<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "MusD transposable elements and their impact on endogenous gene regulation"^^ . "In this study, I investigated the role of MusD endogenous retroviruses as controlling elements in the loci they are inserted in and a novel mechanism through which the host genome could restrict their ability to change gene expression patterns. De novo insertions of two MusD elements into the Fgf8 locus were found to be the cause of Dactylaplasia mutations. When MusDs are situated between the regulatory elements driving Fgf8 in the limb apical ectodermal ridge (AER) and its promoter, they act as enhancer blockers and down-regulate Fgf8 expression in this domain. Concomitantly, they also hijack these enhancers to drive their own expression in the limbs. We propose that MusD’s enhancer-blocking activity concurrent with its transcription has a broader impact on the locus by re-routing some Fgf8 enhancers to new target genes, giving rise to ectopic expression of these genes in lieu of Fgf8. This model could also account for the phenotypically related but genomically distinct SHFM3 condition, where large duplications in the orthologous human locus cause a limb malformation similar to Dactylaplasia. They are moving a subset of Fgf8-enhancers away from this gene, a situation that possibly makes them accessible to other genes. Using mouse chromosomal engineering, we showed indeed that such structural changes in the locus are leading to ectopic expression of genes in Fgf8 expression domains. We tested two candidate genes from the locus to assess if their ectopic expression could phenocopy the disease. While we did not manage to reproduce the ectrodactyly phenotype, ectopic-expression of Lbx1 in the AER led to preaxial polydactylies, a feature also observed in several SHFM3 patients (specific for this form of ectrodactly). Thus, it is possible that this already complex disorder involves the combined action of multiple ectopically expressed genes from the locus. Therefore, gene expression programs in this SHFM3/Dactylaplasia locus seem to be altered in related ways for genomically distinct human and mouse mutations. To further understand how MusD could exert this effect, I examined the enhancer blocking activity of MusDs using ex-vivo assays. These experiments identified several regions within MusD, which have insulator properties as strong as the prototypic HS4 region from the chicken beta-globin locus. This is providing strong evidence that MusDs could interfere with the expression of endogenous genes, by working as a mobile insulator element. Indeed, I showed that of a MusD found between the co-regulated Olig2 and Olig1 genes led to changes in their overall and relative expression levels. These changes and the effects of MusD in Dactylaplasia mice were intriguingly only observed if these elements were unmethylated. When their 5’ LTRs were epigenetically repressed, gene expression levels were similar to wild type (i.e. in the absence of MusD) and no phenotype was observed. These observations suggested that MusD expression and effects were depending on epigenetic control over this element. Importantly, the epigenetic status of MusD appeared to be strictly dependent on the presence of an additional locus, Mdac, which is polymorphic amongst mouse strains. The resistant strain had completely methylated MusD 5’LTRs in contrast to almost complete lack of methylation in the permissive strain, hence the origin of the Mdac allele determined the cytosine methylation levels of MusD 5’LTR. This effect is limited to a few of MusD elements, as many of them are in heterochromatin regions. Nevertheless, Mdac seems to be a general controlling factor of MusD, since the strain-specific, differential methylation is consistent in all tested tissues independent of its expression. MusD elements have almost identical LTRs with ETnII elements. However, Mdac did not affect the 5’LTR methylation status of ETnIIs, indicating that Mdac is acting specifically on MusD elements. I genetically mapped the Mdac locus to a small interval of 1.3-1.7 Mb. Interestingly, this region is structurally variable between resistant and permissive strains, with the permissive strains carrying deletion of a cluster of KRAB-ZFP genes and pseudogenes present in the resistant strains. Zinc finger domains of KRAB-ZFPs provide a modular sequence specific binding and their KRAB domain recruits repressing chromatin modifiers. Supporting this identification, we found that a BAC that partially covers the mapped region and contains one KRAB-ZFP from the resistant strain could lead to MusD repression when added to ES cells from a permissive strain. Furthermore, we showed that the deletion of KAP1 in resistant strains led to up-regulation of MusD, along side with other elements. Our findings argue that KRAB-ZFP play major role in counteracting ERVs and that a specific KRAB-ZFP from the Mdac region is targeting repressive modification to MusD elements. "^^ . "2011" . . . . . . . . "Tugce"^^ . "Aktas"^^ . "Tugce Aktas"^^ . . . . . . "MusD transposable elements and their impact on endogenous gene regulation (PDF)"^^ . . . "diss_AktasT_2011.pdf"^^ . . . "MusD transposable elements and their impact on endogenous gene regulation (Other)"^^ . . . . . . "indexcodes.txt"^^ . . . "MusD transposable elements and their impact on endogenous gene regulation (Other)"^^ . . . . . . "lightbox.jpg"^^ . . . "MusD transposable elements and their impact on endogenous gene regulation (Other)"^^ . . . . . . "preview.jpg"^^ . . . "MusD transposable elements and their impact on endogenous gene regulation (Other)"^^ . . . . . . "medium.jpg"^^ . . . "MusD transposable elements and their impact on endogenous gene regulation (Other)"^^ . . . . . . "small.jpg"^^ . . "HTML Summary of #12753 \n\nMusD transposable elements and their impact on endogenous gene regulation\n\n" . "text/html" . . . "570 Biowissenschaften, Biologie"@de . "570 Life sciences"@en . .