Marie-Christine Simmler

A sex chromosome rearrangement in a human XX male caused by Alu—Alu recombination

Human XX maleness is often due to the presence of Y-specific DNA, resulting from abnormal interchange of terminal parts of the short arms of the X and Y chromosomes. In an XX male, a rearrangement is observed at locus DXYS5, the most proximal Yp locus detected in this patient. Cloning and analysis of the rearranged DNA fragment revealed pseudoautosomal sequences located beyond the breakpoint. We propose that this XX male arose by abnormal crossing over between DXYS5 on the Y chromosome and a pseudoautosomal locus on the X chromosome during paternal meiosis. Sequence analysis of the junction shows that homologous recombination occurred between two Alu sequences from these otherwise nonhomologous regions. The site of recombination is localized to the putative transcription promoter region of the Alu sequences.

Adaptation of the interspersed repetitive sequence polymerase chain reaction to the isolation of mouse DNA probes from somatic cell hybrids on a hamster background

A strategy for the rapid isolation of DNA probes from radiation-fusion Chinese hamster cell hybrids containing overlapping portions of the murine X chromosome based on the interspersed repetitive sequence polymerase chain reaction (IRS-PCR) previously used with human somatic cell hybrids has been developed. This specific amplification of mouse DNA on a hamster background depends on the use of primers directed to the B2 short interspersed repeat element family and the R repeat, from the long interspersed repeat element family, L1. Two sets of amplification conditions, which gave specific amplification of mouse DNA from either a mouse X-monochromosomal hybrid or irradiation-fusion hybrids having reduced X content, were defined. The mouse X-only chromosome hybrid yielded approximately 20 discrete reproducible bands, while the irradiation-fusion hybrids yielded between 1 and 10 discrete products. Comparison of different irradiation-fusion hybrids has allowed the definition of both specific and shared products corresponding to different regions within the overlapping X-chromosome fragments present within these hybrids. Use of such hybrids and the IRS-PCR technique has allowed the isolation of probes corresponding to the central region of the mouse X chromosome that contains the X-inactivation center. The method should be widely applicable to the isolation of mouse DNA sequences from mouse hybrid cell lines on either human or Chinese hamster backgrounds.

Localization and expression analysis of a novel conserved brain expressed transcript, Brx/BRX, lying within the Xic/XIC candidate region

Abstract. The X inactivation center candidate region (Xic/XIC in mouse and human) is poorly characterized for the presence of transcription units. Only two conserved genes have been isolated to date, Xist/XIST and Cdx4/CDX4. The other known gene lying within this region, Tsx, has been identified so far only in rodents by analyzing the complete genomic sequence of a 94-kb region distal to Xist. Here, we report the characterization of an additional gene lying within this 94-kb sequenced region. Brx, for Brain X-linked gene, is a rare transcript preferentially expressed in the brain. It is normally X-inactivated in the mouse. Localisation of BRX, its human homolog has shown the gene to be located within the orthologous but inverted human CDX4-XIST segment. These results suggest that the gene order of the region encompassing the Cdx4–Xist interval in the mouse is similar in human. Comparison of the Xist–Brx and Brx–Cdx4 regions in mouse and human indicates that these intervals are three times longer in human than in mouse. BRX is a new potential candidate for one of the X-linked mental retardation syndromes mapped within the pericentromeric region of the human X Chromosome (Chr).

Characterization of the central region containing the X-inactivation center and terminal region of the mouse X Chromosome using irradiation and fusion gene transfer hybrids

The irradiation and fusion gene transfer (IFGT) procedure provides a means of isolating subchromosomal fragments for use in the mapping of loci and for cloning probes from a particular area of a chromosome. Using this procedure, two large panels of somatic cell hybrids that contain mouse X Chromosome (Chr) fragments have been generated. These hybrid panels were generated by irradiating the monochromosomal mouse-hamster hybrid HYBX, which retains the mouse X Chr, with either 10 K or 50 K rads of X-irradiation followed by fusion with a recipient Chinese hamster cell line. IFGT hybrids retaining mouse matcrial were generated at high frequency. These hybrids were used to orient loci in the X-inactivation center region that had not been resolvable in our interspecies backcross panel and also to map, within the terminal region of the X Chr, repeat elements detected by the probe p15-4. These hybrids not only complement existing interspecies meiotic mapping panels for the detailed analysis of specific regions of particular chromosomes, but also provide a potential source of material for chromosome-specific probe isolation.

[25]Selected methods related to the mouse as a model system

Publisher Summary The power of model systems for the study of genome structure and function and for the dissection of complex traits is, by now, well established. For a variety of reasons, the mouse remains the experimental mammal of choice for genetic research. The possibility of establishing crosses that exploit the many strains and mutations accumulated over the years constitutes just one reason for the extensive use of the mouse as a model system. This chapter presents insights into some of the strengths and originality of mouse genetics that may prove of help to nonmouse geneticists and highlights selected techniques that have contributed to the progress made in mouse genetics. The initial steps in positional cloning involve the definition of the genetic interval containing a disease gene or mutation. The size of the genetic interval depends on both the number of informative meioses and the number of polymorphic markers available for the region under study. The genus, Mus , has been divided into a complex species containing the four major biochemical groupings— Mus musculus domesticus , Mus m. musculus , Mus castaneus , and Mus bactrianus ,—all of which can be treated as subspecies, in addition to several distinct species such as the western Mediterranean mouse, M. spretus . The degree of fertility among different members of the genus ranges from complete sterility to reduced fertility and is correlated with the degree of taxon divergence.

A Deletion Map of the Human Y Chromosome Based on DNA Hybridization

The genomes of 27 individuals (19 XX males, two XX hermaphrodites, and six persons with microscopically detectable anomalies of the Y chromosome) were analyzed by hybridization for the presence or absence of 23 Y-specific DNA restriction fragments. Y-specific DNA was detected in 12 of the XX males and in all six individuals with microscopic anomalies. The results are consistent with each of these individuals carrying a single contiguous portion of the Y chromosome; that is, the results suggest a deletion map of the Y chromosome, in which each of the 23 Y-specific restriction fragments tested can be assigned to one of seven intervals. We have established the polarity of this map with respect to the long and short arms of the Y chromosome. On the short arm, there is a large cluster of sequences homologous to the X chromosome. The testis determinant(s) map to one of the intervals on the short arm.