Complete Sets Of Chromosomes Research Articles

Two distinct types of mitochondrial DNA segregation in mouse-rat hybrid cells: Stochastic segregation and chromosome-dependent segregation

Two distinct patterns of mitochondrial DNA (mtDNA) segregation were found in different mouse-rat hybrid cell lines. On mouse-rat hybrid cell line, H2, retained complete sets of chromosomes and mtDNAs of both mouse and rat. Even after cultivation for about one year after cloning, the H2 cell population still retained both parental mtDNAs. However, when mtDNAs of H2 subclones were examined, it was found that some individual cells in the H2 cell population contained only mouse or only rat mtDNA, although they still retained complete sets of both kinds of parental chromosomes. This type of mtDNA segregation, named stochastic segregation, is bidirectional and may be caused by the repetition of random sharing of mouse and rat mtDNAs with daughter cells. This segregation occurred spontaneously during long-term cultivation. The second type of mtDNA segregation, named chromosome-dependent segregation, was found in the other mouse-rat hybrid cell lines that segregated either mouse or rat chromosomes. In these hybird cells, chromosomes and mtDNA of the same species co-segregated. This second type of segregation is unidirectional. The types of mtDNA segregation appear to depend on the stability of the parental chromosomes in the hybrid cells. When both mouse and rat chromosomes retain stably, mtDNA shows stochastic segregation. On the contrary, when either species of chromosomes is segregated from the cells, mtDNA shows chromosome-dependent segregation.

Coexistence of expressed and non-expressed α-fetoprotein genes in somatic cell hybrids

Hybrids have been generated between mouse hepatoma cells, which actively synthesize α-fetoprotein (AFP), and adult hepatocytes, where AFP production is shut off. These hybrids maintain an active synthesis of mouse AFP. Using a specific radioimmunoassay, we found that rat AFP production is not activated. Southern blot analysis showed that mouse and rat AFP DNA sequences can be distinguished and that hybrid clones possessing something close to the complete chromosome sets of both parents have retained both parental AFP DNA sequences. Thus expressed and non-expressed AFP genes coexist in these hybrid cells as if their expression were dependent on a cis-acting event.

Characterization of mitochondrial DNA in chloramphenicol-resistant interspecific hybrids and a cybrid.

We have examined the restriction endonuclease cleavage patterns exhibited by the mitochondrial DNAs (mtDNA) of four chloramphenicol-resistant (CAPR) human x mouse hybrids and one CAPR cybrid derived from CAPR HeLa cells and CAPS mouse RAG cells. Restriction fragments of mtDNAs were separated by electrophoresis and transferred by the Southern technique to diazobenzyloxymethyl paper. The covalently bound DNA fragments were hybridized initially with 32P-labeled complementary RNA (cRNA) prepared from human mtDNA and, after removal of the human probe, hybridized with mouse [32P]cRNA prepared from mouse mtDNA. Three hybrids which preferentially segregated human chromosomes and the cybrid exhibited mtDNA fragments indistinguishable from mouse cells. One hybrid, ROH8A, which exhibited "reverse" chromosome segregation, contained only human mtDNA. The pattern of chromosome and mtDNA segregation observed in these hybrids and the cybrid support the hypothesis that a complete set of human chromosomes must be retained if a human-mouse hybrid is to retain human mitochondrial DNA.

Suppression of the transformed phenotype of hepatoma cells after hybridization with normal diploid fibroblasts

Hybrids were generated between mouse hepatoma cells which exhibit a transformed phenotype, and rat normal diploid fibroblasts. Most isolated hybrid clones contain a single set of chromosomes from each parent. Such clones grow to low saturation densities and are unable to grow or to form colonies in soft agar. The transformed phenotype of the parental hepatoma cells is thus suppressed in these hybrids. Suppression is very stable; however, subclones which have regained a transformed phenotype could be selected; these subclones show a significant reduction of their chromosome number. Amongst the hybrid clones isolated after fusion, a few are characterized by an excess of mouse chromosomes and a reduced number of rat chromosomes. Such clones exhibit a transformed phenotype. Our results show that, provided the hybrids contain an almost complete single set of chromosomes of each parent, spontaneous transformation behaves as a recessive trait in hybrids formed with normal diploid cells.

Association of human chromosome 14 with a ts defect in G 1, of Chinese hamster K12 cells

Somatic cell hybrids between human lymphoblastoid cells (Raji) and temperature-sensitive Chinese hamster cells (K12) were selected from monolayer cultures in MEM at 40 °C. A total of 21 hybrid clones were isolated and karyotyped. All clones contained a near complete set of Chinese hamster chromosomes and 1 to 5 human chromosomes. Human chromosome 14 was present in the hybrid cells of all clones; and was the only human chromosome retained in 10 clones. The presence of human chromosome 14 in hybrids was further confirmed by the demonstration of human nucleoside phosphorylase activity in the hybrid cells. Only one hybrid clone was positive for EBNA, the Epstein-Barr virus antigen present in Raji cells. These findings indicate that human chromosome 14 contains the necessary information for the K12 cells to overcome their G 1 defect in the cell cycle and grow at non-permissive temperature. The present study lends strong support to the possibility that different steps in the G 1 phase of the cell cycle are controlled by genes located on different chromosomes.

Spontaneous expression of murine endogenous viruses in hamster X mouse hybrid cells

AbstractThe spontaneous expression patterns of murine leukemia virus (MuLV) from mouse spleen cultures and hamster × mouse spleen hybrid cells were compared. The hybrid cells preferentially segregated mouse while retaining a complete set of hamster chromosomes. Virus expression patterns showed considerable mouse strain differences in both parental and hybrid cells. None of 13 BALB/c spleen cultures expressed virus while 6 of 20 hybrid clones expressed N‐tropic or N‐tropic and X‐tropic viruses. All AKR spleen cultures and 5 of 7 hybrids expressed N‐tropic but not X‐tropic virus. X‐tropic virus expression was detected in all 6 NZB spleen cultures and in 5 of 8 hybrids. Virus expression did not occur in NIH Swiss or NIH Swiss/Nude (nu/nu) spleen or hybrid cultures. A major structural locus (Akv‐1) for N‐tropic virus expression has been assigned to chromosome 7 in AKR mice by recombi‐national genetics and is closely linked to the gene for glucose phosphate isomerase (Gpi‐1). Analysis of AKR hybrids confirmed the requirement of chromosome 7 for initial expression of mouse N‐tropic virus and, in addition, excluded the role of all other mouse chromosomes in this phenomenon. Eighteen of 20 BALB/c clones retained chromosome 7, including 6 virus‐positive clones, suggesting that chromosome 7 may be necessary but is not sufficient for N‐tropic virus expression in this strain. Hybrid clones with examples of asynteny were found for all other chromosomes. Long‐term passage and sub‐cloning studies of AKR and BALB/c virus‐positive hybrids indicated that virus‐positive clones segregated independently of chromosome 7 markers. Spontaneous expression of X‐tropic virus in NZB hybrid clones was syntenic with the gene for‐enylate kinase (Ak‐1) which is assigned to chromosome 2. A relatively small number of NZB hybrid clones were studied and, a firm gene assignment cannot be made, because only one discordant clone each was found for chromosomes 1, 3, 10, 19. Our studies indicate that spontaneous expression of MuLV strains does not require the following MuLV‐related genes: Fv‐1 (chromosome 4), Fv‐2 (chromosome 9), Rec‐1 (replication of ecotropic virus, chromosome 5), Gv‐1 and H‐2 (chromosome 17).

Delayed malignancy and altered growth properties of somatic cell hybrids between rat hepatoma and mouse L‐cells

Somatic cell hybrids of mouse L-cells with rat HTC cells were studied for their growth properties in vitro and tumorigenicity in vivo. Three hybrid clones were selected for detailed study. All were delayed in tumor formation in nude mice compared with the parent lines despite their varied growth properties in vitro. One clone was sensitive to density dependent inhibition of growth (DDIG) and had a relatively low saturation density. A second clone was not sensitive to DDIG and had a higher saturation density. The third clone had atypical morphology, was insensitive to DDIG, and had a relatively high saturation density. All of the clones studied produced colonies suspended in agarose gel which were much smaller than those of the parents incubated for the same period of time. Only the pattern of growth in agarose gel corresponded to the delayed tumor formation in vivo of the hybrids. Sensitivity to DDIG and saturation density were not consistent with tumor growth. The hybrid clone that was sensitive to DDIG was the only one of the three that had a nearly complete set of chromosomes derived from each of the parents. The chromosome numbers of all three clones were unchanged after growth in agarose or as tumors in the nude mice.

Genetics of somatic mammalian cells: genetic, immunologic, and biochemical analysis with Chinese hamster cell hybrids containing selected human chromosomes.

Through hybridization of specific Chinese hamster cell auxotrophs with human cells and selection in media lacking the nutritional supplements required by the former cells, a series of stable hybrid clones can be prepared. These hybrids have genomes consisting of a common part--the complete or almost complete set of Chinese hamster chromosomes, plus a variable part--one or a few human chromosomes. The identity of the human chromosomes can be varied by utilizing different Chinese hamster auxotrophs and the appropriate selective media. The human chromosomes present can be determined by a combination of cytogenetic analysis with chromosome banding and testing for specific human marker genes. Hybrids containing single human chromosomes 11 and 12 and the combination of both 11 and 12 are described. The system appears to lend itself to various studies such as identification of human cell surface antigens, determination of their chromosomal loci, measurement of their distribution among cells of normal human tissues, study of interrelations among syntenic and asyntenic genes, and mutational analysis of the human genome.

Extinction of liver-specific functions in hybrids between differentiated and dedifferentiated rat hepatoma cells.

A cross has been performed between dedifferentiated rat hepatoma cells and the differentiated cells from which they were derived. 10 hybrid clones, containing the complete chromosome sets of both parents, show extinction of 4 liver-specific enzymes: tyrosine aminotransferase (E.C. 2.6.1.5), alanine aminotransferase (E.C. 2.6.1.2), and the liver-specific isozymes of alcohol dehydrogenase (E.C. 1.1.1.1) and aldolase (E.C. 4.1.2.13). Moreover, the 4 hybrid clones examined do not produce albumin . The only function of the differentiated parent which is not extinguished in the hybrid cells is inducibility of the aminotransferases. For 3 of the hybrid clones, extinction of 3 of the 4 enzymes is incomplete, but these clones do not differ in modal chromosome number from those which show more complete extinction of the enzymes. Subcloning of several of the hybrids revealed that the phenotype of the hybrids is very stable; 4 subclones showing reexpression of intermediate levels of the enzymes are characterized. These results show that dedifferentiation of the parental cells is not due to the simple loss of some factor required for the maintenance of expression of differentiated functions, and suggest that dedifferentiation is due to the activation of some control mechanism, whose final effect is negative, and which may be a part of the epigenotype of the embryonic hepatocyte.

The analysis of malignancy by cell fusion. VI. Hybrids between different tumour cells.

ABSTRACT Previous studies with a variety of transplantable mouse tumours showed that in hybrids between malignant and non-malignant cells, malignancy behaved as a recessive character: the hybrid cells, so long as they retained something close to the complete parental chromosome sets, had little or no ability to grow progressively in vivo. In the experiments we now describe the heritable lesions determining the malignant phenotype were further explored by comple mentation analysis in which the various tumour cells were fused with each other. Forty-two clonal populations derived from twelve crosses between different kinds of tumour cells were examined. Only one cross generated hybrid cells with reduced tumorigenicity: in all other cases the hybrid cells formed were highly malignant. It thus appears that, in a wide range of different tumours, the lesions determining the malignant phenotype, although recessive, fail to complement each other.

Cytogenetics of Stem‐Rust Resistance in an Agrotricum Line1

Low transmission of resistance to stem rust and to adult‐plant leaf rust in crosses between the Agrotricum line NE66536 and Triticum aestivum L. em. Thell. prompted this cytogenetic study. Monosomic analysis showed that stem‐rust resistance was carried on an Agropyron chromosome which had substituted for chromosome 6D of wheat but could also substitute for 6A. Pollen with the Agropyron chromosome instead of 6D was slightly less competitive than pollen with a complete set of wheat chromosomes. Transmission of stem‐rust resistance in crosses to ‘Chinese Spring’ was a good fit to expected segregation ratios for plants having two independent univalents in place of a bivalent. Transmission of resistance in crosses to ‘Omaha’ was considerably lower than expected. It is proposed that differential alien chromosome instability in different genetic backgrounds leads to variability in the rate of univalent misdivision and somatic loss, resulting in variable transmission rates.

The analysis of malignancy by cell fusion: IV. hybrids between tumour cells and a malignant l cell derivative

ABSTRACT Previous experiments showed that when a range of different highly malignant mouse tumour cells were fused with L cell derivatives of low tumorigenicity, the resulting hybrid cells, so long as they retained something close to the complete chromosome sets of both parent cells, had little or no ability to grow progressively in vivo. Tumours arising from the injection of such hybrids were produced not by progressive growth of the cells injected, but by selective overgrowth of cells from which certain specific, but as yet unidentified, chromosomes had been eliminated. In the present experiments the same malignant mouse tumour cells were fused with a highly malignant L cell derivative selected from the wild type cell population by passage through the animal. In all cases the resulting hybrid cells were found to be highly malignant; and the chromosome constitutions of the tumours arising from the injection of these hybrids were not significantly different from those of the cells injected. These findings confirm the interpretation given to the previous work: the L cell derivatives of low tumorigenicity contribute to the hybrid cells some factor, linked to specific chromosomes, that suppresses the malignant character of the tumour cell, and this suppression is removed, with consequent reappearance of the malignant phenotype, when certain chromosomes are eliminated.

Induced Polyploidy in Legumes

Seeds and seedlings of Glycine max variety Biloxi and C. max variety UPI have been treated with aqueous solution of colchicine. Seedling treatments have been found to yield tetraploid plants in both the varieties.In the tetraploids, deformed, thick and dark green leaves, stunted growth, delayed flowering, changes in size and frequency of stomata and pollen grains and reduced fertility have been observed and discussed with reference to previous observations. More than three leaf-lets have been observed in the tetraploids and the size of the leaf-lets has increased. C1 generation has also been studied.Meiotic studies in the tetraploid revealed different combinations of uni-, bi-, tri- and quadri-valents with tetraploid number of chromosomes. Exact doubling of chromosomes was observed in comparatively few cells. PMCs with complete set of chromosomes involving quadrivalent formation have not been observed. Occurrence of high frequency of bivalents has been discussed. Maximum number of quadrivalents has been found to be six.

The analysis of malignancy by cell fusion. II. Hybrids between Ehrlich cells and normal diploid cells.

ABSTRACT When Ehrlich ascites cells were fused with diploid fibroblasts, isolated directly from the animal, the resulting hybrid cells regularly produced progressive tumours. However, an analysis of a range of clonal populations of these hybrid cells, each derived from a separate primary fusion, revealed that the chromosomal constitution of these cells was highly unstable; all cell populations were found to have already undergone substantial chromosome losses by the time enough cells were available to permit chromosomal analysis. Thus, although these hybrid cells were highly tumorigenic, the tumours arising from them were not composed of cells with complete parental chromosome sets, but of cells from which some chromosomes had been eliminated.

Chromosome studies of the lethal hybrid Rana pipiens ♀ × Rana catesbeiana ♂

Developmental arrest of amphibian interspecific hybrids about the time of gastrulation may be causally related to chromosomal breakage and loss during cleavage. This paper presents the karyotypes of white blood cells of adult Rana pipiens and Rana catesbeiana, and evidence that hybrids between Rana pipiens ♀ × Rana catesbeiana ♂ retain complete haploid chromosome sets from both parental species shortly before arrest at the early gastrula stage. Both species have 13 pairs of homomorphic chromosomes. Individual real and relative chromosome lengths are very similar in both species, as are centromere positions in the two karyotypes. Two chromosome pairs in Rana catesbeiana (Nos. 7 and 10) contain prominent constrictions; the constrictions are present only in chromosomes of pair No. 10 in Rana pipiens. Metaphase figures from hybrid blastulae contained no ring chromosomes or acentric fragments; no anaphase bridges were seen. Most figures in which chromosomes could be counted contained 26 chromosomes, and the frequency of figures with abnormal chromosome numbers was less than that from control Rana pipiens blastulae. Relative lengths of individual chromosomes from hybrid karyotypes were the same as those from controls. Karyotypes from hybrid embryos contained three chromosomes with prominent constrictions, one falling into pair No. 7—for which there was no homolog with a constriction—and two into pair No. 10. The lengths of the longer chromosome segments of hybrid pair No. 10 were significantly different from one another; those of controls were not. The conclusion that functional inadequacy of nucleocytoplasmic interactions during cleavage can account for early developmental arrest without associated karyotypic abnormality is discussed. The relationship of chromosomal damage to blastula and gastrula arrest in other experimental systems is considered, and the Rana pipiens ♀ × Rana catesbeiana ♂ hybrid is suggested as a system amenable to further study of genetic dysfunction before gastrulation.

Idiogram and trisomy of the water vole (Arvicola terrestris L.), a favourable animal for cytogenetic research.

The chromosomes of the water vole (Arvicola terrestris L.) were investigated in 2 female and 5 male animals from three different parts of Sweden. The somatic chromosomes were studied in direct preparations of cornea and bone marrow and in tissue cultures of testis, lung and heart. Meiosis was studied in one male. The chromosome number was 2n=36. No differences in regard to chromosome number and morphology were found among the seven control animals studied. Different chromosome types are represented and the karyotype of the species is favourable for chromosome studies. — An idiogram of the water vole was constructed from measurements of complete chromosome sets from ten heart cells. — In addition to the above normal material one young water vole, trapped in nature, was found to have 37 chromosomes and was trisomic for the smallest autosome. This autosome had a secondary constriction and took part in “satellite associations”. The cytologic similarities to Down's syndrome in man are striking and it is hoped that the water vole will become a valuable laboratory mammal, especially for elucidation of the chromosomal mechanisms of non-disjunction. The trisomic water vole had no obvious phenotypic abnormalities, but at least one feature was not within normal limits — its tail was unusually short. Also, the development of certain teeth was somewhat aberrant. Whether short tail and dental deformities are symptoms correlated with trisomy for the smallest autosome in the water vole is an open question so far.

The genome separation in mitoses of rat liver

Model squashes with gelatine cubes containing 8 files like the chromosomes ofBellevalia romana (2n=8) showed the chromosomes only in groupings that correspond to the original position of metaphase chromosomes. The metaphase chromosomes in root tip cells ofBellevalia romana are arranged at random; there is neither somatic pairing nor genome segregation (= grouping of metaphase chromosomes into two complete chromosome sets). In contradiction to these results, the chromosomes in the regenerating liver cells (2n=42) show a certain precentage of grouping into complete genomes. It is concluded that in rat liver cells a mechanism exists which, starting with the genome segregation, may produce a change in chromosome number. Thus these same euploid or aneuploid chromosome numbers can be explained which are really observed in normal and treated rat liver. 4 possibilities of such mechanism are discussed.

POLYGENOMIC HYBRIDS IN GOSSYPIUM. II. MOSAIC FORMATION AND SOMATIC REDUCTION

IN THE COURSE of a study of species relations in Gossypium, two series of synthetic amphiploids have been produced, tetraploids from doubling F1 hybrids between diploid species, and hexaploids from doubling of hybrids between natural allotetraploid and diploid species. These synthetic amphiploids may be crossed among themselves, and with natural *species, both diploid and tetraploid. Hence it has so far been possible in Gossypium to obtain series of hybrids combining complete chromosome sets from two, three or four different species, and having the diploid, triploid, tetraploid, pentaploid or hexaploid multiple of the basic chromosome number 13. During a cytological and morphological investigation of these complex hybrids, a number of instances of unexpected and striking color mosaics have been noted. In some types of polygenomic hybrids involving three or four species, mosaic formation is a characteristic morphological feature, while in a number of others it occurs sporadically. In addition, one clear case of somatic reduction has been found. These two phenomena will be presented together, since recent investigations of Huskins and his coworkers (Huskins, 1948a, b; Wilson and Cheng, 1949; Huskins and Cheng, 1950) suggest that somatic segregation and somatic reduction may, in some cases, have a common cytological basis. For a detailed explanation of genome symbols -and the genome formulae of hybrids used in this paper, based on Beasley's nomenclature (1940) . the reader is referred to the first paper of this series (Brown and Menzel, 1952). Letters A, B, C, D, and E represent cytologically differentiated groups of genomes (n = 13), while subscripts identify particular species of a genome group. (AD) refers to the genomes of the natural allotetraploid species (n = 13 + 13 _26). Thus both the chromosome number and the number of species combined may be inferred from the genome formula of a given plant. MOSAIcs.-One series of complex trispecies hybrids has been obtained by intercrossing allohexaploids derived from hybrids of G. hirsutum X a diploid species. The hexaploid hybrids so far studied, comprising 18 different species combinations, all share one marked morphological peculiarity: the universal occurrence among them of color mosaics in petals and leaves. This is most striking and was first observed in six hybrids having the hexaploid 2(AD) 1C1 as one parent. In all of these, the mauve petal color carried by the C1 genome is

Salivary gland chromosomes of Drosaphila virilis

The relation between the salivary gland chromosomes and the linkage groups of Drosophila virilis was studied, and a chart involving the complete set of the salivary gland chromosomes was presented (Plate).The detail statement on this problem was published in the Cytologia (Vol. 7 No. 1-2 pp. 272-275).