CENP-A associated complex satellite DNA in the kinetochore of the Indian muntjac

Chromatin Structure and Dynamics: Focus on Neuronal Differentiation and Pathological Implication

Chromatin structure is an essential regulator of gene expression. Its state of compaction contributes to the regulation of genetic programs, in particular during differentiation. Epigenetic processes, which include post-translational modifications of histones, DNA methylation and implication of non-coding RNA, are powerful regulators of gene expression. Neurogenesis and neuronal differentiation are spatio-temporally regulated events that allow the formation of the central nervous system components. Here, we review the chromatin structure and post-translational histone modifications associated with neuronal differentiation. Studying the impact of histone modifications on neuronal differentiation improves our understanding of the pathophysiological mechanisms of chromatinopathies and opens up new therapeutic avenues. In addition, we will discuss techniques for the analysis of histone modifications on a genome-wide scale and the pathologies associated with the dysregulation of the epigenetic machinery.

Satellite DNA in Neotropical Deer Species

The taxonomy and phylogenetics of Neotropical deer have been mostly based on morphological criteria and needs a critical revision on the basis of new molecular and cytogenetic markers. In this study, we used the variation in the sequence, copy number, and chromosome localization of satellite I-IV DNA to evaluate evolutionary relationships among eight Neotropical deer species. Using FISH with satI-IV probes derived from Mazama gouazoubira, we proved the presence of satellite DNA blocks in peri/centromeric regions of all analyzed deer. Satellite DNA was also detected in the interstitial chromosome regions of species of the genus Mazama with highly reduced chromosome numbers. In contrast to Blastocerus dichotomus, Ozotoceros bezoarticus, and Odocoileus virginianus, Mazama species showed high abundance of satIV DNA by FISH. The phylogenetic analysis of the satellite DNA showed close relationships between O. bezoarticus and B. dichotomus. Furthermore, the Neotropical and Nearctic populations of O. virginianus formed a single clade. However, the satellite DNA phylogeny did not allow resolving the relationships within the genus Mazama. The high abundance of the satellite DNA in centromeres probably contributes to the formation of chromosomal rearrangements, thus leading to a fast and ongoing speciation in this genus, which has not yet been reflected in the satellite DNA sequence diversification.

Sequence Analysis and FISH Mapping of Four Satellite DNA Families among Cervidae

Centromeric and pericentromeric chromosome regions are occupied by satellite DNA. Satellite DNAs play essential roles in chromosome segregation, and, thanks to their extensive sequence variability, to some extent, they can also be used as phylogenetic markers. In this paper, we isolated and sequenced satellite DNA I-IV in 11 species of Cervidae. The obtained satellite DNA sequences and their chromosomal distribution were compared among the analysed representatives of cervid subfamilies Cervinae and Capreolinae. Only satI and satII sequences are probably present in all analysed species with high abundance. On the other hand, fluorescence in situ hybridisation (FISH) with satIII and satIV probes showed signals only in a part of the analysed species, indicating interspecies copy number variations. Several indices, including FISH patterns, the high guanine and cytosine (GC) content, and the presence of centromere protein B (CENP-B) binding motif, suggest that the satII DNA may represent the most important satellite DNA family that might be involved in the centromeric function in Cervidae. The absence or low intensity of satellite DNA FISH signals on biarmed chromosomes probably reflects the evolutionary reduction of heterochromatin following the formation of chromosome fusions. The phylogenetic trees constructed on the basis of the satellite I-IV DNA relationships generally support the present cervid taxonomy.

Variation and Evolution of the Meiotic Requirement for Crossing Over in Mammals

The segregation of homologous chromosomes at the first meiotic division is dependent on the presence of at least one well-positioned crossover per chromosome. In some mammalian species, however, the genomic distribution of crossovers is consistent with a more stringent baseline requirement of one crossover per chromosome arm. Given that the meiotic requirement for crossing over defines the minimum frequency of recombination necessary for the production of viable gametes, determining the chromosomal scale of this constraint is essential for defining crossover profiles predisposed to aneuploidy and understanding the parameters that shape patterns of recombination rate evolution across species. Here, I use cytogenetic methods for in situ imaging of crossovers in karyotypically diverse house mice (Mus musculus domesticus) and voles (genus Microtus) to test how chromosome number and configuration constrain the distribution of crossovers in a genome. I show that the global distribution of crossovers in house mice is thresholded by a minimum of one crossover per chromosome arm, whereas the crossover landscape in voles is defined by a more relaxed requirement of one crossover per chromosome. I extend these findings in an evolutionary metaanalysis of published recombination and karyotype data for 112 mammalian species and demonstrate that the physical scale of the genomic crossover distribution has undergone multiple independent shifts from one crossover per chromosome arm to one per chromosome during mammalian evolution. Together, these results indicate that the chromosomal scale constraint on crossover rates is itself a trait that evolves among species, a finding that casts light on an important source of crossover rate variation in mammals.

Organization and evolution of a novel cervid satellite DNA with yeast CDEI-like repeats

Background

It has been proposed that pericentromeric satellite DNA arises from the progressive proximal expansion of ancient centromeric DNA. In an attempt to recover putative ancestral centromeric DNA, we microdissected the pericentromeric/centromeric DNA from the chromosome X + 3 of Indian muntjac (Muntiacus muntjak vaginalis) and constructed a microclone-library of the X + 3 centromeric DNA.

Results

A new cervid satellite DNA element, designated as satellite VI, was isolated from this library. Fluorescence in situ hybridization (FISH) studies revealed that satellite VI is predominately located on the distal pericentromeric region of the Indian muntjac chromosome X + 3 and on the pericentromeres of several Old World deer species studied. Its sequence is organized as 11-bp monomeric (ATCACGTGGGA) tandem repeats. Further sequencing on a BAC clone of Indian muntjac harboring this repeat showed that an array of this repeat stretches over approximately 5 kb followed by approximately 3 kb of interspersed repetitive sequences, such as long interspersed elements (LINEs), short interspersed elements (SINEs), and long terminal repeats (LTRs).

Conclusions

Based on the chromosomal localization, genomic and sequence organization, and copy numbers of satellite VI in deer species studied, we postulate that this newly found satellite DNA could be a putative ancient cervidic centromeric DNA that is still preserved in some Old World deer. Interestingly, the first eight nucleotides of the 11-bp monomeric consensus sequences are highly conserved and identical to the CDEI element in the centromere of the budding yeast Saccharomyces cerevisiae. The centromeric/pericentromeric satellite DNA harboring abundant copies of CDEI sequences is the first found in a mammalian species. Several zipper-like d (GGGA)2 motifs were also found in the (ATCACGTGGGA)n repeat of satellite VI DNA. Whether the satellite VI is structurally and functionally correlated with the CDEI of centromere of budding yeast and whether a zipper-like structure forms in satellite VI require further studies.

The evolutionary life cycle of the resilient centromere

The centromere is a chromosomal structure that is essential for the accurate segregation of replicated eukaryotic chromosomes to daughter cells. In most centromeres, the underlying DNA is principally made up of repetitive DNA elements, such as tandemly repeated satellite DNA and retrotransposable elements. Paradoxically, for such an essential genomic region, the DNA is rapidly evolving both within and between species. In this review, we show that the centromere locus is a resilient structure that can undergo evolutionary cycles of birth, growth, maturity, death and resurrection. The birth phase is highlighted by examples in humans and other organisms where centromere DNA deletions or chromosome rearrangements can trigger the epigenetic assembly of neocentromeres onto genomic sites without typical features of centromere DNA. In addition, functional centromeres can be generated in the laboratory using various methodologies. Recent mapping of the foundation centromere mark, the histone H3 variant CENP-A, onto near-complete genomes has uncovered examples of new centromeres which have not accumulated centromere repeat DNA. During the growth period of the centromere, repeat DNA begins to appear at some, but not all, loci. The maturity stage is characterised by centromere repeat accumulation, expansions and contractions and the rapid evolution of the centromere DNA between chromosomes of the same species and between species. This stage provides inherent centromere stability, facilitated by repression of gene activity and meiotic recombination at and around the centromeres. Death to a centromere can result from genomic instability precipitating rearrangements, deletions, accumulation of mutations and the loss of essential centromere binding proteins. Surprisingly, ancestral centromeres can undergo resurrection either in the field or in the laboratory, via as yet poorly understood mechanisms. The underlying principle for the preservation of a centromeric evolutionary life cycle is to provide resilience and perpetuity for the all-important structure and function of the centromere.

How can satellite DNA divergence cause reproductive isolation? Let us count the chromosomal ways

Satellites are one of the most enigmatic parts of the eukaryotic genome. These highly repetitive, noncoding sequences make up as much as half or more of the genomic content and are known to play essential roles in chromosome segregation during meiosis and mitosis, yet they evolve rapidly between closely related species. Research over the last several decades has revealed that satellite divergence can serve as a formidable reproductive barrier between sibling species. Here we highlight several key studies on Drosophila and other model organisms demonstrating deleterious effects of satellites and their rapid evolution on the structure and function of chromosomes in interspecies hybrids. These studies demonstrate that satellites can impact chromosomes at a number of different developmental stages and through distinct cellular mechanisms, including heterochromatin formation. These findings have important implications for how loci that cause postzygotic reproductive isolation are viewed.

Organization and molecular evolution of CENP-A--associated satellite DNA families in a basal primate genome

Centromeric regions in many complex eukaryotic species contain highly repetitive satellite DNAs. Despite the diversity of centromeric DNA sequences among species, the functional centromeres in all species studied to date are marked by CENP-A, a centromere-specific histone H3 variant. Although it is well established that families of multimeric higher-order alpha satellite are conserved at the centromeres of human and great ape chromosomes and that diverged monomeric alpha satellite is found in old and new world monkey genomes, little is known about the organization, function, and evolution of centromeric sequences in more distant primates, including lemurs. Aye-Aye (Daubentonia madagascariensis) is a basal primate and is located at a key position in the evolutionary tree to study centromeric satellite transitions in primate genomes. Using the approach of chromatin immunoprecipitation with antibodies directed to CENP-A, we have identified two satellite families, Daubentonia madagascariensis Aye-Aye 1 (DMA1) and Daubentonia madagascariensis Aye-Aye 2 (DMA2), related to each other but unrelated in sequence to alpha satellite or any other previously described primate or mammalian satellite DNA families. Here, we describe the initial genomic and phylogenetic organization of DMA1 and DMA2 and present evidence of higher-order repeats in Aye-Aye centromeric domains, providing an opportunity to study the emergence of chromosome-specific modes of satellite DNA evolution in primate genomes.

Complex genomic organization of Indian muntjac centromeric DNA

A 69-kb Indian muntjac bacterial artificial chromosome (BAC) clone that screened positive for Cervid satellites I and IV was selected for complete sequence analysis and further characterization. The sequences of this BAC clone were found in the centromeres and in some interstitial sites of Indian muntjac chromosomes. Sequence analyses showed that the BAC clone contained a 14.5 kb Cervid satellite I-like DNA element and a 9 kb Cervid satellite IV-like DNA element. In addition, it contained 51 regions each organized in a complex fashion, with sequences homology to intersperse repetitive sequences such as LINEs, SINEs, LTRs, other published DNA elements, and unassigned sequences. The FISH patterns of seven non-satellite sequence elements generated from the BAC clone showed mainly specific to centromeres of the Indian muntjac representing novel centromeric DNAs of the species. Furthermore, FISH signals and Southern blot patterns of these elements suggest the existence of a not yet identified repetitive sequence with giant repeated monomers. Positive FISH signals of these elements were also detected in the centromeric regions of Formosan muntjac. This suggests that these newly identified non-Cervid satellite DNA sequences have been conserved in the centromere of the Formosan muntjac.

Comparative sequence analyses reveal sites of ancestral chromosomal fusions in the Indian muntjac genome

Comparative mapping and sequencing was used to characterize the sites of ancestral chromosomal fusions in the Indian muntjac genome.

Background

Indian muntjac (Muntiacus muntjak vaginalis) has an extreme mammalian karyotype, with only six and seven chromosomes in the female and male, respectively. Chinese muntjac (Muntiacus reevesi) has a more typical mammalian karyotype, with 46 chromosomes in both sexes. Despite this disparity, the two muntjac species are morphologically similar and can even interbreed to produce viable (albeit sterile) offspring. Previous studies have suggested that a series of telocentric chromosome fusion events involving telomeric and/or satellite repeats led to the extant Indian muntjac karyotype.

Results

We used a comparative mapping and sequencing approach to characterize the sites of ancestral chromosomal fusions in the Indian muntjac genome. Specifically, we screened an Indian muntjac bacterial artificial-chromosome library with a telomere repeat-specific probe. Isolated clones found by fluorescence in situ hybridization to map to interstitial regions on Indian muntjac chromosomes were further characterized, with a subset then subjected to shotgun sequencing. Subsequently, we isolated and sequenced overlapping clones extending from the ends of some of these initial clones; we also generated orthologous sequence from isolated Chinese muntjac clones. The generated Indian muntjac sequence has been analyzed for the juxtaposition of telomeric and satellite repeats and for synteny relationships relative to other mammalian genomes, including the Chinese muntjac.

Conclusions

The generated sequence data and comparative analyses provide a detailed genomic context for seven ancestral chromosome fusion sites in the Indian muntjac genome, which further supports the telocentric fusion model for the events leading to the unusual karyotypic differences among muntjac species.

Chromosomal distribution and organization of three cervid satellite DNAs in Chinese water deer (Hydropotes inermis)

The species-specific profile and centromeric heterochromatin localization of satellite DNA in mammalian genomes imply that satellite DNA may play an important role in mammalian karyotype evolution and speciation. A satellite III DNA family, CCsatIII was thought to be specific to roe deer (Capreolus capreolus). In this study, however, this satellite DNA family was found also to exist in Chinese water deer (Hydropotes inermis) by PCR-Southern screening. A satellite III DNA element of this species was then generated from PCR-cloning by amplifying this satellite element using primer sequences from the roe deer satellite III clone (CCsatIII). The newly generated satellite III DNA along with previously obtained satellite I and II DNA clones were used as probes for FISH studies to investigate the genomic distribution and organization of these three satellite DNA families in centromeric heterochromatin regions of Chinese water deer chromosomes. Satellite I and II DNA were observed in the pericentric/centric regions of all chromosomes, whereas satellite III was distributed on 38 out of 70 chromosomes. The distribution and orientation of satellite DNAs I, II and III in the centromeric heterochromatin regions of the genome were further classified into four different types. The existence of a Capreolus-like satellite III in Chinese water deer implies that satellite III is not specific to the genus Capreolus (Buntjer et al., 1998) and supports the molecular phylogeny classification of Randi et al. (1998) which suggests that Chinese water deer and roe deer are closely related.

The CNA1 histone of the ciliate Tetrahymena thermophila is essential for chromosome segregation in the germline micronucleus

Ciliated protozoans present several features of chromosome segregation that are unique among eukaryotes, including their maintenance of two nuclei: a germline micronucleus, which undergoes conventional mitosis and meiosis, and a somatic macronucleus that divides by an amitotic process. To study ciliate chromosome segregation, we have identified the centromeric histone gene in the Tetrahymena thermophila genome (CNA1). CNA1p specifically localizes to peripheral centromeres in the micronucleus but is absent in the macronucleus during vegetative growth. During meiotic prophase of the micronucleus, when chromosomes are stretched to twice the length of the cell, CNA1p is found localized in punctate spots throughout the length of the chromosomes. As conjugation proceeds, CNA1p appears initially diffuse, but quickly reverts to discrete dots in those nuclei destined to become micronuclei, whereas it remains diffuse and is gradually lost in developing macronuclei. In progeny of germline CNA1 knockouts, we see no defects in macronuclear division or viability of the progeny cells immediately following the knockout. However, within a few divisions, progeny show abnormal mitotic segregation of their micronucleus, with most cells eventually losing their micronucleus entirely. This study reveals a strong dependence of the germline micronucleus on centromeric histones for proper chromosome segregation.

Anti-CENP-H antibodies in patients with Sjogren's syndrome

Anti-centromere antibody (ACA) has been reported to be associated with Sjogren's syndrome (SS) and the clinical significance of anti-CENP-H antibody remains unknown. To determine the clinical significance of anti-CENP-H and anti-centromere antibodies in primary SS, sera from 62 patients with primary SS and 40 normal controls were examined for anti-SS-A/SS-B antibodies, ACA and anti-CENP-H antibodies, by enzyme-linked immunosorbent assay and indirect immunofluorescence (IIF), respectively. Of the 62 serum samples with primary SS, 17 were positive with ACA and anti-CENP-H antibodies. Sera from SS patients with anti-CENP-H and ACA antibodies do not contain anti-SS-A/Ro and/or anti-SS-B/La antibodies. No anti-CENP-H antibody was found in sera of normal controls. An increased frequency of ACA and anti-CENP-H antibodies was found for the first time in patients with SS. Anti-CENP-H antibodies and anti-SS-A/Ro or anti-SS-B/La antibodies are present mutually exclusive. Patients with anti-CENP-H antibodies had a lower frequency of rheumatoid factor (RF). SS can be subdivided serologically into two groups; group one with anti-SS-A/Ro and/or anti-SS-B/La antibody, group two with ACA and/or anti-CENP-H antibodies. We recommend that ACA or anti-CENP-H antibodies should be considered as one of the serological markers for SS.

Sequencing of a rice centromere uncovers active genes

Centromeres are the last frontiers of complex eukaryotic genomes, consisting of highly repetitive sequences that resist mapping, cloning and sequencing. The centromere of rice Chromosome 8 (Cen8) has an unusually low abundance of highly repetitive satellite DNA, which allowed us to determine its sequence. A region of approximately 750 kb in Cen8 binds rice CENH3, the centromere-specific H3 histone. CENH3 binding is contained within a larger region that has abundant dimethylation of histone H3 at Lys9 (H3-Lys9), consistent with Cen8 being embedded in heterochromatin. Fourteen predicted and at least four active genes are interspersed in Cen8, along with CENH3 binding sites. The retrotransposons located in and outside of the CENH3 binding domain have similar ages and structural dynamics. These results suggest that Cen8 may represent an intermediate stage in the evolution of centromeres from genic regions, as in human neocentromeres, to fully mature centromeres that accumulate megabases of homogeneous satellite arrays.

Characterization of ancestral chromosome fusion points in the Indian muntjac deer

Tandem fusion, a rare evolutionary chromosome rearrangement, has occurred extensively in muntjac karyotypic evolution, leading to an extreme fusion karyotype of 6/7 (female/male) chromosomes in the Indian muntjac. These fusion chromosomes contain numerous ancestral chromosomal break and fusion points. Here, we designed a composite polymerase chain reaction (PCR) strategy which recovered DNA fragments that contained telomere and muntjac satellite DNA sequence repeats. Nested PCR confirmed the specificity of the products. Two-color fluorescence in situ hybridization (FISH) with the repetitive sequences obtained and T2AG3 telomere probes showed co-localization of satellite and telomere sequences in Indian muntjac chromosomes. Adjacent telomere and muntjac satellite sequences were also seen by fiber FISH. These data lend support to the involvement of telomere and GC-rich satellite DNA sequences during muntjac chromosome fusions.

Structure-specific DNA-binding proteins as the foundation for three-dimensional chromatin organization

Any functions of tandem repetitive sequences need proteins that specifically bind to them. Telomere-binding TRF2/MTBP attaches telomeres to the nuclear envelope in interphase due to its rod-domain-like motif. Interphase nuclei organized as a number of sponge-like ruffly round chromosome territories that could be rotated from outside. SAF-A/hnRNP-U and p68-helicase are proteins suitable to do that. Their location in the interchromosome territory space, ATPase domains, and the ability to be bound by satellite DNAs (satDNA) make them part of the wires used to help chromosome territory rotates. In case of active transcription p68-helicase can be involved in the formation of local "gene expression matrices" and due to its satDNA-binding specificity cause the rearrangement of the local chromosome territory. The marks of chromatin rearrangement, which have to be heritable, could be provided by SAF-A/hnRNP-U. During telophase unfolding the proper chromatin arrangement is restored according to these marks. The structural specificity of both proteins to the satDNAs provides a regulative but relatively stable mode of binding. The structural specificity of protein binding could help to find the "magic" centromeric sequence. With future investigations of proteins with the structural specificity of binding during early embryogenesis, when heterochromatin formation goes on, the molecular mechanisms of the "gene gating" hypothesis (Blobel, 1985) will be confirmed.

The centromere paradox: stable inheritance with rapidly evolving DNA

Every eukaryotic chromosome has a centromere, the locus responsible for poleward movement at mitosis and meiosis. Although conventional loci are specified by their DNA sequences, current evidence favors a chromatin-based inheritance mechanism for centromeres. The chromosome segregation machinery is highly conserved across all eukaryotes, but the DNA and protein components specific to centromeric chromatin are evolving rapidly. Incompatibilities between rapidly evolving centromeric components may be responsible for both the organization of centromeric regions and the reproductive isolation of emerging species.

A novel chromatin immunoprecipitation and array (CIA) analysis identifies a 460-kb CENP-A-binding neocentromere DNA

Centromere protein A (CENP-A) is an essential histone H3-related protein that constitutes the specialized chromatin of an active centromere. It has been suggested that this protein plays a key role in the epigenetic marking and transformation of noncentromeric genomic DNA into functional neocentromeres. Neocentromeres have been identified on more than two-thirds of the human chromosomes, presumably involving different noncentromeric DNA sequences, but it is unclear whether some generalized sequence properties account for these neocentromeric sites. Using a novel method combining chromatin immunoprecipitation and genomic array hybridization, we have identified a 460-kb CENP-A-binding DNA domain of a neocentromere derived from the 20p12 region of an invdup (20p) human marker chromosome. Detailed sequence analysis indicates that this domain contains no centromeric alpha-satellite, classical satellites, or other known pericentric repetitive sequence motifs. Putative gene loci are detected, suggesting that their presence does not preclude neocentromere formation. The sequence is not significantly different from surrounding non-CENP-A-binding DNA in terms of the prevalence of various interspersed repeats and binding sites for DNA-interacting proteins (Topoisomerase II and High-Mobility-Group protein I). Notable variations include a higher AT content similar to that seen in human alpha-satellite DNA and a reduced prevalence of long terminal repeats (LTRs), short interspersed repeats (SINEs), and Alus. The significance of these features in neocentromerization is discussed.

A novel chromatin immunoprecipitation and array (CIA) analysis identifies a 460-kb CENP-A-binding neocentromere DNA

Centromere protein A (CENP-A) is an essential histone H3-related protein that constitutes the specialized chromatin of an active centromere. It has been suggested that this protein plays a key role in the epigenetic marking and transformation of noncentromeric genomic DNA into functional neocentromeres. Neocentromeres have been identified on more than two-thirds of the human chromosomes, presumably involving different noncentromeric DNA sequences, but it is unclear whether some generalized sequence properties account for these neocentromeric sites. Using a novel method combining chromatin immunoprecipitation and genomic array hybridization, we have identified a 460-kb CENP-A-binding DNA domain of a neocentromere derived from the 20p12 region of an invdup (20p) human marker chromosome. Detailed sequence analysis indicates that this domain contains no centromeric alpha-satellite, classical satellites, or other known pericentric repetitive sequence motifs. Putative gene loci are detected, suggesting that their presence does not preclude neocentromere formation. The sequence is not significantly different from surrounding non-CENP-A-binding DNA in terms of the prevalence of various interspersed repeats and binding sites for DNA-interacting proteins (Topoisomerase II and High-Mobility-Group protein I). Notable variations include a higher AT content similar to that seen in human alpha-satellite DNA and a reduced prevalence of long terminal repeats (LTRs), short interspersed repeats (SINEs), and Alus. The significance of these features in neocentromerization is discussed.

Interstitial colocalization of two cervid satellite DNAs involved in the genesis of the Indian muntjac karyotype

A number of repetitive DNA clones were generated from PCR amplifications of Indian muntjac genomic DNA using primer sequences derived from a white tailed deer satellite II DNA sequence. One clone (Mmv-0.7) was characterized and shown to be a cervid satellite II DNA clone. Multiple colored FISH studies with cervid satellite I (C5) and this satellite II clone (Mmv-0.7) to Chinese muntjac metaphase chromosomes localized both satellite DNAs at the pericentromeric regions of all chromosomes except for chromosome 3 and the Y chromosome, whereas chromosome 3 exhibited pericentromeric satellite II DNA only. Where distinguishable, the pericentromeric satellite II signals appeared terminally oriented with respect to satellite I. Six pairs of Chinese muntjac autosomes had interstitial satellite I sites with four of these autosomal pairs (chromosomes 1, 2 and two other smaller autosomal pairs) also exhibiting interstitial satellite II signals. An interstitial site on the X chromosome was found to have satellite II signals. For the Indian muntjac chromosomes, FISH studies revealed a pericentromeric hybridization for satellites I and II as well as 27 distinct interstitial hybridization sites, each having at least one of the satellite DNAs. These data were used to more precisely define the chromosome fusion-associated breakpoints that presumably led to the formation of the present-day Indian muntjac karyotype. It further hints at the possibility that the Indian muntjac karyotype may have evolved directly from a 2n = 70 ancestral karyotype rather than from an intermediate 2n = 46 Chinese muntjac-like karyotype.