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ABSTRACT: Stem cells can divide symmetrically to generate two similar daughter cells and expand the stem cell pool or asymmetrically to self-renew and generate differentiating daughter cells. The proper balance between symmetric and asymmetric division is critical for the generation and subsequent repair of tissues. Furthermore, unregulated stem cell division has been shown to result in tumorous overgrowth. The Drosophila nervous system has proved to be a fruitful model system for studying the biology of neural stem cell division and uncovering the molecular mechanisms that, when disrupted, can lead to tumor formation. We are using the Drosophila embryonic and larval nervous systems as models to study the regulation of symmetric and asymmetric stem cell division.Cold Spring Harbor Symposia on Quantitative Biology 02/2009; 73:523-8.
Article: Neural stem cell transcriptional networks highlight genes essential for nervous system development.Tony D Southall, Andrea H Brand[show abstract] [hide abstract]
ABSTRACT: Neural stem cells must strike a balance between self-renewal and multipotency, and differentiation. Identification of the transcriptional networks regulating stem cell division is an essential step in understanding how this balance is achieved. We have shown that the homeodomain transcription factor, Prospero, acts to repress self-renewal and promote differentiation. Among its targets are three neural stem cell transcription factors, Asense, Deadpan and Snail, of which Asense and Deadpan are repressed by Prospero. Here, we identify the targets of these three factors throughout the genome. We find a large overlap in their target genes, and indeed with the targets of Prospero, with 245 genomic loci bound by all factors. Many of the genes have been implicated in vertebrate stem cell self-renewal, suggesting that this core set of genes is crucial in the switch between self-renewal and differentiation. We also show that multiply bound loci are enriched for genes previously linked to nervous system phenotypes, thereby providing a shortcut to identifying genes important for nervous system development.The EMBO Journal 10/2009; 28(24):3799-807. · 9.20 Impact Factor
Tony D Southall, Andrea H Brand[show abstract] [hide abstract]
ABSTRACT: The correct control of gene expression is essential for the proper development of organisms. Abnormal expression of genes can lead to cancerous growth and certain diseases. To understand how gene expression is controlled on a genome-wide scale, methods for assaying transcription factor binding sites are required. There are two prevailing techniques for mapping protein-chromatin interactions, ChIP (chromatin immunoprecipitation) and DamID (DNA adenine methyltransferase identification). Both of these methods, when combined with microarray technology, can provide powerful insights into transcription factor function, higher order chromatin structure and gene regulatory networks. In vivo chromatin profiling studies are now being performed on model organisms, targeting specific tissues to help generate more accurate maps of protein-DNA interactions.Briefings in Functional Genomics and Proteomics 07/2007; 6(2):133-40.
Article: Prospero acts as a binary switch between self-renewal and differentiation in Drosophila neural stem cells.Semil P Choksi, Tony D Southall, Torsten Bossing, Karin Edoff, Elzo de Wit, Bettina E Fischer, Bas van Steensel, Gos Micklem, Andrea H Brand[show abstract] [hide abstract]
ABSTRACT: Stem cells have the remarkable ability to give rise to both self-renewing and differentiating daughter cells. Drosophila neural stem cells segregate cell-fate determinants from the self-renewing cell to the differentiating daughter at each division. Here, we show that one such determinant, the homeodomain transcription factor Prospero, regulates the choice between stem cell self-renewal and differentiation. We have identified the in vivo targets of Prospero throughout the entire genome. We show that Prospero represses genes required for self-renewal, such as stem cell fate genes and cell-cycle genes. Surprisingly, Prospero is also required to activate genes for terminal differentiation. We further show that in the absence of Prospero, differentiating daughters revert to a stem cell-like fate: they express markers of self-renewal, exhibit increased proliferation, and fail to differentiate. These results define a blueprint for the transition from stem cell self-renewal to terminal differentiation.Developmental Cell 01/2007; 11(6):775-89. · 14.03 Impact Factor
Article: The SzA mutations of the B subunit of the Drosophila vacuolar H+ ATPase identify conserved residues essential for function in fly and yeast.Juan Du, Laura Kean, Adrain K Allan, Tony D Southall, Shireen A Davies, Christopher J McInerny, Julian A T Dow[show abstract] [hide abstract]
ABSTRACT: V-ATPases play multiple roles in eukaryotes: in Drosophila, null mutations are recessive lethal. Here, mutations underlying five extant lethal alleles of vha55, encoding the B subunit, were identified, including a premature termination codon and two mutations very close to residues thought to participate in the catalytic site of the enzyme. Lethality of these alleles could be reverted by transformation of flies with a wild type vha55::GFP fusion, confirming that the lethal phenotype described for these alleles was due to defects in V-ATPase function. The chimeric protein was correctly localised to the apical domain of the Malpighian (renal) tubule, and restored fluid transport function to wild-type levels. No dominant-negative phenotype was apparent in heterozygotes. When the vha55::GFP fusion was driven ubiquitously, fluorescent protein was only detectable in tissues known to contain high levels of V-ATPase, suggesting that vha55 requires stoichometric co-expression of other subunits to be stable. Yeast (Saccharomyces cerevisiae) deleted for the corresponding gene (Deltavma2) demonstrated a pH-sensitive growth phenotype that was rescued by the vha55::GFP construct. Deltavma2 yeast could not be rescued with fly cDNAs encoding any of the mutant vha55 alleles, confirming the functional significance of the mutated residues. In yeast, bafilomycin-sensitive ATPase activity and growth rate correlated with the ability of different constructs to rescue the pH-sensitive conditional-lethal phenotype. These classical Drosophila mutants thus identify residues that are essential for function in organisms with wide phylogenetic separation.Journal of Cell Science 07/2006; 119(Pt 12):2542-51. · 6.11 Impact Factor