Non-coding transcripts far upstream of the epsilon-globin gene are distinctly expressed in human primary tissues and erythroleukemia cell lines

An intergenic non-coding RNA promoter required for histone modifications in the human β-globin chromatin domain

Transcriptome analyses show a surprisingly large proportion of the mammalian genome is transcribed; much more than can be accounted for by genes and introns alone. Most of this transcription is non-coding in nature and arises from intergenic regions, often overlapping known protein-coding genes in sense or antisense orientation. The functional relevance of this widespread transcription is unknown. Here we characterize a promoter responsible for initiation of an intergenic transcript located approximately 3.3 kb and 10.7 kb upstream of the adult-specific human β-globin genes. Mutational analyses in β-YAC transgenic mice show that alteration of intergenic promoter activity results in ablation of H3K4 di- and tri-methylation and H3 hyperacetylation extending over a 30 kb region immediately downstream of the initiation site, containing the adult δ- and β-globin genes. This results in dramatically decreased expression of the adult genes through position effect variegation in which the vast majority of definitive erythroid cells harbor inactive adult globin genes. In contrast, expression of the neighboring ε- and γ-globin genes is completely normal in embryonic erythroid cells, indicating a developmentally specific variegation of the adult domain. Our results demonstrate a role for intergenic non-coding RNA transcription in the propagation of histone modifications over chromatin domains and epigenetic control of β-like globin gene transcription during development.

A genomic analysis of RNA polymerase II modification and chromatin architecture related to 3' end RNA polyadenylation

Genomic analyses have been applied extensively to analyze the process of transcription initiation in mammalian cells, but less to transcript 3' end formation and transcription termination. We used a novel approach to prepare 3' end fragments from polyadenylated RNA, and mapped the position of the poly(A) addition site using oligonucleotide arrays tiling 1% of the human genome. This approach revealed more 3' ends than had been annotated. The distribution of these ends relative to RNA polymerase II (PolII) and di- and trimethylated lysine 4 and lysine 36 of histone H3 was compared. A substantial fraction of unannotated 3' ends of RNA are intronic and antisense to the embedding gene. Poly(A) ends of annotated messages lie on average 2 kb upstream of the end of PolII binding (termination). Near the termination sites, and in some internal sites, unphosphorylated and C-terminal domain (CTD) serine 2 phosphorylated PolII (POLR2A) accumulate, suggesting pausing of the polymerase and perhaps dephosphorylation prior to release. Lysine 36 trimethylation occurs across transcribed genes, sometimes alternating with stretches of DNA in which lysine 36 dimethylation is more prominent. Lysine 36 methylation decreases at or near the site of polyadenylation, sometimes disappearing before disappearance of phosphorylated RNA PolII or release of PolII from DNA. Our results suggest that transcription termination loss of histone 3 lysine 36 methylation and later release of RNA polymerase. The latter is often associated with polymerase pausing. Overall, our study reveals extensive sites of poly(A) addition and provides insights into the events that occur during 3' end formation.

Control of beta globin genes

The developmental changes in expression of the beta like genes from embryonic to adult stages of human life are controlled at least partially at the level of the promoter sequences of these genes and their binding factors, and competition for promoter specific interactions with the locus control region (LCR). In recent years, the control of beta globin genes has also been investigated at the level of chromatin structure involving the chemical modification of histones and their remodelling by DNA dependent ATPases (SMARCA) containing protein complexes. The role of intergenic RNA is also being investigated with renewed interest. Although a wealth of information on the structure/function relationship of the LCR and globin promoters has been gathered over more than two decades, the fundamental nature of the control of these genes at the molecular level is still not completely understood. In the following pages, we intend to briefly describe the progress made in the field and discuss future directions.

Intergenic transcription, cell-cycle and the developmentally regulated epigenetic profile of the human beta-globin locus

Several lines of evidence have established strong links between transcriptional activity and specific post-translation modifications of histones. Here we show using RNA FISH that in erythroid cells, intergenic transcription in the human β-globin locus occurs over a region of greater than 250 kb including several genes in the nearby olfactory receptor gene cluster. This entire region is transcribed during S phase of the cell cycle. However, within this region there are ∼20 kb sub-domains of high intergenic transcription that occurs outside of S phase. These sub-domains are developmentally regulated and enriched with high levels of active modifications primarily to histone H3. The sub-domains correspond to the β-globin locus control region, which is active at all developmental stages in erythroid cells, and the region flanking the developmentally regulated, active globin genes. These results correlate high levels of non-S phase intergenic transcription with domain-wide active histone modifications to histone H3.