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

Par Towb1, Andreas Bergmann2 and Steven A. Wasserman1,*

1 Section of Cell and Developmental Biology, Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0634, USA
2 Department of Biochemistry and Molecular Biology, University of Texas, M.D. Anderson Cancer Center, Houston, Texas 77030-4095, USA



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  		Fig. 1. The Tube localization gradient is enhanced in tub2 mutant embryos. (A,B) Paired images from a wild-type embryo, showing a longitudinal optical section in the plane of the dorsoventral axis. The embryo is stained with fluorescein-conjugated antibodies to Dorsal (A) and with antibodies to Tube detected with a Cy3-conjugated secondary antibody (B). (C,D) Surface images of (C) a wild-type embryo and (D) a tub2 embryo, stained with antibodies to Tube, ventrolateral aspect. In each image, an arrow indicates the approximate position of the ventral midline.

 


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  		Fig. 2. The Tube localization gradient is enhanced in pelle mutant embryos. All images are surface views of embryos stained with antibodies to Tube detected with a Cy3-conjugated secondary antibody. (A) pll25, lateral view of the posterior pole. (B) pll078; (C) pll16; (D) pll074, composite images, lateral aspect. In each image, an arrow indicates the approximate position of the ventral midline.

 


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  		Fig. 3. Tube gradient formation is regulated at the level of the Tube/Pelle interaction. (A) dl1 embryo stained with antibodies to Tube detected with a Cy3-conjugated secondary antibody. Surface view of the anterior pole, lateral aspect. (B) Wild-type embryo stained with antibodies to Toll detected with a Cy3-conjugated secondary antibody. Surface view of the ventral aspect. (C,D) pll078 embryos stained with antibodies to Toll as above; composite images, surface view of the lateral aspect. In each image, an arrow indicates the approximate position of the ventral midline.

 


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  		Fig. 4. Biochemical characterization of selected pelle mutations. The pelle alleles that were assayed in this experiment are indicated across the top. wt, wild type. (Top panel) Phosphorylation of Tube by Pelle mutant proteins. (Middle panel) Autophosphorylation of Pelle mutant proteins. (Bottom panel) Pelle protein levels in the indicated mutant backgrounds, as assayed by immunoblotting.

 


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  		Fig. 5. Sequence alignment of Pelle with related protein kinase catalytic domains. Listed are the catalytic domains of D. melanogaster Pelle (gi|158046), Caenorhabditis elegans Pelle (gi|7505619), mouse IRAK-1 (sp|Q62406), Arabidopsis thaliana receptor kinase (gi|7488290), human FGF receptor 1 (gi|3114385, PDB: 1FGI) and human C-Jun N-terminal kinase (gi|5542282, PDB: 1JNK). Roman numerals indicate the positions of the 12 conserved subdomains found in all eukaryotic protein kinases. Red cylinders indicate alpha helices found in both the FGF-R and the JNK structure; red arrows indicate beta sheets present in both structures. Amino acids shown above the alignment indicate the substitutions found in pelle mutant alleles; pink indicates a loss-of-function allele, while red indicates a loss-of-function allele with antimorphic activity. In the alignment, residues in bold type are present in greater than 95% of kinases, residues in dark blue are present in greater than 70% of kinases, and residues in light blue are similar in greater than 50% of kinases. Residues in green are conserved in the Pelle family, but are uncommon (present in less than 15% of a broad sampling) in other eukaryotic protein kinases (Hanks and Hunter, 1995).

 


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  		Fig. 6. Model for Pelle-mediated feedback in the dorsoventral signal transduction pathway. Control is shown as passing from each protein in the cascade in a linear fashion, although it is probable that all components are present in a large signaling complex (Edwards et al., 1997; Shen and Manley, 1998; Yang and Steward, 1997). Not all components that may be acting in this cascade have been included in this diagram (Grosshans et al., 1999; Zapata et al., 2000).

 

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© The Company of Biologists Ltd 2001