Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Selfish gene may undermine genome police

05.03.2013
Biologists have been observing the “selfish” genetic entity segregation distorter (SD) in fruit flies for decades. Its story is a thriller among molecules, in which the SD gene destroys maturing sperm that have a rival chromosome. A new study reveals a tactic that gives SD’s villainy an extra edge.

For a bunch of inanimate chemical compounds, the nucleic and amino acids caught up in the infamous “selfish” segregation distorter (SD) saga have put on quite a soap opera for biologists since the phenomenon was discovered in fruit flies 50 years ago. A new study, a highlight in the March issue of the journal Genetics, provides the latest plot twist.


A subcellular life and death struggle
Healthy spermatids (maturing sperm) of a fly, left, are decimated in a setting dominated by a “segregation distorter,” right. A runaway snippet of code that rapidly copies itself helps target spermatids for fatal attacks. Credit: Reenan lab/Brown University

In TV listings the series would be described this way: “A gene exploits a rival gene’s excesses, sabotaging any sperm that bear a rival’s chromosome.” The listing is not an exaggeration except for ascribing malicious intent to strings of biochemicals. When male flies make their sperm, the SD gene (call it “A”) manages to rig meiosis — the specialized cell division that makes sex cells — so that maturing sperm that bear chromosomes with the susceptible allele (call that one “a”) end up defective and discarded. They never even leave the testes.

It is murder of a sort. Similar selfish systems occur in mammals, including humans.

In the Genetics study conducted at Brown University, scientists uncover new clues about how the SD gene might be gaming the system against “a.” It’s a plot so fiendish, only an aggregation of genetic bases could evolve it. It also deepens biologists’ understanding of an instance in which life violates a fundamental balance predicted by the father of genetics, Gregor Mendel.

“Mendel’s first law is that different alleles of a gene will segregate,” said Robert Reeenan, professor of biology and the study’s senior author. “If we have two alleles — big A and little a — then Mendel says 50 percent of the sperm at random will get the big A and 50 percent of the sperm will get the little a. But some SD (A) alleles are so strong they pretty much kill off all the non-SD (a) chromosomes.

“This is a real cheater, a real stinker,” Reenan said. “Most genes, like most people, are good upstanding citizens, but some genes want to hog all the resources, hog all the benefit.”

The SD backstory

What makes the “a” allele susceptible to SD’s subterfuge is the number of copies it harbors of a runaway snippet of genetic code called Responder. A few copies of Responder are no problem, but hundreds of copies make “a” susceptible. Some alleles have thousands of copies and only one in a thousand survives.

Genomes try to root out parasites like Responder by creating and dispatching proteins into the nucleus and the cytoplasm. These police proteins are armed with “police sketches” of the parasites in the form of small RNA transcripts.

The new plot twist

It struck Reenan and lead author Selena Gell that this policing system — because it targets self-copiers like Responder — might somehow have a role in the SD saga. They decided to find out by purposely perturbing the system.

In the experiments described in Genetics, Reenan and Gell show that engineered mutations in the police gene named Aubergine (others on the force in the experiments are called Piwi, Squash, and Zucchini) amplify SD chromosomes’ success in eliminating Responder-laden sperm, compared to that of SD chromosomes without Aubergine’s help. The results show that this police system suppresses Responder, and therefore SD. It also means that if SD somehow can upset the policing system, it can have a field day.

“We’re the first to have experimentally shown that mutations in the system can modify the degree of distortion,” Reenan said. “We used homologous recombination to knock in a mutation specifically on the SD chromosome to compromise Aubergine, and that’s exactly what we saw: the chromosome became more selfish.”

Reenan and Gell did not go so far as to determine whether known SD-promoting genes called Enhancer of SD, Stabilizer of SD, and Modifier of SD act by interfering with Aubergine or its buddies on the force, but Reenan said that is among the next things his group will look into.

In the meantime, he reflects, it may not be entirely fair for biologists to label SD as “selfish” and not Responder as well. As an out-of-control self-repeater in the genome, Responder is surely no prize, and SD performs something of a service by taking it out when it can.

The whole story is really a clash of the selfish. “Humans, flies, all of us have been attacked for millennia by selfish genetic elements that want to make as many copies as possible,” Reenan said.

Sometimes, as in SD flies, there are no apparent ill effects, but when the selfish genes come in the form of viruses or other kinds of transposons, there can be trouble. So investigating the tactics of selfish genes is not merely the stuff of biological soap operas.

Gell, who was supported by a National Science Foundation Predoctoral Fellowship during the research, is now a postdoctoral scholar at Harvard University.

Editors: Brown University has a fiber link television studio available for domestic and international live and taped interviews, and maintains an ISDN line for radio interviews. For more information, call (401) 863-2476.

David Orenstein | EurekAlert!
Further information:
http://www.brown.edu

Further reports about: Little Brown Bats Responder SELFISH amino acid chromosomes

More articles from Life Sciences:

nachricht Closing in on advanced prostate cancer
13.12.2017 | Institute for Research in Biomedicine (IRB Barcelona)

nachricht Visualizing single molecules in whole cells with a new spin
13.12.2017 | Wyss Institute for Biologically Inspired Engineering at Harvard

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

Im Focus: Successful Mechanical Testing of Nanowires

With innovative experiments, researchers at the Helmholtz-Zentrums Geesthacht and the Technical University Hamburg unravel why tiny metallic structures are extremely strong

Light-weight and simultaneously strong – porous metallic nanomaterials promise interesting applications as, for instance, for future aeroplanes with enhanced...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

A whole-body approach to understanding chemosensory cells

13.12.2017 | Health and Medicine

Water without windows: Capturing water vapor inside an electron microscope

13.12.2017 | Physics and Astronomy

Cellular Self-Digestion Process Triggers Autoimmune Disease

13.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>