No abstract

Many bacteria live as intracellular symbionts, causing persistent infections within insects. One extraordinarily common infection is that of Wolbachia pipientis, which infects 40% of insect species and induces reproductive effects. The bacteria are passed from generation to generation both vertically (through the oocyte) and horizontally (by environmental transmission). Maintenance of the infection within Drosophila melanogaster is sensitive to the regulation of actin, as Wolbachia inefficiently colonizes strains hemizygous for the profilin or villin genes. Therefore, we hypothesized that Wolbachia must depend on the host actin cytoskeleton. In this study, we identify and characterize a Wolbachia protein (WD0830) that is predicted to be secreted by the bacterial parasite. Expression of WD0830 in a model eukaryote (the yeast Saccharomyces cerevisiae) induces a growth defect associated with the appearance of aberrant, filamentous structures which colocalize with rhodamine-phalloidin-stained actin. Purified WD0830 bundles actin in vitro and cosediments with actin filaments, suggesting a direct interaction of the two proteins. We characterized the expression of WD0830 throughout Drosophila development and found it to be upregulated in third-instar larvae, peaking in early pupation, during the critical formation of adult tissues, including the reproductive system. In transgenic flies, heterologously expressed WD0830 localizes to the developing oocyte. Additionally, overexpression of WD0830 results in increased Wolbachia titers in whole flies, in stage 9 and 10 oocytes, and in embryos, compared to controls, suggesting that the protein may facilitate Wolbachia’s replication or transmission. Therefore, this candidate secreted effector may play a role in Wolbachia’s infection of and persistence within host niches.

Relatively little is known about how microtubule motors are controlled or about how the functions of different cytoskeletal systems are integrated. A yeast two-hybrid screen for proteins that bind to Drosophila Enabled (Ena), an actin polymerization factor that is negatively regulated by Abl tyrosine kinase, identified kinesin heavy chain (Khc), a member of the kinesin-1 subfamily of microtubule motors. Coimmunoprecipitation from Drosophila cytosol confirmed a physical interaction between Khc and Ena. Kinesin-1 motors can carry organelles and other macromolecular cargoes from neuronal cell bodies toward terminals in fast-axonal-transport. Ena distribution in larval axons was not affected by mutations in the Khc gene, suggesting that Ena is not itself a fast transport cargo of Drosophila kinesin-1. Genetic interaction tests showed that in a background sensitized by reduced Khc gene dosage, a reduction in Abl gene dosage caused distal paralysis and axonal swellings. A concomitant reduction in ena dosage rescued those defects. These results suggest that Ena/VASP, when not inhibited by the Abl pathway, can bind Khc and reduce its transport activity in axons. INTRODUCTIONThe activities of the F-actin and microtubule cytoskeletons are linked in cellular processes such as secretion, cytokinesis, and axon outgrowth, but relatively little is known about mechanisms that coordinate the activities of the two filament systems. The nonreceptor tyrosine kinase Abl, aberrant forms of which are implicated in human leukemia, influences axon outgrowth and other F-actin-dependent processes (Woodring et al., 2003;Hernandez et al., 2004). Recent work suggests that Abl also influences microtubule polymerization in the axon growth cone via interactions with Orbit and that a mouse Abl-related protein, Arg, can crosslink F-actin with microtubules in the cell periphery (Lee et al., 2004;Miller et al., 2004). In part, the influence of Abl on F-actin-dependent processes is mediated by its regulatory interaction with Ena/VASP proteins, which can modulate actin filament length, branching pattern, and bundle formation (reviewed by Krause et al., 2003;Kwiatkowski et al., 2003). Ena/VASP proteins have three conserved regions. The N-terminal EVH1 domain (133 amino acids, Gertler et al., 1996) can bind the focal-adhesion proteins vinculin and zyxin, as well as the growth-cone guidance receptor Robo/ Sax3. The central proline-rich region can bind profilin, which facilitates the addition of G-actin monomers to F-actin plusends. It can also bind Abl and other SH3-domain proteins. The C-terminal EVH2 domain (226 amino acids, Gertler et al., 1996) has both G-and F-actin binding sites and has been shown to mediate Ena/VASP multimerization (reviewed by Krause et al., 2003;Kwiatkowski et al., 2003).In Drosophila development, Ena and Abl are known to have an antagonistic relationship. Zygotic mutations in the ena or Abl gene cause axon growth-cone guidance defects and lethality, but normal axon guidance and viability can be restored by combining ena and Ab...

The methodology outlined herein provides an approach to isolating high quality RNA from Kupffer cells, without altering the tissue integrity.

The most common intracellular bacterial infection is Wolbachia pipientis, a microbe that manipulates host reproduction and is used in control of insect vectors. Phenotypes induced by Wolbachia have been studied for decades and range from sperm-egg incompatibility to male killing. How Wolbachia alters host biology is less well understood. Previously, we characterized the first Wolbachia effector – WalE1, which encodes a synuclein domain at the N terminus. Purified WalE1 sediments with and bundles actin and when heterologously expressed in flies, increases Wolbachia titer in the developing oocyte. In this work, we first identify the native expression WalE1 by Wolbachia infecting both fly cells and whole animals. WalE1 appears as aggregates, separate from Wolbachia cells. We next show that WalE1 co-immunoprecipitates with the host protein Past1 and that WalE1 manipulates host endocytosis. Yeast expressing WalE1 show deficiency in uptake of FM4-64 dye, and flies harboring mutations in Past1 or overexpressing WalE1 are sensitive to AgNO3, a hallmark of endocytosis defects. Finally, we also show that Past1 null flies harbor more Wolbachia overall and in late egg chambers. Our results identify interactions between a Wolbachia secreted effector and a host protein and point to yet another important host cell process impinged upon by Wolbachia.