ISSN 1062-3604, Russian Journal of Developmental Biology, 2006, Vol. 37, No. 3, pp. 131–138. © Pleiades Publishing, Inc., 2006.
Original Russian Text © K.Yu. Kazachenko, P.V. Avdonin, 2006, published in Ontogenez, 2006, Vol. 37, No. 3, pp. 163–170.
RNA interference is a phenomenon of speciﬁc sup-
pression of gene expression at the level of mRNA, also
called posttranscriptional silencing, widespread in ani-
mal and plant cells. In vivo, this mechanism is used to
protect the genome against viral infections, trans-
posons, and transgenes. This phenomenon has been
described in many organisms, from protists to verte-
brates (Caplen et al., 2001; McManus and Sharp, 2002;
Zeng et al., 2002; Zou et al., 2003).
Small interfering RNA (siRNA) is an RNA duplex,
the length of each strand amounts to 21 nucleotides, on
average. Each strand carries two
residues on the
3'-end. These characteristics are extremely important
for the functioning of siRNAs as silencers and appear
as a result of the action of an evolutionarily conserva-
tive enzyme from the RNAse III family, nucleases spe-
ciﬁc for double-stranded RNA (dsRNA). Figure 1
shows a schematic diagram of the action of double-
stranded siRNA, as well as the mechanism of its forma-
tion from a longer dsRNA by means of RNAse Dicer.
SiRNAs induce sequence-speciﬁc degradation of
mRNA through interaction with iRNA-induced silenc-
ing complex (RISC). The RISC complex of mammals
includes the factor of elongation of eukaryotic transla-
tion eIF2C2, as well as proteins GEM3 and GEM4, fac-
tors containing a characteristic site of ATP binding, so-
called DEAD BOX, and fulﬁlling the function of RNA-
helicases, enzymes unwinding the double RNA strand.
The function of 3'-terminal uridils consists in interac-
tion with dinucleotide AA of target mRNA.
INVOLVEMENT OF siRNA IN DEVELOPMENT
During work on the project of
genome, a small group of the genes of small non-
coding mRNAs was found. The products of transcrip-
tion of two genes,
, were characterized
most fully. Mature transcripts of these genes, 22 nucle-
otides long, are formed via processing of characteristic
“hairpin” precursors, ca. 70 nucleotides long, by means
of Dicer, since the knockout of this enzyme led to accu-
mulation of nonprocessed products of these two genes
(Ambros, 2001; McManus et al., 2002). It was shown
by genetic analysis that both genes affect postembry-
onic development of the nematode. In nematodes,
, the early larval stages are repeated in
the adult state, while those mutant for
do not pass
the stage of molting and do not reach the adult state.
The products of this group of genes were called
“microRNAs”. MicroRNAs have many characteristics
common with those of siRNA. Similarly with siRNAs,
their precursors are processed by means of Dicer. Like
siRNAs, microRNAs are integrated in a ribonucleopro-
tein complex, similar, if not identical, to the RISC com-
plex. Moreover, it was shown that microRNA-
ble of triggering the in vitro degradation of RNA, fully
complementary in the area of interaction It turned out
were evolutionarily conservative in
practically all bilaterally symmetrical animals.
Homologs of the gene
(and of its target) were
found in insects and vertebrates. Thus, the presence of
regulatory genes of microRNAs is not a speciﬁc feature
of nematodes; this class represents a family of genes
originating from an ancestor, a small RNA gene. It is
estimated that only in nematodes, the number of
Vector Systems of RNA Interference
K. Yu. Kazachenko and P. V. Avdonin
Kol’tsov Institute of Developmental Biology, Russian Academy of Sciences, ul. Vavilova 26, GSP-1, Moscow, 119991 Russia
Received August 5, 2005; in ﬁnal form, October 13, 2005
—RNA interference is a mechanism of posttranslational (at the level of mRNA) gene silencing.
Sequence-speciﬁc mRNA degradation is realized with the help of small interfering RNAs produced by process-
ing of a precursor using Dicer, an enzyme from the RNAse III family. This mechanism is now widely used
in vitro on cultures of mammalian cells in order to elucidate functions of individual genes by gene speciﬁc
knockdown. Analogs of small interference RNAs are intensely expressed during embryogenesis. The mecha-
nism of RNA interference plays an especially important role in embryogenesis of invertebrates. Identiﬁcation
of the functions of small noncoding RNAs is essential for understanding the genetic mechanisms underlying
individual developmental stages. In order to integrate small interference RNAs in mammalian cells, various sys-
tems have been developed that allow both transient (for 48 h) and stable expression in vitro. These systems are
considered in the present review.
: RNA interference, vectors, small interfering RNAs.