Differences In Chromosome Size Research Articles

Cytogenetic analysis of three species of the genus Haemulon (Teleostei: Haemulinae) from Margarita Island, Venezuela

This paper describes the karyotype analysis of Haemulon aurolineatum, Haemulon bonariensis and Haemulon plumierii, by Giemsa staining, C-banding, Ag-staining and fluorescent in situ hybridization (FISH), to locate the 18S and 5S rRNA genes. Diploid modal count in the three species was 2n = 48 acrocentric elements. Except for pair 24, which exhibited an unmistakable secondary constriction in all three species, it was not possible to classify them as homologous to each other because differences in chromosome size were too slight between adjacent pairs within a size-graded series. Ag-NOR clusters were located in pair 24 in the three species with signal located on the secondary constriction of these chromosomes. C-banding demonstrated that the three species share the same distribution pattern of the constitutive heterochromatin with centromeric heterochromatic blocks in the 23 chromosome pairs and a pericentromeric block in pair 24 which is coincident with the NORs. FISH experiments showed that 18S rDNA sequences were located coincident with the Ag-NOR site in the three species; however, differences in both the number and chromosome distribution of 5S-rDNA cluster were detected among them. Our data suggest that chromosome evolution of Haemulon has been preserved from major changes in the karyotypic macrostructure, whereas microstructural changes have occurred.

Clonal propagation and the fast generation of karyotype diversity: anin vitro Leishmaniamodel

In the present work we studied the karyotype stability during long-term in vitro maintenance in 3 cloned strains of Leishmania (Viannia) peruviana, Leishmania (Viannia) braziliensis and a hybrid between both species. Only the L. (V.) peruviana strain showed an unstable karyotype, even after subcloning. Four chromosomes were studied in detail, each of them characterized by homologous chromosomes of different size (heteromorphy). Variations in chromosome patterns during in vitro maintenance were rapid and discrete, involving loss of heteromorphy or appearance of additional chromosome size variants. The resulting pattern was not the same according to experimental conditions (subinoculation rate or incubation temperature), and interestingly, this was associated with differences in growth behaviour of the respective parasites. No change in total ploidy of the cells was observed by flow cytometry. We discuss several mechanisms that might account for this variation of chromosome patterns, but we favour the occurrence of aneuploidy, caused by aberrant chromosome segregation during mitosis. Our results provide insight into the generation of karyotype diversity in natural conditions and highlight the relativity of the clone concept in parasitology.

Common themes and cell type specific variations of higher order chromatin arrangements in the mouse

BackgroundSimilarities as well as differences in higher order chromatin arrangements of human cell types were previously reported. For an evolutionary comparison, we now studied the arrangements of chromosome territories and centromere regions in six mouse cell types (lymphocytes, embryonic stem cells, macrophages, fibroblasts, myoblasts and myotubes) with fluorescence in situ hybridization and confocal laser scanning microscopy. Both species evolved pronounced differences in karyotypes after their last common ancestors lived about 87 million years ago and thus seem particularly suited to elucidate common and cell type specific themes of higher order chromatin arrangements in mammals.ResultsAll mouse cell types showed non-random correlations of radial chromosome territory positions with gene density as well as with chromosome size. The distribution of chromosome territories and pericentromeric heterochromatin changed during differentiation, leading to distinct cell type specific distribution patterns. We exclude a strict dependence of these differences on nuclear shape. Positional differences in mouse cell nuclei were less pronounced compared to human cell nuclei in agreement with smaller differences in chromosome size and gene density. Notably, the position of chromosome territories relative to each other was very variable.ConclusionChromosome territory arrangements according to chromosome size and gene density provide common, evolutionary conserved themes in both, human and mouse cell types. Our findings are incompatible with a previously reported model of parental genome separation.

A naturally occurring point mutation in the 13-mer R repeat affects the oriC function of the large chromosome of Vibrio cholerae O1 classical biotype.

The genome of Vibrio cholerae consists of two circular chromosomes of different sizes. Here, a comparative analysis of the replication origins of the large chromosomes (oriCIvc) of classical and El Torbio types of the pathogen is reported. Extensive nucleotide sequence analyses revealed that the oriCIvc region has six DnaA boxes instead of the five found in Escherichia coli oriC. The additional DnaA box, designated Rv, was unique in V. cholerae as well as in other members of the family Vibrionaceae. However, Rv was not found to be essential for the autonomous replication function of the 307-bp oriCIvc minimal region. In contrast to El Tor and the recently evolved V. cholerae 0139 strains, the oriCIvc region of the classical biotype showed only a single base transition (T-->G) in a highly conserved AT-rich 13-mer R repeat region. From the minichromosome copy number and its transformational efficiency analyses, it appears that the single base substitution in the oriCIvc of the classical biotype has a significant effect on its replication initiation.

Karyotype Evolution in Aeshna (Aeshnidae, Odonata)

The haploid DNA content of Aeshna confusa (2n = 27, n = 13 + XO, male). A. bonariensis (2n = 26, n = 12 + neo-XY, male) and A. cornigera planaltica (2n = 16, n = 7 + neo-XY, male) has been determined (2.16 ± 0.16 pg, 1.81 ± 0.17 pg, and 2.08 ± 0.08 pg, respectively). Despite the differences in chromosome size and number, differences in DNA content between species are not significant. The karyotypic analysis of Aeshna species leads to the conclusion that fusions between autosome.s or autosome and the sex chromosome, are the only chromosome rearrangement that occurred during evolution. In the species here studied, fusions have taken place with a minimal loss of DNA; however, other species of the genus show important differences in genome size, which cannot only be justified by fusion events.

Cytogenetical Analysis of Chromosomal Aberration Due to Translocation Between the 23rd and 25th Linkage Groups in the Silkworm, Bombyx Mori

The Chromosome aberration “T(23;25)Nd, which has been identified by genetical studies as an attachment or translocation between chromosomes of the 23rd and 25th linkage groups, was investigated cytogenetically. In the cross of T(23;25)Nd/tub;oy x tub;oy, only the parental combination of chromosomes was produced. The ++ larvae segregating in this cross formed primary spermatocytes with 27 chromosome pairs, which is one pair less than normal. Primary spermatocytes of tub oy larvae had 28 chromosome pairs, which is the standard number for this animal. The chromosome number of all the embryos formed from this cross was 2n =55 and 2n =56 (normal chromosome number) in a ratio of one to one. In 2n =55 cells one large chromosome was observed, which appears to have been the result of fusion between two chromosomes. Moreover, in the ++ larvae at the diakinesis stage of the oocyte, two chromosomes of different sizes were arranged tandemly along the large chromosome. We conclude that the present chromosomal aberration has originated from a reciprocal translocation with break points close to the telomeres in both chromosomes of the 23rd and the 25th linkage groups.

Molecular and phenotypic description of Pneumocystis wakefieldiae sp. nov., a new species in rats

Organisms in the genus Pneumocystis are fungi that reside in the lungs of mammals that can cause a lethal pneumonia once the hosts lose immune function. The genus Pneumocystis contains many members, but only two species have been described formally to date, P. carinii, the type species found in rats, and P. jirovecii, resident in human beings. Rats have been shown to harbor another organism in addition to P. carinii, Pneumocystis wakefieldiae sp. nov., formerly known as Pneumocystis carinii f. sp. ratti, which is described here. Although often found together and morphologically similar, P. carinii and P. wakefieldiae are phenotypically and genetically divergent. We used the phylogenetic species recognition approach to distinguish these organisms as two distinct species and estimated the evolutionary time of their separation. Nucleotide sequence comparisons of seven homologous genes showed 4–7% divergence between the P. wakefieldiae and P. carinii sequences, which was in contrast to the 0–0.8% divergence observed within P. carinii species. Even greater divergence (30%) occurred in sequences located between genes. The MSG (major surface glycoprotein) gene families of P. carinii and P. wakefieldiae are 35% divergent from one another and differ with respect to sequence elements associated with regulation of their transcription. Differences in reactivity of monoclonal antibodies and polyclonal antisera reflected these genetically distinct surface antigens. Karyotypic analysis of P. wakefieldiae produced a single profile that was distinct from all 12 profiles known for P. carinii. Eight homologous genes were localized to chromosomes of different sizes in the two species. The cumulative genotypic and phenotypic data support a species distinction between these two organisms.

Molecular and Phenotypic Description of Pneumocystis wakefieldiae sp. nov., a New Species in Rats

Organisms in the genus Pneumocystis are fungi that reside in the lungs of mammals that can cause a lethal pneumonia once the hosts lose immune function. The genus Pneumocystis contains many members, but only two species have been described formally to date, P. carinii, the type species found in rats, and P. jirovecii, resident in human beings. Rats have been shown to harbor another organism in addition to P. carinii, Pneumocystis wakefieldiae sp. nov., formerly known as Pneumocystis carinii f. sp. ratti, which is described here. Although often found together and morphologically similar, P. carinii and P. wakefieldiae are phenotypically and genetically divergent. We used the phylogenetic species recognition approach to distinguish these organisms as two distinct species and estimated the evolutionary time of their separation. Nucleotide sequence comparisons of seven homologous genes showed 4–7% divergence between the P. wakefieldiae and P. carinii sequences, which was in contrast to the 0–0.8% divergence observed within P. carinii species. Even greater divergence (30%) occurred in sequences located between genes. The MSG (major surface glycoprotein) gene families of P. carinii and P. wakefieldiae are 35% divergent from one another and differ with respect to sequence elements associated with regulation of their transcription. Differences in reactivity of monoclonal antibodies and polyclonal antisera reflected these genetically distinct surface antigens. Karyotypic analysis of P. wakefieldiae produced a single profile that was distinct from all 12 profiles known for P. carinii. Eight homologous genes were localized to chromosomes of different sizes in the two species. The cumulative genotypic and phenotypic data support a species distinction between these two organisms.

Cytogenetics and chromosome banding patterns in Caesalpinioideae and Papilionioideae species of Pará, Amazonas, Brazil

Despite the abundance of woody legumes in Brazilian Amazonian rain forests, there are few chromosome counts on the native species of this important region. The present work presents such data for 13 species of Caesalpinioideae (the genera Bauhinia, Caesalpinia, Cassia, Chamaecrista and Senna) and Papilionioideae (Bowdichia, Centrosema and Dioclea) collected from 17 natural populations. Our report represents the first chromosome counts for the genera Bowdichia and Dioclea and for four of the studied species. Observations are made on chromosome morphology, size, condensing behaviour and interphase nucleus structure. Banding with fluorochromes carried out for the first time in Caesalpinioideae revealed discrete CMA+/DAPI– terminal (GC-rich) bands on 2–4 chromosome pairs of most species analysed, with a few species presenting discrete CMA–/DAPI+ (AT-rich) bands. Significant differences in chromosome size, morphology and condensing behaviour were observed among members of the controversial tribe Cassieae (Cassia, Chamaecrista and Senna), revealing the tribe to be a heterogeneous group from the karyological point of view.

Conventional karyotype and nucleolar organizer regions of the toadfish <i>Halobatrachus didactylus</i> (Schneider, 1801) (Pisces: Batrachoididae)

For this report, we studied the conventional karyotype and the NOR-bearing chromosomes in the toadfish Halobatrachus didactylus . We found a karyotype of 46 chromosomes made up of 8 metacentric, 12 submetacentric, and 26 acrocentric elements (FN = 66). No heteromorphic sex chromosomes were observed in the species. Metacentric chromosomes were easily classified as homologous pairs according to their morphology and L/S ratio. The rest of the chromosomes could not be accurately classified as homologous pairs because differences in chromosome size and L/S ratio were too slight between adjacent pairs within a size-ranged series. A single pair of NOR-bearing chromosomes was found. Active NORs were terminally located in a submetacentric pair of chromosomes.

A Karyotype Comparison Between Two Closely Related Species of Acrostichum

Acrostichum aureum and A. danaeifolium are morphologically similar sympatric species which grow in mangrove communities. To evaluate the cytological differences between these species, their karyotypes were analyzed with conventional staining, triple-staining with chromomycin A3 (CMA), distamycin A (DA) and DAPI, silver nitrate, and in situ hybridization with 45S rDNA as probe. Both species have the same chromosome number (2n = 60) with only small differences in chromosome size and morphology. The CMA banding pattern revealed four terminal bands in A. danaeifolium and six in A. aureum. DAPI bands were not found. The maximum number of nucleoli per interphase nucleus and the number of 45S rDNA sites were consistent with the number of CMA bands: four in A. danaeifolium and six in A. aureum. All meiotically analyzed materials showed 30II with normal chromosome pairing and segregation, except in one plant with a chromosome bridge and fragment in cells of anaphase I and II. It is suggested that sympatry and karyotypic orthoselection have contributed to keep the morphological and karyological similarities in such widespread species.

Properties of Bacillus thuringiensis isolated from bank voles.

To assess the properties of B. thuringiensis naturally occurring in the intestines of bank voles. Seventeen Bacillus thuringiensis strains, exhibiting typical growth on selective medium for the B. cereus group and characterized by the ability to produce parasporal crystals, were isolated from bank voles trapped in the Łomza Landscape Park of the Narew River Valley (north-east Poland). All isolates were characterized by pulsed field gel electrophoresis (PFGE) of chromosomal DNA and SDS polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell proteins. Six pulsotypes were found with PFGE typing, using SmaI or NotI as restriction enzymes. Significant differences in chromosome size, ranging from 2.4 to 4.2 Mb for the B. thuringiensis strains studied, were noted. Strain heterogeneity in pulsotypes was also reflected by the similarity of whole-cell protein profiles of the strains. Environmental isolates and reference strains grouped at 71% similarity according to SDS-PAGE data and at 84% on the basis of biochemical tests. B. thuringiensis from intestines of bank voles demonstrated an important level of heterogeneity. The comparison of PFGE profiles and SDS-PAGE of whole-cell protein patterns may be useful to evaluate the relationship between B. thuringiensis isolates. The results presented in this paper may help to explain the diversity of B. thuringiensis.

The human genome structure and organization.

Genetic information of human is encoded in two genomes: nuclear and mitochondrial. Both of them reflect molecular evolution of human starting from the beginning of life (about 4.5 billion years ago) until the origin of Homo sapiens species about 100,000 years ago. From this reason human genome contains some features that are common for different groups of organisms and some features that are unique for Homo sapiens. 3.2 x 10(9) base pairs of human nuclear genome are packed into 23 chromosomes of different size. The smallest chromosome - 21st contains 5 x 10(7) base pairs while the biggest one -1st contains 2.63 x 10(8) base pairs. Despite the fact that the nucleotide sequence of all chromosomes is established, the organisation of nuclear genome put still questions: for example: the exact number of genes encoded by the human genome is still unknown giving estimations from 30 to 150 thousand genes. Coding sequences represent a few percent of human nuclear genome. The majority of the genome is represented by repetitiVe sequences (about 50%) and noncoding unique sequences. This part of the genome is frequently wrongly called "junk DNA". The distribution of genes on chromosomes is irregular, DNA fragments containing low percentage of GC pairs code lower number of genes than the fragments of high percentage of GC pairs.

Amplification of ribosomal RNA genes in acute myeloid leukemia.

Gene amplification is a relatively rare event in acute myeloid leukemia (AML). Double minutes (dmin) and homogeneously staining regions are well established phenomena as cytogenetic correlates of gene amplification. Recently, however, two additional mechanisms leading to gene amplification, i.e., segmental jumping translocations and formation of ring chromosomes, have been described. We report four patients with AML, in whom bone marrow cells exhibited amplifications of ribosomal RNA (rRNA) genes in the form of ring chromosomes or a hsr. In two patients, the MLL gene, and in one patient the CBFA2 gene were shown to be co-amplified with rRNA genes. In two of the four patients, multiple copies of alpha-satellite sequences of the centromeres 13 and 21, respectively, were also demonstrated. In three of the four patients, the clinical course was very aggressive, leading to death within 2-8 months. In these three patients, complex karyotype abnormalities were found, whereas the karyotype of Patient 4 was characterized only by supernumerary ring 21 chromosomes of different sizes and a trisomy 8 in half of the metaphases. Modes of origin and clinical significance of the amplification of rRNA genes are discussed.

INTRASPECIFIC HETEROGENEITY IN THE MINI-EXON GENE LOCALIZATION OFLEISHMANIA(VIANNIA)PANAMENSISANDLEISHMANIA(VIANNIA)GUYANENSISFROM COLOMBIA

Intraspecific heterogeneity was demonstrated in the mini-exon gene localization from Leishmania (Viannia) panamensis and L. (Viannia) guyanensis. Different karyotypes were detected in human isolates circulating in endemic areas of Colombia. The presence of mini-exon gene sequences on chromosomes of different sizes, ranging from 370 to 800 kb in L. (V.) panamensis and from 500 to 800 kb in L. (V.) guyanensis, was observed and was neither strain nor species specific. In some cases, hybridization with 2 chromosomes in the same strain was observed. The variability of chromosomal localization of mini-exon gene sequences of these 2 species highlights the genetic variability of the Viannia subgenus and the potential utility of the mini-exon gene as a molecular epidemiologic marker.

Analysis of the electrophoretic karyotype ofFlammulina velutipes

The karyotype ofFlammulina velutipes (Curt.: Fr.) Sing. was analyzed electrophoretically using contourclamped homogeneous electric field gel electrophoresis and hybridization with DNA probes. The chromosomal DNA from the monokaryon (Fv-4K) and the dikaryon (Fv-4) were resolved into six and eight bands, respectively. The sizes of the chromosomes ranged from 1.9 to 6.0 megabase (Mb) pairs. Each of the separated bands of chromosomal DNA was identified by use of five cloned probes. The number of these chromosomes was estimated to be 6 and 12, respectively; and the size of the entire genome was estimated to be about 20.1 and 38.6Mb, respectively. From a comparison of the hybridization patterns, the existence of allelic chromosomes of different sizes was deduced in the Fv-4 strain.

Reduced virulence caused by meiotic instability of the TOX2 chromosome of the maize pathogen Cochliobolus carbonum.

The mechanisms by which pathogenic fungi evolve are poorly understood. Production of the host-selective cyclic peptide HC-toxin is controlled by a complex locus, TOX2, in the plant pathogen Cochliobolus carbonum. Crosses between toxin-producing (Tox2+) and toxin-nonproducing (Tox2-) isolates, as well as crosses between isolates in which the TOX2 genes were on chromosomes of different size, yielded progeny that had lost one or more copies of one or more of the TOX2 genes. Of approximately 200 progeny analyzed, eight (4%) had lost at least one TOX2 gene. All of them still had at least one functional copy of all of the known genes required for HC-toxin production (HTS1, TOXA, TOXC, and TOXE). Most deletion strains could be explained by simple chromosome breaks resulting in the loss of major contiguous portions (0.8 to 1.4 Mb) of the 3.5-Mb TOX2 chromosome, whereas others had more complicated patterns. All deletion strains had normal growth and were fertile, indicating that the 1.4 Mb of DNA contained no essential housekeeping genes. Most strains were also still virulent (Tox2+), but two had a novel phenotype of reduced virulence (RV), characterized by smaller lesions that expanded at a reduced rate and an inability to colonize plants systemically. Although the RV strains made no detectable HC-toxin in culture, the RV phenotype was dependent on the presence of a functional copy of HTS1, which encodes the central enzyme in HC-toxin biosynthesis. We propose that the RV strains still make a low level of HC-toxin, at least in planta, and that this is due to the loss of one or more genes that contribute to, but are not absolutely required for, HC-toxin synthesis.

Differences in chromosome number and genome rearrangements in the genus Brucella.

We have studied the genomic structure and constructed the SpeI, PacI and I-CeuI restriction maps of the four biovars of the pathogenic bacterium Brucella suis. B. suis biovar 1 has two chromosomes of 2.1 Mb and 1.15 Mb, similar to those of the other Brucella species: B. melitensis, B. abortus, B. ovis and B. neotomae. Two chromosomes were also observed in the genome of B. suis biovars 2 and 4, but with sizes of 1.85 Mb and 1.35 Mb, whereas only one chromosome with a size of 3.1 Mb was found in B. suis biovar 3. We show that the differences in chromosome size and number can be explained by rearrangements at chromosomal regions containing the three rrn genes. The location and orientation of these genes confirmed that these rearrangements are due to homologous recombination at the rrn loci. This observation allows us to propose a scheme for the evolution of the genus Brucella in which the two chromosome-containing strains can emerge from an hypothetical ancestor with a single chromosome, which is probably similar to that of B. suis biovar 3. As the genus Brucella is certainly monospecific, this is the first time that differences in chromosome number have been observed in strains of the same bacterial species.

Chromosomal reorganization during meiosis of Saccharomyces cerevisiae baker's yeasts.

The genomic constitution of two S. cerevisiae baker's yeasts and their meiotic products have been analyzed by pulsed-field gel-electrophoresis, hybridization with specific gene probes, marker segregation, and flow cytometry. The parental strains have chromosomal patterns substantially different from those of laboratory strains used as controls. This pattern is partly the result of there being more than one copy of homologous chromosomes of different size, as judged by Southern-blot hybridization carried out with specific gene probes. Flow cytometry indicated that the strains have a 2.7 C DNA content. Tetrad analysis showed disomy for some chromosomes and tetrasomy for others. When two complete tetrads were subjected to molecular analysis the results confirmed instances of segregation of homologous chromosomes of different size. However, the presence of chromosomal bands absent in the parentals and the disappearance of chromosomal bands present in the parental strains were frequently seen. This result was attributed to two different phenomena: (1) the presence of multiple Ty1 and Ty2 transposable elements which seem to undergo interchromosomal translocation together with amplification, giving rise to differences in chromosomal size; (2) the presence of multiple Y' subtelomeric regions, giving rise to asymmetrical homologous recombination and, as a consequence, differences between the size of the recombinant chromosomes and the non-recombinant parental chromosomes. Chromosomal reorganization occurs with a very high frequency during meiosis. By contrast, mitosis is very stable, as judged by the reproducible electrophoretic karyotype shown by the parental strains in successive generations.

Homologues of the 24-kDa Flagellar Ca2+-Binding Protein Gene ofTrypanosoma cruziAre Present in Other Members of the Trypanosomatidae Family

A full-length cDNA encoding the 24-kDa flagellar Ca2+-binding protein (FCaBP) of the Dm28c clone ofTrypanosoma cruziwas cloned and characterized. Comparison of the deduced amino acid sequence with those of the FCaBPs of otherT. cruzistrains revealed greater than 97% sequence conservation. FCaBP-like genes are found inTrypanosoma conorhini, Trypanosoma freitasi, Trypanosoma lewisi, Herpetomonas megaseliae, Leptomonas seymouri,andPhytomonas serpens,but not inCrithidia deanei, Leishmania amazonensis,orEndotrypanum schaudinni. Among variousT. cruzistrains, FCaBP genes are located on chromosomes of different size, although all strains possess multiple FCaBP genes organized as tandemly arranged gene families. Northern and Western blot analyses revealed that FCaBP mRNAs are produced in all organisms possessing FCaBP-hybridizing sequences, indicating that expression of FCaBP or an FCaBP-like protein is common to a number of trypanosomatid species.