Late Replication Patterns Research Articles

A study of some tumours of human origin—II: Chromosome and late replication analysis of parental tumours, metastasis and ascites of the HR 18 rat tumour

The HR 18 rat tumour derived from a human melanocarcinoma was propagated in solid and permanent ascites form, and heterotransplanted in AKR mice. In the new host the HR 18 tumour preserved its original chromosome constitution and behaved as aggressively as in rat. The karyological uniformity of the HR 18 tumour may account for the invading character of the tumour, as a selected cellular variant, with high malignant potentiality. The comparative chromosome analysis of parental tumour, lung metastasis and ascites form revealed similarities between the solid tumoural forms and differences between these latter and the ascites form. The tumoural growth medium influences the chromosome structure of the neoplastic cells. Late replication pattern of ascites cells was characteristic to rat, some heterochromatic regions were altered, which may be correlated to the malignant transformation of the cells.

The somatic chromosomes of the small Indian mongoose: autoradiographic analysis of an unbalanced translocation heterozygote.

The somatic karyotype of the small Indian mongoose <i>(Herpesies auropunctatus </i>Hodgson)was investigated and found to contain 2N = 36 in the female (NF = 68) and 2N = 35 in the male (NF = 66). The female specimen studied was a mosaic (approximately 25%) for an unbalanced translocation, which was ascertained through a large submetacentric marker chromosome. Sex-chromatin determinations revealed approximately 30 % of positive cells to contain two sex-chromatin masses. Autoradiographic analysis identified the X chromosome as a medium-sized metacentric element. However, only one arm of the X was late replicating, and in 30% of the cells both X chromosomes showed late-replication patterns of only one arm. No discernable Y chromosome was evident in male cells.

Intraspecies autosomal polymorphism and chromosome replication in Akodon molinae (Rodentia-Cricetidae).

Cell spreads from bone marrow, spleen, testis and liver of four male and four female Akodon molinae (Rodentia:Cricetidae) were used for chromosome analysis and sex chromatin scoring. Chromosome replication at the beginning and end of the S period were analysed in bone marrow cells.In five animals (three males and two females) the diploid chromosome number was 42; the other three (1 male and 2 females) had a modal number of 43. In the former animals pairs 1,2,19,20 and the Y chromosome were easily identified morphologically. Chromosomes 1 were large and metacentric. In specimens with 43 chromosomes, pairs 2-20-XY were similar to those of animals with 42. Instead of having two number 1 homologues, these animals showed three unpaired chromosomes, one chromosome 1, one subterminal chromosome (1a) homologue of the long arm of the chromosome 1 and one submetacentric chromosome (1b) homologue of the short arm of the chromosome 1 Chromosomes 1a and 1b were considered to have arisen by a Robertsonian mechanism of centric fission of chromosome 1 plus a pericentric inversion.Studies of sex chromosome replication showed that the Y chromosome was the last to start and to end DNA synthesis in male complements. In females one X chromosome was the last to start replication. No late replicating X chromosome at the end of the S period was found. Coincidently, no sex chromatin could be detected in females.Analysis of late replication patterns in chromosomes 1, 1a and 1b, indicates that pericentric inversions can shift the replicating moment of the chromosomal regions involved in the rearrangement.

Late-replicating Y chromosome in spermatogonia of the Chinese hamster (<i>Cicetulus griseus</i>)

The Y chromosome of the Chinese hamster is late replicating in spermatogonial mitoses labelled <i>in vivo</i>. During the last two hours of the S phase the long arm of the Y replicates the majority of its DNA. The short arm terminates replication before this. Replication of the long arm of the X takes place earlier in S, whereas the short arm of the X is synchronous with that of the Y. Two small metacentric autosomes are also late replicating, in synchrony with the long arm of the Y. The distinct pattern of late replication of the Y chromosome of spermatogonia is in agreement with our experience with other mammals. The replication patterns of spermatogonia and a morphological study of the XY bivalent in primary spermatocytes indicate that the X and Y chromosomes pair by their short arms.

Late DNA replication pattern in human haemopoietic cells: A comparative investigation using a high resolution quantitative autoradiography

A quantitative autoradiographic technique was used to compare DNA duplication during the final phase of the synthesis period (about 30 min) in chromosomes of lymphocytes, erythroblasts and human bone marow cells. The duration of the G2 period in the three tissues was determined and a calculation was made in order to establish at which point before the beginning of this period each pair of chromosomes had completed synthesis. It was observed that the length of the single G2 period is very much the same in all three tissues. It was therefore possible to conclude that, in 19 chromosome pairs, synthesis will terminate in the last 10 min of the S period and in the other 5 pairs in the last 5 min. The synthetic activity rate of each pair of chromosomes, in the three types of haemopoietic cells, did not present significant differences either in the overall period or in the time intervals into which this period was subdivided (using time analysis based on a cumulative distribution method). Detection of late-labelling zones at the subchromosomic level, using a new technique, made it possible to obtain characteristic patterns for many chromosomes; but we were unable to detect qualitative or quantitative differences between the cells of different tissues.

Pattern of DNA replication of the sex chromosomes in three males, two with XYY and one with XXYY karotype.

INVESTIGATIONS of the pattern of DNA replication have shown that the X chromosomes in normal female cells exhibit marked asynchrony and one of them has a pronounced pattern of late replication. Other chromosomes differ also with respect to the time of DNA synthesis. In male cells it has been found that the Y chromosome replicates late compared with chromosomes of the 21–22 group1,2. This relatively late replication pattern of the Y chromosome has also been found in other mammals3–5. Investigations in patients with additional X chromosomes have shown that all X chromosomes in excess of one have pronounced late replicating patterns, similar to that of one of the X chromosomes in normal female cells6–10. As far as we know there have been only two previous references to the replication pattern of cells with two Y chromosomes. The presence of two heavily labelled presumptive Y chromosomes in an XYY male was quoted as a personal communication from Castilla, Breg and Miller, in the review by Miller11. Kikuchi and Sandberg12 studied replication patterns in two males with XYY karyotype.

Transplantation behavior and cytogenetic characteristics of a spontaneous reticulum cell sarcoma in the golden hamster.

AbstractDuring a period of 2 1/2 years, 33 spontaneous reticulum‐cell sarcomas arose in our colony of golden hamsters. One of the tumors, made transplantable in the solid and the ascitic form, is described with regard to behavior in homologous hosts and to cytogenetic characteristics. During four years of transplantation, the tumor changed its pattern of growth and, after an initial phase of localized growth, displayed a leukemialike mode of spread resulting in the death of the hosts on the 6th or 7th day irrespective of site of transplantation. Animals of the same passage reacted differently to tumor implantation: some hamsters developed large tumors without tumor cell spread, others showed very small tumors with heavy tumor cell dissemination. These different modes of growth are assumed to be dependent on host factors.Chromosome analyses were carried out on tumor cells of different transplantation generations. The chromosomes in cells of the 38th generation did not differ from normal hamster cells, except for a higher variation in the number of chromosomes. Within the next 15 passages the karyotype changed considerably, but from then on remained stable with a stemline of 44 chromosomes and six markers. The late replication pattern of sex chromosomes and of most of the autosomes seems to be the same for both normal hamster cells and tumor cells.The DNA content of the tumor cells was found to correspond to the modal chromosome number.No causal relationship between changes in growth characteristics and in karyotype could be established.

Late replication patterns of chromosomal DNA in somatic tissues of the Chinese hamster

Using a method of continuous labeling in vivo in the adult male Chinese hamster, patterns of late DNA replication were studied in tissues representative of the three germ layers: bone marrow, corneal epithelium, and regenerating hepatic parenchyma. One common pattern was observed. A study of the relative lengths of the G2 period in five somatic tissues revealed the following variations: lymph node cells, 1- 1 2 hours; jejunal crypt cells, 1- 3 4 hours; bone marrow, 2 hours; corneal epithelium, 3- 1 4 hours and regenerating hepatic perenchymal cells, 5 hours.

DNA replication patterns of the sex chromosomes of the pigeon (Columba livia domestica).

The late replication pattern of the pigeon chromosomes was studied by means of the technique of terminal uptake of tritiated thymidine and autoradiography. The W-chromosome in the female completed replication after the other macrochromosomes. The Z-chromosome in the female and both Z-chromosomes in the male terminated DNA synthesis at the same time as the remaining macrochromosomes. The microchromosomes were later replicating than the macrochromosomes. It is inferred that late replication, at least in the case of the W-chromosome, signifies genetic inactivation in somatic cells. The absence of asynchronous replication of a Z-chromosome in the homogametic sex suggests that sex determination in the pigeon might depend on a gene dosage mechanism similar to that responsible for the ‘autosexing’ phenomenon.

Chromosomes of testicular teratomas.

Eight testicular teratomas arising in proven males were examined for nuclear sex chromatin. Nuclear DNA content was measured in seven of the tumors and attempts were made to study the karyotype in seven and the chromosome late-replication pattern in five. Sex-chromatin-positive stromal, endothelial and epithelial cells possessing near-diploid or near-triploid DNA values were present in five of the eight tumors. Aneuploid DNA values of chromatin-negative regions corresponded with the aneuploid karyotype found in six tumors. The modal chromosome numbers ranged from 53 to 111 Not only was there marked karyotypic instability within each tumor but there was no overall similarity between different tumors. The terminal sequence of chromosome replication, successfully studied in two cases, one of which possessed sex-chromatin-positive cells, failed to reveal a late-replicating X-chromosome. Unfortunately, it was impossible to prove that the chromatin-positive teratoma did not contain a second X-chromosome: the failure to demonstrate an unequivocal XX sex chromosome constitution might be connected with special cultural requirements of the sex-chromatin-positive cells. However, other varieties of embryonic and undifferentiated cell tumors in males have been reported to display nuclear sex chromatin, and even certain normal testicular elements are sex-chromatin-positive. It is concluded that the existence of sex-chromatin-positive teratomas in males does not necessarily imply production from haploid gametes. The present observations do not rule out gametal origin. However, they provide more support for the idea that teratomas arise from diploid cells, possibly misplaced blastomere or primordial germ cells.

DNA REPLICATION PATTERNS OF THE SEX CHROMOSOMES IN SOMATIC CELLS OF THE SYRIAN HAMSTER.

The pattern of terminal DNA synthesis of the sex chromosomes of the Syrian hamster was studied by means of tritiated-thymidine incorporation and autoradiography. In the <i>female</i>, an entire X-chromosome and the long arm of the other X-chromosome underwent late replication. In the <i>male</i>, one of the largest submetacentric chromosomes and the long arm of the X-chromosome underwent late replication. It was presumed that this uniquely late-replicating large submetacentric chromosome was the Y-chromosome. The pattern of late replication among the autosomes was similar in both sexes and included approximately half the smallest pair of median metacentric chromosomes and the short arms of many of the larger submetacentric chromosomes. The asynchronous duplication pattern of the sex chromosomes observed in the Syrian hamster bore a striking resemblance to that previously reported in established cell lines derived from the Chinese hamster. This similarity attests to the close taxonomic relationship of these two species and is not inconsistent with the hypothesis of polyploid evolution of the Syrian hamster.