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A Functionally Conserved Gene Regulatory Network Module Governing Olfactory Neuron Diversity

ABSTRACT: Sensory neuron diversity is required for organisms to decipher complex environmental cues. In Drosophila, olfactory environment is detected by 50 different olfactory receptor neuron (ORN) classes that are clustered in combinations within distinct sensilla subtypes. Each sensilla subtype houses stereotypically clustered 1-4 ORN identities that arise through asymmetric divisions from a single multipotent sensory organ precursor (SOP). How each class of SOPs acquires a unique differentiation potential that accounts for ORN diversity is unknown. Previously, we reported a critical component of SOP diversification program, Rotund (Rn), which functions to increase ORN diversity by generating novel developmental trajectories from existing precursors within each independent sensilla type lineages. Here, we show that Rn, along with BarH1/H2, Bric-à-brac (Bab), Apterous (Ap) and Dachshund (Dac), constitute a functionally conserved transcription factor (TF) network, previously shown to pattern the segmentation of the leg, that patterns the developing olfactory tissue. Precursors with diverse ORN differentiation potentials are selected from concentric rings defined by unique combinations of these TFs along the proximodistal axis of the developing antennal disc. The combinatorial code that demarcates each precursor field is set up by cross-regulatory interactions among different factors within the network. Modifications of this network lead to predictable changes in the diversity of sensilla subtypes and ORN pools. In light of our data, we propose a molecular map that defines

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE75986 | GEO | 2015/12/16

SECONDARY ACCESSION(S): PRJNA305904

REPOSITORIES: GEO

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Project description:The olfactory sensory system is formed by the coordinated morphogenesis and differentiation of the peripheral olfactory epithelium (OE) and the anterior forebrain. At early stages, immature olfactory receptor neurons (ORN) elongate their axons to penetrate the brain basement membrane, contact and form synapses with projection neurons of the olfactory bulb primordium. Axonal elongation is accompanied by migration of the GnRH+ neurons, followed by their ingression in the septo-hypothalamic area of the forebrain. This process is specifically impaired in the KallmannM-bM-^@M-^Ys syndrome (KS), a disorder characterized by anosmia and central hypogonadism. A set of transcription factors are master regulators of olfactory connectivity and GnRH neuron migration. We explored the transcriptional network underlying this process, by profiling the OE and adjacent mesenchyme at distinct embryonic ages. We also profiled the OE from embryos null for Dlx5, a homeogene essential for olfactory development, that causes a KS-like phenotype when deleted. We also applied analysis of conserved co-expression to integrate the obtained data with information on KS disease genes. The prevalent categories of genes differentially expressed during development are neuronal differentiation, extracellular remodelling and cell adhesion. From the analysis of Dlx5 mutant tissues we identify about 120 genes with a prevalence of intermediate filaments, cell signalling, epithelial and neuronal differentiation. Filtering for true OE expression and for the presence of Dlx5 binding sites, yielded twenty genes, of the following categories: 1) transmembrane adhesion/receptor molecules, 2) axon-glia interaction molecules, 3) synaptic proteins, 4) scaffold/adapter for signalling molecules. To functionally analyze these genes in vivo, we used three zebrafish fluorescent reporter zebrafish strains, in which we monitored early phases of olfactory/GnRH development upon gene downmodulation. The depletion of three (of five) Dlx5 targets affected axonal extension and targeting, while two (of two) altered GnRH neuron position and neurite organization. In one experiment we compare the olfactrory sensory epithelium from wild-type embryos, at three times of development, i.e. E11.5, E12.5 and E14.5. In a second experiment we compare the olfactory sensory epithelium from wild-type embryo with that from Dlx5 knock-out embryos, at the age E12.5

Project description:The olfactory sensory system is formed by the coordinated morphogenesis and differentiation of the peripheral olfactory epithelium (OE) and the anterior forebrain. At early stages, immature olfactory receptor neurons (ORN) elongate their axons to penetrate the brain basement membrane, contact and form synapses with projection neurons of the olfactory bulb primordium. Axonal elongation is accompanied by migration of the GnRH+ neurons, followed by their ingression in the septo-hypothalamic area of the forebrain. This process is specifically impaired in the Kallmann’s syndrome (KS), a disorder characterized by anosmia and central hypogonadism. A set of transcription factors are master regulators of olfactory connectivity and GnRH neuron migration. We explored the transcriptional network underlying this process, by profiling the OE and adjacent mesenchyme at distinct embryonic ages. We also profiled the OE from embryos null for Dlx5, a homeogene essential for olfactory development, that causes a KS-like phenotype when deleted. We also applied analysis of conserved co-expression to integrate the obtained data with information on KS disease genes. The prevalent categories of genes differentially expressed during development are neuronal differentiation, extracellular remodelling and cell adhesion. From the analysis of Dlx5 mutant tissues we identify about 120 genes with a prevalence of intermediate filaments, cell signalling, epithelial and neuronal differentiation. Filtering for true OE expression and for the presence of Dlx5 binding sites, yielded twenty genes, of the following categories: 1) transmembrane adhesion/receptor molecules, 2) axon-glia interaction molecules, 3) synaptic proteins, 4) scaffold/adapter for signalling molecules. To functionally analyze these genes in vivo, we used three zebrafish fluorescent reporter zebrafish strains, in which we monitored early phases of olfactory/GnRH development upon gene downmodulation. The depletion of three (of five) Dlx5 targets affected axonal extension and targeting, while two (of two) altered GnRH neuron position and neurite organization.

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A Functionally Conserved Gene Regulatory Network Module Governing Olfactory Neuron Diversity

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