Analysis of sister-chromatid exchanges.

Two requirements for the cytogenetic analysis of sister-chromatid exchanges (SCEs) in somatic cells are (1) a population of actively proliferating cells that will provide an adequate number of metaphases and (2) sister chromatids that in some way are differentially labeled or stained in the metaphases. SCEs can be recognized as abrupt discontinuities in the staining patterns of the two chromatids of a metaphase chromosome at what appear to be identical sites, with reciprocal switching from one chromatid to its sister. This protocol uses phytohemagglutinin (PHA)-stimulated cultures of blood lymphocytes as a source of proliferating cells.

Physical mapping of the bloom syndrome region by the identification of YAC and P1 clones from human chromosome 15 band q26.1.

The gene for Bloom syndrome (BLM) has been mapped to human chromosome 15 band q26.1 by homozygosity mapping. Further refinement of the location of BLM has relied upon linkage-disequilibrium mapping and somatic intragenic recombination.

Somatic intragenic recombination within the mutated locus BLM can correct the high sister-chromatid exchange phenotype of Bloom syndrome cells.

Cells from persons with Bloom syndrome feature an elevated rate of sister-chromatid exchange (SCE). However, in some affected persons a minority of blood lymphocytes have a normal SCE rate. Persons who inherit the Bloom syndrome gene BLM identical by descent from a common ancestor very rarely exhibit this high-SCE/low-SCE mosaicism; conversely, mosaicism arises predominantly in persons who do not share a common ancestor.

Physical and genetic mapping of the CDR gene with particular reference to its position with respect to the FRAXA site.

This study narrows down the localization of the gene coding for the cerebellar degeneration-related protein (CDR 34) to the upper boundary of the FRAXA and reports the finding of two common RFLPs respectively identified at an RsaI site flanking the 3' end of the gene and at a Hincll site flanking its 5' end. Segregation analysis carried out in the CEPH-pedigrees for the new CDR/RsaI-RFLP versus other polymorphic loci of the region has established a tight linkage with the markers DXS105/DX98 and absence of measurable linkage with two clusters of markers respectively located proximally to the FRAXA (F9, DXS102, DXS51, and DXS369) or distally to it (DXS52, DXS304). In addition, two recombinants were found among 23 scorable sibs identified in the Sardinian pedigrees segregating for the Martin-Bell Syndrome (MBS) and the CDR/RsaI variants.

Preferential integration of the Ad5/SV40 hybrid virus at the highly recombinogenic human chromosomal site 1p36.

Human fibroblasts transformed with an adenovirus-5/simian virus 40 recombinant construct (Ad5/SV40) were analyzed to determine the chromosomal site(s) of virus integration. This was firstly done by in situ hybridization using metaphase and prometaphase chromosomes and 125I-labeled Ad5 DNA. Out of seven transformed cell lines (six of clonal origin and one uncloned), six were proven to have integrated the viral genome at the short- or the long-subtelomeric regions of autosome 1, two regions known to include chromosomal modification sites induced by acute infection with Ad12.