Yeast Artificial Chromosome Cloning of the Xq13.3-q21.31 Region and Fine Mapping of a Deletion Associated with Choroideremia and Nonspecific Mental Retardation

Abstract

Microscopically detectable deletions and X;autosome translo cations have previously facilitated the construction of a highresolution interval map of the Xq21 region. Here, we have generated three yeast artificial chromosome contigs spanning approximately 7 megabases of the X ql3.3-q2L 31 region. In addition, a novel deletion associated with choroideremia and m ental retardation was identified and mapped in detail The proximal deletion endpoint was positioned between the loci DXS995 and DXS232, which enabled us to confirm the criti cal region for a locus involved in mental retardation. The dis tal deletion endpoint is situated in the Xq21.33 band, which allowed us to refine the order of several markers in this region.

A duplication/paracentric inversion associated with familial X-linked deafness (DFN3) suggests the presence of a regulatory element more than 400 kb upstream of the POU3F4 gene

“…If this mechanism plays a role in the Xq2i region, it is directional in nature, since a large deletion 120 kb distal to the POU3F4 gene (patient AP; Fig. 4), is associated with mental retardation and choroideremia, but not with hearing impairment (20). It remains to be investigated whether tran scriptional silencing of the respective genes is due to posi tion effects, To explain the DFN3 phenotype in patient 5086, we favour a model in which the proposed inversion separates a control element, most likely an enhancer element, from the POU3F4 transcription unit.…”

“…If the expression of this gene depends on the presence of an enhancer situated proximal to the POU3F4 gene, small mutations or chromo somal abnormalities might be found in the chromosomal region centromeric to the cosmid contig. To investigate this region in more detail, a YAC clone from this particular region was recently isolated (20) and the construction of a cosmid contig is underway. Elucidation of the molecular mechanism respons ible for the DFN3 phenotype in patients with structural abnormalities at a large distance from the POU3F4 gene will yield important new insights into the regulation of this gene.…”

A Novel Ribosomal S6-Kinase (RSK4; RPS6KA6) Is Commonly Deleted in Patients with Complex X-Linked Mental Retardation

“…Although our YAC 979a10 isolate is smaller than the original clone (780 kb instead of 1600 kb), the same markers could be PCR-amplified (data not shown). This indicates that YAC 979a10 spans the MRX critical interval including the gap in the Xq21 YAC contig constructed by Van der Maarel et al (1995).…”

“…Physical finemapping of the Xq21 deletions previously enabled us to clone the genes underlying CHM and DFN3, denoted REP-1 and POU3F4, respectively (Cremers et al, 1990b;de Kok et al, 1995;van Bokhoven et al, 1994b). The gene underlying MRX in patients with this contiguous gene syndrome has been mapped to a region between POU3F4 and REP-1 (May et al, 1995;van der Maarel et al, 1995). We have narrowed down the MRX critical region in Xq21 by fine-mapping the deletion in patients with DFN3.…”

X chromosome map at 75-kb STS resolution, revealing extremes of recombination and GC content.

“…The current 13 contigs, with their bracketing markers, index positions roughly in megabases, and relevant references to some of the significant partial published versions (in addition to Schlessinger et al 1991 andNelson et al 1995), are as follows, from Xpter to Xqter: Xpter-DXS6667 (0-52 Mb; Coffey et al 1992; Monaco et al 1992;Alitalo et al 1995;Black et al 1995;Ferrero et al 1995;Ried et al 1995;Trump et al 1996; Boycott et al 1996); OATL2-centromere (52-58.5 Mb;Miller et al 1995); centromere; DXS62-DXS1 (62-63 Mb); DXS1-DXS1225 (63-79 Mb; Villard et al 1995);DXS447-DXS26 (79-84 Mb;van der Maarel et al 1995);DXS995-TBG (84-106 Mb;Vetrie et al 1994;Forbes et al 1996, Sargent et al 1996; DXS7667-COL4A5 (107-109.5 Mb;Srivastava et al 1995); DXS1210-DXS287 (109.5-113 Mb); DXS1059-DXS8088 (113-118.5 Mb); DXS7308-DXS7872 (118.5-120 Mb); ANT2-DXS7317 (120-124 Mb); DXS8081-DXS1206 (124-131 Mb); and DXS1339-Xqter (131-160 Mb; Palmieri et al 1994;Rogner et al 1994; Pilia et al 1996; Zucchi et al 1996).…”