Ras is Required for Toll Signaling in the Drosophila Embryo

AbstractThe evolutionarily conserved Toll signaling pathway controls innate immunity across phyla and embryonic patterning in insects. In the Drosophila embryo Toll is required to establish gene expression domains along the dorsal-ventral axis. Pathway activation induces degradation of the IκB inhibitor Cactus resulting in a nuclear gradient of the NFκB effector Dorsal. Here we investigate how cactus modulates Toll signals through its effects on the Dorsal gradient and Dorsal target genes. Quantitative analysis using a series of loss and gain-of-function conditions shows that the ventral and lateral aspects of the Dorsal gradient behave differently respective to Cactus fluctuations. Unexpectedly, Cactus favors Dorsal nuclear localization required as response to high Toll signals at the ventral side of the embryo. Furthermore, N-terminal deleted Cactus mimics these effects, indicating that the ability of Cactus to favor Toll stems from mobilization of a free Cactus pool induced by the Calpain A protease. These results indicate that unexplored mechanisms are at play to ensure a correct response to high Toll signals.Summary:The IκB protein Cactus favors high Toll signals, revealing that the ventral and lateral aspects of the Dorsal/NFκB nuclear gradient behave differently respective to Cactus concentrations in the Drosophila embryo.

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sog and dpp exert opposing maternal functions to modify toll signaling and pattern the dorsoventral axis of the Drosophila embryo

Development ◽

10.1242/dev.127.16.3631 ◽

2000 ◽

Vol 127 (16) ◽

pp. 3631-3644

Author(s):

H. Araujo ◽

E. Bier

Keyword(s):

Pattern Formation ◽

Concentration Gradient ◽

Drosophila Embryo ◽

Related Protein ◽

Nf Kappa B ◽

Dorsoventral Axis ◽

Present Evidence ◽

Toll Signaling ◽

Toll Receptor ◽

Dorsal Ectoderm

The short gastrulation (sog) and decapentaplegic (dpp) genes function antagonistically in the early Drosophila zygote to pattern the dorsoventral (DV) axis of the embryo. This interplay between sog and dpp determines the extent of the neuroectoderm and subdivides the dorsal ectoderm into two territories. Here, we present evidence that sog and dpp also play opposing roles during oogenesis in patterning the DV axis of the embryo. We show that maternally produced Dpp increases levels of the I(kappa)B-related protein Cactus and reduces the magnitude of the nuclear concentration gradient of the NF(kappa)B-related Dorsal protein, and that Sog limits this effect. We present evidence suggesting that Dpp signaling increases Cactus levels by reducing a signal-independent component of Cactus degradation. Epistasis experiments reveal that sog and dpp act downstream of, or in parallel to, the Toll receptor to reduce translocation of Dorsal protein into the nucleus. These results broaden the role previously defined for sog and dpp in establishing the embryonic DV axis and reveal a novel form of crossregulation between the NF(kappa)B and TGF(beta) signaling pathways in pattern formation.

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Spätzle regulates the shape of the Dorsal gradient in the Drosophila embryo

Development ◽

10.1242/dev.128.12.2309 ◽

2001 ◽

Vol 128 (12) ◽

pp. 2309-2319 ◽

Cited By ~ 1

Author(s):

Donald Morisato

Keyword(s):

Drosophila Embryo ◽

Single Peak ◽

Egfr Signaling ◽

Toll Signaling ◽

Perivitelline Fluid

Dorsal-ventral polarity of the Drosophila embryo is established by a nuclear gradient of Dorsal protein, generated by successive gurken-Egfr and spätzle-Toll signaling. Overexpression of extracellular Spätzle dramatically reshapes the Dorsal gradient: the normal single peak is broadened and then refined to two distinct peaks of nuclear Dorsal, to produce two ventral furrows. This partial axis duplication, which mimics the ventralized phenotype caused by reduced gurken-Egfr signaling, arises from events in the perivitelline fluid of the embryo and occurs at the level of Spätzle processing or Toll activation. The production of two Dorsal peaks is addressed by a model that invokes action of a diffusible inhibitor, which is proposed to normally regulate the slope of the Dorsal gradient.

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The protein kinase Pelle mediates feedback regulation in the Drosophila Toll signaling pathway

Development ◽

10.1242/dev.128.23.4729 ◽

2001 ◽

Vol 128 (23) ◽

pp. 4729-4736 ◽

Cited By ~ 1

Author(s):

Par Towb ◽

Andreas Bergmann ◽

Steven A. Wasserman

Keyword(s):

Protein Kinase ◽

Immunofluorescence Microscopy ◽

Nuclear Translocation ◽

Adaptor Protein ◽

Feedback Regulation ◽

Kinase Domain ◽

Drosophila Embryo ◽

Confocal Immunofluorescence Microscopy ◽

Toll Signaling ◽

Confocal Immunofluorescence

Dorsoventral polarity in the Drosophila embryo is established through a signal transduction cascade triggered in ventral and ventrolateral regions. Activation of a transmembrane receptor, Toll, leads to localized recruitment of the adaptor protein Tube and protein kinase Pelle. Signaling through these components directs degradation of the IκB-like inhibitor Cactus and nuclear translocation of the Rel protein Dorsal. Here we show through confocal immunofluorescence microscopy that Pelle functions to downregulate the signal-dependent relocalization of Tube. Inactivation of the Pelle kinase domain, or elimination of the Tube-Pelle interaction, dramatically increases Tube recruitment to the ventral plasma membrane in regions of active signaling. We also characterize a large collection of pelle alleles, identifying the molecular lesions in these alleles and their effects on Pelle autophosphorylation, Tube phosphorylation and Tube relocalization. Our results point to a mechanism operating to modulate the domain or duration of signaling downstream from Tube and Pelle.

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Laser scanning confocal microscopic analysis of cytoskeletal and nuclear reorganization in live Drosophila embryos

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100146710 ◽

1993 ◽

Vol 51 ◽

pp. 174-175

Author(s):

William Theurkauf

Keyword(s):

Laser Scanning ◽

Microscopic Analysis ◽

Large Cell ◽

Early Embryo ◽

Drosophila Embryo ◽

Cortical Actin ◽

Nuclear Reorganization ◽

Cytoskeletal Elements ◽

Microtubule Structure ◽

Drosophila Embryos

Cell division in eucaryotes depends on coordinated changes in nuclear and cytoskeletal components. In Drosophila melanogaster embryos, the first 13 nuclear divisions occur without cytokinesis. During the final four divisions, nuclei divide in a uniform monolayer at the surface of the embryo. These surface divisions are accompanied by dramatic changes in cortical actin and microtubule structure (Karr and Alberts, 1986), and inhibitor studies indicate that these changes are essential to orderly mitosis (Zalokar and Erk, 1976). Because the early embryo is syncytial, fluorescent probes introduced by microinjection are incorporated in structures associated with all of the nuclei in the blastoderm. In addition, the nuclei divide synchronously every 10 to 20 min. These characteristics make the syncytial blastoderm embryo an excellent system for the analysis of mitotic reorganization of both nuclear and cytoskeletal elements. However, the Drosophila embryo is a large cell, and resolution of cytoskeletal filaments and nuclear structure is hampered by out-of focus signal.

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