The Effect of Distance on Long-Range Chromatin Interactions

Abstract

We have used gene competition to distinguish between possible mechanisms of transcriptional activation of the genes of the human beta-globin locus. The insertion of a second beta-globin gene at different points in the locus shows that the more proximal beta gene competes more effectively for activation by the locus control region (LCR). Reducing the relative distance between the genes and the LCR reduces the competitive advantage of the proximal gene, a result that supports activation by direct interaction between the LCR and the genes. Visualization of the primary transcripts shows that the level of transcription is proportional to the frequency of transcriptional periods and that such periods last approximately 8 min in vivo. We also find that the position of the beta-globin gene in the locus is important for correct developmental regulation.

Joining the loops: β‐Globin gene regulation

“…1A). The genes are positioned on the chromosome in the order of their expression during development (1,2). Their expression is changed in a process called ''switching.''…”

“…Introduction of a b-globin gene between the LCR and c-gene leads to premature activation of the b-gene and a strong reduction in expression of the c-gene (11). Introduction of a second b-gene in the locus causes the more proximal gene to be highest expressed, but the total output of the two b-genes together is not increased (2), similar to what has been found in patients that actively express the c-globin genes in the adult stage (12). In human adult tissues, the switch leading to the expression of the further downstream located band d-genes is achieved by active silencing of the embryonic and fetal genes (13)(14)(15).…”

Chromosome translocations in multiple myeloma

“…The t(4;14) translocation shows that translocations involving an IgH switch region can result in dysregulation of putative oncogenes on both derivative chromosomes, each under control of a di erent enhancer. However, it is also possible that a single Ig enhancer, which may possess at least some of the properties of a locus control region (LCR), can dysregulate two di erent genes, a result that has been well documented for the LCR in the beta globin locus (Bulger and Groudine, 1999;Dillon et al, 1997;Max, 1999). In addition, we have learned from studies of the globin locus that although the LCR preferentially a ects the closest gene, more distal genes can be selectively expressed at certain stages of development.…”

Altered DNA-binding specificity mutants of EKLF and Sp1 show that EKLF is an activator of the β-globin locus control region in vivo

“…Oligonucleotide probes detecting nuclear transcription spots of the endogenous ␣-globin genes were used to determine the number of erythroid cells (Tewari et al 1996). Human ␤-globin nuclear transcription signals were visualized with four oligonucleotides derived from intron 1; as two of these probes overlap partially with exon sequences, cytoplasmic ␤-globin mRNA can also be detected (Dillon et al 1997). The presence of cytoplasmic mRNA shows that a cell has expressed the transgene at some point in time, whereas the presence of nuclear precursor RNA at the site of transcription is indicative of active transcription because precursor RNAs are rapidly processed (Wijgerde et al 1995).…”

“…Four biotinylated oligonucleotides were used to detect human ␤-globin transcription. This probe mixture is directed against intron 1; two of the oligonucleotides overlap partially with exon sequences and thus cytoplasmic ␤-globin mRNA can also be detected (Dillon et al 1997). Three DIGlabeled mouse ␣-globin intron-specific oligonucleotides were used to reveal the erythroid cells (Tewari et al 1996).…”