Biology Reference
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layer is also capable of generating different classes of antimicrobial peptides
(AMPs) and reactive oxygen species (ROS) locally (
Lemaitre & Hoffmann,
2007
). The hemolymph contains immune cells that can phagocytose and
isolate pathogens. Finally, the fat body is the center for humoral immunity,
where a number of conserved immune signaling pathways, including the
Toll pathway, Imd pathway, the JAK-STAT pathway, JNK, and p38 path-
ways are known to act (
Lemaitre &Hoffmann, 2007
). Here, we focus on the
role of miRNAs as local or systemic factors in the
D. melanogaster
immune
system.
6.1. miR-8
miR-8
is expressed in the fat body and has been shown to regulate the pro-
duction of AMPs (
Choi &Hyun, 2012
). In
miR-8
null flies, the basal level of
antifungal peptide Drosomycin and antimicrobial peptide Diptericin, which
is effective against Gram-negative bacteria, are increased in non-pathogen
challenged flies. The increased Drosomycin levels are observed specifically
in the fat body. Furthermore,
miR-8
flies exhibit a higher occurrence of mel-
anization, an indicator of auto-immune reaction. Genetic rescue experi-
ments introducing
miR-8
back in the fat body of null flies reduced
the elevated AMP levels, and also the incidence of melanization. Thus,
miR-8
is necessary to function to keep the basal immune activity low in non-
pathogen challenged flies, although the role of
miR-8
during pathogenic
infection remains unclear.
6.2. miR-959
964 cluster
In addition to their roles in synchronizing circadian behaviors including
feeding and metabolism, members of the
miR-959
-
964 cluster
also ensure
circadian control of immunity (
Vodala et al., 2012
). The
miR-959
-
964
clus-
ter is expressed in the pericerebral fat body, a site implicated in local immune
response (
Lee & Edery, 2008
), and the levels of many mRNAs involved in
immune functions are altered in the mutant. Cluster mutants display a tem-
porally shifted survival curve when infected with
Pseudomonas aeruginosa
(
Vodala et al., 2012
). Physiologically relevant targets of this cluster of
miRNAs remain unidentified, but may include the metallopeptidase
ance-
4
and the antifungal AMP
drosomycin
since these were identified as respon-
sive targets of the
miR-959-964 Cluster
in cell culture reporter experiments
(
Vodala et al., 2012
).
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