The Experts below are selected from a list of 16959 Experts worldwide ranked by ideXlab platform
Andrew C Perkins - One of the best experts on this subject based on the ideXlab platform.
-
three fingers on the switch kruppel like factor 1 regulation of γ globin to β globin Gene Switching
Current Opinion in Hematology, 2013Co-Authors: Michael R Tallack, Andrew C PerkinsAbstract:Purpose of reviewKruppel-like factor 1 (KLF1) regulates most aspects of erythropoiesis. Many years ago, transgenic mouse studies implicated KLF1 in the control of the human γ-globin to β-globin switch. In this review, we will integrate these initial studies with recent developments in human Genetics
-
specific activation of human beta globin Gene expression by the transcription factor ikaros
Blood, 2005Co-Authors: Andrew C Perkins, Peter Papathanasiou, Christopher C Goodnow, Janelle R KeysAbstract:The zinc finger transcription factor Ikaros is recognized as a key regulator of lymphocyte differentiation. Recently Generated dominant negative mutants have hinted at a broader role in haematopoietic stem cell Generation. Most recently, a mouse strain, IkarosPlastic, with a point mutation in Ikaros that disrupts DNA binding but preserves efficient assembly of Ikaros protein complexes, is embryonically lethal due to severe defects in erythrocyte differentiation (Papathanasiou P, et al,. Immunity, 2003). (1). These mice display normal murine globin Gene expression in the fetal liver. However in humans the globin locus is under alternative regulatory control, particularly with respect to the fetal-to-adult globin switch. Thus, to determine if Ikaros plays a role in human globin Switching we crossed the IkarosPlastic mice with mice transgenic for a YAC containing the entire human b-globin locus, which show human fetal to adult globin Gene Switching from E12 to E17. Embryos were harvested from E12.5 to E15.5 and globin expression was determined in the fetal liver by real-time PCR (relative to actin). At all time points human gamma-globin Gene expression was not significantly altered by the presence of the IkarosPlastic mutatation (relative expression Ikaroswt/wt 1±0.11, IkarosPlastic/Plastic 0.82±0.12). In contrast, human beta-globin Gene expression was significantly down-regulated in IkarosPlastic fetal livers (relative expression Ikaroswt/wt 1±0.14, IkarosPlastic/Plastic 0.18±0.07). Interestingly, neither murine a- or b-globin Gene expression was significantly different to wild type mice, which suggests that the transcription factor Ikaros plays a specific role in the transcriptional activation of the human b-globin Gene during development. The mechanism by which this occurs remains to be elucidated, however it is intriguing to consider that Ikaros may act as a potentiator of transcription for erythroid specific transcription factors such as EKLF. Experiments to address this will be presented.
Tim M Townes - One of the best experts on this subject based on the ideXlab platform.
-
klf1 regulates bcl11a expression and gamma to beta globin Gene Switching
Nature Genetics, 2010Co-Authors: Dewang Zhou, Kaimao Liu, Chiaowang Sun, Kevin M Pawlik, Tim M TownesAbstract:We show that knockdown of KLF1 in human and mouse adult erythroid progenitors markedly reduces BCL11A levels and increases human γ-globin/β-globin expression ratios. These results suggest that KLF1 controls globin Gene Switching by directly activating β-globin and indirectly repressing γ-globin Gene expression. Controlled knockdown of KLF1 in adult erythroid progenitors may provide a method to activate fetal hemoglobin expression in individuals with β-thalassemia or sickle cell disease.
-
klf1 regulates bcl11a expression and gamma to beta globin Gene Switching
Nature Genetics, 2010Co-Authors: Dewang Zhou, Kaimao Liu, Chiaowang Sun, Kevin M Pawlik, Tim M TownesAbstract:We show that knockdown of KLF1 in human and mouse adult erythroid progenitors markedly reduces BCL11A levels and increases human gamma-globin/beta-globin expression ratios. These results suggest that KLF1 controls globin Gene Switching by directly activating beta-globin and indirectly repressing gamma-globin Gene expression. Controlled knockdown of KLF1 in adult erythroid progenitors may provide a method to activate fetal hemoglobin expression in individuals with beta-thalassemia or sickle cell disease.
Michael Bender - One of the best experts on this subject based on the ideXlab platform.
-
β globin Gene Switching and dnase i sensitivity of the endogenous β globin locus in mice do not require the locus control region
Molecular Cell, 2000Co-Authors: Michael Bender, Michael Bulger, Jennie CloseAbstract:We have Generated mice with a targeted deletion of the beta-globin locus control region (LCR). Mice homozygous for the deletion die early in embryoGenesis but can be rescued with a YAC containing the human beta-globin locus. After germline passage, deletion of the LCR leads to a severe reduction in expression of all mouse beta-like globin Genes, but no alteration in the developmental specificity of expression. Furthermore, a DNase I-sensitive "open" chromatin conformation of the locus is established and maintained. Thus, the dominant role of the LCR in the native locus is to confer high-level transcription, and elements elsewhere in the locus are sufficient to establish and maintain an open conformation and to confer developmentally regulated globin Gene expression.
-
β globin Gene Switching and dnase i sensitivity of the endogenous β globin locus in mice do not require the locus control region
Molecular Cell, 2000Co-Authors: Michael Bender, Michael Bulger, Jennie CloseAbstract:Abstract We have Generated mice with a targeted deletion of the β- globin locus control region (LCR). Mice homozygous for the deletion die early in embryoGenesis but can be rescued with a YAC containing the human β- globin locus. After germline passage, deletion of the LCR leads to a severe reduction in expression of all mouse β-like globin Genes, but no alteration in the developmental specificity of expression. Furthermore, a DNase I–sensitive "open" chromatin conformation of the locus is established and maintained. Thus, the dominant role of the LCR in the native locus is to confer high-level transcription, and elements elsewhere in the locus are sufficient to establish and maintain an open conformation and to confer developmentally regulated globin Gene expression.
James E. Haber - One of the best experts on this subject based on the ideXlab platform.
-
mating type Gene Switching in saccharomyces cerevisiae
Microbiology spectrum, 2015Co-Authors: Chengsheng Lee, James E. HaberAbstract:The budding yeast Saccharomyces cerevisiae has two alternative mating types designated MAT a and MATα. These are distinguished by about 700 bp of unique sequences, Ya or Yα, including divergent promoter sequences and part of the open reading frames of Genes that regulate mating phenotype. Homothallic budding yeast, carrying an active HO endonuclease Gene, HO, can switch mating type through a recombination process known as Gene conversion, in which a site-specific double-strand break (DSB) created immediately adjacent to the Y region results in replacement of the Y sequences with a copy of the opposite mating type information, which is harbored in one of two heterochromatic donor loci, HMLα or HMR a. HO Gene expression is tightly regulated to ensure that only half of the cells in a lineage switch to the opposite MAT allele, thus promoting conjugation and diploid formation. Study of the silencing of these loci has provided a great deal of information about the role of the Sir2 histone deacetylase and its associated Sir3 and Sir4 proteins in creating heterochromatic regions. MAT Switching has been examined in great detail to learn about the steps in homologous recombination. MAT Switching is remarkably directional, with MAT a recombining preferentially with HMLα and MATα using HMR a. Donor preference is controlled by a cis-acting recombination enhancer located near HML. RE is turned off in MATα cells but in MAT a binds multiple copies of the Fkh1 transcription factor whose forkhead-associated phosphothreonine binding domain localizes at the DSB, bringing HML into conjunction with MAT a.
-
Chromosome breakage and repair.
Genetics, 2006Co-Authors: James E. HaberAbstract:FROM time to time one of my colleagues working at a medical school commiserates with me because I spend ∼40 hr a year lecturing to undergraduates. I always reply that teaching has compelled me to learn a lot of material that I would not have known about had I taught only my specialized subject. These forays into the “beyond” were instrumental in moving my research in new directions. Three articles that I published in Genetics in the early 1980s (McCusker and Haber 1981; Haber and Thorburn 1984; Haber et al. 1984) were the result of learning about, in order to teach, classic Genetic experiments in Drosophila and maize. When I arrived at Brandeis I was assigned to teach Genetics, a subject I had never studied as either an undergraduate or a graduate student2. I was fortunate to team up in teaching with Jeff Hall, a master Geneticist, who taught me much of the lore of Drosophila and maize, to add to the yeast Genetics that my lab and I were slowly learning3. I was particularly interested in Barbara McClintock's study of the “Activator (Ac)/Dissociator (Ds)” transposable elements whose excisions led to cycles of breakage–fusion–bridge (BFB) of broken chromosome ends that Generated chromosomal truncations. Her studies resonated strongly with the behavior of apparently broken chromosomes that we were studying in budding yeast as a consequence of mating-type Gene Switching. The study of yeast mating-type (MAT) Gene Switching has provided gainful employment for many scientists interested in cell-type regulation, Gene silencing, chromosome architecture, and DNA repair. Haploid cells express either the MATa or the MATα allele and mate with cells of the opposite type, but cells expressing both MATa and MATα are nonmating. But most unusual was that homothallic MATa cells could switch to MATα, or vice versa, as often as every cell division. Takano and Oshima (1970; Oshima and Takano 1971) showed that Switching depended on two distant loci that they viewed as “controlling elements,” similar to those defined by McClintock in maize. Hicks et al. (1977) made the insightful suggestion that these two loci were in fact unexpressed copies of mating-type information (now called HMLα and HMRa) that could be transposed to replace the original MAT allele. Extending the mutational analysis of Mackay and Manney (1974) and the sometimes-published work of the inventive Don Hawthorne (Hawthorne 1963; see also Herskowitz 1988), Strathern et al. (1981) proposed that MATα encoded both a repressor of a-specific Genes (MATα2) and a positive regulator of α-specific Genes (MATα1). Thus a matα1 matα2 mutant proved to be a-like. The transposition/replacement of MAT alleles occurs very frequently in homothallic cells, expressing the HO Gene encoding a site-specific endonuclease, but is very rare in heterothallic strains where HO is inactive. One way we tried to study these rare events was by mating two heterothallic MATα strains together, on the assumption that if one of them switched to MATa, it would readily conjugate with a MATα cell, as first shown by Hawthorne (1963). We took up this approach (McCusker and Haber 1981) and found that indeed ∼25% of MATα × MATα matings did appear to result from such switches, leading to stable MATa/MATα diploids. However, most of the events were different and were often Genetically unstable, giving rise to colonies with multiple phenotypes. Many matings arose from the creation of an at least transient a-like cell (presumably lacking expression of both MATα1 and MATα2), allowing it to mate with another α-mater. In some cases the resulting diploids were 2n-1 aneuploids that had lost the entire, presumably broken, chromosome. In many instances the diploids that were still heterozygous for markers distal to the MAT locus, but now α-mating. The most interesting group resulted in the loss of the all the markers distal to and including MATα. Many of these colonies gave evidence of continuing genomic instability, with the loss of additional markers on chromosome III. Among nine stable derivatives we analyzed in detail, eight were homozygous for MATα and more distal markers, but one contained a truncation of the right arm from at least MAT to the end of the chromosome. This last type was reminiscent of outcomes described in maize after the transposition of the Ds element. The truncation in yeast was one of the first examples of the apparent acquisition of a new telomere, either by de novo addition or by a nonreciprocal translocation. Before the days of genome sequencing, it was not possible to be more precise. Viewed from today's perspective, we imagine that the diploids still heterozygous for the right arm repaired the chromosome break by Gene conversion, becoming MATα/MATα. Those that became homozygous for the distal region likely resulted from break-induced replication (BIR, also known as recombination-dependent DNA replication) in which one end of the double-strand break (DSB) established a replication fork that could copy >100 kb to the end of the homologous, template chromosome (Morrow et al. 1997; Kraus et al. 2001; Davis and Symington 2004; Malkova et al. 2005). It is also possible that some of the diploids showing loss of heterozygosity for markers distal to MAT arose from reciprocal exchanges accompanying Gene conversion because we did not recover instances in which the distal regions became homozygous wild type. In the same year that John McCusker examined MATα × MATα matings in heterothallic strains, Barbara Weiffenbach was studying similar genomic instability in homothallic strains (Weiffenbach and Haber 1981). Malone and Esposito (1980) had shown that MAT Switching was lethal in the absence of the RAD52 recombination Gene, suggesting that the process had similarities to the repair of X-ray-induced damage. It was not until 1982 that Strathern et al. (1982) showed that MAT Switching did indeed involve a DSB. I had isolated a recessive mutation, swi1-1, that reduced, but did not eliminate, MAT Switching (Garvik and Haber 1977); hence we could study a population of MATα rad52 cells in which several percent of the cells in each Generation attempted to switch; such cells became a-like. This made it possible for us to examine newly Generated broken chromosomes, importantly with all the breaks initiating at the same place. We mated these cells with a heterothallic MATα strain and recovered diploids in which the broken chromosome was repaired by Gene conversion, by BIR, or by new telomere addition. We again found that many of these diploids exhibited genomic instability, so that the colonies that arose were sectored for markers on chromosome III. Again, there were cases where the broken chromosome was completely lost and others in which there were stable outcomes in which markers distal to MAT were hemizyous or homozygous4.
-
mating type Gene Switching in saccharomyces cerevisiae
Annual Review of Genetics, 1998Co-Authors: James E. HaberAbstract:Saccharomyces cerevisiae can change its mating type as often as every Generation by a highly choreographed, site-specific recombination event that replaces one MAT allele with different DNA sequences encoding the opposite allele. The study of this process has yielded important insights into the control of cell lineage, the silencing of Gene expression, and the formation of heterochromatin, as well as the molecular events of double-strand break-induced recombination. In addition, MAT Switching provides a remarkable example of a small locus control region--the Recombination Enhancer--that controls recombination along an entire chromosome arm.
Jennie Close - One of the best experts on this subject based on the ideXlab platform.
-
β globin Gene Switching and dnase i sensitivity of the endogenous β globin locus in mice do not require the locus control region
Molecular Cell, 2000Co-Authors: Michael Bender, Michael Bulger, Jennie CloseAbstract:We have Generated mice with a targeted deletion of the beta-globin locus control region (LCR). Mice homozygous for the deletion die early in embryoGenesis but can be rescued with a YAC containing the human beta-globin locus. After germline passage, deletion of the LCR leads to a severe reduction in expression of all mouse beta-like globin Genes, but no alteration in the developmental specificity of expression. Furthermore, a DNase I-sensitive "open" chromatin conformation of the locus is established and maintained. Thus, the dominant role of the LCR in the native locus is to confer high-level transcription, and elements elsewhere in the locus are sufficient to establish and maintain an open conformation and to confer developmentally regulated globin Gene expression.
-
β globin Gene Switching and dnase i sensitivity of the endogenous β globin locus in mice do not require the locus control region
Molecular Cell, 2000Co-Authors: Michael Bender, Michael Bulger, Jennie CloseAbstract:Abstract We have Generated mice with a targeted deletion of the β- globin locus control region (LCR). Mice homozygous for the deletion die early in embryoGenesis but can be rescued with a YAC containing the human β- globin locus. After germline passage, deletion of the LCR leads to a severe reduction in expression of all mouse β-like globin Genes, but no alteration in the developmental specificity of expression. Furthermore, a DNase I–sensitive "open" chromatin conformation of the locus is established and maintained. Thus, the dominant role of the LCR in the native locus is to confer high-level transcription, and elements elsewhere in the locus are sufficient to establish and maintain an open conformation and to confer developmentally regulated globin Gene expression.