Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The beak of the squid

30.07.2004


Researchers reveal Argonaute2 as the catalytic engine of mammalian RNA interference




RNA interference (RNAi) has emerged as a fundamentally important biological phenomenon and as a versatile, powerful tool for biomedical research. In organisms from fungi and flies to plants and mammals, RNAi plays a multifaceted role in molecular biology by silencing genes through chromatin remodeling, interfering with protein synthesis, and--in its best-studied mode of action--quashing gene expression by cleaving messenger RNA. Experimental applications of RNAi have spurred the exploration of gene function in many basic research, drug discovery, and clinical settings. Until now, however, the identity of the molecular scissors that carry out RNAi-mediated messenger RNA cleavage has not been revealed.

Two studies published this week in Science have resolved this mystery by establishing that Argonaute2, a signature protein component of the RNA interference machinery, provides the cutting action that carries out RNAi-mediated messenger RNA cleavage. The studies were conducted at Cold Spring Harbor Laboratory by research groups led by Greg Hannon and Leemor Joshua-Tor.


Hannon’s group focused on sorting out the functions of four mammalian Argonaute family members (Ago1, 2, 3, and 4). First, through a biochemical approach, Hannon and his colleagues found that only a single Argonaute family member, Ago2, supports the formation of mRNA cleavage-competent complexes in vitro.

To extend these biochemical findings to an in vivo setting, and to further explore the specialization of Argonaute family member function, Hannon’s group disrupted the mouse Ago2 gene by targeted insertional mutagenesis. The researchers observed an embryonic lethal phenotype and striking developmental abnormalities in Ago2 homozygotes.

All Ago2 homozygous embryos displayed defects in neural tube structure, with half of the embryos showing complete failure of neural tube closure in the head region. The embryos also had enlarged hearts and pronounced swelling of the pericardial cavity, and were severely developmentally delayed compared to their wild-type and heterozygous littermates. In contrast to the critical developmental role of Ago2 revealed by these findings, work by researchers elsewhere has shown that other Argonaute family members are dispensable for development.

Hannon and his colleagues reasoned that if Ago2 is uniquely capable of assembling into mRNA cleavage-competent complexes in vivo, then mouse cells lacking Ago2 but containing other Ago proteins should be incapable of carrying out experimentally-triggered, siRNA-mediated mRNA cleavage.

The researchers observed just such a result with Ago2-deficient mouse cells, and showed further that a plasmid encoding human Ago2 (but not Ago1) could restore siRNA-mediated mRNA cleavage to Ago2-deficient mouse cells.

Hannon’s study was consistent with the possibility that Argonaute2 provides the "Slicer" activity of RNAi-mediated mRNA cleavage. However, the possibility that a different protein provides Slicer activity could not be ruled out. Fortunately, Leemor Joshua-Tor’s group, also at Cold Spring Harbor Laboratory, was simultaneously conducting x-ray crystallographic studies of an Argonaute protein (PfAgo) from the hyperthermophilic archaebacterium, Pyrococcus furiosus.

When Joshua-Tor and her colleagues determined the crystal structure of PfAgo, they found that the PIWI domain of PfAgo belongs to the RNase H family of enzymes, whose members have RNA cleavage activity. This finding immediately implicated Argonaute itself as the protein that provides the Slicer activity of RNAi in mammals and other organisms.

Hannon and Joshua-Tor had previously shown that another domain of Argonaute proteins, the PAZ domain, recognizes the 3’ ends of siRNAs. That observation, combined with her group’s discovery that the PIWI domain of PfAgo belongs to the RNase H family, enabled Joshua-Tor to propose a model for siRNA-targeted mRNA cleavage by Argonaute (see figure).

Collectively, the two new studies establish that Argonaute2 is the catalytic engine of mammalian RNAi and provide a specific, structural mechanism for siRNA-targeted mRNA cleavage by Argonaute.

Given the role of RNA interference in a wide variety of biological processes and the intense interest in RNAi as a tool for both basic and applied research, the studies by Hannon and Joshua-Tor are a significant advance toward a comprehensive understanding of one of the most intriguing and far-reaching biological phenomena to be uncovered in recent years.

*The term "Argonaute" refers to the squid-like appearance of the leaves of Arabidopsis mutants lacking AGO1 gene function (Bohmert et al., 1998). See also the Greek myth Jason and the Argonauts and the squid, Argonauta argo.

Cold Spring Harbor Laboratory is a private, non-profit basic research and educational institution. Under the leadership of Dr. Bruce Stillman, a member of the National Academy of Sciences and a Fellow of the Royal Society (London), more than 350 scientists at the Laboratory conduct groundbreaking research in cancer, neurobiology, plant molecular genetics, genomics, and bioinformatics.

Peter Sherwood | EurekAlert!
Further information:
http://www.cshl.edu

More articles from Life Sciences:

nachricht What happens in the cell nucleus after fertilization
06.12.2016 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt

nachricht Researchers uncover protein-based “cancer signature”
05.12.2016 | Universität Basel

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Simple processing technique could cut cost of organic PV and wearable electronics

06.12.2016 | Materials Sciences

3-D printed kidney phantoms aid nuclear medicine dosing calibration

06.12.2016 | Medical Engineering

Robot on demand: Mobile machining of aircraft components with high precision

06.12.2016 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>