An RNAi screen for secreted factors and cell-surface players in coordinating neuron and glia development in Drosophila (original) (raw)
Related papers
Development, 1997
Two classes of glial cells are found in the embryonic Drosophila CNS, midline glial cells and lateral glial cells. Midline glial development is triggered by EGF-receptor signalling, whereas lateral glial development is controlled by the gcm gene. Subsequent glial cell differentiation depends partly on the pointed gene. Here we describe a novel component required for all CNS glia development. The tramtrack gene encodes two zinc-finger proteins, one of which, ttkp69, is expressed in all non-neuronal CNS cells. We show that ttkp69 is downstream of gcm and can repress neuronal differentiation. Double mutant analysis and coexpression experiments indicate that glial cell differentiation may depend on a dual process, requiring the activation of glial differentiation by pointed and the concomitant repression of neuronal development by tramtrack.
Expression profiling of glial genes during Drosophila embryogenesis
Developmental Biology, 2006
In the central nervous system of Drosophila, the induction of the glial cell fate is dependent on the transcription factor glial cells missing (gcm). Though a considerable number of other genes have been shown to be expressed in all or in subsets of glial cells, the course of glial cell differentiation and subtype specification is only poorly understood. This prompted us to design a whole genome microarray approach comparing gcm gain-of-function and, for the first time, gcm loss-of-function genetics to wildtype in time course experiments along embryogenesis. The microarray data were analyzed with special emphasis on the temporal profile of differential regulation. A comparison of both experiments enabled us to identify more than 300 potential gcm target genes. Validation by in situ hybridization revealed expression in glial cells, macrophages, and tendon cells (all three cell types depend on gcm) for 70 genes, of which more than 50 had been unknown to be under gcm control. Eighteen genes are exclusively expressed in glial cells, and their dependence on gcm was confirmed in situ. Initial considerations regarding the role of the newly discovered glial genes are discussed based on gene ontology and the temporal profile and subtype specificity of their expression. This collection of glial genes provides an important basis for the clarification of the genetic network controlling various aspects of glial development and function.
Glia relay differentiation cues to coordinate neuronal development in Drosophila
Science (New York, N.Y.), 2017
Neuronal birth and specification must be coordinated across the developing brain to generate the neurons that constitute neural circuits. We used the Drosophila visual system to investigate how development is coordinated to establish retinotopy, a feature of all visual systems. Photoreceptors achieve retinotopy by inducing their target field in the optic lobe, the lamina neurons, with a secreted differentiation cue, epidermal growth factor (EGF). We find that communication between photoreceptors and lamina cells requires a signaling relay through glia. In response to photoreceptor-EGF, glia produce insulin-like peptides, which induce lamina neuronal differentiation. Our study identifies a role for glia in coordinating neuronal development across distinct brain regions, thus reconciling the timing of column assembly with that of delayed differentiation, as well as the spatiotemporal pattern of lamina neuron differentiation.
Control of midline glia development in the embryonic Drosophila CNS
Mechanisms of Development, 1997
The midline glial cells are required for correct formation of the axonal pattern in the embryonic ventral nerve cord of Drosophila. Initially, six midline cells form an equivalence group with the capacity to develop as glial cells. By the end of embryonic development three to four cells are singled out as midline glial cells. Midline glia development occurs in two steps, both of which depend on the activation of the Drosophila EGF-receptor homolog and subsequent rasl/raf-mediated signal transduction. Nuclear targets of this signalling cascade are the ETS domain transcription factors pointedP2 and yan. In the midline glia pointedP2 in turn activates the transcription of argos, which encodes a diffusible negative regulator of EGF-receptor signalling. © 1997 Elsevier Science Ireland Ltd.
he central nervous system (CNS) consists of an enormous number of cells, and large cellular variance, integrated into an elaborate network. The CNS is the most complex animal organ, and therefore its establishment must be controlled by many different genetic programs. Considering the high level of complexity in the human CNS, addressing issues related to human neurodevelopment represents a major challenge. Since comparative studies have revealed that neurodevelopmental programs are well conserved through evolution, on both the genetic and functional levels, studies on invertebrate neurodevelopmental programs are often translatable to vertebrates. Indeed, the basis of our current knowledge about vertebrate CNS development has been greatly aided by studies on invertebrates, and in particular on the Drosophila melanogaster (fruit fly) model system. This thesis attempted to identify novel genes regulating neural cell specification and proliferation in the CNS, using the Drosophila model system. Moreover, I aimed to address how those genes govern neural progenitor cells (neuroblasts; NBs) to obtain/maintain their stemness identity and proliferation capacity, and how they drive NBs through temporal windows and series of programmed asymmetric division, which gradually reduces their stemness identity in favor of neural differentiation, resulting in appropriate lineage progression. In the first project, we conducted a forward genetic screen in Drosophila embryos, aimed at isolating genes involved in regulation of neural proliferation and specification, at the single cell resolution. By taking advantage of the restricted expression of the neuropeptide FMRFa in the last-born cell of the NB lineage 5-6T, the Ap4 neuron, we could monitor the entire lineage progression. This screen succeeded in identifying 43 novel genes controlling different aspects of CNS development. One of the genes isolated, Ctr9, displayed extra Ap4/FMRFa neurons. Ctr9 encodes a component of the RNA polymerase II complex Paf1, which is involved in a number of transcriptional processes. The Paf1C, including Ctr9, is highly conserved from yeast to human, and in the past couple of years, its importance for transcription has become increasingly appreciated. However, studies in the Drosophila system have been limited. In the screen, we isolated the first mutant of Drosophila Ctr9 and conducted the first detailed phenotypic study on its function in the Drosophila embryonic CNS. Loss of function of Ctr9 leads to extra NB numbers, higher proliferation ratio and lower expression of neuropeptides. Gene expression analysis identified several other genes regulated by Ctr9, which may explain the Ctr9 mutant phenotypes. In summary, we identified Ctr9 as an essential gene for proper CNS development in Drosophila, and this provides a platform for future study on the Drosophila Paf1C. Another interesting gene isolated in the screen was worniou (wor), a member of the Snail family of transcription factors. In contrast to Ctr9, which displayed additional Ap4/FMRFa neurons, wor mutants displayed a loss of these neurons. Previous studies in our group have identified many genes acting to stop NB lineage progression, but how NBs are pushed to proliferate and generate their lineages was not well known. Since wor may constitute a “driver” of proliferation, we decided to study it further. Also, we identified five other transcription factors acting together with Wor as pro-proliferative in both NBs and their daughter cells. These “drivers” are gradually replaced by the previously identified late-acting “stoppers.” Early and late factors regulate each other and the cell cycle, and thereby orchestrate proper neural lineage progression.
Neuroscience Research, 1996
Inhibitory signals of cellular differentiation from differentiating cells play an important role in regulating the number and spatial distribution of distinctive types of cells in developing tissues. Several types of inhibitory mechanisms of cellular differentiation have been identified by making full use of the developmental genetics of Drosophila compound eyes. These inhibitory mechanisms are distinct from each other in their signal transduction cascades and/or their role in the pattern formation of the developing Drosophila eye. The following events occur: firstly a diffusible protein, Scabrous (Sca), is required to confer regular spacings of the founder cells, R8 cells, or preommatidial clusters in the developing eye disc via an unknown signal transduction cascade, secondly the Notch-signalling is at least required for the single-out of the R8 cells within the pre-ommatidial cluster possibly by preventing other cells in the equivalent groups from adapting fates as R8 cells. Notch-signalling activates a simple signal cascade mediating communication between the plasma membrane and nucleus not via protein phosphorylation. In contrast, a novel diffusible ligand,.Argos, was likely to be required subsequently to the selection of R8 cells. Argos was shown to inhibit the activation of a receptor tyrosine kinase, DER, and the subsequent signal transduction in the Ras/MAPK cascade (the third inhibitory mechanism). We proposed that the role of Argos is to regulate the number of differentiated cells by controlling cellular differentiation and subsequent programmed cell death. The distinct roles of these inhibitory signals in the developing Drosophila eye are discussed in detail.
Glial cell development in Drosophila
International Journal of Developmental Neuroscience, 2001
In the Drosophila central nervous system (CNS) about 10% of the cells are of glial nature. A set of molecular markers has allowed unraveling a number of genes controlling glial cell fate determination as well as genes required for glial cell differentiation.
loco encodes an RGS protein required for Drosophila glial differentiation
Development (Cambridge, England), 1999
In Drosophila, glial cell development depends on the gene glial cells missing (gcm). gcm activates the expression of other transcription factors such as pointed and repo, which control subsequent glial differentiation. In order to better understand glial cell differentiation, we have screened for genes whose expression in glial cells depends on the activity of pointed. Using an enhancer trap approach, we have identified loco as such a gene. loco is expressed in most lateral CNS glial cells throughout development. Embryos lacking loco function have an normal overall morphology, but fail to hatch. Ultrastructural analysis of homozygous mutant loco embryos reveals a severe glial cell differentiation defect. Mutant glial cells fail to properly ensheath longitudinal axon tracts and do not form the normal glial-glial cell contacts, resulting in a disruption of the blood-brain barrier. Hypomorphic loco alleles were isolated following an EMS mutagenesis. Rare escapers eclose which show impa...