A comprehensive temporal patterning gene network in Drosophila medulla neuroblasts revealed by single-cell RNA sequencing
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PROVIDER: PRJNA708282 | ENA |
REPOSITORIES: ENA
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Project description:During development, neural stem cells are temporally patterned to sequentially generate a variety of neural types before exiting the cell cycle. Temporal patterning is well-studied in Drosophila, where neural stem cells called neuroblasts sequentially express cascades of Temporal Transcription Factors (TTFs) to control the birth-order dependent neural specification. However, currently known TTFs were mostly identified through candidate antibody screening and may not be complete. In addition, many fundamental questions remain concerning the TTF cascade initiation, progression, and termination. It is also not known why temporal progression only happens in neuroblasts but not in their differentiated progeny. In this work, we performed single-cell RNA sequencing of Drosophila medulla neuroblasts of all ages to study the temporal patterning process with single-cell resolution. Our scRNA-seq data revealed that sets of genes involved in different biological processes show high to low or low to high gradients as neuroblasts age. We also identified a list of novel TTFs, and experimentally characterized their roles in the temporal progression and neural fate specification. Our study revealed a comprehensive temporal gene network that patterns medulla neuroblasts from start to end. Furthermore, we found that the progression and termination of this temporal cascade also require transcription factors differentially expressed along the differentiation axis (neuroblasts -> -> neurons). Lola proteins function as a speed modulator of temporal progression in neuroblasts; while Nerfin-1, a factor required to suppress de-differentiation in post-mitotic neurons, acts at the final temporal stage together with the last TTF of the cascade, to promote the switch to gliogenesis and the cell cycle exit. Our comprehensive study of the medulla neuroblast temporal cascade illustrated mechanisms that might be conserved in the temporal patterning of neural stem cells.
2021-12-27 | GSE168553 | GEO
Project description:In this work, we show that the expression of one temporal transcription factor(TTF), Sloppy-paired (Slp), in the Drosophila medulla TTF cascade, is regulated directly by two other TTFs and the Notch signaling pathway. We show that the previous TTF, Eyeless, another TTF Scro and Su(H)/NICD regulate the transcription of Slp through binding to two cis-regulatory elements in the slp locus. Slp expression is delayed when Notch signaling is lost or when cell cycle progression is blocked, which also cause loss of Notch signaling. Furthermore, we show that supplying Notch signaling can rescue the delayed Slp expression in cell-cycle arrested neuroblasts. Thus our work demonstrates that Notch signaling cooperates with TTFs to promote the progression of the TTF transcriptional cascade.
2022-08-10 | GSE188643 | GEO
Project description: Not available
| S-EPMC3701960 | biostudies-literature
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.
2022-09-19 | GSE205934 | GEO
Project description:One neural stem cell can produce multiple transiently amplifying, intermediate neural progenitors (INP), which collectively yield diverse neuronal types. It is unclear if and how serially derived INPs contribute to neuron fate diversification. Drosophila type II neuroblasts, like mammalian neural stem cells, deposit neurons and also glia through INPs. The consecutively born INPs in a given lineage produce morphologically distinct progeny, presumably due to their inheritance of different temporal factors from the INP-producing progenitor. To uncover the underlying temporal fating mechanisms, we profiled type II neuroblasts' transcriptome across time. Our results reveal opposing temporal gradients of Imp and Syp RNA-binding proteins (descending and ascending, respectively). Maintaining high Imp throughout serial INP production expands the number of neurons/glia with early temporal fate at the expense of cells with late fate. Conversely, precocious upregulation of Syp reduces the number of cells with early fate. Further, we reveal that the transcription factor, Seven-up initiates progression of the Imp/Syp gradients. Interestingly, neuroblasts apparently locked in their beginning Imp/Syp levels can still yield progeny with a small range of early fates. We propose that the Seven-up-initiated Imp/Syp gradients create coarse temporal windows within type II neuroblasts to pattern INPs, which subsequently undergo fine-tuned subtemporal patterning.
2018-01-23 | GSE94445 | GEO
Project description:Neural stem cells (NSCs) generate highly diverse neurons over time by acquiring new features, a phenomenon called as temporal patterning. However the mechanisms underlying temporal patterning still remains poorly understood. Here, we describe a method that allows to isolate different temporal stages of Drosophila transit amplifying cells called intermediate neural porgenitors (INPs). We identified odd-paired (opa) as the regulator of the transition from first to second temporal stages, which are defined by D and Grh expression. We demonstrated that opa is required for correct neural output and brain morphology. We showed that opa achieves this transition via repressing D. Together with upstream SWI/SNF complex, D and opa forms an incoheren feed forward loop, which results in successive expression of temporal identities.
2019-07-29 | GSE127516 | GEO
Project description:The brain consists of hundreds or thousands of different neuronal types that are generated through multiple divisions of neuronal stem cells. These stem cells have the capacity to generate different neuronal types at different stages of their development. In Drosophila, this temporal patterning is driven by the successive expression of temporal transcription factors (tTFs). While a number of tTFs are known in different animals and across various parts of the nervous system, these have been mostly identified by informed guesses and antibody availability. We used single-cell mRNA sequencing to identify the likely complete series of tTFs that specify most Drosophila medulla neurons in the optic lobe. We tested the genetic interactions among these tTFs. While we verify the general principle that tTFs regulate the progression of the series by activating the next tTFs in the series and repressing the previous ones, we also identify more complex regulations. Two of the tTFs, Eyeless and Dichaete, act as hubs integrating the input of several upstream tTFs before allowing the series to progress and in turn regulating the expression of several tTFs. Moreover, we show that tTFs not only specify neuronal identity but also control subsequent neuronal differentiation. We find that terminal differentiation genes, such as neurotransmitter-related genes, are present as transcripts, but not as proteins, in immature larval neurons days before they are being used in functioning neurons; we show that these mechanisms are conserved in humans. Our results offer a comprehensive description of a temporal series of tTFs in a neuronal system, offering mechanistic insights into the regulation of the progression of the series and the regulation of neuronal diversity. This represents a proof-of-principle for the use of single-cell mRNA sequencing for the comparison of temporal patterning across phyla that can lead to an understanding of how the human brain develops and how it has evolved.
2022-01-01 | GSE167266 | GEO
Project description:Generating diverse neurons involves spatially distinct neural stem cells that show age dependent developmental fates. Drosophila neuroblasts produce long, diverse yet stereotyped series of distinct neurons, called lineages. We searched for novel temporal factors that could pattern such extended lineages by RNA-sequencing of specific neuroblasts at various developmental times. We found that two RNA-binding proteins, Imp and Syp, display opposing high-to-low and low-to-high temporal gradients with distinct dynamics in specific lineages. Manipulating Imp/Syp levels in mushroom body neuroblasts revealed opposing roles in the specification of early and late temporal fates, primarily via regulation of Chinmo translation. This study implicates the opposing Imp/Syp gradients as temporal morphogens that encode stem cell age and govern birth time-dependent offspring cell fate through post-transcriptional regulation of temporal dentity genes.
2015-10-21 | GSE71103 | GEO
Project description: Not available
| S-EPMC7377279 | biostudies-literature
Project description:The process that partitions the nascent vertebrate central nervous system into forebrain, midbrain, hindbrain, and spinal cord after neural induction is of fundamental interest in developmental biology, and is known to be dependent on Wnt/beta-catenin signaling at multiple steps. Neural induction specifies neural ectoderm with forebrain character that is subsequently posteriorized by graded Wnt signaling: embryological and mutant analyses have shown that progressively higher levels of Wnt signaling induce progressively more posterior fates. However, the mechanistic link between Wnt signaling and the molecular subdivision of the neural ectoderm into distinct domains in the anteroposterior (AP) axis is still not clear. To better understand how Wnt mediates neural AP patterning, we performed a temporal dissection of neural patterning in response to manipulations of Wnt signaling in zebrafish. We show that Wnt-mediated neural patterning in zebrafish can be divided into three phases: (I) a primary AP patterning phase, which occurs during gastrulation, (II) a mes/r1 (mesencephalon-rhombomere 1) specification and refinement phase, which occurs immediately after gastrulation, and (III) a midbrain-hindbrain boundary (MHB) morphogenesis phase, which occurs during segmentation stages. A major outcome of these Wnt signaling phases is the specification of the major compartment divisions of the developing brain: first the MHB, then the diencephalic-mesencephalic boundary (DMB). The specification of these lineage divisions depends upon the dynamic changes of gene transcription in response to Wnt signaling, which we show primarily involves transcriptional repression or indirect activation. We show that otx2b is directly repressed by Wnt signaling during primary AP patterning, but becomes resistant to Wnt-mediated repression during late gastrulation. Also during late gastrulation, Wnt signaling becomes both necessary and sufficient for expression of wnt8b, en2a, and her5 in mes/r1. We suggest that the change in otx2b response to Wnt regulation enables a transition to the mes/r1 phase of Wnt-mediated patterning, as it ensures that Wnts expressed in the midbrain and MHB do not suppress midbrain identity, and consequently reinforce formation of the DMB. These findings integrate important temporal elements into our spatial understanding of Wnt-mediated neural patterning and may serve as an important basis of a better understanding of neural patterning defects that have implications in human health.
2020-02-29 | GSE146124 | GEO