres and telomeres to ensure proper chromosome segregation during nuclear divisions and to protect the chromosome ends from deterioration and fusion, respectively. While centromeric sequences may differ between species, with arrays of tandemly repeated sequences and retrotransposons being the most abundant sequence types in plant centromeres, telomeric sequences are usually highly conserved among plants and other organisms. The genome size of the carnivorous genus Genlisea (Lentibulariaceae) is highly variable. Here we study evolutionary sequence plasticity of these chromosomal domains at an intrageneric level. We show that Genlisea nigrocaulis (1C = 86 Mbp; 2n = 40) and G. hispidula (1C = 1550 Mbp; 2n = 40) differ as to their DNA composition at centromeres and telomeres. G. nigrocaulis and its close relative G. pygmaea revealed mainly 161 bp tandem repeats, while G. hispidula and its close relative G. subglabra displayed a combination of four retroelements at centromeric positions. G. nigrocaulis and G. pygmaea chromosome ends are characterized by the Arabidopsis-type telomeric repeats (TTTAGGG); G. hispidula and G. subglabra instead revealed two intermingled sequence variants (TTCAGG and TTTCAGG). These differences in centromeric and, surprisingly, also in telomeric DNA sequences, uncovered between groups with on average a > 9-fold genome size difference, emphasize the fast genome evolution within this genus. Such intrageneric evolutionary alteration of telomeric repeats with cytosine in the guanine-rich strand, not yet known for plants, might impact the epigenetic telomere chromatin modification.

Karyotype evolution supports the molecular phylogeny in the genus Ranunculus (Ranunculaceae)

Karyotype evolution can be reconstructed by the characterization of chromosome morphology, based on the position of centromeres. Different karyotypes often reflect speciation events within phylogenies as they can establish crossing barriers between species. Hence, evolution of karyotypes often is congruent with splits and differentiation of clades within phylogenies of angiosperm genera. Here we study karyotype evolution in the big cosmopolitan genus Ranunculus and in related genera to test the hypothesis that karyotypes are congruent with major clades. We investigated karyotypes on mitoses of 36 species, evaluated literature records for additional 87 species, and reconstructed ancestral states by mapping karyotypes onto a published molecular phylogenetic tree. Altogether ten karyotypes can be discriminated as character states, eight based on the base number x=8, and two on the base number x=7. The ancestral type within Ranunculus is characterized by four metacentric and four submetacentric/subtelocentric chromosomes, and dominates in five major basal clades of Ranunculus (R. subg. Auricomus) and in four of the related genera (Coptidium, Halerpestes, Kumlienia, and Trautvetteria). Another four karyotypes are ancestral and predominant in two major clades within Ranunculus (R. subg. Ranunculus), while three further ones occur only on terminal branches of the buttercup phylogeny. Among related genera, Ficaria and Ceratocephala also show derived karyotypes. Karyotype morphology thus supports generic and infrageneric classifications based on molecular and morphological data. Karyotype evolution drives in general to increasing number of chromosomes with asymmetric arms, and to a reduction from x=8 to x=7 chromosomes. A review of interspecific homoploid hybridization in sympatric species, and of crossing experiments suggests enhanced crossability of species with the same karyotype and strong crossing barriers between those with different karyotypes. We conclude that karyotype evolution is a major driver of speciation and differentiation of clades within Ranunculus.

The completed genome sequence of the pathogenic ascomycete fungus Fusarium graminearum.

BackgroundAccurate genome assembly and gene model annotation are critical for comparative species and gene functional analyses. Here we present the completed genome sequence and annotation of the reference strain PH-1 of Fusarium graminearum, the causal agent of head scab disease of small grain cereals which threatens global food security. Completion was achieved by combining (a) the BROAD Sanger sequenced draft, with (b) the gene predictions from Munich Information Services for Protein Sequences (MIPS) v3.2, with (c) de novo whole-genome shotgun re-sequencing, (d) re-annotation of the gene models using RNA-seq evidence and Fgenesh, Snap, GeneMark and Augustus prediction algorithms, followed by (e) manual curation.ResultsWe have comprehensively completed the genomic 36,563,796 bp sequence by replacing unknown bases, placing supercontigs within their correct loci, correcting assembly errors, and inserting new sequences which include for the first time complete AT rich sequences such as centromere sequences, subtelomeric regions and the telomeres. Each of the four F. graminearium chromosomes was found to be submetacentric with respect to centromere positioning. The position of a potential neocentromere was also defined. A preferentially higher frequency of genetic recombination was observed at the end of the longer arm of each chromosome. Within the genome 1529 gene models have been modified and 412 new gene models predicted, with a total gene call of 14,164. The re-annotation impacts upon 69 entries held within the Pathogen-Host Interactions database (PHI-base) which stores information on genes for which mutant phenotypes in pathogen-host interactions have been experimentally tested, of which 59 are putative transcription factors, 8 kinases, 1 ATP citrate lyase (ACL1), and 1 syntaxin-like SNARE gene (GzSYN1). Although the completed F. graminearum contains very few transposon sequences, a previously unrecognised and potentially active gypsy-type long-terminal-repeat (LTR) retrotransposon was identified. In addition, each of the sub-telomeres and centromeres contained either a LTR or MarCry-1_FO element. The full content of the proposed ancient chromosome fusion sites has also been revealed and investigated. Regions with high recombination previously noted to be rich in secretome encoding genes were also found to be rich in tRNA sequences. This study has identified 741 F. graminearum species specific genes and provides the first complete genome assembly for a Sordariomycetes species.ConclusionsThis fully completed F. graminearum PH-1 genome and manually curated annotation, available at Ensembl Fungi, provides the optimum resource to perform interspecies comparative analyses and gene function studies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1756-1) contains supplementary material, which is available to authorized users.

Stable Patterns of CENH3 Occupancy Through Maize Lineages Containing Genetically Similar Centromeres.

While the approximate chromosomal position of centromeres has been identified in many species, little is known about the dynamics and diversity of centromere positions within species. Multiple lines of evidence indicate that DNA sequence has little or no impact in specifying centromeres in maize and in most multicellular organisms. Given that epigenetically defined boundaries are expected to be dynamic, we hypothesized that centromere positions would change rapidly over time, which would result in a diversity of centromere positions in isolated populations. To test this hypothesis, we used CENP-A/cenH3 (CENH3 in maize) chromatin immunoprecipitation to define centromeres in breeding pedigrees that included the B73 inbred as a common parent. While we found a diversity of CENH3 profiles for centromeres with divergent sequences that were not inherited from B73, the CENH3 profiles from centromeres that were inherited from B73 were indistinguishable from each other. We propose that specific genetic elements in centromeric regions favor or inhibit CENH3 accumulation, leading to reproducible patterns of CENH3 occupancy. These data also indicate that dramatic shifts in centromere position normally originate from accumulated or large-scale genetic changes rather than from epigenetic positional drift.

Proliferation-dependent positioning of individual centromeres in the interphase nucleus of human lymphoblastoid cell lines.

The cell nucleus is a highly organized structure and plays an important role in gene regulation. Understanding the mechanisms that sustain this organization is therefore essential for understanding genome function. Centromeric regions (CRs) of chromosomes have been known for years to adopt specific nuclear positioning patterns, but the significance of this observation is not yet completely understood. Here, using a combination of fluorescence in situ hybridization and immunochemistry on fixed human cells and high-throughput imaging, we directly and quantitatively investigated the nuclear positioning of specific human CRs. We observe differential attraction of individual CRs toward both the nuclear border and the nucleoli, the former being enhanced in nonproliferating cells and the latter being enhanced in proliferating cells. Similar positioning patterns are observed in two different lymphoblastoid cell lines. Moreover, the positioning of CRs differs from that of noncentromeric regions, and CRs display specific orientations within chromosome territories. These results suggest the existence of not-yet-characterized mechanisms that drive the nuclear positioning of CRs and therefore pave the way toward a better understanding of how CRs affect nuclear organization.

DNA Sequence-Specific Binding of CENP-B Enhances the Fidelity of Human Centromere Function

Human centromeres are specified by a stably inherited epigenetic mark that maintains centromere position and function through a two-step mechanism relying on self-templating centromeric chromatin assembled with the histone H3 variant CENP-A, followed by CENP-A-dependent nucleation of kinetochore assembly. Nevertheless, natural human centromeres are positioned within specific megabase chromosomal regions containing α-satellite DNA repeats, which contain binding sites for the DNA sequence-specific binding protein CENP-B. We now demonstrate that CENP-B directly binds both CENP-A's amino-terminal tail and CENP-C, a key nucleator of kinetochore assembly. DNA sequence-dependent binding of CENP-B within α-satellite repeats is required to stabilize optimal centromeric levels of CENP-C. Chromosomes bearing centromeres without bound CENP-B, including the human Y chromosome, are shown to mis-segregate in cells at rates several-fold higher than chromosomes withCENP-B-containing centromeres. These data demonstrate a DNA sequence-specific enhancement by CENP-B of the fidelity of epigenetically defined human centromere function.