摘要:

Relative nuclear DNA content and nuclear area were determined in fast growing, karyotypically normal, fibroblastic cell cultures derived from five human females. In two cultures H3 thymidine autoradiographic and photometric determinations were combined on the same nuclei. This allowed the separation of nuclei into three groups: those with the lowest mean DNA values which did not take up H3 thymidine are in the G1 period (2d group); those with intermediate DNA values which did take up thymidine are presumably synthesizing DNA and are in the S period; those which have double the mean 2d group DNA value and did not take up thymidine are a mixture of nuclei in the G2 period with some true tetraploids 4d group). The overall frequency of sex chromatin positive nuclei in the cultures studied ranges from 64 to 78%. Sex chromatin positive nuclei occur with about the same frequency in 2d and S nuclei but are somewhat more frequent in 4d nuclei. In three cultures the relative DNA content of sex chromatin was determined. Sex chromatin of 4d nuclei contain about twice as much DNA as those of 2d nuclei; the DNA content of sex chromatin of S nuclei is between that of 2d and 4a nuclei but closer to the mean 2d value. Sex chromatin can be identified in labelled S nuclei. These observations clearly indicate that the condensed, sex chromatin forming X chromosome does not despiralize completely during DNA replication as some authors have suggested. The DNA content of sex chromatin positive and negative nuclei is identical within each nuclear group. The areas of sex chromatin positive 2d group nuclei are larger than for negative nuclei, but this difference is only significant in one of the cultures where a large number of nuclei were measured. It is concluded that failure of the X chromosome to condense in some nuclei of females is not related to DNA

ISSN:1424-8581    

DOI:10.1159/000129926

出版商:S. Karger AG    

年代:1967

数据来源: Karger

摘要:

To determine the status of heterochromatin while it was undergoing DNA synthesis, human female fibroblasts were exposed for a brief period of time (three minutes) to tritiated thymidine and immediately fixed. Autoradiography demonstrated that the sex chromatin body retains its heterochromatic form during DNA replication. This was confirmed by the observation that the percentage of sex chromatin positive cells was not significantly different for cells in the S period of the cell cycle as compared with cells in the G1 or G2 period. The nature of the labeling differentiated three types of sex chromatin bodies: those that were unlabeled; those that labeled with a grain density equivalent to euchromatin (early labeled); and those that labeled with a grain density much greater than that of the surrounding euchromatin (late labeled). Of 138 cells, the sex chromatin was unlabeled in 34%; early labeled in 45%; late labeled in 21%. These fractions were multiplied by the duration of the S phase of DNA synthesis (7.5 hours) determined on the same culture of cells. This demonstrated that the inactive X chromosome does not begin DNA replication until 2.5 hours after the onset of replication of euchromatin. It then continues with an intensity of labeling equivalent to euchromatin for 3.4 hours, and continues replication for 1.6 hours after most euchromatin has ceased replication. The total duration of replication of the inactive X chromosome was approximately five hours, compared with over six hours for euchromatin. The implications of these observations in relation to histones, chromosome coiling, DNA and RNA synthesis, number of replicons in the nucleus and sex chromatin negative cells are discussed.

ISSN:1424-8581    

DOI:10.1159/000129927

出版商:S. Karger AG    

年代:1967

数据来源: Karger

摘要:

The DNA values, in arbitrary units, have been measured in human fibroblast-like cells grown in tissue culture. Three cultures were available. Each cell nucleus was further classified according to the presence or absence of Barr bodies, or the presence of multiple chromocentres. Nuclear areas were also measured. The DNA values of all cultures fell into two main classes, which were interpreted to represent nuclei before and after DNA synthesis respectively. A smaller number of cells with intermediate DNA values were presumed to be in the process of DNA synthesis. It was found that the incidence of Barr bodies was higher in cells which had completed DNA synthesis than in those with the basic DNA value. In cells with intermediate DNA values, the incidence of Barr bodies was higher than in cells with the basic DNA values but lower than in cells which had completed DNA synthesis. These results are in agreement with those of other workers who found that the Barr body is not absent throughout DNA synthesis. In all DNA classes, nuclei with multiple chromocentres were the smallest, and cells with a single Barr body were smaller than those lacking a Barr body. The mean nuclear areas rose stepwise with each DNA class, although there was considerable intra-class variation.

ISSN:1424-8581    

DOI:10.1159/000129928

出版商:S. Karger AG    

年代:1967

数据来源: Karger

摘要:

Timing differences of the G2 periods were found among bone marrow cells labelled with 3H-thymidine in vivo, cultured kidney cells labelled in vitro and spermatogonia labelled in vivo, within the same species and also within single individuals. Differences in the timing of sex chromosome replication patterns were found among the same types of cells. The Y chromosome was extremely late-replicating in spermatogonial mitoses and also asynchronous in cultured kidney cells after four hours of contact with tritiated thymidine. Identification of differences in replication of the sex chromosomes was difficult in the bone marrow of both species; when labelled in vivo, the G2 period of these cells is on the average shorter than that of the other cell types. A morphological and autoradiographic study of mouse interphase nuclei of cultured cells did not reveal a direct relationship between appearance of multiple heteropycnotic masses in both sexes and the patterns of chromosome replication. It was found that one category of nuclei has a single sex chromatin body only in the female. The rat female nuclei have a clear, single sex chromatin.

ISSN:1424-8581    

DOI:10.1159/000129929

出版商:S. Karger AG    

年代:1967

数据来源: Karger

摘要:

The possibility that the distributive pairing mechanism which operates in Drosophila melanogaster meiosis may also operate in mammals and be a causal factor in the production of aneuploidy was tested in the mouse. This was done by determining the segregation of the single maternal X-chromosome and the T6 translocation among the offspring of XO females heterozygous for the translocation. Although the appearance of animals partially trisomic for the chromosomal material of the T6 marker chromosome substantiated existing cytological evidence that the T6 marker chromosome is frequently present as a univalent in the meiotic divisions of translocation heterozygotes, no evidence for the distributive pairing of the univalent X with the univalent marker was obtained. The results do not, therefore, support the concept that distributive pairing may occur between non-homologous chromosomes in the mouse.

ISSN:1424-8581    

DOI:10.1159/000129930

出版商:S. Karger AG    

年代:1967

数据来源: Karger

ISSN:1424-8581    

DOI:10.1159/000129931

出版商:S. Karger AG    

年代:1967

数据来源: Karger