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!
Scientists coax proteins to form synthetic structures with method that mimics nature
15.01.2019 | University of Texas at Austin
DNA library of apoid wasps published
15.01.2019 | Staatliche Naturwissenschaftliche Sammlungen Bayerns
Cellulose obtained from wood has amazing material properties. Empa researchers are now equipping the biodegradable material with additional functionalities to produce implants for cartilage diseases using 3D printing.
It all starts with an ear. Empa researcher Michael Hausmann removes the object shaped like a human ear from the 3D printer and explains:
The phenomenon of so-called superlubricity is known, but so far the explanation at the atomic level has been missing: for example, how does extremely low friction occur in bearings? Researchers from the Fraunhofer Institutes IWM and IWS jointly deciphered a universal mechanism of superlubricity for certain diamond-like carbon layers in combination with organic lubricants. Based on this knowledge, it is now possible to formulate design rules for supra lubricating layer-lubricant combinations. The results are presented in an article in Nature Communications, volume 10.
One of the most important prerequisites for sustainable and environmentally friendly mobility is minimizing friction. Research and industry have been dedicated...
Just in time for Christmas, a Mars-analogue mission in Morocco, coordinated by the Robotics Innovation Center of the German Research Center for Artificial Intelligence (DFKI) as part of the SRC project FACILITATORS, has been successfully completed. SRC, the Strategic Research Cluster on Space Robotics Technologies, is a program of the European Union to support research and development in space technologies. From mid-November to mid-December 2018, a team of more than 30 scientists from 11 countries tested technologies for future exploration of Mars and Moon in the desert of the Maghreb state.
Close to the border with Algeria, the Erfoud region in Morocco – known to tourists for its impressive sand dunes – offered ideal conditions for the four-week...
Research opens doors in photonic quantum information processing, optical signal processing and microwave photonics
Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new integrated photonics platform that can...
A team of experimentalists at the U.S. Department of Energy's Ames Laboratory and theoreticians at University of Alabama Birmingham discovered a remarkably long-lived new state of matter in an iron pnictide superconductor, which reveals a laser-induced formation of collective behaviors that compete with superconductivity.
"Superconductivity is a strange state of matter, in which the pairing of electrons makes them move faster," said Jigang Wang, Ames Laboratory physicist and...
14.01.2019 | Event News
12.12.2018 | Event News
10.12.2018 | Event News
15.01.2019 | Life Sciences
15.01.2019 | Information Technology
15.01.2019 | Materials Sciences