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Williams, Michael
Publications (4 of 4) Show all publications
Williams, M., Habayeb, M. & Hultmark, D. (2007). Reciprocal regulation of Rac1 and Rho1 in Drosophila circulating immune surveillance cells.. J Cell Sci, 120(Pt 3), 502-11
Open this publication in new window or tab >>Reciprocal regulation of Rac1 and Rho1 in Drosophila circulating immune surveillance cells.
2007 (English)In: J Cell Sci, ISSN 0021-9533, Vol. 120, no Pt 3, p. 502-11Article in journal (Refereed) Published
Abstract [en]

In many cell types it is evident that the small GTPases Rac and Rho regulate each other's activities. What is unclear is exactly how this regulation occurs. To further elucidate this interaction we examined the activities of Rac1 and Rho1 in Drosophila cellular immune surveillance cells. In larvae the cellular immune response involves circulating cells (hemocytes) that can be recruited from a hematopoietic organ located behind the brain, as well as a sessile population found just underneath the larval cuticle. We demonstrate for the first time that Rho-kinase activation requires both Rho1 and the Drosophila c-Jun N-terminal kinase (Basket). We also show that Rac1, via Basket, regulates Rho1 activity, possibly by inhibiting RhoGAPp190. In the reciprocal pathway, co-expression of dominant negative Rho-kinase and constitutive active Rho1 induces a Rac1-like phenotype. This induction requires the formin Diaphanous. Co-expression of dominant negative Rho-kinase and constitutive active Rho1 also induces filopodia formation, with Diaphanous enriched at the tips. The Rac1-like phenotypes, and filopodia formation, could be blocked by co-expression of dominant negative Rac1. Finally, though dominant negative Rac1 is able to block filopodia formation in the overexpression experiments, only Rac2 is necessary for filopodia formed by hemocytes after parasitization.

Keywords
Animals, Drosophila/enzymology/genetics/*immunology, Drosophila Proteins/genetics/*immunology/metabolism, Fluorescent Antibody Technique; Direct, Gene Expression Regulation; Enzymologic/*immunology, Hemocytes/cytology/enzymology/*immunology, Immunity; Cellular/immunology, JNK Mitogen-Activated Protein Kinases/immunology/metabolism, Larva, rac GTP-Binding Proteins/genetics/*immunology/metabolism, rho GTP-Binding Proteins/genetics/*immunology/metabolism
Identifiers
urn:nbn:se:umu:diva-17043 (URN)17227793 (PubMedID)
Available from: 2007-10-28 Created: 2007-10-28 Last updated: 2018-06-09Bibliographically approved
Williams, M., Wiklund, M.-L., Wikman, S. & Hultmark, D. (2006). Rac1 signalling in the Drosophila larval cellular immune response.. J Cell Sci, 119(Pt 10), 2015-24
Open this publication in new window or tab >>Rac1 signalling in the Drosophila larval cellular immune response.
2006 (English)In: J Cell Sci, ISSN 0021-9533, Vol. 119, no Pt 10, p. 2015-24Article in journal (Refereed) Published
Abstract [en]

The Drosophila larval cellular immune response involves cells (hemocytes) that can be recruited from a hematopoietic organ located behind the brain, as well as a sessile population of cells found just underneath the larval cuticle arranged in a segmental pattern. By using two Rac1 GTPase effector-loop mutants together with epistasis studies, we show that Rac1 requires the Drosophila melanogaster Jun N-terminal kinase Basket (Bsk), as well as stable actin formation to recruit the sessile hemocyte population. We show that actin stabilization is necessary for Rac1-induced hemocyte activation by lowering cofilin (encoded by the twinstar gene tsr) expression in blood cells. Removing Bsk by RNAi suppressed Rac1-induced release of sessile hemocytes. RNAi against Bsk also suppressed Rac1 induction of lamellocytes, a specialized population of hemocytes necessary for the encapsulation of invading pathogens. Furthermore, Rac1 and Bsk are involved in regulating the formation of actin- and focal adhesion kinase (FAK)-rich placodes in hemocytes. Lastly, Rac1 and Bsk are both required for the proper encapsulation of eggs from the parasitoid wasp Leptipolina boulardi. From these data we conclude that Rac1 induces Bsk activity and stable actin formation for cellular immune activation, leading to sessile hemocyte release and an increase in the number of circulating hemocytes.

Keywords
Actin Depolymerizing Factors/metabolism, Actins/biosynthesis/immunology, Animals, Cell Adhesion/immunology, Drosophila Proteins/genetics/*immunology/metabolism, Drosophila melanogaster/enzymology/*immunology/parasitology, Enzyme Induction, Fluorescent Antibody Technique/*methods, Hemocytes/cytology/enzymology/*immunology, Immunity; Cellular/immunology, JNK Mitogen-Activated Protein Kinases/immunology/metabolism, Larva, Pseudopodia/physiology, Wasps/physiology, rac GTP-Binding Proteins/genetics/*immunology/metabolism
Identifiers
urn:nbn:se:umu:diva-17049 (URN)16621891 (PubMedID)
Available from: 2007-10-28 Created: 2007-10-28 Last updated: 2018-06-09Bibliographically approved
Williams, M., Ando, I. & Hultmark, D. (2005). Drosophila melanogaster Rac2 is necessary for a proper cellular immune response.. Genes Cells, 10(8), 813-23
Open this publication in new window or tab >>Drosophila melanogaster Rac2 is necessary for a proper cellular immune response.
2005 (English)In: Genes Cells, ISSN 1356-9597, Vol. 10, no 8, p. 813-23Article in journal (Refereed) Published
Abstract [en]

It has been reported that during Drosophila embryonic development, and in cell culture, that the Rac GTPases are redundant. To better elucidate Rac function in Drosophila, we decided to study the role of Rac2 in larval cellular defense reactions against the parasitiod Leptopilina boulardi. Here we show a dramatic effect in the context of cellular immunity where, unlike embryonic development, Rac2 appears to have a non-redundant function. When an invading parasitoid is recognized as foreign, circulating hemocytes (blood cells) should recognize and attach to the egg chorion. After attachment the hemocytes should then spread to form a multilayered capsule surrounding the invader. In Rac2 mutants this process is disrupted. Immune surveillance cells, known as plasmatocytes, adhere to the parasitoid egg but fail to spread, and septate junctions do not assemble, possibly due to mislocalization of the Protein 4.1 homolog Coracle. Finally, larger cells known as lamellocytes attach to the capsule but also fail to spread, and there is a lack of melanization. From these results it appears that Rac2 is necessary for the larval cellular immune

Keywords
Animals, Cell Communication, Cell Count, Drosophila melanogaster/immunology/metabolism, Fluorescent Antibody Technique, Hemocytes/immunology, Larva/parasitology, Mutation, Phylogeny, Wasps/immunology, rac GTP-Binding Proteins/genetics/*immunology/physiology
Identifiers
urn:nbn:se:umu:diva-17052 (URN)16098145 (PubMedID)
Available from: 2007-10-28 Created: 2007-10-28 Last updated: 2018-06-09Bibliographically approved
Zettervall, C.-J., Anderl, I., Williams, M., Palmer, R., Kurucz, E., Ando, I. & Hultmark, D. (2004). A directed screen for genes involved in Drosophila blood cell activation. Proceedings of the National Academy of Sciences of the United States of America, 101(39), 14192-14197
Open this publication in new window or tab >>A directed screen for genes involved in Drosophila blood cell activation
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2004 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 101, no 39, p. 14192-14197Article in journal (Refereed) Published
Abstract [en]

An attack by a parasitic wasp activates a vigorous cellular immune response in Drosophila larvae. This response is manifested by an increased number of circulating cells, the hemocytes, and by the appearance of a specialized class of hemocyte, the lamellocytes, which participate in the encapsulation and killing of the parasite. To study the molecular mechanisms of this response, we have overexpressed different genes in the hemocytes, by using the GAL4-upstream activating sequence system and a hemocyte-specific Hemese-GAL4 driver. Multiple transgenes were tested, representing several important signaling pathways. We found that the proliferation response and the activation of lamellocyte formation are independent phenomena. A drastic increase in the number of circulating hemocytes is caused by receptor tyrosine kinases, such as Egfr, Pvr, and Alk, as well as by the downstream signaling components Ras85D and pointed, supporting the notion that the Ras-mitogen-activated protein kinase pathway regulates hemocyte numbers. In the case of Pvr and Alk, this phenotype also is accompanied by lamellocyte formation. By contrast, constitutively active hopscotch and hemipterous give massive activation of lamellocyte formation with little or no increase in total hemocyte numbers. This finding indicates that both the Jak/Stat and the Jun kinase pathways affect lamellocyte formation. Still other signals, mediated by aop(ACT), Toll(10b), and Rac1 expression, cause a simultaneous increase in lamellocyte and total cell numbers, and the same effect is seen when WNT signaling is suppressed. We conclude that the activation of a cellular response is complex and affected by multiple signaling pathways.

Place, publisher, year, edition, pages
Washington: National Academy of Sciences, 2004
Keywords
Animals, Drosophila/*genetics/*immunology/parasitology, Drosophila Proteins/genetics/metabolism, Female, Gene Expression, Hemocytes/enzymology/immunology/parasitology/*physiology, Larva/immunology/metabolism/parasitology, Male, Phenotype, Receptor Protein-Tyrosine Kinases/metabolism, Recombinant Fusion Proteins/genetics/metabolism, Signal Transduction, Transgenes/*genetics, Wasps/immunology, beta-Galactosidase/genetics, ras Proteins/metabolism
National Category
Infectious Medicine
Identifiers
urn:nbn:se:umu:diva-17054 (URN)10.1073/pnas.0403789101 (DOI)000224211400042 ()15381778 (PubMedID)
Available from: 2007-10-28 Created: 2007-10-28 Last updated: 2018-06-09Bibliographically approved
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