Chromosome Structure

The standard rye cultivar `Imperial' and a structural variant carrying an intact 1R chromosome and two telocentric 1R chromosomes (short and long arms)were used to investigate expression patterns of homologous rDNA loci, and the influence of chromosome structural change on their interphase organisation and relative disposition. Sequential silver staining and in situ hybridization with the rDNA probe pTa71, established a correspondence between the expression and organization patterns of rDNA domains in metaphase and interphase cells. In most cells of the cultivar Imperial, nucleolar organizer region (NOR)silver staining on metaphase chromosomes with equivalent numbers of rDNA genes revealed a size heteromorphism between homologous rDNA loci, resulting from their differential expression. NOR heteromorphism in the structural variant line was significantly reduced. The preferential activity of one NOR over its homologue was found to be random within cells and independent of parental...

The most conspicuous difference among chromosomes and genomes in Arachis species, the patterns of heterochromatin, was mainly modeled by differential amplification of different members of one superfamily of satellite DNAs. Divergence in repetitive DNA is a primary driving force for genome and chromosome evolution. Section Arachis is karyotypically diverse and has six different genomes. Arachis glandulifera (D genome) has the most asymmetric karyotype and the highest reproductive isolation compared to the well-known A and B genome species. These features make A. glandulifera an interesting model species for studying the main repetitive components that accompanied the genome and chromosome diversification in the section. Here, we performed a genome-wide analysis of repetitive sequences in A. glandulifera and investigated the chromosome distribution of the identified satellite DNA sequences (satDNAs). LTR retroelements, mainly the Ty3-gypsy families "Fidel/Feral" and "Pipoka/Pipa", were the most represented. Comparative analyses with the A and B genomes showed that many of the previously described transposable elements (TEs) were differently represented in the D genome, and that this variation accompanied changes in DNA content. In addition, four major satDNAs were characterized. Agla_CL8sat was the major component of pericentromeric heterochromatin, while Agla_CL39sat, Agla_CL69sat, and Agla_CL122sat were found in heterochromatic and/or euchromatic regions. Even though Agla_CL8sat belong to a different family than that of the major satDNA (ATR-2) found in the heterochromatin of the A, K, and F genomes, both satDNAs are members of the same superfamily. This finding suggests that closely related satDNAs of an ancestral library were differentially amplified leading to the major changes in the heterochromatin patterns that accompanied the karyotype and genome differentiation in Arachis.

In normal human somatic cells, telomere dysfunction causes cellular senescence, a stable proliferative arrest with tumour suppressing properties. Whether telomere dysfunctioninduced senescence (TDIS) suppresses cancer growth in humans, however, is unknown. Here, we demonstrate that multiple and distinct human cancer precursor lesions, but not corresponding malignant cancers, are comprised of cells that display hallmarks of TDIS. Furthermore, we demonstrate that oncogenic signalling, frequently associated with initiating cancer growth in humans, dramatically affected telomere structure and function by causing telomeric replication stress, rapid and stochastic telomere attrition, and consequently telomere dysfunction in cells that lack hTERT activity. DNA replication stress induced by drugs also resulted in telomere dysfunction and cellular senescence in normal human cells, demonstrating that telomeric repeats indeed are hypersensitive to DNA replication stress. Our data reveal that TDIS, accelerated by oncogene-induced DNA replication stress, is a biological response of cells in human cancer precursor lesions and provide strong evidence that TDIS is a critical tumour suppressing mechanism in humans.

We studied the karyotypes of Hassar cf. orestis and an undescribed Hassar species from the Jarí River and Opsodoras ternetzi, H. orestis and Platydoras cf. costatus from the Xingú River, all with 2n = 58. Constitutive heterochromatin is located in the centromere in most metacentric pairs; in some chromosomes this banding is not present, or it is located on the whole chromosome arm or in the distal regions. The NOR is located on a single biarmed pair at a distal region of the short arm in H. cf. orestis, H. orestis and P. cf. costatus at a distal region of the long arm in O. ternetzi and at a proximal region of the long arm in the Hassar species. In all species (except for Hassar sp.) the CMA3 analysis revealed a rich G-C region coincident with the NOR. Probably inversions occurred in the NOR chromosome during the chromosomal differentiation of the Doradidae species here described.

The high-order structure of metaphase chromosomes remains still under investigation, especially the 30-nm structure that is still controversial. Advanced 3D imaging has provided useful information for our understanding of this detailed structure. It is evident that new technologies together with improved sample preparations and image analyses should be adequately combined. This mini review highlights 3D imaging used for chromosome analysis so far with future imaging directions also highlighted.

Many years of extensive studies of metazoan mitochondrial genomes have established differences in gene arrangements and genetic codes as valuable phylogenetic markers. Understanding the underlying mechanisms of replication, transcription and the role of the control regions which cause e.g. different gene orders is important to assess the phylogenetic signal of such events. This review summarises and discusses, for the Metazoa, the general aspects of mitochondrial transcription and replication with respect to control regions as well as several proposed models of gene rearrangements. As whole genome sequencing projects accumulate, more and more observations about mitochondrial gene transfer to the nucleus are reported. Thus occurrence and phylogenetic aspects concerning

Chromosome evolution presents an enigma in the mega-diverse Lepidoptera. Most species exhibit constrained chromosome evolution with nearly identical haploid chromosome counts and chromosome-level gene collinearity among species more than 140 million years divergent. However, a few species possess radically inflated chromosomal counts due to extensive fission and fusion events. To address this enigma of constraint in the face of an exceptional ability to change, we investigated an unprecedented reorganization of the standard lepidopteran chromosome structure in the green-veined white butterfly (Pieris napi). We find that gene content in P. napi has been extensively rearranged in large collinear blocks, which until now have been masked by a haploid chromosome number close to the lepidopteran average. We observe that ancient chromosome ends have been maintained and collinear blocks are enriched for functionally related genes suggesting both a mechanism and a possible role for selection in determining the boundaries of these genome-wide rearrangements.

Euploid chromosome balance is vitally important for normal development, but is profoundly changed in many tumors. Is each tumor dependent on its own structurally and numerically changed chromosome complement that has evolved during its development and progression? We have previously shown that normal chromosome 3 transfer into the KH39 renal cell carcinoma line and into the Hone1 nasopharyngeal carcinoma line inhibited their tumorigenicity. The aim of the present study was to distinguish between a qualitative and a quantitative model of this suppression. According to the former, a damaged or deleted tumor suppressor gene would be restored by the transfer of a normal chromosome. If so, suppression would be released only when the corresponding sequences of the exogenous normal chromosome are lost or inactivated. According to the alternative quantitative model, the tumor cell would not tolerate an increased dosage of the relevant gene or segment. If so, either a normal cell derived, or...

Cichla monoculus, Cichla temensis (peacock bass or tucunaré), and its presumed hybrids, were cytogenetically analyzed. The fish were collected at three distinct sites in the central Amazon basin, namely in the Uatumã (C. monoculus, C. temensis and their natural hybrid), Jaú (C. temensis), and Solimõ es rivers (C. monoculus). The two species and the natural hybrid showed the same diploid number, 2n 0/48 acrocentric chromosomes. Single NORs were detected in the distal region of the long arm in all three species. However, in C. monoculus, the NOR was found on the second pair of the complement, in C. temensis, on the third pair and in the hybrid two NOR patterns were found, one on the second pair and the other on the third pair of chromosomes. The two species and the hybrid have their constitutive heterochromatin located in the pericentromeric region of all chromosomes and an interstitial C-band located on the largest chromosome pair. The great similarity in the chromosome number and morphology, chromosome size class differences, the NOR patterns and C-banding suggested chromosomal stasis during speciation and hybridization of Cichla .

A/hum sphaerocephalon is a species with a high number of secondary constrictions and with ultraand interindividual variation in their number. We analysed whether all the secondary constrictions are involved in nucleolus formation, whether the same variability exists in the number of NOR, and the mechanism(s) responsible for this variability. Our cytological data have shown that (i) all the secondary constrictions may be involved in the nucleolus organization, (ii) the variability in number is in accordance with the numbers of NOR, and (iii) the variability could be due to unequal exchanges among ribosomal genes on homologous and non-homologous chromosomes. Ribosomal DNA sequence homogeneity detected in this species supports this conclusion.

Cichla monoculus, Cichla temensis (peacock bass or tucunaré), and its presumed hybrids, were cytogenetically analyzed. The fish were collected at three distinct sites in the central Amazon basin, namely in the Uatumã (C. monoculus, C. temensis and their natural hybrid), Jaú (C. temensis), and Solimõ es rivers (C. monoculus). The two species and the natural hybrid showed the same diploid number, 2n 0/48 acrocentric chromosomes. Single NORs were detected in the distal region of the long arm in all three species. However, in C. monoculus, the NOR was found on the second pair of the complement, in C. temensis, on the third pair and in the hybrid two NOR patterns were found, one on the second pair and the other on the third pair of chromosomes. The two species and the hybrid have their constitutive heterochromatin located in the pericentromeric region of all chromosomes and an interstitial C-band located on the largest chromosome pair. The great similarity in the chromosome number and morphology, chromosome size class differences, the NOR patterns and C-banding suggested chromosomal stasis during speciation and hybridization of Cichla .

Cichla monoculus, Cichla temensis (peacock bass or tucunaré), and its presumed hybrids, were cytogenetically analyzed. The fish were collected at three distinct sites in the central Amazon basin, namely in the Uatumã (C. monoculus, C. temensis and their natural hybrid), Jaú (C. temensis), and Solimõ es rivers (C. monoculus). The two species and the natural hybrid showed the same diploid number, 2n 0/48 acrocentric chromosomes. Single NORs were detected in the distal region of the long arm in all three species. However, in C. monoculus, the NOR was found on the second pair of the complement, in C. temensis, on the third pair and in the hybrid two NOR patterns were found, one on the second pair and the other on the third pair of chromosomes. The two species and the hybrid have their constitutive heterochromatin located in the pericentromeric region of all chromosomes and an interstitial C-band located on the largest chromosome pair. The great similarity in the chromosome number and morphology, chromosome size class differences, the NOR patterns and C-banding suggested chromosomal stasis during speciation and hybridization of Cichla .

We studied the karyotypes of Hassar cf. orestis and an undescribed Hassar species from the Jarí River and Opsodoras ternetzi, H. orestis and Platydoras cf. costatus from the Xingú River, all with 2n = 58. Constitutive heterochromatin is located in the centromere in most metacentric pairs; in some chromosomes this banding is not present, or it is located on the whole chromosome arm or in the distal regions. The NOR is located on a single biarmed pair at a distal region of the short arm in H. cf. orestis, H. orestis and P. cf. costatus at a distal region of the long arm in O. ternetzi and at a proximal region of the long arm in the Hassar species. In all species (except for Hassar sp.) the CMA3 analysis revealed a rich G-C region coincident with the NOR. Probably inversions occurred in the NOR chromosome during the chromosomal differentiation of the Doradidae species here described.

Telomeres are specialized structures at the end of eukaryotic chromosomes that are required to preserve genome integrity, chromosome stability and nuclear architecture. Telomere maintenance and function are established epigenetically in several eukaryotes. However, the exact chromatin enzymatic modifications regulating telomere homeostasis are poorly understood. In Drosophila melanogaster, telomere length and stability are maintained through the retrotransposition of specialized telomeric sequences and by the specific loading of protecting capping proteins, respectively. Here, we show that the loss of the essential and evolutionarily conserved histone deacetylase Rpd3, the homolog of mammalian HDAC1, causes aberrant telomeric fusions on polytene chromosome ends. Remarkably, these telomere fusion defects are associated with a marked decrease of histone H4 acetylation, as well as an accumulation of heterochromatic epigenetic marks at telomeres, including histone H3K9 trimethylation an...

A comprehensive review of cytogenetic features is provided for the large hemipteran suborder Auchenorrhyncha, which currently contains approximately 42,000 valid species. This review is based on the analysis of 819 species, 483 genera, and 31 families representing all presently recognized Auchenorrhyncha superfamilies, e.i. Cicadoidea (cicadas), Cercopoidea (spittle bugs), Membracoidea (leafhoppers and treehoppers), Myerslopioidea (ground-dwelling leafhoppers), and Fulgoroidea (planthoppers). History and present status of chromosome studies are described, as well as the structure of chromosomes, chromosome counts, trends and mechanisms of evolution of karyotypes and sex determining systems, their variation at different taxonomic levels and most characteristic (modal) states, occurrence of parthenogenesis, polyploidy, B-chromosomes and chromosome rearrangements, and methods used for cytogenetic analysis of Auchenorrhyncha.

Main conclusion The most conspicuous difference among chromosomes and genomes in Arachis species, the patterns of heterochromatin, was mainly modeled by differential amplification of different members of one superfamily of satellite DNAs. Divergence in repetitive DNA is a primary driving force for genome and chromosome evolution. Section Arachis is karyotypically diverse and has six different genomes. Arachis glandulifera (D genome) has the most asymmetric karyotype and the highest reproductive isolation compared to the well-known A and B genome species. These features make A. glandulifera an interesting model species for studying the main repetitive components that accompanied the genome and chromosome diversification in the section. Here, we performed a genome-wide analysis of repetitive sequences in A. glandulifera and investigated the chromosome distribution of the identified satellite DNA sequences (satDNAs). LTR retroelements, mainly the Ty3-gypsy families "Fidel/Feral" and "Pipoka/Pipa", were the most represented. Comparative analyses with the A and B genomes showed that many of the previously described transposable elements (TEs) were differently represented in the D genome, and that this variation accompanied changes in DNA content. In addition, four major satDNAs were characterized. Agla_CL8sat was the major component of pericentromeric heterochromatin, while Agla_CL39sat, Agla_CL69sat, and Agla_CL122sat were found in heterochromatic and/or euchromatic regions. Even though Agla_CL8sat belong to a different family than that of the major satDNA (ATR-2) found in the heterochromatin of the A, K, and F genomes, both satDNAs are members of the same superfamily. This finding suggests that closely related satDNAs of an ancestral library were differentially amplified leading to the major changes in the heterochromatin patterns that accompanied the karyotype and genome differentiation in Arachis.

The high-order structure of metaphase chromosomes remains still under investigation, especially the 30-nm structure that is still controversial. Advanced 3D imaging has provided useful information for our understanding of this detailed structure. It is evident that new technologies together with improved sample preparations and image analyses should be adequately combined. This mini review highlights 3D imaging used for chromosome analysis so far with future imaging directions also highlighted.

In normal human somatic cells, telomere dysfunction causes cellular senescence, a stable proliferative arrest with tumour suppressing properties. Whether telomere dysfunctioninduced senescence (TDIS) suppresses cancer growth in humans, however, is unknown. Here, we demonstrate that multiple and distinct human cancer precursor lesions, but not corresponding malignant cancers, are comprised of cells that display hallmarks of TDIS. Furthermore, we demonstrate that oncogenic signalling, frequently associated with initiating cancer growth in humans, dramatically affected telomere structure and function by causing telomeric replication stress, rapid and stochastic telomere attrition, and consequently telomere dysfunction in cells that lack hTERT activity. DNA replication stress induced by drugs also resulted in telomere dysfunction and cellular senescence in normal human cells, demonstrating that telomeric repeats indeed are hypersensitive to DNA replication stress. Our data reveal that TDIS, accelerated by oncogene-induced DNA replication stress, is a biological response of cells in human cancer precursor lesions and provide strong evidence that TDIS is a critical tumour suppressing mechanism in humans.

The standard rye cultivar ‘Imperial’ and a structural
variant carrying an intact 1R chromosome and two
telocentric 1R chromosomes (short and long arms) were
used to investigate expression patterns of homologous
rDNA loci, and the influence of chromosome structural
change on their interphase organisation and relative
disposition. Sequential silver staining and in situ
hybridization with the rDNA probe pTa71, established a
correspondence between the expression and organization
patterns of rDNA domains in metaphase and interphase
cells. In most cells of the cultivar Imperial, nucleolar
organizer region (NOR) silver staining on metaphase
chromosomes with equivalent numbers of rDNA genes
revealed a size heteromorphism between homologous rDNA loci, resulting from their differential expression.
NOR heteromorphism in the structural variant line was
significantly reduced. The preferential activity of one NOR
over its homologue was found to be random within cells and
independent of parental origin. Nucleotypic modifications
mediated by changes in the 1R chromosome structure
include increased proximity between homologous rDNA
loci in interphase, and an increase in the frequency of cells
with intra-nucleolar ribosomal condensed chromatin.
These results seem to indicate a ‘sequence recognition’
process for the regulation of homologous loci.