Rapid physical mapping of YAC inserts by random integration of I-Sce I sites

We have developed a novel strategy, based on the random insertionby homeologous recombination of artificial I-Sce I sites withinmammalian repetitive DNA sequences, which should greatly facilitatethe high resolution physical mapping of large DNA fragmentscloned in YAC. A set of transgenic yeast strains containingappropriately spaced I-Sce I sites within the YAC insert definesa series of nested physical intervals against which new genes,clones or DNA fragments can be mapped by simple hybridisation.Sequential hybridisation using such a series of nested YAC fragmentsas probes can also allow the rapid sorting of phage or cosmidlibraries into contigs. This approach, which has been appliedto a YAC containing a 460 kb insert from the mouse X chromosome,may also have applications for the restriction mapping of largegenomic segments, mapping of exons and the search for homologousgenes.     

Transgenic mice carrying an Xist-containing YAC

The initiation of X-chromosome inactivation in female mammals is controlled by a key locus, the X-inactivation centre (Xic). The Xist gene, which maps to the candidate region for Xic and is expressed exclusively from the inactive X chromosome, is thought to be an essential component of the Xic. To test whether sequences spanning several hundred kilobases and including Xist from the Xic region are capable of initiating inactivation, we have created a series of transgenic mice using a 460 kb yeast artificial chromosome (YAC). Analysis in these mice of the expression of Xist, of a LacZ reporter gene and of two genes in the region that are normally silent on the inactive X chromosome, suggests that essential sequences for Xist expression and X-inactivation may be absent in these transgenic animals.      

Angelman syndrome: how many genes to remain silent?

The clinical features of Angelman syndrome (AS) include microcephaly, severe mental retardation, "puppet-like" ataxic gait with jerky arm movements, hyperactivity, bouts of inappropriate laughter, EEG abnormalities, and seizures. The frequency of occurrence of AS is in the range of 1/10,000 to 1/20,000 births. The AS locus maps to the imprinted chromosome 15q11-q13 region and the disease is caused by the absence of a normal maternal contribution to this region. The genetic complexity of AS is revealed by the existence of at least four molecular classes. A candidate AS gene, ubiquitin protein ligase 3A ( UBE3A/E6-AP ), has been identified, and mutations of this gene have been detected in several cases of AS. Moreover, UBE3A is expressed predominantly from the maternal allele in brain, strongly supporting its causative role in AS. However, there is evidence to suggest that, in addition to UBE3A , another gene(s) may be involved either directly in AS and/or indirectly by regulating UBE3A expression. Received: March 13, 1998 / Accepted: April 8, 1998     

Cloning and characterization of a murine brain specific gene Bpx and its human homologue lying within the Xic candidate region

The X inactivation centre (Xic) is a cis-acting locus thought to play a key role in the initiation of X-inactivation. We have cloned and characterized a new gene, Bpx, lying distal to the murine Xist. Bpx, which is specifically expressed in the brain, shows strong homology to genes encoding nucleosome assembly proteins and is normally X- inactivated in mice. Isolation and localization of BPX, its human homologue, has shown the gene to be located centromeric to XIST in man. The Xq13 region, whose orientation is apparently globally conserved between man and mouse, must therefore contain an inversion of at least 600 kb spanning the XIST sequence and including the CDX4 and BPX genes.