Project description:Dorsal-ventral (DV) patterning of the Drosophila embryo is initiated by Dorsal, a sequence specific transcription factor distributed in a broad nuclear gradient in the precellular embryo.Previous studies have identified as many as 70 protein-coding genes and one microRNA gene that are directly or indirectly regulated by this gradient. A gene regulation network, or circuit diagram, including the functional interconnections among 40 Dorsal target genes and 20 associated tissue-specific enhancers, has been determined for the initial stages of gastrulation. Here, we attempt to extend this analysis by identifying additional DV patterning genes using a recently developed whole-genome tiling array. This analysis led to the identification of another 30 protein-coding genes, including the Drosophila homolog of Idax, an inhibitor of Wnt signaling. In addition, remote 5' exons were identified for at least 10 of the ~100 protein-coding genes that were missed in earlier annotations. As many as 9 intergenic, uncharacterized transcription units were identified, including two that contain known microRNAs, miR-1 and miR-9a. We discuss the potential functions of these newly identified genes, and suggest that intronic enhancers are a common feature of the DV gene network. Keywords: gene expression, dorsal-ventral pattern genes, tiling array
Project description:Embryonic development requires the establishment of directional axes. In Drosophila, spatially discrete expression of transcription factors determines the anterior to posterior organization of the early embryo, while the Toll and TGF-beta signalling pathways determine the early dorsal to ventral pattern. Embryonic MAPK/ERK signaling contributes to both anterior to posterior patterning in the terminal regions and to dorsal to ventral patterning during oogenesis and embryonic stages. Here we describe a novel loss of function mutation in the Raf kinase gene, which leads to loss of ventral cell fates as seen through the loss of the ventral furrow, the absence of Dorsal/NF-kB nuclear localization, the absence of mesoderm determinants Twist and Snail, and the expansion of TGF-beta. Gene expression analysis showed cells adopting ectodermal fates similar to loss of Toll signaling. Our results combine novel mutants, live imaging, optogenetics and transcriptomics to establish a novel role for Raf, that appears to be independent of the MAPK cascade, in embryonic patterning.
Project description:Whole-Genome Analysis of Dorsal-Ventral Patterning in the Drosophila Embryo. The maternal Dorsal regulatory gradient initiates the differentiation of several tissues in the early Drosophila embryo. Whole-genome microarray assays identified as many as 40 new Dorsal target genes, which encode a broad spectrum of cell signaling proteins and transcription factors. Evidence is presented that a tissue-specific form of the NF-Y transcription complex is essential for the activation of gene expression in the mesoderm. Tissue-specific enhancers were identified for new Dorsal target genes, and bioinformatics methods identified conserved cis-regulatory elements for coordinately regulated genes that respond to similar thresholds of the Dorsal gradient. The new Dorsal target genes and enhancers represent one of the most extensive gene networks known for any developmental process. Stathopoulos et al., Cell, Vol 111, 687-701, November 2002.
Project description:We report the systematic identification of BMP (bone morphogenetic protein) target genes in zebrafish during dorsal-ventral patterning using RNA-sequencing.
Project description:Spatial patterning of neural stem cell populations is a powerful mechanism by which to generate neuronal diversity. In the developing Drosophila medulla, the symmetrically dividing stem cells of the outer proliferation center (OPC) crescent are spatially patterned by the non-overlapping expression of three transcription factors: Vsx1 in the center, Optix in the adjacent arms and Rx in the tips. These spatial genes compartmentalize the OPC and, together with the temporal patterning of the neuroblasts derived from the OPC, act to diversify medulla neuronal fates. The observation that the dorsal and ventral halves of the OPC grow as distinct compartments, together with the fact that a subset of neuronal types are generated from only one half of the crescent, suggests that additional transcription factors spatially pattern the OPC along the D-V axis. Here, we identify the spalt (salm and salr) and disco (disco and disco-r) genes as the D-V patterning transcription factors of the OPC. Spalt and Disco are differentially expressed in the dorsal and ventral OPC from the embryo through to the third instar larva, where they cross-repress each other to form a sharp dorsal-ventral boundary. We show that hedgehog is necessary for disco expression in the embryonic optic placode and that disco is subsequently required for the development of the ventral OPC and its neuronal progeny. We further demonstrate that this D-V patterning axis acts independently of Vsx1-Optix-Rx and thus propose that Spalt and Disco represent a third OPC patterning axis that may act to further diversify medulla fates.