Introduction: RNAi in insect genetics and crop
protection
A decade has passed since the initial discovery of RNA
interference (RNAi) in the nematode Caenorhabditis elegans
[1], and it is now clear that double-stranded RNA
(dsRNA)-mediated gene silencing is a conserved mechanism
in many eukaryotes [2,3] (Box 1, Figure 1). Since its
initial description the technique has become a valuable tool
for functional genomics in insects, particularly in studying
gene function in the model insect Drosophila melanogaster
[4–6]. The preferred delivery methodology in the majority
of insect studies has been microinjection of nanogram
amounts of long dsRNA, synthesized in vitro, into the
insect haemoceol [7]. This method of delivery contrasts
with the situation in C. elegans, where RNAi effects can be
produced by feeding bacteria expressing dsRNA [8,9], or
even by soaking nematodes in dsRNA solution [10]. Microinjection
of dsRNA in insects was considered to be necessary
to produce RNAi effects because the complete genome
sequence for D. melanogaster (and, subsequently, for other
insects) has shown that they lack genes encoding RNAdependent
RNA polymerase (RdRP). RdRP is the enzyme
necessary for the siRNA amplification step that leads to
persistent and systemic RNAi effects [11]. The RdRP function
is defined by a characteristic domain, designated
PF05183 in the PFAM database (http://pfam.sanger.ac.uk),
that has been identified in gene products of eukaryotic
microorganisms, fungi, plants, nematodes and a
primitive vertebrate (Branchiostoma floridae – a cephalochordate)
but not in insects, molluscs or other vertebrates.
The absence of RdRP in insects predicts that any effects of
RNAi will be limited to cells that have taken up dsRNA
Introduction: RNAi in insect genetics and cropprotectionA decade has passed since the initial discovery of RNAinterference (RNAi) in the nematode Caenorhabditis elegans[1], and it is now clear that double-stranded RNA(dsRNA)-mediated gene silencing is a conserved mechanismin many eukaryotes [2,3] (Box 1, Figure 1). Since itsinitial description the technique has become a valuable toolfor functional genomics in insects, particularly in studyinggene function in the model insect Drosophila melanogaster[4–6]. The preferred delivery methodology in the majorityof insect studies has been microinjection of nanogramamounts of long dsRNA, synthesized in vitro, into theinsect haemoceol [7]. This method of delivery contrastswith the situation in C. elegans, where RNAi effects can beproduced by feeding bacteria expressing dsRNA [8,9], oreven by soaking nematodes in dsRNA solution [10]. Microinjectionof dsRNA in insects was considered to be necessaryto produce RNAi effects because the complete genomesequence for D. melanogaster (and, subsequently, for otherinsects) has shown that they lack genes encoding RNAdependentRNA polymerase (RdRP). RdRP is the enzymenecessary for the siRNA amplification step that leads topersistent and systemic RNAi effects [11]. The RdRP functionis defined by a characteristic domain, designatedPF05183 in the PFAM database (http://pfam.sanger.ac.uk),that has been identified in gene products of eukaryoticmicroorganisms, fungi, plants, nematodes and aprimitive vertebrate (Branchiostoma floridae – a cephalochordate)but not in insects, molluscs or other vertebrates.The absence of RdRP in insects predicts that any effects ofRNAi will be limited to cells that have taken up dsRNA
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