C-terminal BRE overexpression in 11q23-rearranged and t(8;16) acute myeloid leukemia is caused by intragenic transcription initiation

Overexpression of the BRE (brain and reproductive organ-expressed) gene defines a distinct pediatric and adult acute myeloid leukemia (AML) subgroup. Here we identify a promoter enriched for active chromatin marks in BRE intron 4 causing strong biallelic expression of a previously unknown C-terminal BRE transcript. This transcript starts with BRE intron 4 sequences spliced to exon 5 and downstream sequences, and if translated might code for an N terminally truncated BRE protein. Remarkably, the new BRE transcript was highly expressed in over 50% of 11q23/KMT2A (lysine methyl transferase 2A)-rearranged and t(8;16)/KAT6A-CREBBP cases, while it was virtually absent from other AML subsets and normal tissues. In gene reporter assays, the leukemia-specific fusion protein KMT2A-MLLT3 transactivated the intragenic BRE promoter. Further epigenome analyses revealed 97 additional intragenic promoter marks frequently bound by KMT2A in AML with C-terminal BRE expression. The corresponding genes may be part of a context-dependent KMT2A-MLLT3-driven oncogenic program, because they were higher expressed in this AML subtype compared with other groups. C-terminal BRE might be an important contributor to this program because in a case with relapsed AML, we observed an ins(11;2) fusing CHORDC1 to BRE at the region where intragenic transcription starts in KMT2A-rearranged and KAT6A-CREBBP AML.

Analysis of the DNA-binding profile and function of TALE homeoproteins reveals their specialization and specific interactions with Hox genes/proteins

The interactions of Meis, Prep, and Pbx1 TALE homeoproteins with Hox proteins are essential for development and disease. Although Meis and Prep behave similarly in vitro, their in vivo activities remain largely unexplored. We show that Prep and Meis interact with largely independent sets of genomic sites and select different DNA-binding sequences, Prep associating mostly with promoters and housekeeping genes and Meis with promoter-remote regions and developmental genes. Hox target sequences associate strongly with Meis but not with Prep binding sites, while Pbx1 cooperates with both Prep and Meis. Accordingly, Meis1 shows strong genetic interaction with Pbx1 but not with Prep1. Meis1 and Prep1 nonetheless coregulate a subset of genes, predominantly through opposing effects. Notably, the TALE homeoprotein binding profile subdivides Hox clusters into two domains differentially regulated by Meis1 and Prep1. During evolution, Meis and Prep thus specialized their interactions but maintained significant regulatory coordination.

Taking a functional genomics approach in molecular medicine

The elucidation of genetic components of human diseases at the molecular level provides crucial information for developing future causal therapeutic intervention. High-throughput genome sequencing and systematic experimental approaches are fuelling strategic programs designed to investigate gene function at the biochemical, cellular and organism levels. Bioinformatics is one important tool in functional genomics, although showing clear limitations in predicting ab initio gene structures, gene function and protein folds from raw sequence data. Systematic large-scale data-set generation, using the same type of experiments that are used to decipher the function of single genes, are being applied on entire genomes. Comparative genomics, establishment of gene catalogues, and investigation of cellular and tissue molecular profiles are providing essential tools for understanding gene function in complex biological networks.

Molecular cloning and characterization of the Fugu rubripes MEST/COPG2 imprinting cluster and chromosomal localization in Fugu and Tetraodon nigroviridis

We isolated Fugu genomic clones using the human MEST (Mesoderm-Specific Transcript) cDNA as probe. Sequence analysis revealed the presence of MEST and three additional genes which show homology to plant DNBP (DNA-Binding Protein), vertebrate COPG2 (Coat Protein Gamma 2), as well as to human and mouse UCN (Urocortin). Structures of Fugu and human MEST, COPG2 and UCN genes are very similar. Since MEST and COPG2 are neighboring genes on human chromosome 7q32, we can conclude that we identified their orthologs and that linkage of these genes is evolutionarily conserved in vertebrates. Unlike human MEST which underlies isoform-specific imprinting and is methylated in a parent-of-origin-specific fashion, the CpG island of the Fugu ortholog is completely methylated. The translation start of Fugu MEST is identical to the non-imprinted human isoform which is in good agreement with the assumption that genomic imprinting is restricted to mammals. Comparative mapping of these genes by fluorescence in-situ hybridization to metaphase chromosomes of Fugu rubripes and Tetraodon nigroviridis showed clear signals on one of the smallest acrocentric chromosomal pairs, which in Fugu, can be easily classified by its unique triangular shape.

Disruption of the Rev3l-encoded catalytic subunit of polymerase zeta in mice results in early embryonic lethality

Polymerase zeta (Pol zeta) is an error-prone DNA polymerase [1], which in yeast is involved in trans-lesion synthesis (TLS) and is responsible for most of the ultraviolet (UV) radiation-induced and spontaneous mutagenesis [2-4]. Pol zeta consists of three subunits: REV1, a deoxycytidyl-transferase [5]; REV7, of unclear function [6]; and REV3, the catalytic subunit. REV3 alone is sufficient to carry out TLS, but association with REV1 and REV7 enhances its activity [5, 7]. Experiments using human cells treated with UV radiation indicate also that mammalian Pol zeta is involved in TLS [7]. The peculiar mutagenic activity of Pol zeta [4,7,8] suggests a possible role in somatic hypermutation of immunoglobulin (Ig) genes [9]. Here, we report that, unlike in yeast where the REV3 gene is not essential for life [4], disruption of the mouse homologue (Rev3l) resulted in early embryonic lethality. In Rev3l(-/-) embryos, no haematopoietic cells other than erythrocytes could be identified in the yolk sac. Rev3l(-/-) haematopoietic precursors were unable to expand in vitro and no haematopoietic cells could be derived from the intraembryonic haematogenic compartment (splanchnopleura). Fibroblasts could not be derived from the Rev3l(-/-) embryos, and Rev3l(-/-) embryonic stem (ES) cells could not be obtained. This is the first evidence that an enzyme involved in TLS is critical for mammalian development.

Genomic structure of a copy of the human TPTE gene which encompasses 87 kb on the short arm of chromosome 21

The testis-expressed human TPTE is a putative transmembrane tyrosine phosphatase, probably involved in signal transduction pathways of the endocrine and/or the spermatogenetic function of the testis. TPTE was mapped to the pericentromeric region of human chromosomes 21 and 13, and to chromosomes 15, 22, and Y. It is unknown which of the TPTE copies are transcribed, contain intronic sequences, and/or have open reading frames. Here, in silico analysis of the genomic sequence of human chromosome 21 allowed the determination of the genomic structure of a copy of the TPTE gene. This copy consists of 24 exons and spans approximately 87 kb. The mapping position of this copy of TPTE on the short arm of chromosome 21 was confirmed by FISH using the BAC 15L0C0 clone as a probe that contains almost the entire TPTE gene. This is the first description of the genomic sequence of a non-RNR gene on the short arm of human acrocentric chromosomes.

The DNA sequence of human chromosome 21

Chromosome 21 is the smallest human autosome. An extra copy of chromosome 21 causes Down syndrome, the most frequent genetic cause of significant mental retardation, which affects up to 1 in 700 live births. Several anonymous loci for monogenic disorders and predispositions for common complex disorders have also been mapped to this chromosome, and loss of heterozygosity has been observed in regions associated with solid tumours. Here we report the sequence and gene catalogue of the long arm of chromosome 21. We have sequenced 33,546,361 base pairs (bp) of DNA with very high accuracy, the largest contig being 25,491,867 bp. Only three small clone gaps and seven sequencing gaps remain, comprising about 100 kilobases. Thus, we achieved 99.7% coverage of 21q. We also sequenced 281,116 bp from the short arm. The structural features identified include duplications that are probably involved in chromosomal abnormalities and repeat structures in the telomeric and pericentromeric regions. Analysis of the chromosome revealed 127 known genes, 98 predicted genes and 59 pseudogenes.

Criteria for gene identification and features of genome organization: analysis of 6.5 Mb of DNA sequence from human chromosome 21

To establish criteria for and the limitations of novel gene identification, to identify novel genes of potential relevance to Down Syndrome and to investigate features of genome organization, 6. 550kb. In total, 41 novel gene models were predicted, and for a subset of these, RT-PCR experiments helped to verify and refine the models, and were used to assess expression in early development and in adult brain regions of potential relevance to Down syndrome. Results suggest generally low and/or restricted patterns of expression, and also reveal examples of complex alternative processing, especially in brain, that may have important implications for regulation of protein function. Analysis of complete gene structures of the known genes identified a number of very large introns, a number of very short intergenic distances, and at least one potentially bi-directional promoter. At least 3/4 of known genes and 1/2 of predicted genes are associated with CpG islands. For novel genes, three cases of overlapping genes are predicted. Results of these analyses illustrate some of the complexities inherent in mammalian genome organization and some of the limitations of current sequence analysis technologies. They also doubled the number of potential genes within the region.

Characterization of a highly complex region in Xq13 and mapping of three isodicentric breakpoints associated with preleukemia

The chromosomal abnormality represented by an isodicentric X chromosome [idic(X)(q13)] is associated with a subset of acute myeloid leukemia (AML) and preleukemia observed in elderly females. A previous study localized the breakpoints of two acquired isodicentric X chromosomes associated with myelodysplasia to a 450-kb region proximal to the XIST gene. Here we report the construction and extensive characterization of a reliable 1-Mb P1 artificial chromosome and bacterial artificial chromosome contig covering a highly problematic region in Xq13 that includes the previously described isodicentric breakpoint region. In addition to mapping of the brain-specific gene (NAP1L2) and the phosphoglyceryl kinase alpha subunit 1 gene (PHKA1) and generation and mapping of a large number of STSs throughout the contig, we have mapped a putative transcriptional regulatory protein (HDACL1), and 35 ESTs. Sequencing data, Southern blot analysis, and fiber-FISH analysis have permitted characterization of extensive region-specific duplications and triplications in addition to an unusually high concentration of long interspersed repeat elements, both of which could be implicated in isodicentric chromosome formation and other Xq13 chromosome aberrations. FISH analysis of metaphase chromosomes from two previously unpublished AML patients and one preleukemic patient using cosmid clones and selected subclones allowed mapping of the idic(X)(q13) breakpoints to a 100-kb interval, consistent with the involvement of an X-linked gene in the genesis of this form of preleukemia, disruption of which may represent a preliminary step in progression to AML. Assembly and physical mapping of this complex 1-Mb contig establish a foundation for ongoing sequencing and gene identification projects in the region.

Characterization of a novel gene, C21orf6, mapping to a critical region of chromosome 21q22.1 involved in the monosomy 21 phenotype and of its murine ortholog, orf5

Phenotypic and molecular analyses of patients with partial chromosome 21 monosomy enabled us to define a region, spanning 2.4 Mb between D21S190 and D21S226, associated with arthrogryposis, mental retardation, hypertonia, and several facial anomalies. The markers of the region were used to screen a total human PAC library (Ioannou, RZPD). We isolated 57 PACs, which formed primary contigs. EST clusters (UNIGENE collection) located in a 6-Mb interval, between D21S260 and D21S263, were mapped in individual bacterial clones. We mapped the WI-17843 cluster to the PAC clone J12100, which contains the two anchor markers LB10T and LA329. The open reading frame extends over 960 bp, with three putative start codons. The 1695-bp cDNA containing a polyadenylation signal should correspond to the full-length cDNA. From the genomic sequence, we deduced that the gene contained five exons and that there was a putative promoter sequence upstream from exon 1. In silico screening of DNA databases revealed similarity with a murine EST. The corresponding cDNA (1757 bp) sequence was very similar (>85%) to the human cDNA and had an open reading frame of 876 nucleotides. Somatic hybrid mapping localized the cDNA to mouse chromosome 16. EST analyses and RT-PCR indicated that the third exon in the human gene (exon 2 in the mouse) undergoes alternative splicing. Northern blot hybridization showed that the gene was ubiquitously expressed in humans and mice. The longest mouse clone was used to generate riboprobes, which were hybridized to murine embryos at stages E-9.5, E-10.5, E-12.5, E-13.5, and E-14.5-15, to study the pattern of expression during development. Ubiquitous labeling was observed, with strong signals restricted to limited areas of the telencephalon, the mesencephalon, and the interrhombomeric regions in the central nervous system, and other regions of the body such as the limb buds, branchial arches, and somites.

A contiguous 3-Mb sequence-ready map in the S3-MX region on 21q22.2 based on high- throughput nonisotopic library screenings

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.

The mouse Aire gene: comparative genomic sequencing, gene organization, and expression

Mutations in the human AIRE gene (hAIRE) result in the development of an autoimmune disease named APECED (autoimmune polyendocrinopathy candidiasis ectodermal dystrophy; OMIM 240300). Previously, we have cloned hAIRE and shown that it codes for a putative transcription-associated factor. Here we report the cloning and characterization of Aire, the murine ortholog of hAIRE. Comparative genomic sequencing revealed that the structure of the AIRE gene is highly conserved between human and mouse. The conceptual proteins share 73% homology and feature the same typical functional domains in both species. RT-PCR analysis detected three splice variant isoforms in various mouse tissues, and interestingly one isoform was conserved in human, suggesting potential biological relevance of this product. In situ hybridization on mouse and human histological sections showed that AIRE expression pattern was mainly restricted to a few cells in the thymus, calling for a tissue-specific function of the gene product.

AIRE encodes a nuclear protein co-localizing with cytoskeletal filaments: altered sub-cellular distribution of mutants lacking the PHD zinc fingers

The gene responsible for autoimmune polyendocrino-pathy candidiasis ectodermal dystrophy (APECED) recently has been positionally cloned to 21q22.3. This novel gene, AIRE, encodes for a predicted 57.7 kDa protein featuring two PHD-type zinc fingers shared by other proteins involved in chromatin-mediated tran-scriptional regulation. APECED is an autosomal recessive condition characterized by multiple polyendocrinopathies, and the typical triad of APECED symptoms includes hypoparathyroidism, primary adrenocortical failure and chronic mucocutaneous candidiasis. The aetiology of APECED is linked directly to mutations within the coding region of AIRE. These mutations are predicted to lead to truncated forms of the protein lacking at least one of the PHD zinc fingers. In this study, we have investigated the sub-cellular localization of AIRE expressed transiently in COS cells and fibroblasts. We found that AIRE has a dual nuclear and cytoplasmic localization. The wild-type protein is directed to speckled domains in the nucleus and also shows co-localization with cytoskeletal filaments. N-terminal AIRE fragments deleted for the PHD domain show altered nuclear localization, suggesting that the APECED mutations may elicit their primary effects in the nucleus.

Mapping ESTs by fiber-FISH

A visual transcript map of six genes was constructed on the chromosome 21q22.3 by high resolution fluorescence in situ hybridization (FISH). Expressed sequence tags (ESTs) from six genes-PWP2, KNP1, AIRE, C21orf3, SMT3A, and C21orf1-were successfully localized by fiber-FISH by use of sensitive tyramide-based detection. The sizes of the ESTs varied between 315 to 956 bp and most of them map within the 3'-untranslated region. The ESTs were assigned to and subsequently ordered within cosmid, PAC, and BAC clones hybridized on DNA fibers. Physical distances between ESTs and known markers were determined. Our results demonstrate the feasibility and accuracy of visual mapping EST sequences in relation to known markers. The main advantage of this approach is that it can be applied to finely map any of the database ESTs for positional cloning efforts. The sensitivity, specificity, and reproducibility of this high-resolution EST mapping technique is evaluated.

Bacterial contig map of the 21q11 region associated with Alzheimer's disease and abnormal myelopoiesis in Down syndrome

We present a high-resolution bacterial contig map of 3.4 Mb of genomic DNA in human chromosome 21q11-q21, encompassing the region of elevated disomic homozygosity in Down Syndrome-associated abnormal myelopoiesis and leukemia, as well as the markers, which has shown a strong association with Alzheimer's Disease that has never been explained. The map contains 89 overlapping PACs, BACs, or cosmids in three contigs (850, 850, and 1500 kb) with two gaps (one of 140-210 kb and the second <5 kb). To date, eight transcribed sequences derived by cDNA selection, exon trapping, and/or global EST sequencing have been positioned onto the map, and the only two genes so far mapped to this cytogenetic region, STCH and RIP140 have been precisely localized. This work converts a further 10% of chromosome 21q into a high-resolution bacterial contig map, which will be the physical basis for the long-range sequencing of this region. The map will also enable positional derivation of new transcribed sequences, as well as new polymorphic probes, that will help in elucidation of the role the genes in this region may play in abnormal myelopoiesis and leukemia associated with trisomy 21 and Alzheimer's Disease.

Cloning of a novel human putative type Ia integral membrane protein mapping to 21q22.3

The distal part of human chromosome 21q22.3 is exceptionally gene rich and contains several loci that have been linked to hereditary disorders. In the course of constructing an extensive transcript map for chromosome 21, we have isolated numerous coding segments in 21q22.3 that represent potential candidate genes in this region. Following this approach, we have cloned a novel single-copy gene (C21orf3) (HGMW-approved symbol C21orf1) expressed as a unique 2.69-kb mRNA in a wide range of tissues. We have precisely mapped C21orf3 by fiber FISH distal to marker D21S171. The C21orf3 gene encodes a predicted protein of 180 residues that does not share any sequence homology with other known proteins. C21orf3 harbors predicted structural features of a type Ia integral membrane protein and contains a tetrapeptide motif (YXRF) observed in several cell surface proteins involved in signal transduction. Although the function of C21orf3 is still unknown, this novel gene may play an important role in a cell trafficking mechanism.

Transcriptional map of the 2.5-Mb CBR-ERG region of chromosome 21 involved in Down syndrome

The region of chromosome 21 between genes CBR and ERG (CBR-ERG region), which spans 2.5 Mb on 21q22.2, has been defined by analysis of patients with partial trisomy 21. It contributes significantly to the pathogenesis of many characteristics of Down syndrome, including morphological features, hypotonia, and mental retardation. Cosmid contigs covering 80% of the region were constructed and EcoRI maps produced. These cosmids were used for exon trapping and cDNA selection from three cDNA libraries (fetal brain, fetal liver, and adult skeletal muscle). Isolated exons and cDNAs were mapped on the EcoRI map, organized into contigs, sequenced, and used as probes for Northern blot analysis of RNA from fetal and adult tissues. We identified 27 genuine or highly probable transcriptional units evenly distributed along the CBR-ERG region. Eight of the transcriptional units are known genes.

Gene defect behind APECED: a new clue to autoimmunity

The molecular background of human autoimmunity is poorly understood. Although many autoimmune diseases have a genetic basis, the actual disease appearance results from a complex interplay between genes and environment and thus these diseases represent typical multifactorial diseases. Even with molecular tools provided by the Human Genome Project, it still remains a challenge to identify the predisposing DNA variants behind such multifactorial traits. Two strategies have been suggested to provide short-cuts to the dissection of the genetic background of complex autoimmune diseases: (i) identification of genes in rare human diseases with a strong autoimmune component or (ii) unravelling loci causing phenotypes resembling autoimmune diseases in inbred mice strains. Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a monogenic autosomal disease with a recessive inheritance pattern, characterized by multiple autoimmune endocrinopathies, chronic mucocutaneous candidiasis and ectodermal dystrophies. Since it is the only known human autoimmune disease inherited in a Mendelian fashion, it provides an excellent model to analyse the genetic component of human autoimmunity. The causative gene for APECED was isolated recently by a traditional positional cloning strategy by two independent groups. The cDNA for the APECED gene proved to originate from a novel gene, AIRE , which is expressed prevalently in thymus, pancreas and adrenal cortex. Multiple mutations in AIRE have been identified in APECED patients. The predicted proline-rich AIRE polypeptide harbours two PHD-type zinc finger motifs and contains a putative nuclear targeting signal suggesting its involvement in the regulation of transcription. In the future, functional analysis of the AIRE protein both in vitro and in vivo will provide valuable insight not only into the molecular pathogenesis of APECED but also into the aetiology of autoimmunity in general.

A new inward rectifier potassium channel gene (KCNJ15) localized on chromosome 21 in the Down syndrome chromosome region 1 (DCR1)

The Down syndrome chromosome region-1 (DCR1) on subband q22.2 of chromosome 21 is thought to contain genes contributing to many features of the trisomy 21 phenotype, including dysmorphic features, hypotonia, and psychomotor delay. Isolation, mapping, and sequencing of trapped exons and captured cDNAs from cosmids of this region have revealed the presence of a gene (KCNJ15) encoding a potassium (K+) channel belonging to the family of inward rectifier K+ (Kir) channels. The amino acid sequence deduced from the 1125-bp open reading frame indicates that this gene is a member of the Kir4 subfamily; it has been named Kir4.2. It is expressed in kidney and lung during human development and in several adult tissues including kidney and brain. After Kir3.2 (GIRK2), Kir4.2 is the second K+ channel gene of this type described within the DCR1.

Primate homologues of rat TGN38: primary structure, expression and functional implications

cDNAs encoding the human and macaque homologues of rat TGN38 have been cloned and sequenced. The proteins have a highly conserved N terminus (comprising the signal peptide) and C terminus (comprising part of the lumenal domain, the membrane spanning region and cytoplasmic tail) but vary in the other part of the lumenal domain, which contains the repeat region. Whereas rat TGN38 contains 6 tandem repeats of an 8mer, both primate proteins possess 14 tandem repeats of a 14mer sequence. The human protein, like rat TGN38, is localised primarily to the TGN but is present on the cell surface and returns via endosomes. This behaviour is consistent with conservation of the membrane spanning region and the cytoplasmic tail, which contain the retention and retrieval signals, respectively, for localisation in the TGN. The unexpected differences in the lumenal domain can best be rationalised by the fact that both types of repeat domains have most of the properties of mucins. We suggest that TGN38 homologues are mucin-like molecules that regulate membrane traffic to and from the TGN.

A new member of the proprotein convertase gene family (LPC) is located at a chromosome translocation breakpoint in lymphomas

A new member of the proprotein convertase gene family (LPC) has been identified at a chromosome translocation breakpoint occurring in a high grade lymphoma. The translocation t(11;14)(q23;q32) has been molecularly cloned and shown to be the result of a fusion between an intron in the 3' -untranslated region of LPC with a sequence close to the switch region S gamma 4 of the IGH locus. The LPC gene encodes a protein of 785 amino acids with substantial homology to furin and the other members of the proprotein convertase family and represents a novel target for chromosome translocation and subsequent deregulation.

AF6 gene on chromosome band 6q27 maps distal to the minimal region of deletion in epithelial ovarian cancer

Chromosome 6 has been shown to contain at band q27 a minimal region of deletion associated with epithelial ovarian cancers and AF6, a gene disrupted in acute myeloid leukemia with t(6;11)(q27;q23). Using rapid amplification of cDNA ends by polymerase chain reaction, the breakpoint in AF6 was confirmed and a cDNA clone identified. This clone was used as a probe to screen a chromosome 6 cosmid library, and a single cosmid C-109F0645 was isolated. By fluorescence in situ hybridization, C-109F0465 was found to map distal to the critically deleted region associated with ovarian malignancies. AF6 is therefore distinct from and lies telomeric to this region.

Down syndrome-critical region contains a gene homologous to Drosophila sim expressed during rat and human central nervous system development

Many features of Down syndrome might result from the overdosage of only a few genes located in a critical region of chromosome 21. To search for these genes, cosmids mapping in this region were isolated and used for trapping exons. One of the trapped exons obtained has a sequence very similar to part of the Drosophila single-minded (sim) gene, a master regulator of the early development of the fly central nervous system midline. Mapping data indicated that this exonic sequence is only present in the Down syndrome-critical region in the human genome. Hybridization of this exonic sequence with human fetal kidney poly(A)+ RNA revealed two transcripts of 6 and 4.3 kb. In situ hybridization of a probe derived from this exon with human and rat fetuses showed that the corresponding gene is expressed during early fetal life in the central nervous system and in other tissues, including the facial, skull, palate, and vertebra primordia. The expression pattern of this gene suggests that it might be involved in the pathogenesis of some of the morphological features and brain anomalies observed in Down syndrome.

Model for a transcript map of human chromosome 21: isolation of new coding sequences from exon and enriched cDNA libraries

The construction of a transcriptional map for human chromosome 21 requires the generation of a specific catalogue of genes, together with corresponding mapping information. Towards this goal, we conducted a pilot study on a pool of random chromosome 21 cosmids representing 2 Mb of non-contiguous DNA. Exon-amplification and cDNA selection methods were used in combination to extract the coding content from these cosmids, and to derive expressed sequences libraries. These libraries and the source cosmid library were arrayed at high density for hybridisation screening. A strategy was used which related data obtained by multiple hybridisations of clones originating from one library, screened against the other libraries. In this way, it was possible to integrate the information with the physical map and to compare the gene recovery rate of each technique. cDNAs and exons were grouped into bins delineated by EcoRI cosmid fragments, and a subset of 91 cDNAs and 29 exons have been sequenced. These sequences defined 79 non-overlapping potential coding segments distributed in 24 transcriptional units, which were mapped along 21q. Northern blot analysis performed for a subset of cDNAs indicated the existence of a cognate transcript. Comparison to databases indicated three segments matching to known chromosome 21 genes: PFKL, COL6A1 and S100B and six segments matching to unmapped anonymous expressed sequence tags (ESTs). At the translated nucleotide level, strong homologies to known proteins were found with ATP-binding transporters of the ABC family and the dihydroorotase domain of pyrimidine synthetases. These data strongly suggest that bona fide partial genes have been isolated. Several of the newly isolated transcriptional units map to clinically important regions, in particular those involved in Down's syndrome, progressive myoclonus epilepsia and auto-immune polyglandular disease. The study presented here illustrates the complementarity of exon-amplification and cDNA selection techniques for generating a large resource of new expressed landmarks, which contribute to the construction of a chromosome 21 transcript map.

An integrated YAC-overlap and 'cosmid-pocket' map of the human chromosome 21

We describe here the construction of an ordered clone map of human chromosome 21, based on the identification of ordered sets of YAC clones covering > 90% of the chromosome, and their use to identify groups of cosmid clones (cosmid pockets) localised to subregions defined by the YAC clone map. This is to our knowledge the highest resolution map of one human chromosome to date, localising 530 YAC clones covering both arms of the chromosome, spanning > 36 Mbp, and localising more than 6300 cosmids to 145 intervals on both arms of the chromosome. The YAC contigs have been formed by hybridising a 6.1 equivalents chromosome 21 enriched YAC collection displayed on arrayed nylon membranes to a series of 115 DNA markers and Alu-PCR products from YACs. Forty eight mega-YACs from the previously published CEPH-Genethon map of sequence tagged sites (STS) have also been included in the contig building experiments. A YAC tiling path was then size-measured and confirmed by gel-fingerprinting. A minimal tiling path of 70 YACs were then used as probes against the 7.5 genome equivalents flow sorted chromosome 21 cosmid library in order to identify the lists of cosmids mapping to alternating shared--non-shared intervals between overlapping YACs ('cosmid pockets'). For approximately 1/5 of the minimal tiling path of YACs, locations and non-chimaerism have been confirmed by fluorescence in situ hybridisation (FISH), and approximately 1/5 of all cosmid pocket assignments have independent, confirmatory marker hybridizations in the ICRF cosmid reference library system. We also demonstrate that 'pockets' contain overlapping sets of cosmids (cosmid contigs). In addition to being an important logical intermediate step between the YAC maps published so far and a future map of completely ordered cosmids, this map provides immediately available low-complexity cosmid material for high resolution FISH mapping of chromosomal aberrations on interphase nuclei, and for rapid positional isolation of transcripts in the highly resolved regions of genetic interest.

Exon-enriched probe derived from a human chromosome 21 YAC by exon-amplification

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Partial physical map of human chromosome 21 from fibroblast and lymphocyte DNA

A partial physical map of the human chromosome 21 including 26 genes and anonymous sequences was established by pulsed-field gel electrophoresis analysis of restriction fragments obtained from lymphocyte and fibroblast DNAs. The sizes of the restriction fragments obtained by total digestion with eight different enzymes were compared in these two tissues. Differences resulting from the variations in the methylation state of the restriction sites were frequently observed. These differences and partial digestions were used to estimate the order and the distances between genes and sequences. Six linkage groups were defined: D21S13-D21S16, D21S1-D21S11, D21S65-D21S17, (D21S55,ERG)-ETS2, BCEI-D21S19-D21S42-D21S113-CBS-CRYA1, and COL6A2-S100B. For six intergenic distances the resolution of previous maps was significantly increased.

New chromosome 21 DNA markers isolated by pulsed field gel electrophoresis from an ETS2-containing Down syndrome chromosomal region

To generate new chromosome 21 markers in a region that is critical for the pathogenesis of Down syndrome (D21S55-MX1), we used pulsed field gel electrophoresis (PFGE) to isolate a 600-kb NruI DNA fragment from the WA17 hybrid cell line, which has retained chromosome 21 as the only human material. This fragment, which contains the oncogene ETS2, was used to construct a partial genomic library. Among the 14 unique sequences that were isolated, 3 were polymorphic markers and contained sequences that are conserved in mammals. Five of these markers mapped on the ETS2-containing NruI fragment and allowed us to define an 800-kb high-resolution PFGE map.

Molecular analysis of 12 patients with the t(8;21) translocation and M2 acute myelogenous leukemia

The t(8;21)(q22;q22) is a nonrandom cytogenetic abnormality associated with acute myelogenous leukemia of the M2 subtype (FAB classification). The 8q- and 21q+ derivative chromosomes have previously been isolated in somatic cell hybrids and used to map the anonymous sequences D21S65 and D21S17, which were proximal and distal, respectively, to the breakpoint on chromosome 21. DNA from a series of 12 t(8;21) patients and 7 controls was analyzed by pulsed field gel electrophoresis. Physical linkage of probes D21S65 and D21S17 on a 2100 kb NruI fragment was established by partial digestion experiments. In all the patients, the translocation generated a rearranged D21S65 NruI fragment of 650 to 750 kb, suggesting heterogeneity in the breakpoints. This heterogeneity was confirmed by using BssHII, SacII, and EagI enzymes. Our results are consistent with the presence of a 100 Kb breakpoint cluster region on chromosome 21 encompassing the AML1 gene. Interestingly, in half of the patients, demethylation of an NruI site located 7 kb proximal to the last exon of the AML1 gene occurred on the nontranslocated chromosome 21.