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Full Abstracts – IMMUNITY AND PATHOGENESIS
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Calcium signaling plays a role in Drosophila cellular immunity and is antagonized by parasitoid wasp venom.
Nathan T. Mortimer, Todd A. Schlenke.
Department of Biology, Emory University, Atlanta, GA.
Drosophila larvae are targeted by a wide range of parasitoid wasps, and mount a robust cellular immune response following parasitization. Parasitoids
attempt to counteract this response by the co-injection of immunomodulatory venom proteins. Thus, identification of wasp venom proteins may allow for a
better understanding of both parasite virulence and host response. We have focused on an uncharacterized parasitoid wasp species of the genus Ganaspis,
caught in southern Florida (and referred to as GanFl). GanFl is a generalist of Drosophila species and has immunosuppressive venom. We used a combined
transcriptomic/proteomic approach to identify GanFl venom proteins and discovered the presence of a highly abundant Serca-type ATPase pump.
Endogenous Serca ATPases regulate ion homeostasis by pumping calcium from the cytosol into ER stores. The presence of such a calcium pump in GanFl
venom led us to hypothesize that the fly cellular immune response may require cytosolic calcium signaling and that this may serve as a target of GanFl
venom activity. We find that intracellular calcium levels are elevated in fly immune cells following parasitization and that this appears to be required to
mount a successful immune response. Further, we find evidence that the virulence mechanism of GanFl is at least partially dependent on its ability to
antagonize calcium signaling in fly immune cells.
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Beta-arrestin Kurtz regulates
Drosophila
Toll signaling and immune system homeostasis through an interaction with SUMO protease Ulp1.
Wenjian
Xu
1
, Saima G. Anjum
1
, Niusha Nikkholgh
1
, Sukanya Basu
1
, Mary Thomas
1
, Tony Ip
2
, Alexey Veraksa
1
. 1) Biology Department, University of
Massachusetts Boston, Boston, MA; 2) Program in Molecular Medicine, UMass Medical School, Worcester, MA.
Our previous studies implicated the
Drosophila
β-arrestin Kurtz (Krz) in the regulation of Toll signaling in the early embryo. Here we extend these studies
to probe the role of Krz in Toll regulation at the larval stages.
krz
mutants and RNAi knockdown animals show increased lamellocyte production, melanotic
mass formation, as well as Dorsal and Dif nuclear localization, suggesting that loss of
krz
results in an upregulation of Toll signaling. Proteomic surveys and
follow-up studies of Krz binding partners have identified Ulp1, a SUMO protease, as a direct Krz interactor. RNAi knockdown of
Ulp1
results in even
stronger phenotypes than loss of
krz
. RT-PCR analysis demonstrated that
Drosomycin
expression is increased in both
krz
mutants and
Ulp1
knockdown
animals. Furthermore,
krz
and
Ulp1
show dosage-sensitive synergistic genetic interactions, which suggests that these two proteins are involved in the same
pathway. Because Ulp1 normally functions as a SUMO deconjugating enzyme, we tested whether Krz plays a role in protein sumoylation. Our studies of
Dorsal sumoylation show that altering Krz levels can affect the efficiency of SUMO deconjugation mediated by Ulp1. Our data suggest that both Krz and
Ulp1 are required for maintaining a precise level of Dorsal sumoylation, which can affect Dorsal activity in the Toll pathway and ultimately regulate larval
immune system homeostasis.
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Drosophila
immune responses to entomopathogenic nematodes and their mutualistic bacteria.
Julio César Castillo, Ioannis Eleftherianos. Department
of Biological Sciences, The George Washington University, Washington DC 20052.
Drosophila melanogaster
has been established as an excellent genetic and genomic model to investigate host-pathogen interactions and innate immune
defense mechanisms. To date, most information on the innate immune response in Drosophila derives from studies that involves bacterial, fungal and viral
pathogens. However, immune reactions to insect parasitic nematodes (entomopathogenic) are still not well understood. The nematode
Heterorhabditis
bacteriophora
lives in symbiosis with the entomopathogenic bacteria
Photorhabdus luminescens
that together are able to invade and kill insects.
Interestingly, these nematode parasites are viable in the absence of their mutualistic bacteria. Although the pathogenicity of
Heterorhabditis
nematodes has
been attributed almost exclusively to the toxins and virulence factors produced by
Photorhabdus
, little is known about the contribution of the nematode
vector to the pathology observed in insects. We have recently developed a method for infecting
Drosophila
adult flies with
Heterorhabditis
nematodes that
contain (symbiotic worms) or lack (axenic worms)
Photorhabdus
. We have used this assay to show that axenic and symbiotic nematodes are equally
pathogenic towards wild-type adult flies. We have further identified which particular immune pathways are activated in
Drosophila
adults following immune
recognition of
Heterorhabditis
nematodes with or without mutualistic
Photorhabdus
and documented the signaling genes that participate in these processes.
Our results generate for the first time fundamental information on the immune detection, interaction and transcriptional regulation of immune signaling
pathways, and activation of effector mechanisms by which
Drosophila
responds to natural insect pathogens, such as the
Heterorhabditis
-
Photorhabdus
complex. Finally, our data suggest that the parasitic nematode
Heterorhabditis
can induce severe pathological effects on
Drosophila
adult flies, and provide
important clues on how two pathogens can come together to exploit a common host.