A Contiguous 3-Mb Sequence-Ready Map in the S3–MX Region on 21q22.2 Based on High- Throughput Nonisotopic Library Screenings

Abstract

Progress in complete genomic sequencing of human chromosome 21 relies on the construction of high-quality bacterial clone maps spanning large chromosomal regions. To achieve this goal, we have applied a strategy based on nonradioactive hybridizations to contig building. A contiguous sequence-ready map was constructed in the Down syndrome congenital heart disease (DS-CHD) region in 21q22.2, as a framework for large-scale genomic sequencing and positional candidate gene approach. Contig assembly was performed essentially by high throughput nonisotopic screenings of genomic libraries, prior to clone validation by (1) restriction digest fingerprinting, (2) STS analysis, (3) Southern hybridizations, and (4) FISH analysis. The contig contains a total of 50 STSs, of which 13 were newly isolated. A minimum tiling path (MTP) was subsequently defined that consists of 20 PACs, 2 BACs, and 5 cosmids covering 3 Mb between D21S3 and MX1. Gene distribution in the region includes 9 known genes (c21–LRP, WRB, SH3BGR, HMG14, PCP4, DSCAM, MX2, MX1, and TMPRSS2) and 14 new additional gene signatures consisting of cDNA selection products and ESTs. Forthcoming genomic sequence information will unravel the structural organization of potential candidate genes involved in specific features of Down syndrome pathogenesis.