R RN NA A i in nt te er rf fe er re en nc ce e i in n n ne em ma at to od de es s a an nd d t th he e c ch ha an nc ce e t th ha at t f fa av vo or re ed d S Sy yd dn ne ey y
B Br re en nn ne er r
Address: Institut Jacques Monod, CNRS - Universities of Paris 7 and 6, Tour 43, 2 place Jussieu, 75251 Paris cedex 05, France.
RNA interference (RNAi), the inactivation of gene
expression by double-stranded (ds) RNA, has become a
major method of gene inactivation in the past ten years. The
fact that the trigger for RNAi is composed of dsRNA was
discovered in the nematode worm Caenorhabditis elegans .
This gene-inactivation method is far from being applicable
to all nematodes, however, especially in the external
application mode used in C. elegans. A recent paper by
Shannon et al. in BMC Molecular Biology  describes its
successful use in two Panagrolaimus species that belong to a
different nematode suborder from C. elegans. This increases
the range of nematode species over which comparative
functional genomics is in principle possible, and reinforces
the accumulating evidence that susceptibility to RNAi is
widely distributed over nematode species.
I Is s R RN NA A i in nt te er rf fe er re en nc ce e a a u un ni iv ve er rs sa al l p ph he en no om me en no on n i in n
e eu uk ka ar ry yo ot te es s? ?
RNAi was first described in plants and has now been found
in a variety of unicellular and multicellular eukaryotes. The
mechanism of inhibition entails the cleavage of the dsRNA
trigger into smaller dsRNAs of 21-23 base pairs, called small
interfering (si)RNAs, which recognize the target mRNA and
lead to its destruction. Sensitivity to long endogenous
dsRNAs may be maintained by selection against the spread
of transposons or viruses or against the spurious expression
of other repetitive sequences, all of which are likely to be
transcribed in both directions to at least some degree, and
thus to produce dsRNA.
It is a particularly convenient feature of C. elegans that it is
sensitive to external dsRNAs provided very simply either by
soaking the worms in a RNA preparation  or by feeding
them with Escherichia coli bacteria expressing dsRNA from a
plasmid , as outlined in Figure 1. Sensitivity to external
dsRNAs is thought to be required for repression of viruses,
although this remains to be directly proven in C. elegans, for
which no natural viruses are known. It requires both a
mechanism for uptake of the dsRNAs into intestinal cells,
and the spread of the interference to other cells . In C.
elegans, this phenomenon has made possible systematic gene-
inactivation screens using a library of bacteria expressing
dsRNAs against most open reading frames. Similar gene
inactivation by feeding with bacteria expressing dsRNAs is
also possible in species of flatworms and cnidarians.
A Ab bs st tr ra ac ct t
The efficiency of RNA interference varies between different organisms, even among nematodes.
A recent report of successful RNA interference in the nematode Panagrolaimus superbus in
BMC Molecular Biology has implications for the comparative study of the functional genomics of
nematode species, and prompts reflections on the choice of Caenorhabditis elegans as a model
Journal of Biology 2008, 7 7: :34
Published: 13 November 2008
Journal of Biology 2008, 7 7: :34 (doi:10.1186/jbiol97)
The electronic version of this article is the complete one and can be
found online at http://jbiol.com/content/7/9/34
© 2008 BioMed Central Ltd