Search

The human genome encodes the blueprint of life, but the function of the vast majority of its nearly three billion bases is unknown. The Encyclopedia of DNA Elements (ENCODE) project has systematically mapped regions of transcription, transcription factor association, chromatin structure and histone modification. These data enabled us to assign biochemical functions for 80% of the genome, in particular outside of the well-studied protein-coding regions. Many discovered candidate regulatory elements are physically associated with one another and with expressed genes, providing new insights into the mechanisms of gene regulation. The newly identified elements also show a statistical correspondence to sequence variants linked to human disease, and can thereby guide interpretation of this variation. Overall, the project provides new insights into the organization and regulation of our genes and genome, and is an expansive resource of functional annotations for biomedical research. The Consortium is funded by grants from the NHGRI as follows: production grants: U54HG004570 (B. E. Bernstein); U01HG004695 (E. Birney); U54HG004563 (G. E. Crawford); U54HG004557 (T. R. Gingeras); U54HG004555 (T. J. Hubbard); U41HG004568 /n(W. J. Kent); U54HG004576 (R. M. Myers); U54HG004558 (M. Snyder);/nU54HG004592 (J. A. Stamatoyannopoulos). Pilot grants: R01HG003143 (J. Dekker); RC2HG005591 and R01HG003700 (M. C. Giddings); R01HG004456-03 (Y. Ruan); U01HG004571 (S. A. Tenenbaum); U01HG004561 (Z. Weng); RC2HG005679 (K. P. White). This project was supported in part by American Recovery and/nReinvestment Act (ARRA) funds from the NHGRI through grants U54HG004570, U54HG004563, U41HG004568, U54HG004592, R01HG003143, RC2HG005591,R01HG003541, U01HG004561, RC2HG005679andR01HG003988(L. Pennacchio). In addition, work from NHGRI Groups was supported by the Intramural Research/nProgram of the NHGRI (L. Elnitski, ZIAHG200323; E. H. Margulies, ZIAHG200341). Research in the Pennachio laboratory was performed at Lawrence Berkeley National Laboratory and at the United States Department of Energy Joint Genome Institute, Department of Energy Contract DE-AC02-05CH11231, University of California.

Accurate control of tissue-specific gene expression plays a pivotal role in heart development, but few cardiac transcriptional enhancers have thus far been identified. Extreme noncoding-sequence conservation has successfully predicted enhancers that are active in many tissues but has failed to identify substantial numbers of heart-specific enhancers. Here, we used ChIP-Seq with the enhancer-associated protein p300 from mouse embryonic day 11.5 heart tissue to identify over 3,000 candidate heart enhancers genome wide. Compared to enhancers active in other tissues we studied at this time point, most candidate heart enhancers were less deeply conserved in vertebrate evolution. Nevertheless, transgenic mouse assays of 130 candidate regions revealed that most function reproducibly as enhancers active in the heart, irrespective of their degree of evolutionary constraint. These results provide evidence for a large population of poorly conserved heart enhancers and suggest that the evolutionary conservation of embryonic enhancers can vary depending on tissue type.

The MultiPipMaker World Wide Web server (http://www.bx.psu.edu) provides a tool for aligning multiple DNA sequences and visualizing regions of conservation among them. This unit describes its use and gives an explanation of the resulting output files and supporting tools. Features provided by the server include alignment of up to 20 very long genomic sequences, output choices of a true, nucleotide-level multiple alignment and/or stacked, pairwise percent identity plots, and support for user-specified annotations of genomic features and arbitrary regions, with clickable links to additional information. Input sequences other than the reference can be fragmented, unordered, and unoriented.

The discovery of hemoglobins in virtually all kingdoms of organisms has shown (1) that the ancestral gene for hemoglobin is ancient, and (2) that hemoglobins can serve additional functions besides transport of oxygen between tissues, ranging from intracellular oxygen transport to catalysis of redox reactions. These different functions of the hemoglobins illustrate the acquisition of new roles by a pre-existing structural gene, which requires changes not only in the coding regions but also in the regulatory elements of the genes. The evolution of different regulated functions within an ancient gene family allows an examination of the types of biosequence data that are informative for various types of issues. Alignment of amino acid sequences is informative for the phylogenetic relationships among the hemoglobins in bacteria, fungi, protists, plants and animals. Although many of these diverse hemoglobins are induced by low oxygen concentrations, to date none of the molecular mechanisms for their hypoxic induction shows common regulatory proteins; hence, a search for matches in non-coding DNA sequences would not be expected to be fruitful. Indeed, alignments of non-coding DNA sequences do not reveal significant matches even between mammalian α- and β-globin gene clusters, which diverged approximately 450 million years ago and are still expressed in a coordinated and balanced manner. They are in very different genomic contexts that show pronounced differences in regulatory mechanisms. The α-globin gene is in constitutively active chromatin and is encompassed by a CpG island, which is a dominant determinant of its regulation, whereas the β-globin gene is in A+T-rich genomic DNA. Non-coding sequence matches are not seen between avian and mammalian β-globin gene clusters, which diverged approximately 250 million years ago, despite the fact that regulation of both gene clusters requires tissue-specific activation of a chromatin domain regulated by a locus control region. The cis-regulatory sequences needed for domain opening and enhancement do show common binding sites for transcription factors. In contrast, alignments of non-coding sequences from species representing multiple eutherian mammalian orders, some of which diverged as long as 135 million years ago, are reliable predictors of novel cis-regulatory elements, both proximal and distal to the genes. Examples include a potential target for the hematopoietic transcription factor TAL1.

Hemoglobin A2 (HbA2), which contains delta-globin as its non-alpha-globin, represents a minor fraction of the Hb found in normal adults. It has been shown recently that HbA2 is as potent as HbF in inhibiting intracellular deoxy-HbS polymerization, and its expression is therefore relevant to sickle cell disease treatment strategies. To elucidate the mechanisms responsible for the low-level expression of the delta-globin gene in adult erythroid cells, we first compared promoter sequences and found that the delta-globin gene differs from the beta-globin gene in the absence of an erythroid Krüppel-like factor (EKLF) binding site, the alteration of the CCAAT box to CCAAC, and the presence of a GATA-1 binding site. Second, serial deletions of the human delta-globin promoter sequence fused to a luciferase (LUC) reporter gene were transfected into K562 cells. We identified both positive and negative regulatory regions in the 5' flanking sequence. Furthermore, a plasmid containing a single base pair (bp) mutation in the CCAAC box of the delta promoter, restoring the CCAAT box, caused a 5.6-fold and 2.4-fold (P.05) increase of LUC activity in transfected K562 cells and MEL cells, respectively, in comparison to the wild-type delta promoter. A set of substitutions that create an EKLF binding site centered at -85 bp increased the expression by 26.8-fold and 6.5-fold (P.05) in K562 and MEL cells, respectively. These results clearly demonstrate that the restoration of either an EKLF binding site or the CCAAT box can increase delta-globin gene expression, with potential future clinical benefit.

Hypersensitive site 3 (HS3) of the beta-like globin locus control region has been implicated as an important regulator of the beta-like globin genes, but the trans factors that bind HS3 have only been partially characterized. Using a five-species alignment (human, galago, rabbit, goat, and mouse) that represents 370 million years of evolution, we have identified 24 phylogenetic footprints in the HS3 core and surrounding regions. Probes corresponding to the human sequence at each footprint have been used in binding studies to identify the nuclear factors that bind within and near these conserved sequence elements. Among the high-affinity interactions observed were several binding sites for proteins with repressor activity, including YY1, CCAAT displacement protein, and G1/G2 complexes (uncharacterized putative repressors) and several binding sites for the stage selector protein. To complement this analysis, orthologous galago sequences were also used to derive probes and the pattern of proteins binding to human and galago probes was compared. Binding interactions differing between these two species could be responsible for the different expression patterns shown by the two gamma genes (galago gamma is embryonic; human gamma is fetal). Alternatively, binding interactions that are conserved in the two species may be important in the regulation of common expression patterns (eg, repression of gamma in adult life).

With the tremendous expansion of molecular sequence data in recent years, multiple alignment is arguably one of the two most important analytic techniques (the other being fast database searching). A number of useful approaches to this problem have previously been developed, but often they are limited to only a subset of multiple-alignment applications and cannot easily deal with the complex structural organization seen in an increasing number of sequences. For example, a single sequence may contain several domains of different evolutionary origins, and the multiplicities and relative ordering of these domains may be quite different among related sequences. Here we describe an integrated set of interactive Unix tools that combines several multiple-alignment techniques with traditional "dot-plot" visualization to provide a flexible environment for approaching complex sequence analysis problems. We apply these tools to the identification and characterization of "catalytic" domains in ras and rho/rac GTPase-activating proteins, to "Src homology" (SH2, SH3) domains in cytoplasmic signaling proteins, to repetitive sequence motifs in the alpha and beta subunits of protein prenyltransferases, and to regulatory DNA sequences in the locus control region of the beta-globin gene cluster.

GATA-1 controls hematopoietic development by activating and repressing gene transcription, yet the in vivo mechanisms that specify these opposite activities are unknown. By examining the composition of GATA-1 associated protein complexes in a conditional erythroid rescue system, we detected the SCL/TAL1, LMO2, Ldb1, E2A complex in vivo at all positively acting GATA-1-bound elements examined. ChIP-on-chip tiling arrays for SCL and Ldb1 revealed that chromatin occupancy of SCL and Ldb1 are extremely tightly correlated. Importantly, they showed a strong tendency for co-occupancy with GATA-1. In deed, all regions occupied by GATA-1 that showed enhancer activity were occupied by SCL and Ldb1, independent of the proximity of E-box sequences. Similarly, the SCL complex is present at all activating GATA elements in megakaryocytes and mast cells. In striking contrast, at sites where GATA-1 functions as a repressor, the SCL complex is depleted. A DNA-binding defective form of SCL maintains association with a subset of active GATA elements indicating that GATA-1 is a key determinant for SCL recruitment. Knockdown of LMO2 selectively impairs activation but not repression by GATA-1. ETO-2, an SCL-associated protein with the potential for transcription repression is also absent from GATA-1-repressed genes but, unlike SCL, fails to accumulate at GATA-1 activated genes. Together, these studies identify the SCL complex as a critical and consistent determinant of positive GATA-1 activity in multiple GATA-1-regulated hematopoietic cell lineages.

In order to understand the coordinate regulation between the alpha-like and beta-like globins during the developmental switches in hemoglobin synthesis, we have studied the rabbit alpha-like globin gene family. A cluster of six linked genes arranged 5'-zeta 1-alpha 1-theta 1-zeta 2-zeta 3-theta 2-3' has been isolated as a set of overlapping clones from a library of rabbit genomic DNA. Blot-hybridization analysis of genomic DNA not only confirms this linkage arrangement but also reveals the presence of additional zeta and theta genes. We propose that this gene cluster was generated by a block duplication of a set of alpha-like genes; the proposed duplication unit is zeta-zeta-alpha-theta. Further duplications of a zeta-zeta-theta set are also proposed to have occurred. As expected for a duplicated locus, the rabbit alpha-like gene cluster contains long blocks of internal homology. The Z homology block is about 7.2 kilobase pairs long and contains the zeta genes; the T homology block is about 4.7 kilobase pairs long and contains a theta gene. Surprisingly, both Z and T homology blocks are flanked by a common junction sequence (J) which contains a region very similar to the 3'-untranslated sequence of an alpha-globin gene. Analysis of the J sequences suggests a recombination mechanism by which the alpha gene could have been deleted from the second set of genes in the cluster (zeta 2-zeta 3-theta 2). The relationships among the genes in characterized alpha-like gene clusters in mammals are summarized. The rabbit gene cluster differs from those of other mammals principally in the loss of a gene orthologous to the human psi alpha 1 and in the block duplication of the zeta-zeta-alpha-theta gene set.

The general pattern of sequence matches between the beta-like globin gene clusters of rabbits and humans are summarized in Fig. 7. The regions of matching sequences are shaded, and it can be seen that the matches extend from one end of the gene cluster to the other. This provides very strong evidence that the ancestral species had a gene cluster containing the parents to all the contemporary beta-like globin genes in the same arrangement that we observe today. Much of the intergenic DNA has been diverging at a rate consistent with neutral drift, but smaller regions can be detected that are diverging more slowly and which are good candidates for functional sequences. The comparisons between this same gene cluster in mouse and humans show many fewer matches in the intergenic regions (Shehee et al., 1989), indicating either an earlier split between rodents and primates or a faster rate of divergence in rodents. However, this more divergent sequence may prove particularly valuable in a search for functional sequences, especially in a three-way alignment between the sequenced gene clusters. Every repetitive element in homologous segments of the rabbit and human beta-like globin gene clusters interrupts the homology; no repeat is in the same position in both species. Hence all the repeats have been inserted into the gene clusters after the divergence between lagomorphs and primates. This is true even for the L1 repeats, which are very similar between species in their ORF regions. This pattern of interspersion of repeats in long orthologous regions shows that many members of the LINE and SINE families are recent additions to the genome, and that these repeats are in fact transposable elements. It is easy to imagine negative and neutral effects of the expansion and transpositions of these repeat families, but some positive effect has not been ruled out. One of the intriguing inferences from the observations about repeats is that the ancestral gene cluster may not have contained repetitive elements. If it did, then those repeats have been completely replaced by different repeats independently in lagomorphs and primates.

The most upstream hypersensitive site (HS) of the beta-globin locus control region (LCR) in humans (5' HS 5) and chickens (5' HS 4) can act as an insulating element in some gain of function assays and may demarcate a beta-globin domain. We have mapped the most upstream HSs of the mouse beta-globin LCR and sequenced this region. We find that mice have a region homologous to human 5' HS 5 that is associated with a minor HS. In addition we map a unique HS upstream of 5' HS 5 and refer to this novel site as mouse 5' HS 6. We have also generated mice containing a targeted deletion of the region containing 5' HS 5 and 6. We find that after excision of the selectable marker in vivo, deletion of 5' HS 5 and 6 has a minimal effect on transcription and does not prevent formation of the remaining LCR HSs. Taken together these findings suggest that the most upstream HSs of the mouse beta-globin LCR are not necessary for maintaining the beta-globin locus in an active configuration or to protect it from a surrounding repressive chromatin environment.