摘要:

Expression of the fragile X site fra(X)(q27.3) was studied in thymidine-prototrophic and auxotrophic human-mouse somatic cell hybrids. In these cells, low thymidylate stress, achieved by 5-fluoro-2’-deoxyuridine (FdU) treatment and by limiting the exogenous supply of thymidine (dT), induced fragile X expression. High thymidylate stress, produced by supplying excess amounts of dT, was also effective in inducing fragile X expression, even in a hybrid clone that retained a fragile X chromosome as the only human chromosome; addition of deoxycytidine (dC) completely abolished this effect. In contrast, 5-bromo-2’-deoxyuridine (BrdU) did not induce fragile X expression. Cell-cycle analysis of BrdU-deprived thymidine-auxotrophic hybrid cells indicated that one round of DNA replication under thymidylate stress conditions is sufficient for fragile X expression. Our results suggest that the expression is an intrinsic property of the fragile site itself, which is believed to be composed of replicon clusters with pyrimidine-rich DNA sequence

ISSN:1424-8581    

DOI:10.1159/000132543

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The G-banded karyotype of the creeping vole, Microtus oregoni, prepared from animals trapped in Oregon and Washington, is presented. The two populations had similar autosomal banding patterns but exhibited striking differences in their sex chromosomes. The X chromosome of voles captured in Oregon was 39% longer than that of voles trapped in Washington. The length difference was primarily due to an increase in size of light G-bands, which, in both populations, comprised large segments of the X chromosome. On C-banding, the X chromosome exhibited major blocks of constitutive heterochromatin corresponding to the light G-bands. In contrast, the Y chromosome of the Oregon voles was 24% shorter than that of the Washington voles and lacked the short arm and some terminal bands present in the Washington voles.

ISSN:1424-8581    

DOI:10.1159/000132544

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Chromosome banding studies allowed us to distinguish the sex chromosomes of the emu (Dromaius novaehollandiae), American rhea (Rhea americana), and Darwin’s rhea (Pterocnemia pennata). In each species, we identified the Z chromosome which is very similar to a carinate Z, and the slightly smaller W chromosome. Contrary to the uniformly heterochromatic carinate counterpart, the ratite W chromosome is euchromatic and retains remarkable banding homology to the Z chromosom

ISSN:1424-8581    

DOI:10.1159/000132545

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

In situ hybridization was applied to map different proviral integration sites on murine chromosome 15. The Moloney murine leukemia virus integration site 1, Mlvi-1, was assigned to 15D2, Mlvi-2 to 15A2-B1 and the plasmacytoma variant translocation site 1, Pvt-1 to 15D2-3. The α-globin pseudogene, Hba-3ps, was mapped in close proximity to Mlvi-1 in 15D2

ISSN:1424-8581    

DOI:10.1159/000132546

出版商:S. Karger AG    

年代:1988

数据来源: Karger

ISSN:1424-8581    

DOI:10.1159/000132547

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Nucleolus organizing region (NOR) activity in seven probands with Down syndrome due to a de novo (21 ;21) trans-location and their parents was analyzed on the basis of total Ag-NOR size per cell, mean Ag-NOR size per cell (Xc), mean Ag-NOR size per acrocentic (Xa), and the characteristic Ag-NOR number of each subject. The results showed intercellular variations in total Ag-NOR size per cell in all subjects, as well as interindividual variations in mean Ag-NOR size per cell. When the subjects were grouped according to their characteristic Ag-NOR number and the mean Ag-NOR size per cell for each group (GXc) and the mean Ag-NOR size per acrocentric for each group (GXJ were calculated, a number of interesting and significant correlations were found: (1) GXc correlated perfectly with the group’s characteristic Ag-NOR number, (2) GXa varied inversely with the group’s characteristic Ag-NOR number, and (3) GXc and GXa varied inversely with each other. These results suggest that if the Ag-NOR number of a cell decreases, the total NOR activity of the cell also decreases, but the NOR activity of its chromosomes increases. This finding supports the existence of a compensatory mechanism that regulates NOR activity on the cellular le

ISSN:1424-8581    

DOI:10.1159/000132548

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Chromosomes prepared from EBV-transformed lymphoblastoid cell lines show an achromatic gap or fragile sitelike lesion at llq23.1. The low spontaneous expression of this lesion is greatly enhanced by BrdU and n-butyric acid. The lesion was expressed homozygously in all 16 cell lines examined. It is suggested that the lesion is a viral chromosome modification site.

ISSN:1424-8581    

DOI:10.1159/000132549

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

An increasing incidence of sex-chromosome variation in constitutive heterochromatin, including individuals with mosaic genotypes, has been observed in a single natural population of Nesokia indica, the Indian mole rat. Variations in the heterochromatic areas of the X chromosome are largely due to deletions at R-band-positive regions corresponding to folate-sensitive fragile sites. All individuals with either a pre- or post-zygotic loss or gain of sex-chromosome heterochromatin have so far proved to be infertile. Whether such F, sterility is due to abnormal gonadal development, gametic incompetence, or other factors is not clear. More important is the indication that the constitutive heterochromatin of this species may contain coding DNA sequences with putative regulatory functions.

ISSN:1424-8581    

DOI:10.1159/000132550

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

The human α2-plasmin inhibitor gene (PLI) was mapped by in situ hybridization using a genomic DNA probe which contained exons coding for the signal peptide and a portion of the mature protein. The results allowed the chromosome localization of the gene to 18p11.1→q11

ISSN:1424-8581    

DOI:10.1159/000132551

出版商:S. Karger AG    

年代:1988

数据来源: Karger

摘要:

Chromosomally, Leiopelma archeyi is extremely similar to L. hamiltoni, a closely related species. Both have 2n = 18 chromosomes. Contrary to a previous report, the nucleolar organizer region and secondary constriction in L. archeyi are near the telomere of the smallest, telocentric chromosome, as in L. hamiltoni. The arm-length ratios of all chromosomes are virtually identical in the two species, expect for chromosomes 2 and 3, which show evidence of a past translocation. However, L. archeyi has much less heterochromatin than does L. hamiltoni, and, unlike L. hamiltoni, heteromorphic sex chromosomes are not discernable. These frogs demonstrate two stages in the evolution of sex-chromosome differentiation related to the extent of heterochromatin accumulation.

ISSN:1424-8581    

DOI:10.1159/000132552

出版商:S. Karger AG    

年代:1988

数据来源: Karger