Large-scale structure conservation along the entire long arm of human chromosome 21

Cloneless genomic DNA analysis: an efficient and simple methods for de novo genomic sequencing projects and gap filling

The utility of using genomic DNA directly in agarose, i.e. cloneless libraries, in place of large clone libraries, radiation hybrid panels, or chromosome dissection was demonstrated. The advantage of the cloneless library approach is that, in principle, a targeted genomic resource can be developed rapidly for any genomic region using any genomic DNA sample. Here, a human chromosome 20 Not I fragment library was generated by slicing a pulsed field gel lane containing fractionating Not I cleaved DNA from a monosomic hybrid cell line into 2 mm pieces. A reliable PCR method using agarose embedded DNA was developed. InterAlu PCR generated unique patterns of products from adjacent slices (e.g. fractions). Further, the specificity of the interAlu products was demonstrated by FISH analysis and in other hybridization experiments to arrayed interAlu products. STS content mapping was used to order the fractions and also demonstrate the unique content of the library fractions.

A high-resolution metric HAPPY map of human chromosome 14

We have mapped 1001 novel sequence-tagged sites on human chromosome 14. The mean spacing between markers is approximately 90 kb, most markers are mapped with a resolution of better than 100 kb, and physical distances are determined. The map was produced using HAPPY mapping, a simple and widely applicable in vitro approach that is analogous to linkage or to radiation hybrid mapping, but that circumvents many of the difficulties and potential artifacts associated with these methods. We show also that the map serves as a robust scaffold for building physical maps using large-insert clones.

NotI linking/jumping clones of human chromosome 3: mapping of the TFRC, RAB7 and HAUSP genes to regions rearranged in leukemia and deleted in solid tumors

By applying the 'recognition mask' strategy to 300 mammalian sequences containing NotI sites we demonstrated that 5' ends of genes are highly enriched in NotI sites. A NotI linking clone NL2-252 (D3S1678) containing transferrin receptor (TFRC) gene was used as an initial point for chromosomal jumping. One of the jumping clones, J21-045 traverses 210 kbp and links NL2-252 to NL26 (D3S1632), a NotI linking clone containing highly polymorphic sequences. The TFRC gene was mapped to 3q29, close to the telomeric marker D3S2344, by linkage analysis, a panel of hybrid cell lines, GeneBridge 4 panel and FISH. Clone NLM-007 (D3S4302) was found to contain ras-homologous gene RAB7. By FISH and a panel of hybrid cell lines this gene was mapped to 3q21. This region is of particular interest due to frequent rearrangements in different types of leukemia. Clone L2-081 (D3S4283) containing new member of ubiquitin-specific proteases (HAUSP gene) was localized in 3p21 inspiring further investigation of involvement of this gene in development of lung and renal carcinomas.

A compositional map of the cen-q21 region of human chromosome 21

A compositional map of the centromere and of the subcentromeric region of the long arm of human chromosome 21 was established by determining the GC levels (GC is the molar fraction of guanine+cytosine in DNA) of 11 YACs (yeast artificial chromosomes) covering this 13-14 Mb region which extends from the alpha-satellite sequences of the C(entromeric) band q11.1, through R(everse) band q11.2, to the proximal part of G(iemsa) band q21. The entire region is made up of GC-poor, or L, isochores with only one GC-rich H1 isochore, at least 2 Mb in size, located in band q21. The almost identical GC levels of the centromeric alpha-satellite repeats (38.5%), of R band q11.2 (39%), and of G bands (38-40%) provide a direct demonstration that base composition cannot be the only cause of the cytogenetic differences between C, G, and the majority of R bands, namely the H3- R bands (which do not contain the GC-richest H3 isochores). The results obtained also show that isochores may be as long as 6 Mb, at least in the GC-poor regions of the genome, and support previous observations suggesting that YACs from isochore borders are unstable and/or difficult to clone. Genes and CpG islands are very rare in the GC-poor region investigated, as expected from the fact that their concentration is proportional to the GC levels of the isochores in which they are contained.

Direct cDNA selection with DNA microdissected from mouse chromosome 16: isolation of novel clones and construction of a partial transcription map of the C3-C4 region

A group of cDNA segments was selected by direct hybridization of mouse cerebellar cDNAs against genomic DNA pools generated by microdissection of the mouse chromosome 16 (MMU16) C3-C4 region. After elimination of repetitive sequences and adjustment for redundancy among clones, 34 novel cDNA fragments were isolated. The MMU16 origin of clones was confirmed by genetic linkage mapping. Reverse transcription PCR indicated that approximately 68% of the cDNAs represent transcripts that are expressed in adult mouse cerebellum. Northern blotting showed that some of these are predominantly or solely expressed in brain. This work demonstrates that DNA microdissected from banded MMU16 can be used for direct cDNA selection, thus enabling construction of a new, region-specific partial transcription map. This selected cDNA library should be a useful reagent for further molecular neurobiological studies.

Random-breakage mapping method applied to human DNA sequences

The random-breakage mapping method [Game et al. (1990) Nucleic Acids Res., 18, 4453-4461] was applied to DNA sequences in human fibroblasts. The methodology involves NotI restriction endonuclease digestion of DNA from irradiated calls, followed by pulsed-field gel electrophoresis, Southern blotting and hybridization with DNA probes recognizing the single copy sequences of interest. The Southern blots show a band for the unbroken restriction fragments and a smear below this band due to radiation induced random breaks. This smear pattern contains two discontinuities in intensity at positions that correspond to the distance of the hybridization site to each end of the restriction fragment. By analyzing the positions of those discontinuities we confirmed the previously mapped position of the probe DXS1327 within a NotI fragment on the X chromosome, thus demonstrating the validity of the technique. We were also able to position the probes D21S1 and D21S15 with respect to the ends of their corresponding NotI fragments on chromosome 21. A third chromosome 21 probe, D21S11, has previously been reported to be close to D21S1, although an uncertainty about a second possible location existed. Since both probes D21S1 and D21S11 hybridized to a single NotI fragment and yielded a similar smear pattern, this uncertainty is removed by the random-breakage mapping method.

A long-range physical map of human chromosome 21q22.1 band from the YAC continuum

The human Chromosome (Chr) 21q22.1 region contains several genes for cytokines and neurotransmitters and the gene for superoxide dismutase (mutant forms of which can cause familial amyotrophic lateral sclerosis). A region of approximately 5.8 Mb encompassing D21S82 and the glycinamide ribonucleotide transformylase (GART) loci was covered by overlapping YAC clones, which were contiguously ordered by clone walking with sequence-tagged site (STSs). A total of 76 markers, including 29 YAC end-specific STSs, were unambiguously ordered in this 5.8-Mb region, and the average interval between markers was 76 kb. Restriction maps of the YAC clones with rare-cutting enzymes were simultaneously prepared, and the restriction sites were aligned to obtain a consensus restriction map of the proximal region of the 21q22.1 band. The restriction map made from 44 overlapping YACs contains 54 physically assigned STSs. By integrating the consensus map of the adjacent 1.8-Mb region, we obtained a fine physical map spanning 6.5 Mb of human Chr 21q22.1. This map contains 24 precisely positioned end-specific STSs and 12 NotI-linking markers. More than 39 potential CpG islands were identified in this region and were found to be unevenly distributed. This physical map and the YACs should be useful as a reference map and as a resource for further structural analysis of the Giemsa-negative band (R-band) of Chr 21q22.1.

1.8-megabases fine physical map encompassing IFNAR and AML1 loci on human chromosome 21q22.1

A long-range restriction map of the 1.8-megabases (mb) region encompassing the area between the interferon-alpha receptor and the acute myelogenous leukemia loci on human chromosome 21q22.1 was constructed after analysis of both the contiguous yeast artificial chromosome (YAC) clones and genomic DNA. Analysis of pulsed-field gel electrophoresis of lymphoblastoid DNA digested with three rare-cutting enzymes, Not I, Mlu I, and Nru I, revealed the positions of 17 markers on each restriction map. The 1.8-mb YAC contig that covers this region was obtained through YAC walking mediated by sequence-tagged sites (STSs), with 29 STSs including 12 newly generated YAC end-specific STSs. The consensus restriction map from 15 overlapping YACs and the positioning of the STS markers on each clone allowed 24 markers including 4 Not I-linking STSs to be ordered and mapped physically. Comparison of the maps revealed that the proximal region contains more unmethylated CpG islands than the distal region, which suggests that many expressed genes are in the proximal region. This fine consensus physical map will be informative and useful for construction of contigs of cosmid, P1, or BAC clones for further large-scale sequencing in this gene-rich region.

Repair of x-ray-induced DNA double-strand breaks in specific Not I restriction fragments in human fibroblasts: joining of correct and incorrect ends

An assay that allows measurement of absolute induction frequencies for DNA double-strand breaks (dsbs) in defined regions of the genome and that quantitates rejoining of correct DNA ends has been used to study repair of dsbs in normal human fibroblasts after x-irradiation. The approach involves hybridization of single-copy DNA probes to Not I restriction fragments separated according to size by pulsed-field gel electrophoresis. Induction of dsbs is quantitated from the decrease in the intensity of the hybridizing restriction fragment and an accumulation of a smear below the band. Rejoining of dsbs results in reconstitution of the intact restriction fragment only if correct DNA ends are joined. By comparing results from this technique with results from a conventional electrophoresis assay that detects all rejoining events, it is possible to quantitate the misrejoining frequency. Three Not I fragments on the long arm of chromosome 21 were investigated with regard to dsb induction, yielding an identical induction rate of 5.8 X 10(-3) break per megabase pair per Gy. Correct dsb rejoining was measured for two of these Not I fragments after initial doses of 80 and 160 Gy. The misrejoining frequency was about 25% for both fragments and was independent of dose. This result appears to be representative for the whole genome as shown by analysis of the entire Not I fragment distribution. The correct rejoining events primarily occurred within the first 2 h, while the misrejoining kinetics included a much slower component, with about half of the events occurring between 2 and 24 h. These misrejoining kinetics are similar to those previously reported for production of exchange aberrations in interphase chromosomes.

A set of inter-Alu PCR markers for chromosome 21 generated from pulsed-field gel-fractionated NotI restriction fragments

Genomic probes can be efficiently obtained for specific chromosomal regions by PCR amplification of gel slices containing fractionated restriction enzyme-cleaved DNA. Here, single-copy, human-specific DNA sequences were amplified using inter-Alu PCR on gel slices containing a NotI digest of DNA from hybrid cell line WAV17. Rodent cell line WAV17 contains human chromosome 21. About 75% of the 0.15- to 3-kb inter-Alu PCR products could be regionally assigned, en masse, by hybridization experiments using inter-Alu PCR probes generated from cell lines containing portions of chromosome 21. This work produced 10 new chromosome 21 markers that came from regions of 21q containing few useful markers. These markers were needed to finish a NotI restriction map for 21q (Wang and Smith (1994) Genomics 20: 441). This approach provides markers needed to close map gaps and for top-down mapping approaches.

Physical structure of human chromosome 21: an analysis of YACs spanning 21q

We have resolved the sizes of the yeast artificial chromosomes (YACs) from an ordered library spanning the entire long arm of Chromosome (Chr) 21 to examine the proximity of sequence-tagged sites (STS) originally used to position these clones. The average insert length was 540 kilobases, and some 18% of the 765 clones have either lost or generated multiple YACs during cultivation. Comparing the sizes of YACs that share common sites allowed the identification of an additional 8% of the clones with large scale additions or deletions. Maximum physical distances between chromosome markers, as established by the co-occurrence of STS on a single YAC, generally agreed with those estimated by other procedures, except for a large region in 21q21. In addition to providing insights into the structure, mapping and organization of this chromosome, knowledge of the sizes and contents of these clones will greatly facilitate the acquisition of any sequence present in this library.