Small Metacentric Chromosome Research Articles

Nature and distribution of chromosomal intertwinings in Saccharomyces cerevisiae.

To elucidate yeast chromosome structure and behavior, we examined the breakage of entangled chromosomes in DNA topoisomerase II mutants by hybridization to chromosomal DNA resolved by pulsed-field gel electrophoresis. Our study reveals that large and small chromosomes differ in the nature and distribution of their intertwinings. Probes to large chromosomes (450 kb or larger) detect chromosome breakage, but probes to small chromosomes (380 kb or smaller) reveal no breakage products. Examination of chromosomes with one small arm and one large arm suggests that the two arms behave independently. The acrocentric chromosome XIV breaks only on the long arm, and its preferred region of breakage is approximately 200 kb from the centromere. When the centromere of chromosome XIV is relocated, the preferred region of breakage shifts accordingly. These results suggest that large chromosomes break because they have long arms and small chromosomes do not break because they have small arms. Indeed, a small metacentric chromosome can be made to break if it is rearranged to form a telocentric chromosome with one long arm or a ring with an "infinitely" long arm. These results suggest a model of chromosomal intertwining in which the length of the chromosome arm prevents intertwinings from passively resolving off the end of the arm during chromosome segregation.

Chromosomal homologies between Drosophila lebanonensis and D. melanogaster determined by in situ hybridization.

Twelve biotin-labelled recombinant DNA probes were hybridized to polytene chromosomes of Drosophila melanogaster and D. lebanonensis. Probes were chosen in order to cover the whole chromosomal complement. Six probes correspond to known genes from D. melanogaster (RpII215, H3-H4, MHC, hsp28/23, hsp83, hsp70), four probes are clones isolated from a D. subobscura library (Xdh, lambda DsubS3, lambdaDsubG3, lambdaDsubG4) and the remaining two probes correspond to the Adh gene of D. lebanonensis and to one sequence (262), not yet characterized, from the same species. The chromosomal homologies obtained from the in situ hybridization results allow us to determine that Muller's C and D chromosomal elements are fused in the karyotype of D. lebanonensis and constitute the large metacentric chromosome. Single pericentric inversions in the E and B elements have generated the medium and small metacentric chromosomes, respectively. No great changes are detected in Muller's A element, which remains acrocentric. The changes detected in the karyotypic evolution of D. lebanonensis are frequently observed in Drosophila evolution, as deduced from chromosomal homologies of several Drosophila species. The results are also consistent with Muller's proposal that chromosomal elements have been conserved during the evolution of Drosophila.

Confirmation of isochromosome 18p using whole chromosome arm-specific fluorescence in situ hybridization.

Fluorescent in situ hybridization (FISH) using a pool of DNA clones that have been mapped to the short arm of chromosome 18 is described. This arm-specific painting technique was used to analyze the chromosomes of two patients who displayed different clinical pictures. One patient had clinical features consistent with tetrasomy 18p, and the other patient had some of the clinical features associated with trisomy 18. The initial karyotype of both patients showed the presence of a small metacentric marker chromosome, thought to resemble an iso(18p). This interpretation of the karyotype was confirmed for both cases using a specific chromosome arm-painting strategy. While whole-chromosome paints may identify the origin of markers or detect translocations, arm-specific libraries will permit detailed analysis of chromosomal rearrangements when more precise information may be needed.

Karyotyping the Arabian Camel (Camelus dromedarius), Using C-Banding Technique.

The chromosomes of the Arabian camel or the one humped camel, Camelus dromedarius, L. have been studied using cell cultures of peripheral blood lymphocytes. Using C-banding technique, the diploid chromosome number for the C. dromedarius was found to be 74, with a karyotype consisting of 62 acrocentric, 8 metacentric and 2 submetacentric autosomes. The X chromosome is large, metacentric and the Y chromosome is a small metacentric sex chromosome. The fundamental number has been calculated to be 86 chromosomes.

Detailed description and nomenclature of G-banded Arabian camel (Camelus dromedarius) chromosomes

SUMMARYThe chromosomes of the Arabian camel or the one humped camel, Camelus dromedarius, have been studied using cell cultures of peripheral blood lymphocytes. It was found that the diploid chromosome number for the C. dromedarius is 74, with a karyotype consisting of 62 acrocentric, 8 metacentric and 2 submetacentric autosomes. The X chromosome is large metacentric and the B chromosome is a small metacentric sex chromosome. The G-band patterns have also been described for the first time and illustrated idiogrammatically in order to simplify the G-banding nomenclature for C. dromedarius. This could constitute a basis for a standard nomenclature for the chromosomes of the Camelidae.

Chromosome number of theOxalis tuberosa alliance (Oxalidaceae)

Twelve taxa of theOxalis tuberosa alliance were analysed and found to share the same basic chromosome number x = 8. The karyotypes are composed by small metacentric and submetacentric chromosomes. Different ploidy levels were found among the taxa: there were 9 diploids, 1 tetraploid, 1 hexaploid and 1 octoploid. The last ploidy level corresponds toO. tuberosa, the only tuber bearing taxon found so far in the alliance. Cytotaxonomic evidence and evolutionary considerations suggest to classify theO. tuberosa alliance in sect.Herrerea.

Localization of the T-DNA on marker chromosomes in transformed tobacco cells by in situ hybridization

Chromosome and molecular analyses were conducted on tobacco cells which had been transformed by the T-DNA of the Ti-plasmid. These analyses showed that there were specific chromosome rearrangements in the transformed cells (marker chromosomes). There was a positive correlation between the number of marker chromosomes per cell and the oncogenic potential of the transformed cells. However, we show, using the Southern hybridization method, that the TL fragment of T-DNA, but not the TR, clearly hybridizes with nuclear DNA. In situ hybridization was used to locate the insertion site of T-DNA: the hybridization signal was found on a small metacentric chromosome. This chromosome may occur single or translocated onto other chromosomes, to make marker chromosomes. Thus, by locating the T-DNA, we have confirmed the correlation between the marker chromosomes and the oncogenic potential.

Nucleolar activity of B-chromosomes inAllium cernuum (Alliaceae)

Nucleolar activity was analyzed in two samples of plants of the wild onion speciesAllium cernuum, one from Canada (2n=14) and one from the United States of America (2n=14+3B), using phase contrast analysis and C- and Ag-NOR-banding. Three chromosome pairs of the standard A-chromosome complement show small telomeric satellites, which corresponds to the maximum number of Ag-NOR-bands at metaphase and to the telomeric C-heterochromatin. However, the maximum number of nucleoli observed at interphase was eight, indicating that another chromosome pair possesses nucleolar activity. Corresponding results were obtained for the A-chromosome complement of plants from the United States of America, however, these plants further possess three small metacentric supernumerary chromosomes, which show telomeric satellites on both arms, corresponding to two telomeric Ag-NOR-bands observed after silver staining. The presented data clearly indicate that the B-chromosomes ofAllium cernuum possess rDNA gene clusters which show strong nucleolar activity.

Chromosome analysis of a newly established renal carcinoma cell line

A renal cell carcinoma has been established as a cell line in vitro. Repeated chromosome analyses of the cell line revealed a stable clone with the modal chromosome number 80 and three pairs of marker chromosomes, M1-M3. M1 and M2 resulted from a translocation between a chromosome #3 deleted in band p14 and a normal #7: M1 = der(3)t(3;7)(:3p14→cen→3q24::7q21→7qter), and M2 = der(7)t(3;7)(3qter→3q24::7q21→cen→7pter). M3 was a small metacentric chromosome, probably consisting of the centromeric portion of a #3: del(3)(:p14→cen→q12:). No other structural changes were present. Our findings are in agreement with those of previous studies, stating that rearrangements of 3p12–14 are primary cytogenetic events in renal cell carcinomas, even though this can only be inferred in this case. Thus, this cell line may be useful for further molecular and biochemical studies.

Small metacentric marker chromosomes, particularly isochromosomes, in cancer.

At least two types of small metacentrics, which are isochromosomes for 12p and either 4p or 5p, respectively, are significantly associated with certain types of cancer and their formation may represent important stages in the development of these tumours. The specificity of the i(12p) for testicular cancer is now well established (it may also be present, however, in dysgerminomas and mixed Müllerian tumours of the ovary). This review is therefore mainly concerned with another marker, probably an i(5p) although an i(4p) should also be considered. Recent data suggest that this marker represents a significant chromosomal change occurring with a fairly high frequency in a variety of cancers, including carcinomas of the cervix, ovary, breast, bladder and bronchus (excluding small-cell carcinomas). These isochromosomes may contribute to tumour development through gene amplification; consistent with this is the frequent presence of these markers in two or more copies.

Loss of heterozygosity in hypotriploid cell cultures from testicular tumours

We have established cell lines with a hypotriploid chromosome number from four testicular tumours. Each line had at least one Y chromosome and most of the informative centrosome and enzyme markers were heterozygous implying that the tumours originated from germ cells before the first meiotic division. The small metacentric marker chromosome (i12p), specific for testicular tumours, was present in all tumour cell lines and up to three copies were found in some lines. Rearrangements of chromosome 1 and 11 were each found in three out of four tumours. The rearrangements of chromosome 1 all resulted in duplication of 1q and deletion of short-arm material from the same chromosome giving loss of heterozygosity for enzyme markers on 1p. Loss of satellite material from chromosome 13 and the centromere region of chromosome 9 were found in single cases. This study shows that even where the chromosome number of tumour cells is near triploid, regions of the genome can be deleted. The chromosomes most frequently involved in rearrangements, 1, 11, and 12 all contain sites of ras oncogenes and it is suggested that loss of normal alleles could result in homozygosity for mutant oncogenes which may play a part in tumour progression.

Pallister‐Killian syndrome: cytogenetic and molecular studies

Pallister-Killian syndrome is a dysmorphic syndrome characterized by a tissue-limited mosaicism: a majority of fibroblasts have 47 chromosomes with an extra small metacentric chromosome, whereas the karyotype of lymphocytes is normal. In this study, the interpretation of the extra chromosome as composed of two short arms of chromosome 12 is confirmed, using molecular methods. Furthermore, restriction fragment length polymorphisms indicate that the two arms are identical, which is compatible with the hypothesis of an isochromosome 12p. A new feature which may be important in understanding the mechanism of origin of the abnormality is described: the proportion of abnormal mitoses falls dramatically during long-term culture of fibroblasts.

Chromosome changes in germ cell tumors of the testis

Chromosome analysis was performed on short-term cultures established from samples of six tumors of the testis. Histologically, four tumors were embryonal cell carcinomas (three primary, one metastatic) and two of mixed histology with predominance of teratoma. The modal chromosome number was hypotriploid in four tumors, triploid in one, and hypertriploid in another. All tumors contained structurally abnormal chromosomes, ranging in number from 1 to 10 in different cases. A small metacentric marker chromosome, identified as an isochromosome of the short arm of chromosome #12 [i(12p)], was present in all tumors analyzed. Unlike other marker chromosomes, this one was invariably present in at least two copies per metaphase in all cases; all other chromosome markers were present in single copy in all tumors. Together with the previous reports on the presence of i(12p) in seminoma and teratoma of the testis, our findings suggest that this karyotypic abnormality is characteristic for all histologic varieties of germ cell tumors of the testis.

Chromosomal homologies of the genera Vespertilio, Plecotus and Barbastella (Chiroptera: Vespertilionidae)

Q-banding (and partly G-banding) patterns of chromosomes were studied in three species of vespertilionid bats: Vespertilio murinus, Plecotus auritus and Barbastella barbastellus. The chromosomes of these species were identified and compared on the basis of the G-band diagram of Bickham (Cytologia 44, 1979) for the genus Myotis. The additional metacentric chromosomes which Vespertilio shows as compared to Myotis, differ in arm arrangements from those found in Plecotus and Barbastella. Banding patterns of P. auritus and B. barbastellus are nearly identical. It is remarkable that the smallest metacentric chromosome of P. auritus differs clearly in its banding pattern from that of the American P. townsendi. The significance of the results obtained for the systematic position of these species is discussed.

The chromosome complements of shrubbyOxalis species from South America

Twenty species of shrubbyOxalis species native in South America were arranged in six groups according to their karyotype similarities. The first group includes more than half of the species studied, all with 2n = 12 relatively small metacentric chromosomes. The rest of the species from the other groups has different basic chromosome numbers, and exhibits various degrees of chromosome asymmetry and size increase. These latter groups apparently have specialized to habitats with low light intensity such as the forest undergrowth in contrast to the frist group whose members live in open areas (i.e., grasslands, savannas etc.).

Supernumerary chromosomes in Bandicota indica nemorivaga and a female individual with XX/XO mosaicism

Supernumerary chromosomes and an XX/XO mosaic individual of B. i. nemorivaga are described. The supernumeraries are small metacentric chromosomes and are stained all along their length in C-band preparations. They have morphology and staining characteristics similar to those observed in different populations of Rattus rattus. Extensive G-band similarity of the chromosomes of B. i. nemorivaga and R. rattus and the size, shape and staining behaviour of the supernumerary chromosomes in these genera suggest that they have acquired supernumeraries from a common ancestor.

Chromosome analysis of in vitro induced androgenetic haploids of Nicotiana tabacum.

The metaphase chromosomes of the haploid of N. tabacum under study can be divided in 3 groups, the first one being composed of two sub-groups depending on the centromeres position and the absolute length of the individual chromosomes. The third chromosome of the group of the sub-telocentric chromosomes has a satellite and can serve as a marker chromosome. The longest chromosome in the karyotype is that of the sub-group of large metacentric chromosomes while the shortest chromosome is the last one of the sub-group of small metacentric chromosomes. The highest percentage participation in the total length of the metaphase chromosomes is that of the group of metacentric chromosomes (42.75%), the lowest one being that of the group of sub-metacentric chromosomes (18.63%).

The cloning and reintroduction into animal cells of a functional CAD gene, a dominant amplifiable genetic marker

Rodent cells resistant to PALA, a specific inhibitor of the aspartate transcarbamylase activity of the multifunctional CAD protein, overproduce CAD as a result of amplification of the CAD gene. We cloned a functional CAD gene from Syrian hamster cells using a cosmid vector. Two independently isolated cosmids containing CAD genes have inserts 40 and 45 kb long. We introduced the cloned genes into CAD-deficient Chinese hamster ovary (CHO) cell mutants by fusing them with protoplasts of Escherichia coli containing the cosmids. We also introduced the cloned genes into wild-type CHO cells by selecting cells that became resistant to high concentrations of PALA following protoplast fusion. The transformants of the mutant and wild-type CHO cells contain multiple active copies of the donated Syrian hamster CAD genes. The cloned genes in three independent transformants are integrated into host-cell chromosomes at single locations identified by in situ hybridization. In two of these transformants, the genes are located in one X chromosome or in a chromosome resembling the X. In the third case, the genes are located in a small metacentric or rearranged chromosome.

Malformation syndrome associated with small extra chromosome.

We report an infant with a previously apparently unreported lethal malformation syndrome concentrated primarily on the left half of the body, but including midline defects such as meningomyelocele, cleft lip and cleft palate, and imperforate anus. The infant also had a small extra metacentric chromosome in 60% of lymphocytes. It is postulated that the small extra chromosome (whose origin remains unknown) caused the infant's condition, and that its asymmetry is compatible with an uneven distribution of the normal and aneuploid cell lines in the two halves of the body during critical phases of prenatal development.

Partial trisomy 20 confirmed by gene dosage studies

We describe a female infant with multiple congenital anomalies and mental retardation, pre- and postnatal growth failure, microcephaly, unusual facial appearance, and minor skeletal anomalies, all very suggestive of the partial trisomy 20(p) syndrome. Although she was born to karyotypically normal parents, she had an extra small metacentric chromosome. Analysis of metaphase and prometaphase chromosomes by GTG banding and Giemsa 11 staining showed that the extra chromosome was a number 20 with a deletion of the distal end of the long arm. Gene dose studies of adenosine deaminase (ADA) and inosine triphosphatase (ITP) supported the cytogenetic interpretation.