Fixed nucleotide differences on the Y chromosome indicate clear divergence between Equus przewalskii and Equus caballus

The phylogenetic relationship between Equus przewalskii and E. caballus is often a matter of debate. Although these taxa have different chromosome numbers, they do not form monophyletic clades in a phylogenetic tree based on mtDNA sequences. Here we report sequence variation from five newly identified Y chromosome regions of the horse. Two fixed nucleotide differences on the Y chromosome clearly display Przewalski's horse and domestic horse as sister taxa. At both positions the Przewalski's horse haplotype shows the ancestral state, in common with the members of the zebra/ass lineage. We discuss the factors that may have led to the differences in mtDNA and Y-chromosomal observations.     

Polymorphisms associated with the DAZ genes on the human Y chromosome

The human Y chromosome is unique in that it does not engage in pairing and crossing over during meiosis for most of its length. Y chromosome microdeletions, a frequent finding in infertile men, thus occur through intrachromosomal recombination, either within a single chromatid or between sister chromatids. A recently identified polymorphism associated with increased risk for spermatogenic failure, the gr/gr deletion, removes two of the four Deleted in Azoospermia (DAZ) genes in the AZFc region on the Y-chromosome long arm. We found the likely reciprocal duplication product of gr/gr deletion in 5 (6%) of 82 males using a novel DNA-blot hybridization strategy and confirmed the presence of six DAZ genes in three cases by FISH analysis. Additional polymorphisms identified within the DAZ repeat regions of the DAZ genes indicate that sister chromatid exchange plays a significant role in the genesis of deletions, duplications, and polymorphisms of the Y chromosome.     

Sister chromatid exchange assessment by chromosome orientation-fluorescence in situ hybridization on the bovine sex chromosomes and autosomes 16 and 26

Mammalian genome replication and maintenance are intimately coupled with the mechanisms that ensure cohesion between the resultant sister chromatids and the repair of DNA breaks. Although a sister chromatid exchange (SCE) is an error-free swapping of precisely matched and identical DNA strands, repetitive elements adjacent to the break site can act as alternative template sites and an unequal sister chromatid exchange can result, leading to structural variations and copy number change. Here we test the vulnerability for SCEs of the repeat-rich bovine Y chromosome in comparison with X, 16 and 26 chromosomes, using chromosome orientation-fluorescence in situ hybridization. The mean SCE rate of the Y chromosome (0.065 ± 0.029) was similar to that of BTA16 and BTA26 (0.065, 0.055), but was only approximately half of that of the X chromosome (0.142). As the chromosomal length affects the number of SCE events, we adjusted the SCE rates of the Y, 16, and 26 chromosomes to the length of the largest chromosome X resulting in very similar adjusted SCE (SCE(adj)) rates in all categories. Our results - based on 3 independent bulls - show that, although the cattle Y chromosome is a chest full of repeated elements, their presence and the documented activity of repeats in SCE formation does not manifest in significantly higher SCE(adj) rates and suggest the importance of the structural organization of the Y chromosome and the role of alternative mitotic DNA repair mechanisms.     

Abnormal genetic segregation associated with the presence of a Y. w+ chromosome in Drosophila melanogaster

We have observed an abnormal genetic segregation in the progeny of crosses between males of the F71 (y wa/Y.w+) strain and females of various strains carrying marker mutations on their chromosome 2. The Y.w+ chromosome, previously described as possibly being associated with a translocation of the 22D region of chromosome 2, was shown to carry the 21A1-22E4 tip of the 2L chromosome. One chromosome 2 of F71 had a deletion of this region. The abnormal genetic segregation observed in the progeny of different crosses can be explained both by the partial lethality (which becomes severe in some homogeneous genetic backgrounds) due to trisomy of the 21A1-22E4 chromosome 2 fragment and by the lethality associated with monosomy of this 21A1-22E4 segment.     

Molecular phylogenetics of howler monkeys (Alouatta, Platyrrhini). A comparison with karyotypic data

Molecular phylogenetic analyses of seven Brazilian Alouatta species, based on cytochrome b DNA sequence data were carried out. Parsimony and neighbor joining topologies grouped Alouatta belzebul and A. fusca as sister groups in one clade while another, well-supported clade contained A. seniculus as the most basal offshoot, followed by A. nigerrima as a sister lineage of A. macconnelli/A. stramineus. Estimates of inter-specific sequence divergence were generally low, and estimates of the time of divergence indicated that the main Alouatta lineages emerged during a short evolutionary interval. A comparison with karyotypic data confirmed the molecular topology showing a closer relationship between A. macconnelli and A. stramineus in respect to A. nigerrima. It also showed that the XX/XY sex chromosome system was maintained in several lineages while the X1X2Y/X1X1X2X2 system appeared independently at least three times during the radiation of howler monkeys. Moreover, the X1X2Y1Y2/X1X1X2X2 system might have appeared once or, alternatively, twice and independently.     

Incidence of numerical chromosome aberrations in meningioma tumors as revealed by fluorescence in situ hybridization using 10 chromosome-specific probes

OBJECTIVE: Although information on the cytogenetic characteristics of meningioma tumors has accumulated progressively over the past few decades, information on the genetic heterogeneity of meningiomas is still scanty. The aim of the present study was to analyze by interphase fluorescence in situ hybridization (FISH) the incidence of numerical abnormalities for chromosomes 1, 9, 10, 11, 14, 15, 17, 22, X, and Y in a group of 70 consecutive meningioma tumors. Another goal was to establish the potential associations among the altered chromosomes, as a way to assess both intertumoral and intratumoral heterogeneity. METHODS: For the purpose of the study, 70 patients diagnosed with meningioma were analyzed. Interphase FISH for the detection of numerical abnormalities for chromosomes 1, 9, 10, 11, 14, 15, 17, 22, X, and Y was applied to fresh tumor samples from each of the patients studied. RESULTS: The overall incidence of numerical abnormalities was 76%. Chromosome Y in males and chromosome 22 in the whole series were the most common abnormalities (46% and 61%, respectively). Despite the finding that monosomy of chromosome 22/22q(-) deletions are the most frequent individual abnormality (53%), we have observed that chromosome gains are significantly more common than chromosome losses (60% versus 40%). Chromosome gains corresponded to abnormalities of chromosomes 1 (27%), 9 (25%), 10 (23%), 11 (22%), 14 (33%), 15 (22%), 17 (23%), and X in females (35%) and males (23%) whereas chromosome losses apart from chromosome 22 frequently involved chromosomes 14 (19%), X in males (23%), and Y in males (32%). Although an association was found among most gained chromosomes on one side and chromosome losses on the other side, different association patterns were observed. Furthermore, in the latter group, monosomy 22/22q(-) was associated with monosomy X in females and monosomy 14/14q(-) was associated with nulisomy Y in males. In addition, chromosome losses usually involved a large proportion of the tumor cells whereas chromosome gains were restricted to small tumor cell clones, including tetraploid cells. CONCLUSIONS: Our results show that meningiomas are genetically heterogeneous tumors that display different patterns of numerical chromosome changes, as assessed by interphase FISH.     

Reassessment of presumed Y/22 and Y/15 translocations in man using a new technique.

A new chromosome banding technique, distamycin A plus DAPI, has been used to reexamine cases of presumed Y/autosome translocations. In contrast with the results obtained with quinacrine fluorescence (Q-banding), the satellites of acrocentric chromosomes do not fluoresce brightly with this new (DA-DAPI) method, making it more specific for the long arm of the Y chromosome. Previous cases with intensely Q-fluorescent and abnormally long short arms on a chromosome 22 were considered as presumptive 22/Y translocations: The new technique clearly shows that, in these cases, the additional material on 22p is not derived from Yq. In contrast, in other cases the Yq nature of additional material on 15p, in conjunction with the presence of an extra Y-body in interphase nuclei and the presence of a male-specific DNA, supports the previous diagnosis of a presumptive 15/Y translocation.     

The role of sister chromatid cohesiveness and structure in meiotic behaviour

Sister chromatid cores, kinetochores and the connecting strand between sister kinetochores were differentially silver stained to analyse the behaviour of these structures during meiosis in normal and two spontaneous desynaptic individuals of Chorthippus jucundus (Orthoptera). In these desynaptic individuals most of the chromosomes appear as univalents and orient equationally in the first meiotic division. Despite this abnormal segregation pattern, the changes in chromosome structure follow the same timing as in normal individuals and seem to be strictly phase dependent. Chromosomes in the first prometaphase have associated sister kinetochores and sister chromatid cores that lie in the chromosome midline; we propose that this promotes the initial monopolar orientation of chromosomes. However, the requirements of tension for stable attachment to the spindle force the autosomal univalents to acquire amphitelic orientation. Sister kinetochores behave in a chromosome orientation-dependent manner and, in the first metaphase, they appear to be interconnected by a strand that can be detected by silver impregnation, as seen in the second metaphase of wild-type individuals. The disappearance of the sister kinetochore-connecting strand, needed for equational chromatid segregation, however, can only take place in the second meiotic division. This connecting strand is ultimately responsible for the inability of chromosomes to segregate sister chromatids in the first anaphase. Received: 25 March 1997; in revised form: 14 July 1997 / Accepted: 22 August 1997     

Unequal mitotic sister chromatid exchange and different length of Y chromosomes

Summary There is wide variation in the length of the Y chromosome. In the same individual the length varies continuously and is normally distributed. We describe a boy with borderline mental retardation, gross and fine motor coordination difficulty, muscle rigidity, ptosis, clinodactyly, and a Y chromosome of different lengths in two separate cell populations. The most probable explanation of the cytogenetic finding is a mitotic unequal sister chromatid exchange of the Y chromosome.     

Changes in nucleoid morphology and origin localization upon inhibition or alteration of the actin homolog, MreB, of Vibrio cholerae

MreB is an actin homolog required for the morphogenesis of most rod-shaped bacteria and for other functions, including chromosome segregation. In Caulobacter crescentus and Escherichia coli, the protein seems to play a role in the segregation of sister origins, but its role in Bacillus subtilis chromosome segregation is less clear. To help clarify its role in segregation, we have here studied the protein in Vibrio cholerae, whose chromosome I segregates like the one in C. crescentus and whose chromosome II like the one in E. coli or B. subtilis. The properties of Vibrio MreB were similar to those of its homologs in other bacteria in that it formed dynamic helical filaments, was essential for viability, and was inhibited by the drug A22. Wild-type (WT) cells exposed to A22 became spherical and larger. The nucleoids enlarged correspondingly, and the origin positions for both the chromosomes no longer followed any fixed pattern. However, the sister origins separated, unlike the situation in other bacteria. In mutants isolated as A22 resistant, the nucleoids in some cases appeared compacted even when the cell shape was nearly normal. In these cells, the origins of chromosome I were at the distal edges of the nucleoid but not all the way to the poles where they normally reside. The sister origins of chromosome II also separated less. Thus, it appears that the inhibition or alteration of Vibrio MreB can affect both the nucleoid morphology and origin localization.     

Use of repetitive DNA for diagnosis of chromosomal rearrangements

Summary We have used two repeated DNA fragments (3.4 and 2.1 kb) released from Y chromosome DNA by digestion with the restriction endonuclease Hae III to analyze potential Y chromosome/autosome translocations. Two female patients were studied who each had an abnormal chromosome 22 with extra quinacrine fluorescent material on the short arm. The origin of the 22p+ chromosomes was uncertain after standard cytologic examinations. Analysis of one patient's DNA with the Y-specific repeated DNA probes revealed the presence of both the 3.4 and 2.1 kb Y-specific fragments. Thus, in this patient, the additional material was from the Y chromosome. Analysis of the second patient's DNA for Y-specific repeated DNA was negative, indicating that the extra chromosomal segment was not from the long arm of the Y chromosome. These two cases demonstrate that repeated DNA can distinguish between similar appearing aberrant chromosomes and may be useful in karyotypic and prenatal diagnosis.     

Nonfluorescent Y chromosomes. Cytologic evidence of origin

Summary Twelve presumptive structurally altered Y chromosomes were studied with Q-, G-, G-11, C-, Cd, and lateral asymmetric banding techniques and were compared with normal X and Y chromosmes and with an abnormal [i(Yq)] Y chromosome that exhibited intact fluorescence. Significant to this work is the fact that the Y chromosome has a small block of Giemsa-11 heterochromatin adjacent to the centromere on the long arm, while the X chromosome does not, which allows a distinction between the X-and Y-derived chromosomes. Two of the twelve altered chromosomes of either X or Y origin are small nonfluorescent rings. Each ring has a G-11-positive band of heterochromatin at the centromere, confirming Y origin. Each of the normal-length nonfluorescent presumed Ys and a Y with a fluorescent band in the center have one G-11 band at the centromere and another at an equal distance from the end of the long arm, the bands also being Cd positive, indicating that these chromosomes are pseudodicentric. The likely mechanism of origin is a break at the distal bright heterochromatin/ euchromatin junction (or within the bright segment in the chromosome with the bright center band), fusion of the sister chromatids at the breakpoints, and loss of the distal segment.     

Incomplete sister chromatid separation of long chromosome arms

Chromosome segregation ensures the equal partitioning of chromosomes at mitosis. However, long chromosome arms may pose a problem for complete sister chromatid separation. In this paper we report on the analysis of cell division in primary cells from field vole Microtus agrestis, a species with 52 chromosomes including two giant sex chromosomes. Dual chromosome painting with probes specific for the X and the Y chromosomes showed that these long chromosomes are prone to mis-segregate, producing DNA bridges between daughter nuclei and micronuclei. Analysis of mitotic cells with incomplete chromatid separation showed that reassembly of the nuclear membrane, deposition of INner CENtromere Protein (INCENP)/Aurora B to the spindle midzone and furrow formation occur while the two groups of daughter chromosomes are still connected by sex chromosome arms. Late cytokinetic processes are not efficiently inhibited by the incomplete segregation as in a significant number of cell divisions cytoplasmic abscission proceeds while Aurora B is at the midbody. Live-cell imaging during late mitotic stages also revealed abnormal cell division with persistent sister chromatid connections. We conclude that late mitotic regulatory events do not monitor incomplete sister chromatid separation of the large X and Y chromosomes of Microtus agrestis, leading to defective segregation of these chromosomes. These findings suggest a limit in chromosome arm length for efficient chromosome transmission through mitosis.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

One-Step and Stepwise Magnification of a BOBBED LETHAL Chromosome in DROSOPHILA MELANOGASTER

Bobbed lethal (bbl) chromosomes carry too few ribosomal genes for homozygous flies to be viable. Reversion of bbl chromosomes to bb or nearly bb+ occurs under magnifying conditions at a low frequency in a single generation. These reversions occur too rapidly to be accounted for by single unequal sister chromatid exchanges and seem unlikely to be due to multiple sister strand exchanges within a given cell lineage. Analysis of several one-step revertants indicates that they are X-Y recombinant chromosomes which probably arise from X-Y recombination at bb. The addition of ribosomal genes from the Y chromosome to the bbl chromosome explains the more rapid reversion of the bbl chromosome than is permitted by single events of unequal sister chromatid exchange. Analysis of stepwise bbl magnified chromosomes, which were selected over a period of 4-9 magnifying generations, shows ribosomal gene patterns that are closely similar to each other. Similarity in rDNA pattern among stepwise magnified products of the same parental chromosome is consistent with reversion by a mechanism of unequal sister strand exchange.     

Autoradiographic studies of the human Y chromosome

An autoradiographic analysis (using continuous labeling with tritiated thymidine) was made on 317 cells from four normal males. The labeling pattern of the Y chromosome was compared to the first and the last chromosomes to complete replication as well as to G21–22. The Y chromosome was never found to be the last chromosome in the cell to complete replication. Instead, it completed DNA synthesis relatively early (usually among the first 10 chromosomes) but had a distinctively heavy label during the earliest stages of late-S. In 51% of those cells with one labeled G+Y chromosome, a G21–22 was labeled and the Y was not.—It was concluded, therefore, that the human Y chromosome is not a late-replicating chromosome but terminates replication earlier than most of the autosomes. In addition, the Y chromosome cannot be distinguished from the G chromosomes on the basis of a consistent and differential labeling pattern.Supported by USPHS Grant GM 15361.     

Sex chromosome evolution in frogs—helpful insights from chromosome painting in the genus Engystomops

The differentiation of sex chromosomes is thought to be interrupted by relatively frequent sex chromosome turnover and/or occasional recombination between sex chromosomes (fountain-of-youth model) in some vertebrate groups as fishes, amphibians, and lizards. As a result, we observe the prevalence of homomorphic sex chromosomes in these groups. Here, we provide evidence for the loss of sex chromosome heteromorphism in the Amazonian frogs of the genus Engystomops, which harbors an intriguing history of sex chromosome evolution. In this species complex composed of two named species, two confirmed unnamed species, and up to three unconfirmed species, highly divergent karyotypes are present, and heteromorphic X and Y chromosomes were previously found in two species. We describe the karyotype of a lineage estimated to be the sister of all remaining Amazonian Engystomops (named Engystomops sp.) and perform chromosome painting techniques using one probe for the Y chromosome and one probe for the non-centromeric heterochromatic bands of the X chromosome of E. freibergi to compare three Engystomops karyotypes. The Y probe detected the Y chromosomes of E. freibergi and E. petersi and one homolog of chromosome pair 11 of Engystomops sp., suggesting their common evolutionary origin. The X probe showed no interspecific hybridization, revealing that X chromosome heterochromatin is strongly divergent among the studied species. In the light of the phylogenetic relationships, our data suggest that sex chromosome heteromorphism may have occurred early in the evolution of the Amazonian Engystomops and have been lost in two unnamed but confirmed candidate species.Subject terms: Cytogenetics, Evolutionary genetics     

Evolutionary origin of the medaka Y chromosome

Genetic sex determination in an XX-XY chromosome system can be realized through a locus on the Y chromosome that makes the undifferentiated gonad develop into a testis. Although this mechanism is widespread, only in two cases so far have the corresponding master male sex-determining genes been identified. One is Sry, which initiates testes determination in most mammals. The other is dmrt1bY (syn. dmy), from the fish medaka, Oryzias latipes. The mammalian Y is roughly estimated to be over 200 million years old. The medaka Y may be considerably younger. A comparative analysis of the genus Oryzias revealed that one sister species of the medaka has dmrt1bY on a homologous Y chromosome, whereas in another closely related species only a non-sex-linked pseudogene is present. In all other species, dmrt1bY was not detected. The divergence time for the different species was determined with mitochondrial DNA sequences. The timing was confirmed by independent calculations based on dmrt1 sequences. We show that the medaka sex-determining gene originated approximately 10 million years ago. This makes dmrt1bY and the corresponding Y chromosome the youngest male sex-determining system, at least in vertebrates, known so far.     

Pseudodicentric 22;Y translocation transmitted through four generations of a large family without phenotypic repercussion

The most frequent Y-autosome translocations involve an acrocentric autosome and they are frequently familial with neither phenotypic nor reproductive repercussion. However, different Y-autosome translocations have been related to infertility, due to abnormal pairing of the X and Y chromosomes at meiosis and an abnormal XY-body formation or by the disruption of the AZFs (Azoospermic Factor). Rare forms of Y-autosome translocations are those resulting in an unbalanced 45-chromosome karyotype that includes a dicentric Y+autosome chromosome. We describe a new case of a familial pseudodicentric 22;Y that is carried by 19 male members of a large family without phenotypic repercussion. Cytogenetic analysis, fluorescence in situ hybridisation (FISH) and subtelomeric Multiplex Ligation-dependent Probe Amplification (MLPA) assay have been performed. All male members of the family showed the karyotype 45,X,psu dic(22;Y)(p11.2;qter).ish psu dic(22;Y) (SRY+,DYZ3+,D14/D22Z1+). In conclusion, the presence of the dicentric chromosome in the male members of the family reported does not seem to interfere with the correct progression of spermatogenesis.     

Functional disomy of Xp22-pter in three males carrying a portion of Xp translocated to Yq

A number of Xp22;Yq11 translocations involving the transposition of Yq material to the distal short arm of the X chromosome have been described. The reciprocal product, i.e. the derivative Y chromosome resulting from the translocation of a portion of Xp to Yq, has never been recovered. We searched for this reciprocal product by performing dosage analysis of Xp22-pter loci in 9 individuals carrying a non-fluorescent Y chromosome. In three mentally retarded and dysmorphic patients, dosage analysis indicated the duplication of Xp22 loci. Use of the highly polymorphic probe CRI-S232 demonstrated the inheritance of paternal Xp-specific alleles in the probands. In situ hybridization, performed in one case, confirmed that 29CL pseudoautosomal sequences were present, in addition to Xpter and Ypter, in the telomeric portion of Yq. To our knowledge, these are the first cases in which the translocation of Xp material to Yq has been demonstrated. The X and Y breakpoints were mapped in the three patients by dosage and deletion analysis. The X breakpoint falls, in the three cases, in a region of Xp22 that is not recognized as sharing sequence similarities with the Y chromosome, thus suggesting that these translocations are not the result of a homologous recombination event.     

Berenil-induced undercondensation in human heterochromatin

The aromatic diamidine berenil specifically inhibits the condensation of a subset of constitutive heterochromatin in human lymphocyte cultures. In the normal male chromosome complement, only the quinacrine-brilliant Y heterochromatin exhibits distinct undercondensation. The optimal culture conditions for inhibiting heterochromatin condensation are achieved when berenil is added at a final concentration of 150 micrograms/ml 24 h before cell harvest. Various examples of the use of berenil in the analysis of chromosome rearrangements involving quinacrine-brilliant heterochromatin are presented. A variant, giant-satellited chromosome 22 was found to respond to berenil treatment, although its enlarged and quinacrine-bright short-arm region did not contain Y heterochromatin. Southern blot analysis and chromosome in situ hybridization suggested that most chromosome 22 variants do not stem from Y; acrocentric translocations. The experimentally undercondensed Y heterochromatin is characterized by moderate C-band labeling, bright quinacrine fluorescence, and specific silver staining. At the ultrastructural level, undercondensation is associated with loosely packed, mutliply folded chromatin fibers with a diameter of approximately 250 A and organized probably as loops.