C-band Positive Regions Research Articles

Banded karyotypes of Allactaga williamsi from Central Anatolia

A chromosomal study of 2 populations of Allactaga williamsi from Konya province in Central Anatolia, Turkey, was performed. The diploid number of 48 chromosomes was found in all of the 5 specimens examined. All of the chromosomes except the Y were biarmed and could be identified by unique G-banding patterns. The C-banding analysis revealed a considerable amount of constitutive heterochromatin in all chromosomes. The C-band positive regions were distributed mainly in centromeric areas, whereas the Y chromosome stained uniformly and C-negatively. The active NORs were localized in 2 pairs of small metacentric and submetacentric autosomes. The species of the genus Allactaga are apparently conservative in their karyotypic structure.

Repetitive DNA sequences from the X chromosome of the spiny eel (Mastacembelus aculeatus)

To investigate the characters of repetitive DNA sequence in the sex chromosomes of the spiny eel (Mastacembelus aculeatus), the X chromosomal library was screened and a family of repetitive sequence, consisting of Ma 1-Ma 6, was isolated. The fluorescence in situ hybridization (FISH) result confirmed that Ma 1 - Ma 5 dispersed over sex chromosomes and all autosomes, whereas, Ma 6 is sex chromosome-specific and distributed only on the C-band positive regions of X chromosome, and Ma 6 maybe the main components of the heterochromatic regions of X chromosome. This study provides additional information about the evolution of sex chromosomes in lower vertebrates such as fish.

Mapping the distribution of the interstitial telomeric (TTAGGG)n sequences in eight species of Brazilian marsupials (Didelphidae) by FISH and the correlation with constitutive heterochromatin. Do ITS represent evidence for fusion events in American marsupials?

The C-band pattern and the distribution of the (TTAGGG)_n sequence after fluorescence in situ hybridization (FISH), were studied in eight species of Didelphidae marsupials: four species with 2n = 14 (Marmosops parvidens, Marmosops incanus, Marmosa murina and Metachirus nudicaudatus), two species with 2n = 18 (Monodelphis domestica and M. americana), and two with 2n = 22 (Didelphis marsupialis and Lutreolina crassicaudata). The hybridization signals were observed at both termini telomeres of all chromosomes. In addition, interstitial sequences were detected in the pericentromeric region of all chromosomes of Marmosops parvidens, in five chromosome pairs of M. incanus, and in the first pair of Monodelphis domestica. These sites always occur in the region of constitutive heterochromatin, even though C-band positive regions do not always present interstitial telomeric sequences (ITS). We suggest that the interstitial (TTAGGG)_n sequences are associated with satellite DNA and do not necessarily arise through chromosomal rearrangements.

C-band polymorphism in the chromosomes of the musselMytilus galloprovincialisLmk.

SUMMARYThe chromosomes of 346 specimens of Mytilus galloprovincialis, collected at four NW Iberian peninsula sites, were studied using a C-banding technique. Polymorphism for C-banding was detected. According to the banding patterns, three classes of mussels could be distinguished: 1) individuals showing two pairs of submeta/subtelocentric chromosomes bearing NOR-associated heterochromatic regions terminal to their long arms, 2) mussels presenting additional C-bands located at other positions on the NOR-bearing chromosomes or on other chromosomes, and 3) mosaic mussels. The location of the additional C-band positive regions was similar in the four populations studied.

Evolution of a long-range repeat family in chromosome 1 of the genus Mus.

Copy numbers and variation of a clustered long-range repeat family on chromosome (Chr) 1 have been studied in different species of the genus Mus. The repeat sequence was present in all, as inferred from cross-hybridization with probes derived from the Mus musculus repeat family. Copy numbers determined by dot blot hybridization were very low, from three to six per haploid genome in M. caroli, M. cervicolor, and M. cookii. These species form one branch of the phylogenetic tree in the genus Mus. In the other group of phylogenetically related species--M. spicilegus, M. spretus, M. musculus and M. macedonicus--copy numbers ranged from 6 to 1810 per haploid genome. The repeat cluster is cytogenetically visible as a fine C-band in M. macedonicus and as a C-band positive homogeneously staining region (HSR) in several populations of M. m. domesticus and M. m. musculus. When cytogenetically visible, the clusters contained from 179 to 1810 repeats. Intragenomic restriction fragment length polymorphisms (RFLPs), which reflect sequence variation among different copies of the long-range repeat family, increased with higher copy numbers. The high similarity of the RFLP pattern among genomes with C-band positive regions in Chr 1 of M. m. musculus, M. m. domesticus, and M. macedonicus points to a close evolutionary relationship of their Chr 1 repeat families.

Recovery of dissected C-band regions in Crepis chromosomes

Chromosome samples were prepared on a plastic coverslip covered with a polyester membrane and were subjected to the C-banding treatment. The C-band pattern was obtained after Giemsa staining. The C-band positive regions of the Crepis chromosomes were identified, dissected out by irradiation with a micro-laser beam and recovered in Eppendorf tubes.

Chromosomal breakage following treatment of CHO-K1 cells in vitro with U-68,553B is due to induction of undercondensation of heterochromatin.

Preferential breakage of chromosomes at specific sites (so-called "fragile sites") has been observed to occur spontaneously, and has been induced by some metal salts and chemicals. Furthermore, a heterochromatic region of the long arm of the Chinese hamster ovary (CHO) X-chromosome is known to be susceptible to a disproportionately high frequency of spontaneous breakage; unless there is physical displacement of chromatin the resulting achromatic lesions are not scored as structural aberrations. We have encountered such anomalous breakage associated with C-band positive regions of the chromosomes of a CHO-K1 cell line following exposure of the cells to toxic doses of U-68,553B and in this report present evidence that the apparent breaks are due to undercondensed heterochromatin (UH) and evidence that the phenomenon appears to occur at higher frequency in a particular cell line of Chinese hamster. This finding has important implications on the assessment of potential risk due to exposure to the drug. Such apparent breaks at sites of UH in chromosome 1 was not observed in an alternate CHO cell line (CHO-WBL) which supports the notion that the UH associated achromatic lesions in the CHO-K1 line may be a cell line specific phenomenon. Furthermore, careful electron microscopy of the chromosomes revealed chromatin fibers connecting the apparently broken chromosomes. The UH was not observed in the presence of added metabolic activation (S9), and thus the significance of the phenomenon in risk assessment is further reduced. The data presented here provide evidence that sites of UH occur preferentially at locations of C-band positive constitutive heterochromatin in CHO cells; we believe that this is the first report of induced fragile sites in rodent cells in vitro documented in this way. In addition, evidence is presented that U-68,553B lacks the ability to induce breakage in vivo in rodents and lacks the ability to induce chromosome breakage in human peripheral lymphocytes in vitro. Therefore, it is concluded that the positive results with CHO-K1 cells treated with U-68,553B are unlikely to be predictive of a genotoxic hazard. This is a specific example of the importance of careful followup to an in vitro result in risk assessment.

Characterization of seven DA/DAPI-positive bisatellited marker chromosomes by in situ hybridization

Seven dicentric bisatellited marker chromosomes, ascertained at amniocentesis, chorionic villus sampling, and in blood from an abnormal liveborn were characterized cytogenetically. All seven markers demonstrated brilliant bands by the DA/DAPI technique corresponding to C-band positive regions. Although some dicentric DA/DAPI-positive bisatellited markers have been identified as inverted duplicated 15s, recent literature has suggested that DA/DAPI lacks specificity for chromosome 15. Our evaluation of DA/DAPI-positive bisatellited marker chromosomes by in situ hybridization shows that some originate from chromosome 15 whereas DA/DAPI negative bisatellited markers may not be derived from 15. The morphological variations noted in our studies are discussed with respect to nomenclature.

Intragenomic movement, sequence amplification and concerted evolution in satellite DNA in harvest mice,Reithrodontomys: Evidence from in situ hybridization

Three DNA probes isolated from three species of Reithrodontomys (R. montanus, R. megalotis, R. fulvescens) were used to examine within and among species variation in the chromosomal location of satellite DNA and constitutive heterochromatin. These probes hybridized to the centromeric regions on all chromosomes in six species of the subgenus Reithrodontomys. Additionally, nearly all extra-centromeric C-band positive regions (with the exception of some heterochromatic material on the X and Y) hybridized to these probes. Within the subgenus Reithrodontomys both the chromosomal distribution and organization of satellite DNA has changed throughout evolution. The evolutionary transition has been from a totally centromeric position in R. fulvescens to centromeric and non-centromeric regions in other species that have undergone extensive chromosomal rearrangements from the primitive karyotype for peromyscine rodents. In addition, the monomer repeat of the satellite sequence differs between R. fulvescens (monomer defined by PstI) and the remaining species in the subgenus Reithrodontomys (monomer defined by EcoRI). These results suggest at least two amplification events for this satellite DNA sequence. Models and mechanisms concerned with the homogenization and spread of satellite sequences in complex genomes are evaluated in light of the Reithrodontomys data. From a phylogenetic standpoint, the satellite sequences composing heterochromatic regions were restricted to the subgenus Reithrodontomys, which supports morphological differences used to recognize two subgenera, Reithrodontomys and Aporodon. Probes failed to hybridize to any part of the karyotype of R. mexicanus (subgenus Aporodon) or to seven species from other closely related genera (Baiomys, Neotoma, Nyctomys, Ochrotomys, Onychomys, Peromyscus, Xenomys), some of which are considered as potential sister taxa for Reithrodontomys.

In situ nick translation distinguishes between C-band positive regions on mouse chromosomes.

In situ nick translation of mouse metaphase chromosomes by non-radioactive detection means and DNase I digestion followed by Giemsa staining were used to analyse the DNase I resistance of two different C-band positive regions. These were the centromeric heterochromatin of acro- and metacentric chromosomes and an interstitial C-band on chromosome 1 of wild mice, IS(HSR;1C5D)1Lub. Whereas the centromeric heterochromatin was clearly resistant to DNase I, the interstitial C-band showed very high DNase I sensitivity. Among centromeric C-bands, the heterochromatin in Robertsonian fusion biarmed chromosomes was more resistant to DNase I action than was the centromeric heterochromatin of the acrocentric chromosomes.

Cytological evidence of transcription of highly repeated DNA sequences during the lampbrush stage in Triturus cristatus carnifex.

Highly repeated, or satellite, DNA fractions have been isolated from total Triturus cristatus carnifex DNA by renaturation kinetics, caesium salt centrifugation and restriction endonuclease digestion. We have shown by DNA/DNA in situ hybridisation and autoradiography that all of these probes bind to C-band positive regions on mitotic or lampbrush chromosomes of T.c. carnifex. Under conditions of DNA to RNA-transcript in situ hybridisation labelled satellite DNA binds to nascent RNA transcripts that are still associated with the DNA axes of many lampbrush loops. The majority of the loops that label heavily in these experiments are located on the long arms of chromosome I, a region previously shown to be rich in highly repeated DNA and to have many of the properties of heterochromatin. These satellite DNA probes also label many loops on a comparable chromosome region in T. marmoratus, a species closely related to T. cristatus. However, in DNA/RNA-transcript hybrids to other more distantly related species of Triturus, there are no chromosome regions that have the same concentration of labelled loop pairs as the long arms of T.c. carnifex and T. marmoratus, although some loop pairs do label. We have cloned two satellite sequences in pBR322, and have obtained the same results using these pure probes as we obtained using satellite probes isolated by other techniques. These results demonstrate unequivocally that satellite DNA is transcribed on lampbrush chromosomes during oogenesis in crested newts.

Analysis of a BrdU-sensitive site in the cactus mouse (Peromyscus eremicus): chromosomal breakage and sister-chromatid exchange.

When the thymidine analog BrdU was incorporated into the DNA of a fibroblast cell line derived from the cactus mouse Peromyscus eremicus, a chromosome region with an increased frequency of gaps and breaks was observed. Nearly a third of the chromatid aberrations found at this site were associated with a sister-chromatid exchange (SCE) although this chromosome region showed no increase in sister-chromatid exchange in the absence of a gap or break. SCEs were significantly decreased in the remainder of the chromosome arm when it contained an aberration at the unstable site. This BrdU-sensitive region, unlike others reported, was found not to be late-replicating.--In this chromosome complement, the frequency of sister-chromatid exchange in C-band positive regions was significantly lower than that in C-band negative regions.

Induction of distinctive chromosomal bands in selected human subjects with D, G, and Y chromosome anomalies.

The C and G bandings were induced in eight selected human complements with D, G and Y chromosomal aberrations. In a few cases, the Q banding was utilized for additional information. Some of the Robertsonian trans locations and deletions at the constitutive heterochromatin regions were identified by C band alone. In certain cases, however, none of these banding techniques revealed the origin of an anomalous chromosome. It was interesting to note that a complement with C-band positive regions, other than the typical centromeric and Y chromosome heterochromatin, stained negatively upon G-band induction. Most probably, these regions were composed of the species of repititious DNA that express differentially during C- and G-band manifestations.