Facio-scapulo-humeral dystrophy (FSHD), a muscular hereditary disease with a prevalence of 1 in 20,000, is caused by a partial deletion of a subtelomeric repeat array on chromosome 4q. Earlier, we demonstrated the existence in the vicinity of the D4Z4 repeat of a nuclear matrix attachment site, FR-MAR, efficient in normal human myoblasts and nonmuscular human cells but much weaker in muscle cells from FSHD patients. We now report that the D4Z4 repeat contains an exceptionally strong transcriptional enhancer at its 5′-end. This enhancer up-regulates transcription from the promoter of the neighboring FRG1 gene. However, an enhancer blocking activity was found present in FR-MAR that in vitro could protect transcription from the enhancer activity of the D4Z4 array. In vivo, transcription from the FRG1 and FRG2 genes could be down- or up-regulated depending on whether or not FR-MAR is associated with the nuclear matrix. We propose a model for an etiological role of the delocalization of FR-MAR in the genesis of FSHD.

Key Points We propose a novel oncogenic mechanism linked to the perinucleolar relocalization of chromosomal segments resulting from the translocation. MCL and BL translocations result in new Ccnd1 and c-myc nuclear positioning, respectively, and nucleolin-dependent activation in both cases.

SummaryT cell fate is associated with mutually exclusive expression of CD4 or CD8 in helper and cytotoxic T cells, respectively. How expression of one locus is temporally coordinated with repression of the other has been a long-standing enigma, though we know RUNX transcription factors activate the Cd8 locus, silence the Cd4 locus, and repress the Zbtb7b locus (encoding the transcription factor ThPOK), which is required for CD4 expression. Here we found that nuclear organization was altered by interplay among members of this transcription factor circuitry: RUNX binding mediated association of Cd4 and Cd8 whereas ThPOK binding kept the loci apart. Moreover, targeted deletions within Cd4 modulated CD8 expression and pericentromeric repositioning of Cd8. Communication between Cd4 and Cd8 thus appears to enable long-range epigenetic regulation to ensure that expression of one excludes the other in mature CD4 or CD8 single-positive (SP) cells.

Specialised pro-resolving mediators (SPMs) and their cognate G protein-coupled receptors are implicated in autoimmune disorders including chronic inflammation, rheumatoid arthritis, systemic scleroderma, and lupus erythematosus. To date six GPCRs have been paired with numerous endogenous and synthetic ligands. However, the function and downstream signalling of these receptors remains unclear. To address this knowledge gap, we systematically expressed each receptor in a HEK293-Flp-In-CD8a-FLAG cell system. Each receptor was pharmacologically characterised with both synthetic and putative endogenous ligands across different signalling assays, covering both G protein-dependent (G s , G i and G q ), and independent mechanisms (β-arrestin2 recruitment). Three orphan GPCRs previously identified as SPM receptors (GPR18, GPR32 and GPR37) failed to express in HEK293 cells. While we were unsuccessful in identifying an endogenous ligand for FPR2/ALX, with only a modest response to fMLP, we did reveal clear signalling bias away from ERK1/2 phosphorylation for the clinically tested agonist ACT-389949, adding further evidence for its poor efficacy in two phase I studies. We also identified neuroprotectin D1 as a new BLT 1 agonist, implying an alternative target for the neuroprotective effects of the ligand. We confirmed activity for RvE1 at BLT 1 but failed to observe any response at the chemerin 1 receptor. This study provides some much-needed clarity around published receptor-ligand pairings but indicates that the expression and function of these SPM GPCRs remains very much context-dependent. In addition, the identification of signalling bias at FPR2/ALX may assist in guiding design of new FPR2/ALX agonists for the treatment of autoimmune disorders.

AML1 and ETO genes are known partners in the t(8,21) translocation associated with the treatment-related leukaemias in the patients receiving chemotherapy with DNA-topoisomerase II (topo II) poisons. Aim. To determine whether the genes AML1 and ETO are in close proximity either permanently or temporarily in the nucleus. Methods. 3D FISH. Results. We found that in 5 % of untreated cells, alleles of AML1 and ETO are in close proximity. This number increased twofold in the cells treated with the topo II poison etoposide. Surprisingly, in more than 50 % of the cases observed, co-localization of the genes occurred at the nucleoli surface. We found also that the treatment of cells triggers preferential loading of RAD51 onto bcr of the AML1 and ETO genes. Conclusions. Our results suggest that the repair of DNA lesions introduced by topoisomerase II poisons may be mediated simultaneously by multiple mechanisms, which may be the cause of mistakes resulting in translocations.