INTERFEROMICS

INDEX

TOPIC PAGE No.

1) INTRODUCTION 3

2) RNA INTERFERENCE 5

3) DISCOVERY 6

4) CELLULAR MECHANISM 8

5) MicroRNA 9

6) RESEARCH ARTICLES 11

7) RNAI SYSTEM IS AN IN VITRO TRANSCRIPTION SYSTEM 11

8) HIGH-THROUGHPUT RNAI SCREENING IN CULTURED 11

CELLS: A USER’S GUIDE

9) CONCLUSION 14

10) REFERENCE 15

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INTRODUCTION:

Interferomics is a the study of biological events that take place post-transcriptomic pre-translatomically.

It defines one of many levels in an emerging field of Life sciences known as Systems Biology. Systems

biology is a term used to describe a number of trends in bioscience research, and a movement which

draws on those trends. Proponents describe systems biology as a biology-based inter-disciplinary study

field that focuses on complex interactions in biological systems, claiming that it uses a new perspective

(holism instead of reduction). Particularly from year 2000 onwards, the term is used widely in the

biosciences, and in a variety of contexts. An often stated ambition of systems biology is the modeling

and discovery of emergent properties, properties of a system whose theoretical description is only

possible using techniques which fall under the remit of systems biology.

According to the interpretation of Systems Biology as the ability to obtain, integrate and analyze

complex data from multiple experimental sources using interdisciplinary tools, some typical technology

platforms are:

Phenomics: Organismal variation in phenotype as it changes during its life span.

Genomics: Organismal deoxyribonucleic acid (DNA) sequence, including intra-organisamal cell

specific variation. (i.e. Telomere length variation etc.)

Epigenomics / Epigenetics: Organismal and corresponding cell specific transcriptomic regulating

factors not empirically coded in the genomic sequence. (i.e. DNA methylation, Histone Acetelation

etc.).

Transcriptomics: Organismal, tissue or whole cell gene expression measurements by DNA microarrays

or serial analysis of gene expression.

Interferomics: Organismal, tissue, or cell level transcript correcting factors (i.e. RNA interference)

Translatomics / Proteomics: Organismal, tissue, or cell level measurements of proteins and peptides

via two-dimensional gel electrophoresis, mass spectrometry or multi-dimensional protein identification

techniques (advanced HPLC systems coupled with mass spectrometry). Sub disciplines include

phosphoproteomics, glycoproteomics and other methods to detect chemically modified proteins.

Metabolomics: Organismal, tissue, or cell level measurements of all small-molecules known as

metabolites.

Glycomics: Organismal, tissue, or cell level measurements of carbohydrates.

Lipidomics: Organismal, tissue, or cell level measurements of lipids.

In addition to the identification and quantification of the above given molecules further techniques

analyze the dynamics and interactions within a cell. This includes:

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Interactomics: Organismal, tissue, or cell level study of interactions between molecules. Currently the

authoritative molecular discipline in this field of study is protein-protein interactions (PPI), although the

working definition does not pre-clude inclusion of other molecular disciplines such as those defined

here.

Fluxomics: Organismal, tissue, or cell level measurements of molecular dynamic changes over time.

Biomics: Systems analysis of the biome.

The investigations are frequently combined with large scale perturbation methods, including gene-based

(RNAi, mis-expression of wild type and mutant genes) and chemical approaches using small molecule

libraries. Robots and automated sensors enable such large-scale experimentation and data acquisition.

These technologies are still emerging and many face problems that the larger the quantity of data

produced, the lower the quality. A wide variety of quantitative scientists (computational biologists,

statisticians, mathematicians, computer scientists, engineers, and physicists) are working to improve the

quality of these approaches and to create, refine, and retest the models to accurately reflect observations.

The systems biology approach often involves the development of mechanistic models, such as the

reconstruction of dynamic systems from the quantitative properties of their elementary building blocks.

For instance, a cellular network can be modelled mathematically using methods coming from chemical

kinetics and control theory. Due to the large number of parameters, variables and constraints in cellular

networks, numerical and computational techniques are often used.

Other aspects of computer science and informatics are also used in systems biology. These include:

New forms of computational model, such as the use of process calculi to model biological processes

(notable approaches include stochastic π-calculus, BioAmbients, Beta Binders, BioPEPA and Brane

calculus) and constraint-based modeling. Integration of information from the literature, using

techniques of information extraction and text mining.

Development of online databases and repositories for sharing data and models, approaches to database

integration and software interoperability via loose coupling of software, websites and databases, or

commercial suits.

Development of syntactically and semantically sound ways of representing biological models.

RNA Interference is one such cellular mechanism that falls in this category and is to-date the only

known inteferomic phenomenon. Drs Andrew Z. Fire and Craig C. Mello were awarded the Nobel Prize

in Physiology or Medicine in the year of 2006 for their collective discovery of RNA interference.

As a field of study, particularly, the study of the interactions between the components of biological

systems, and how these interactions give rise to the function and behavior of that system (for example,

the enzymes and metabolites in a metabolic pathway).

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As a paradigm, usually defined in antithesis to the so-called reductionist paradigm (biological

organisation), although fully consistent with the scientific method. The distinction between the two

paradigms is referred to in these quotations:

"The reductionist approach has successfully identified most of the components and many of the

interactions but, unfortunately, offers no convincing concepts or methods to understand how system

properties emerge...the pluralism of causes and effects in biological networks is better addressed by

observing, through quantitative measures, multiple components simultaneously and by rigorous data

integration with mathematical models" Science

"Systems biology is about putting together rather than taking apart, integration rather than reduction. It

requires that we develop ways of thinking about integration that are as rigorous as our reductionist

programmes, but different. It means changing our philosophy, in the full sense of the term" Denis Noble

As a series of operational protocols used for performing research, namely a cycle composed of theory,

analytic or computational modelling to propose specific testable hypotheses about a biological system,

experimental validation, and then using the newly acquired quantitative description of cells or cell

processes to refine the computational model or theory. Since the objective is a model of the interactions

in a system, the experimental techniques that most suit systems biology are those that are system-wide

and attempt to be as complete as possible. Therefore, transcriptomics, metabolomics, proteomics and

high-throughput techniques are used to collect quantitative data for the construction and validation of

models.

As the application of dynamical systems theory to molecular biology.

As a socioscientific phenomenon defined by the strategy of pursuing integration of complex data about

the interactions in biological systems from diverse experimental sources using interdisciplinary tools

and personnel.

This variety of viewpoints is illustrative of the fact that systems biology refers to a cluster of

peripherally overlapping concepts rather than a single well-delineated field. However the term has

widespread currency and popularity as of 2007, with chairs and institutes of systems biology

proliferating worldwide.

RNA INTERFERENCE:

RNA interference (RNAi) is a system within living cells that takes part in controlling which genes are

active and how active they are. Two types of small RNA molecules – microRNA (miRNA) and small

interfering RNA (siRNA) – are central to RNA interference. RNAs are the direct products of genes, and

these small RNAs can bind to other specific RNAs (mRNA) and either increase or decrease their

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activity, for example by preventing a messenger RNA from producing a protein. RNA interference has

an important role in defending cells against parasitic genes – viruses and transposons – but also in

directing development as well as gene expression in general.

DISCOVERY:

The discovery of RNAi was preceded first by observations of transcriptional inhibition by antisense

RNA expressed in transgenic plants, and more directly by reports of unexpected outcomes in

experiments performed by plant scientists in the United States and the Netherlands in the early 1990s. In

an attempt to alter flower colors in petunias, researchers introduced additional copies of a gene encoding

chalcone synthase, a key enzyme for flower pigmentation into petunia plants of normally pink or violet

flower color. The overexpressed gene was expected to result in darker flowers, but instead produced less

pigmented, fully or partially white flowers, indicating that the activity of chalcone synthase had been

substantially decreased; in fact, both the endogenous genes and the transgenes were downregulated in

the white flowers. Soon after, a related event termed quelling was noted in the fungus Neurospora

crassa, although it was not immediately recognized as related. Further investigation of the phenomenon

in plants indicated that the downregulation was due to post-transcriptional inhibition of gene expression

via an increased rate of mRNA degradation. This phenomenon was called co-suppression of gene

expression, but the molecular mechanism remained unknown.

Not long after, plant virologists working on improving plant resistance to viral diseases observed a

similar unexpected phenomenon. While it was known that plants expressing virus-specific proteins

showed enhanced tolerance or resistance to viral infection, it was not expected that plants carrying only

short, non-coding regions of viral RNA sequences would show similar levels of protection. Researchers

believed that viral RNA produced by transgenes could also inhibit viral replication.[143] The reverse

experiment, in which short sequences of plant genes were introduced into viruses, showed that the

targeted gene was suppressed in an infected plant. This phenomenon was labeled "virus-induced gene

silencing" (VIGS), and the set of such phenomena were collectively called post transcriptional gene

silencing.

After these initial observations in plants, many laboratories around the world searched for the

occurrence of this phenomenon in other organisms. Craig C. Mello and Andrew Fire's 1998 Nature

paper reported a potent gene silencing effect after injecting double stranded RNA into C. elegans. In

investigating the regulation of muscle protein production, they observed that neither mRNA nor

antisense RNA injections had an effect on protein production, but double-stranded RNA successfully

silenced the targeted gene. As a result of this work, they coined the term RNAi. Fire and Mello's

discovery was particularly notable because it represented the first identification of the causative agent

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for the phenomenon. Fire and Mello were awarded the Nobel Prize in Physiology or Medicine in 2006

for their work.

The RNAi pathway is found in many eukaryotes including animals and is initiated by the enzyme Dicer,

which cleaves long double-stranded RNA (dsRNA) molecules into short fragments of ~20 nucleotides.

The siRNA will be unwound into two ssRNA, namely the passenger strand and the guide strand. The

passenger strand will be degraded, and the guide strand is incorporated into the RNA-induced silencing

complex (RISC). The most well-studied outcome is post-transcriptional gene silencing, which occurs

when the guide strand base pairs with a complementary sequence of a messenger RNA molecule and

induces cleavage by Argonaute, the catalytic component of the RISC complex. This process is known to

spread systemically throughout the organism despite initially limited molar concentrations of siRNA.

The selective and robust effect of RNAi on gene expression makes it a valuable research tool, both in

cell culture and in living organisms because synthetic dsRNA introduced into cells can induce

suppression of specific genes of interest. RNAi may also be used for large-scale screens that

systematically shut down each gene in the cell, which can help identify the components necessary for a

particular cellular process or an event such as cell division. Exploitation of the pathway is also a

promising tool in biotechnology and medicine.

Historically, RNA interference was known by other names, including cosuppression, post transcriptional

gene silencing, and quelling. Only after these apparently unrelated processes were fully understood did

it become clear that they all described the RNAi phenomenon. In 2006, Andrew Fire and Craig C. Mello

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shared the Nobel Prize in Physiology or Medicine for their work on RNA interference in the nematode

worm C. elegans, which they published in 1998.

CELLULAR MECHANISM:

The dicer protein from Giardia intestinalis, which catalyzes the cleavage of dsRNA to siRNAs. The

RNase domains are colored green, the PAZ domain yellow, the platform domain red, and the connector

helix blue.RNAi is an RNA-dependent gene silencing process that is controlled by the RNA-induced

silencing complex (RISC) and is initiated by short double-stranded RNA molecules in a cell's

cytoplasm, where they interact with the catalytic RISC component argonaute. When the dsRNA is

exogenous (coming from infection by a virus with an RNA genome or laboratory manipulations), the

RNA is imported directly into the cytoplasm and cleaved to short fragments by the enzyme Dicer. The

initiating dsRNA can also be endogenous (originating in the cell), as in pre-microRNAs expressed from

RNA-coding genes in the genome. The primary transcripts from such genes are first processed to form

the characteristic stem-loop structure of pre-miRNA in the nucleus, then exported to the cytoplasm to be

cleaved by Dicer. Thus, the two dsRNA pathways, exogenous and endogenous, converge at the RISC

complex.

dsRNA cleavageEndogenous dsRNA initiates RNAi by activating the ribonuclease protein Dicer which

binds and cleaves double-stranded RNAs (dsRNAs) to produce double-stranded fragments of 20–25

base pairs with a 2 nucleotide overhang at the 3' end. Bioinformatics studies on the genomes of multiple

organisms suggest this length maximizes target-gene specificity and minimizes non-specific effects.

These short double-stranded fragments are called small interfering RNAs (siRNAs). These siRNAs are

then separated into single strands and integrated into an active RISC complex. After integration into the

RISC, siRNAs base-pair to their target mRNA and induce cleavage of the mRNA, thereby preventing it

from being used as a translation template.

Exogenous dsRNA is detected and bound by an effector protein, known as RDE-4 in C. elegans and

R2D2 in Drosophila, that stimulates dicer activity.This protein only binds long dsRNAs, but the

mechanism producing this length specificity is unknown.These RNA-binding proteins then facilitate

transfer of cleaved siRNAs to the RISC complex.

In C. elegans, this initiation response is amplified by the cell by the synthesis of a population of

'secondary' siRNAs using the dicer-produced initiating or 'primary' siRNAs as templates. These siRNAs

are structurally distinct from dicer-produced siRNAs and appear to be produced by an RNA-dependent

RNA polymerase (RdRP).

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MicroRNA

The stem-loop secondary structure of a pre-microRNA from Brassica oleracea.Main article: MicroRNA

MicroRNAs (miRNAs) are genomically encoded non-coding RNAs that help regulate gene expression,

particularly during development. The phenomenon of RNA interference, broadly defined, includes the

endogenously induced gene silencing effects of miRNAs as well as silencing triggered by foreign

dsRNA. Mature miRNAs are structurally similar to siRNAs produced from exogenous dsRNA, but

before reaching maturity, miRNAs must first undergo extensive post-transcriptional modification. An

miRNA is expressed from a much longer RNA-coding gene as a primary transcript known as a pri-

miRNA which is processed, in the cell nucleus, to a 70-nucleotide stem-loop structure called a pre-

miRNA by the microprocessor complex. This complex consists of an RNase III enzyme called Drosha

and a dsRNA-binding protein Pasha. The dsRNA portion of this pre-miRNA is bound and cleaved by

Dicer to produce the mature miRNA molecule that can be integrated into the RISC complex; thus,

miRNA and siRNA share the same cellular machinery downstream of their initial processing.

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The siRNAs derived from long dsRNA precursors differ from miRNAs in that miRNAs, especially

those in animals, typically have incomplete base pairing to a target and inhibit the translation of many

different mRNAs with similar sequences. In contrast, siRNAs typically base-pair perfectly and induce

mRNA cleavage only in a single, specific target. In Drosophila and C. elegans, miRNA and siRNA are

processed by distinct argonaute proteins and dicer enzymes.

RISC activation and catalysisThe active components of an RNA-induced silencing complex (RISC) are

endonucleases called argonaute proteins, which cleave the target mRNA strand complementary to their

bound siRNA. As the fragments produced by dicer are double-stranded, they could each in theory

produce a functional siRNA. However, only one of the two strands, which is known as the guide strand,

binds the argonaute protein and directs gene silencing. The other anti-guide strand or passenger strand is

degraded during RISC activation. Although it was first believed that an ATP-dependent helicase

separated these two strands, the process is actually ATP-independent and performed directly by the

protein components of RISC The strand selected as the guide tends to be the one whose 5' end is least

paired to its complement, but strand selection is unaffected by the direction in which dicer cleaves the

dsRNA before RISC incorporation. Instead, the R2D2 protein may serve as the differentiating factor by

binding the more-stable 5' end of the passenger strand.

The structural basis for binding of RNA to the argonaute protein was examined by X-ray

crystallography of the binding domain of an RNA-bound argonaute protein. Here, the phosphorylated 5'

end of the RNA strand enters a conserved basic surface pocket and makes contacts through a divalent

cation (an atom with two positive charges) such as magnesium and by aromatic stacking (a process that

allows more than one atom to share an electron by passing it back and forth) between the 5' nucleotide

in the siRNA and a conserved tyrosine residue. This site is thought to form a nucleation site for the

binding of the siRNA to its mRNA target.

It is not understood how the activated RISC complex locates complementary mRNAs within the cell.

Although the cleavage process has been proposed to be linked to translation, translation of the mRNA

target is not essential for RNAi-mediated degradation. Indeed, RNAi may be more effective against

mRNA targets that are not translated. Argonaute proteins, the catalytic components of RISC, are

localized to specific regions in the cytoplasm called P-bodies (also cytoplasmic bodies or GW bodies),

which are regions with high rates of mRNA decay,miRNA activity is also clustered in P-bodies.

Disruption of P-bodies decreases the efficiency of RNA interference, suggesting that they are the site of

a critical step in the RNAi process.

Transcriptional silencingComponents of the RNA interference pathway are also used in many

eukaryotes in the maintenance of the organization and structure of their genomes. Modification of

histones and associated induction of heterochromatin formation serves to downregulate genes pre-

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transcriptionally; this process is referred to as RNA-induced transcriptional silencing (RITS), and is

carried out by a complex of proteins called the RITS complex. In fission yeast this complex contains

argonaute, a chromodomain protein Chp1, and a protein called Tas3 of unknown function.As a

consequence, the induction and spread of heterochromatic regions requires the argonaute and RdRP

proteins. Indeed, deletion of these genes in the fission yeast S. pombe disrupts histone methylation and

centromere formation, causing slow or stalled anaphase during cell division.In some cases, similar

processes associated with histone modification have been observed to transcriptionally upregulate genes.

The mechanism by which the RITS complex induces heterochromatin formation and organization is not

well understood, and most studies have focused on the mating-type region in fission yeast, which may

not be representative of activities in other genomic regions or organisms. In maintenance of existing

heterochromatin regions, RITS forms a complex with siRNAs complementary to the local genes and

stably binds local methylated histones, acting co-transcriptionally to degrade any nascent pre-mRNA

transcripts that are initiated by RNA polymerase. The formation of such a heterochromatin region,

though not its maintenance, is dicer-dependent, presumably because dicer is required to generate the

initial complement of siRNAs that target subsequent transcripts. Heterochromatin maintenance has been

suggested to function as a self-reinforcing feedback loop, as new siRNAs are formed from the

occasional nascent transcripts by RdRP for incorporation into local RITS complexes. The relevance of

observations from fission yeast mating-type regions and centromeres to mammals is not clear, as

heterochromatin maintenance in mammalian cells may be independent of the components of the RNAi

pathway.

Crosstalk with RNA editing:

The type of RNA editing that is most prevalent in higher eukaryotes converts adenosine nucleotides into

inosine in dsRNAs via the enzyme adenosine deaminase (ADAR). It was originally proposed in 2000

that the RNAi and A→I RNA editing pathways might compete for a common dsRNA substrate.Indeed,

some pre-miRNAs do undergo A→I RNA editing, and this mechanism may regulate the processing and

expression of mature miRNAs. Furthermore, at least one mammalian ADAR can sequester siRNAs

from RNAi pathway components. Further support for this model comes from studies on ADAR-null C.

elegans strains indicating that A→I RNA editing may counteract RNAi silencing of endogenous genes

and transgenes.

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RESEARCH ARTICLES:

1. RNAI SYSTEM IS AN IN VITRO TRANSCRIPTION SYSTEM:

T7 RiboMAX™ Express RNAi SystemThe T7 RiboMAX™ Express RNAi System is an in vitro

transcription system designed for producing milligram amounts of double-stranded RNA (dsRNA) in a

short amount of time. The dsRNA is free of protein and other contaminants and is suitable for use in

RNA interference (RNAi) in both mammalian and nonmammalian systems.

The T7 RiboMAX™ Express RNAi System can be used to synthesize short interfering RNAs (siRNAs)

of 21bp for use in mammalian systems. siRNAs synthesized in vitro have been demonstrated to be as

effective as chemically synthesized siRNAs for inducing RNAi in mammalian cells.

In addition, the T7 RiboMAX™ Express RNAi System can be used for the synthesis of dsRNA

molecules of approximately 200bp or greater, which can be applied to nonmammalian systems. Two

complementary RNA strands are synthesized from DNA template (either plasmid or PCR product). The

resulting RNA strands are annealed after the transcription reaction to form dsRNA. Any remaining

single-stranded RNA and DNA template are removed with a nuclease digestion step. The dsRNA is then

purified by isopropanol precipitation and can be introduced into the organism of choice for RNAi

applications.

2. HIGH-THROUGHPUT RNAI SCREENING IN CULTURED CELLS: A USER’S GUIDE

RNA interference has re-energized the field of functional genomics by enabling genome-scale loss-of-

function screens in cultured cells. Looking back on the lessons that have been learned from the first

wave of technology developments and applications in this exciting field, we provide both a user’s guide

for newcomers to the field and a detailed examination of some more complex issues, particularly

concerning optimization and quality control, for more advanced users. From a discussion of cell lines,

screening paradigms, reagent types and read-out methodologies, we explore in particular the

complexities of designing optimal controls and normalization strategies for these challenging but

extremely powerful studies.

RNA interference: the new somatic cell genetics?

RNAi is evolving into a powerful tool for manipulating gene expression in mammalian cells with

potential utility for investigating gene function, for high-throughput, function-based genetic screens and

potentially for development as a therapeutic tool.

RNAi in mammals:

Given the strong conservation of RNAi-related genes in vertebrates, including Dicer and Argonaute

family members, the expectation was that RNAi would operate in mammalian cells in some capacity.

The first glimpse of RNAi in mammals came from injections of long dsRNAs (?500 nt, similar to those

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used to trigger RNAi in invertebrate systems) into mouse embryos, which resulted in sequence-specific

gene silencing. Several groups,including our own, extended these findings to embryonal cell Lines.

Biochemical and genetic evidence from these studies suggested that RNAi operates in at least a subset

of mammalian cell types, in a Dicer-dependent manner via posttranscriptional mechanisms In somatic

cells, however, the use of conventional dsRNA triggers is limited by antiviral/interferon responses,

including the PKR and RNaseL pathways, which trigger generalized translational repression and

apoptosis in response to dsRNA of >30 bp in length. Even where PKR activity is removed from somatic

cells, by either viral inhibitors or targeted disruption, long dsRNA still triggers a residual nonspecific

repression of gene expression.One way around these nonspecific dsRNA responses is to simply create

dsRNA triggers of <30 bp in length. In the past year, two short dsRNA structures have emerged, which

evoke sequence specific gene silencing in somatic cells without activating antiviral responses. These are

the small interfering RNAs (siRNAs) and the short hairpin RNAs (shRNAs). Both are modeled after

biologically active structures in the RNAi pathway:

Dicer cleavage products and small temporal RNAs, respectively.Tuschl and colleagues and Caplen and

colleagues (Elbashir et al., 2001; Caplen et al., 2001) first demonstrated that small dsRNAs, resembling

siRNAs from other systems, induce sequence-specific gene silencing when transiently transfected into

mammalian cells.These small interfering RNAs (siRNAs) are chemically synthesized emulations of

Dicer cleavage products, which are short RNA duplexes ?19 nt in length with 2 nt 3 overhangson each

strand. The siRNAs presumably bypass the requirement for Dicer and enter the silencing pathway by

incorporation into RISC complexes. The use of siRNAs has been recently reviewed, in detail, and

resources for the design and use of siRNAs are available from Tom Tuschl’s laboratory online

(http://www.mpibpc.gwdg.de/abteilungen/100/105/sirna.html). As an alternative strategy, we and

others have developed in vivo expression constructs for small dsRNA triggers in mammalian cells,

which resemble endogenously expressed hairpin RNAs (Paddison et al., 2002b; Brummelkamp et al.,

2002; Paul

et al., 2002; Sui et al., 2002;Yu et al., 2002; Zeng et al., 2002). This approach uses small inverted

repeats (19–29 nt) expressed from RNA polymerase III promoter to create short hairpin RNAs

(shRNAs), which can then be processed by Dicer and shunted into the RNAi pathway (Figure 1).

However, siRNAs can also be produced in vivo by the expression of complementary 19 or 21 nt RNAs

from separate RNA polymerase III transcription units (Lee et al., 2002; Miyagishi and Taira, 2002; Yu

et al., 2002). For some studies, expressed dsRNA triggers have potential advantages over siRNAs when

combined with well-worn strategies for stable and inducible gene expression in vitro and in vivo. The

details of these strategies are further discussed below. One of the major differences between mammalian

cell RNAi and the response observed, for example, in C. elegans is the apparent lack of amplification of

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the RNAi effect or of “transitive RNAi” (Sijen et al., 2001). In C. elegans, “amplification” may

contribute to heritable, systemic gene silencing . According to one model, amplification of the dsRNA

signal is initially mediated by RNA-dependent RNA polymerases (RdRP). An RNA degradation product

(e.g., an siRNA) may prime RdRPs along the mRNA template, resulting in the production of dsRNA

homologous to sequences 5 (i.e., upstream) of the initially targeted sequence (Sijen et al., 2001). When

combined with transport, amplification results in a self-propagating silencing effect throughout the

organism. In mammalian cell systems, however, transient transfection of RNAi triggers, e.g., long

dsRNA, siRNAs, or shRNAs, results in a transient effect, lasting 2–7 days. The longevity of silencing is

likely dependent on gene expression homeostasis (e.g., abundance of mRNA and protein, stability of the

protein, transcriptional feedback loops, etc.), the half-life of the silencing complex itself, and cell

division, which serves to dilute the effect over time.

CONCLUSION:

The field of life sciences has grown beyond leaps and bounds and since the advent of bioinformatics

many changes have taken place and led to a new dimension and view for the branch. Systems biology in

particular has revolutionized and laid much bigger platform to unravel the secrets of biology. It is a

branch which can describe new trends in bioscience research and helps in understanding the movement

of such trends.

Since 2000 the term systems biology is in the circle of biosciences and has been used in large context

and often used in the area of modeling, discovery of some properties. In technical terms it means the

examination of structure and dynamics of various functions at cellular and organismal level instead of

understanding the characteristics of isolated parts of cells.

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REFERENCE :

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