Skip to main content
. 2004 Nov 17;76(1):8–32. doi: 10.1086/426833

Figure 2.

Figure 2

Figure 2

Details of position-effect cases caused by disruption of long-range gene control. In all cases, the affected gene(s) are shown in red, and other genes are shown in purple or blue. Filled boxes indicate individual exons, and hashed boxes represent full genes. L-shaped black arrows indicate the direction of transcription. A, Human PAX6 locus. The loss of a set of DNase I HSs downstream from one allele causes aniridia. The HSs are located within introns of the adjacent ubiquitously expressed ELP4 gene. Some documented aniridia-associated breakpoints are denoted by blue arrows. The downstream end of the correcting YAC transgene (YA) and the noncorrecting one (YB) are shown in green. Both upstream YAC ends are ∼200 kb 5′ of the PAX6 promoters. Isolated HSs have been shown to act as tissue-specific enhancers for lens and retinal expression. B, The human POU3F4 deafness locus. The microdeletion of an 8-kb region located 900 kb upstream of the gene contains a conserved noncoding sequence, the loss of which leads to congenital deafness. The mouse slf inversion breakpoint X leaves the neural tube enhancer (nt) intact. C, Mouse/human upstream SHH region. A complex hotspot for limb abnormalities is found 1 Mb upstream of SHH, within the introns of LMBR1. The region contains a conserved noncoding element that is capable of functioning as an enhancer that drives SHH expression in the limb bud in both an anterior and posterior zone, as well as a repressor element that silences the anterior expression. The Sasquatch insertion disrupts the anterior repression function, whereas the acheiropodia deletion is thought to disrupt positive enhancer activity. D, Human FSHD region. Deletion of an integral number of D4Z4 repeats from the tip of the long arm of chromosome 4 to below a threshold of 10 repeats results in FSHD. A contentious model suggests that a multiprotein repressor complex fails to bind adequately to the deleted allele, which leads to derepression of several genes in the region proximal to the repeat array and causes the phenotype. E, Human α-globin locus (HBA). Deletion of the polyadenylation signal from the ubiquitously expressed LUC7L gene on the opposite strand leads to transcription of an antisense RNA that runs through the HBA2 gene, resulting in silencing and methylation of the HBA2 promoter. Open ovals indicate unmethylated CpG islands; the gray oval depicts the methylated CpG island. F, Mouse Hoxd cluster. A GCR regulates expression of multiple consecutive Hoxd genes in a tissue-specific manner. In the distal limb, the GCR also regulates the expression of Lnp, Evx2, and Hoxd13–10, whereas in the CNS it controls Lnp and Evx2. G, Mouse IL4/IL13 region. A conserved noncoding element (CNE) located between IL4 and IL13 controls expression of both genes, as well as IL5, but does not influence expression of the KIF3a and RAD50 genes. H, Human β-globin locus (HBB). Deletion of a large genomic region upstream of the human β-globin genes, including the LCR, results in reduced DNase I sensitivity and histone acetylation levels across the locus, which causes loss of globin expression. The β-globin locus is embedded within a region that contains numerous OR genes.