Subchromosomal Regions Research Articles

Characterization of a set of X-linked sequences and of a panel of somatic cell hybrids useful for the regional mapping of the human X chromosome.

We have characterized 19 DNA fragments originating from the human X chromosome. Most of them have been isolated from an X chromosome genomic library (Davies et al. 1981) using a systematic screening procedure. These DNA probes have been used to search for restriction fragment length polymorphisms (RFLP). The frequency of restriction polymorphisms (1 per 350 bp analysed) was lower than expected from data obtained with autosomal fragments. The various probes have been mapped within 12 subchromosomal regions using a panel of human-rodent hybrid cell lines. The validity of the panel was established by hybridization experiments performed with 27 X-specific DNA probes, which yielded information on the relative position of translocation breakpoints on the X chromosome. The DNAs from the various hybrid lines are blotted onto a reusable support which allows one to quickly map any new X-specific DNA fragment. The probes already isolated should be of use to map unbalanced X chromosome aberrations or to characterize new somatic cell hybrid lines. The probes which detect RFLPs define new genetic markers which will help to construct a detailed linkage map of the human X chromosome, and might also serve for the diagnosis of carriers or prenatal diagnosis.

Construction of human genetic linkage maps: II. Methodological issues.

The genetic anatomy of a species consists of the description of the linear arrangement of its genes along chromosomes. Depending on the methods used in this construction, several types of maps can be distinguished. When genes are assigned to chromosomes or to chromosome subregions through somatic cell hybrids or in situ hybridization (McKusick, this volume), the map generated is strictly physical. So it is for molecular maps generated on particular genomic regions by restriction mapping of overlapping DNA sequences, and so will it be when extensive restriction maps are constructed with pulsed-field gel electrophoresis (Schwartz and Cantor 1984; Smith and Cantor, this volume).

Resistance to a malignant lymphoma in chickens is mapped to subregion of major histocompatibility (B) complex.

A genetic recombinant within the major histocompatibility (B) complex of the chicken has revealed the chromosomal subregion effecting resistance to Marek's disease--a malignant lymphoma induced by a herpesvirus. The recombinant, BF21-G19, occurred spontaneously among the progeny of a male heterozygous for resistant BF21-G21 and susceptible BF19-G19 haplotypes. Exposure to Marek's disease of families segregating for the recombinant showed that this new F-G arrangement conferred a level of resistance equivalent to that of the resistant parental haplotype. Thus, a gene, or genes, within or closely linked to the B-F region of the B complex appears to be responsible for the observed resistance to Marek's disease.

Conserved regions of homologous G-banded chromosomes between orders in mammalian evolution: carnivores and primates.

The recent derivation of a biochemical map of 33 loci of the domestic cat (Felis catus) revealed a striking conservation of chromosomal linkage associations between the cat and humans. A comparison of homologous (by linkage criteria) chromosomes by using conventionally extended and high-resolution G-banding of human and feline chromosomes is presented. Four criteria for establishing probable cytogenetic homologies of chromosomal regions were invoked: (i) map placement of homologous genes to the same chromosomes; (ii) cytological correlation of G-banding pattern; (iii) placement of homologous genes, by regional gene mapping, in the region of cytological homology; and (iv) a requirement that the putative region of homology be ancestral and evolutionarily conserved within their respective orders. Five subchromosomal regions (homologous to human chromosome 1p, 2p, 2q, 12, and X) were found to be conserved and homologous by all the stated criteria. The conserved regions constitute nearly 20% by length of the human chromosomal genome. The implications of conservation of chromosome homologies between mammalian orders whose last common ancestor became extinct more than 60 million years ago is discussed.

Assignment of the gene for cytoplasmic superoxide dismutase ( Sod-1 ) to a region of chromosome 16 and of Hprt to a region of the X chromosome in the mouse

In the search for homologous chromosome regions in man and mouse, the locus for cytoplasmic superoxide dismutase (SOD-1; superoxide:superoxide oxidoreductase, EC 1.15.1.1) is of particular interest. In man, the SOD-1 gene occupies the same subregion of chromosome 21 that causes Down syndrome when present in triplicate. Although not obviously implicated in the pathogenesis, SOD-1 is considered to be a biochemical marker for this aneuploid condition. Using a set of 29 mouse-Chinese hamster somatic cell hybrids, we assign Sod-1 to mouse chromosome 16. Isoelectric focusing permits distinction between mouse and Chinese hamster isozymes, and trypsin/Giemsa banding distinguishes mouse from Chinese hamster chromosomes. The mouse fibroblasts used were derived from a male mouse carrying Searle's T(X;16)16H reciprocal translocation in which chromosomes X and 16 have exchanged parts. Analysis of informative hybrids leads to regional assignment of Sod-1 to the distal half of mouse chromosome 16 (16B4 --> ter). Because the Chinese hamster cell line (380) used for cell hybridization is deficient in hypoxanthine phosphoribosyltransferase (HPRT; IMP: pyrophosphate phosphoribosyltransferase, EC 2.4.2.8), that part of the mouse X chromosome carrying the complementing Hprt gene can be identified by selection in hypoxanthine/aminopterin/thymidine medium and counterselection in 8-azaguanine. Mouse Hprt is on the X(T) translocation product containing the proximal region X cen --> XD.

Intrachromosomal gene mapping in man: assignment of nucleoside phosphorylase to region 14cen leads to 14q21 by interspecific hybridization of cells with a t(X;14) (p22;q21) translocation.

The structural gene for purine-nucleoside phosphorylase (NP) has been assigned to a subregion of chromosome 14 by somatic cell hybridization of male and female cells containing the balanced translocation t(X;14) (p22;q21). Peripheral lymphocytes were fused to a pseudodiploid HPRT-deficient established Chinese hamster cell line. 23 primary hybrid clones (10 derived from male and 13 from female cells) were isolated and maintained in HAT selective medium. Parallel subcultures from generations 16, 24, and 40 after clonal isolation were fully karyotyped and analyzed electrophorectically for expression of the human types of NP, HPRT, G6PD, and PGK. The human NP phenotype segregated discordantly with each human chromosome except chromosome 14 and the der(14),t(X;14) translocation chromosome. In all, 8 hybrids which had retained the der(X), t(X;14) translocation chromosome under HAT selective pressure and expressed human HPRT had lost the human NP phenotype. These results indicate localization of the NP gene in region 14pter leads to 14q21.