Crossovers and double-strand DNA breaks do not occur randomly on yeast chromosomes during meiosis, but are greatly influenced by the proximity of the chromosome’s telomere, according to research in the laboratory of Whitehead Fellow Andreas Hochwagen. This work may lead to a better understanding of developmental chromosome abnormalities and birth defects.
Meiosis is a type of cell division that produces cells with only one copy of each chromosome—spores in yeast, and eggs and sperm in higher organisms.
During meiosis, chromosome pairs line up in the middle of the cell. The chromosome pairs are then pulled apart, with complete copies of all of the chromosomes ending up at opposite sides of the cell. To ensure that the chromosomes align properly in the middle of the cell, the chromosomes crossover—swap certain sections of genes. Without the crossovers, the chromosomes could misalign and both copies of a chromosome could end up in one cell. When this happens, the cells die or suffer from severe genetic problems, such as Down syndrome.
Before a crossover can occur at a given site, both strands of a chromosome’s DNA helix must be broken. About half of these double-strand DNA breaks (DSBs) are processed to form crossovers, and the rest are resealed to restore the original chromosomes. The final number of crossovers is relatively small and scientists have long wondered how cells ensure that even the smallest chromosomes undergo at least one crossover. Indeed, in almost half of Down’s Syndrome cases, chromosome 21, one of the smallest human chromosomes, failed to form a crossover in one of the parents.
In a paper published online in Current Biology on November 29, Massachusetts Institute of Technology graduate student Hannah Blitzblau suggests that part of the answer lies in where DSBs are formed. Blitzblau has shown that these DSBs are not scattered randomly throughout the chromosomes, but occur most frequently in a specific band near telomeres, the end caps of chromosomes. When telomeres are spliced into the central part of a chromosome, this DSB “hotspot” effect is still seen at the same distance from the new telomeres.
“This is a simple mechanism for making sure that all chromosomes, even the shortest ones, have the crossovers required for meiosis,” says Blitzbau. “If the breaks occurred randomly, the smallest chromosomes often wouldn’t have any crossovers.”
In addition, Blitzblau showed that DSBs occur at high rates around the central part of the chromosome called the centromere, It was previously thought that DSBs and crossovers rarely occurred in this region.
“This is incredibly surprising,” says Hochwagen. “The chromosomes start the crossover process in the centromeres, but divert and reseal the breaks instead.”
Some of the earlier research had been done in mutant yeast strains; the Whitehead researchers say that the current work in non-mutant yeast is a more accurate representation of normal processes.
This research will help scientists understand chromosome events leading to infertility and birth defects. In addition, although this work does not touch on why some cells divide improperly, Blitzblau and Hochwagen anticipate that the technologies developed for this study will allow researchers to identify sites that are sensitive to breaks caused by agents, such as certain cancer drugs. The investigators are adapting the methods used in yeast to map break-sensitive sites in mammalian cells.
Eric Bender | EurekAlert!
Structure of a mitochondrial ATP synthase
19.11.2019 | Science For Life Laboratory
Mantis shrimp vs. disco clams: Colorful sea creatures do more than dazzle
19.11.2019 | University of Colorado at Boulder
Nanooptical traps are a promising building block for quantum technologies. Austrian and German scientists have now removed an important obstacle to their practical use. They were able to show that a special form of mechanical vibration heats trapped particles in a very short time and knocks them out of the trap.
By controlling individual atoms, quantum properties can be investigated and made usable for technological applications. For about ten years, physicists have...
An international team of scientists, including three researchers from New Jersey Institute of Technology (NJIT), has shed new light on one of the central mysteries of solar physics: how energy from the Sun is transferred to the star's upper atmosphere, heating it to 1 million degrees Fahrenheit and higher in some regions, temperatures that are vastly hotter than the Sun's surface.
With new images from NJIT's Big Bear Solar Observatory (BBSO), the researchers have revealed in groundbreaking, granular detail what appears to be a likely...
The Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Dresden has succeeded in using Selective Electron Beam Melting (SEBM) to...
Carbon nanotubes (CNTs) are valuable for a wide variety of applications. Made of graphene sheets rolled into tubes 10,000 times smaller than a human hair, CNTs have an exceptional strength-to-mass ratio and excellent thermal and electrical properties. These features make them ideal for a range of applications, including supercapacitors, interconnects, adhesives, particle trapping and structural color.
New research reveals even more potential for CNTs: as a coating, they can both repel and hold water in place, a useful property for applications like printing,...
If you've ever tried to put several really strong, small cube magnets right next to each other on a magnetic board, you'll know that you just can't do it. What happens is that the magnets always arrange themselves in a column sticking out vertically from the magnetic board. Moreover, it's almost impossible to join several rows of these magnets together to form a flat surface. That's because magnets are dipolar. Equal poles repel each other, with the north pole of one magnet always attaching itself to the south pole of another and vice versa. This explains why they form a column with all the magnets aligned the same way.
Now, scientists at ETH Zurich have managed to create magnetic building blocks in the shape of cubes that - for the first time ever - can be joined together to...
15.11.2019 | Event News
15.11.2019 | Event News
05.11.2019 | Event News
19.11.2019 | Life Sciences
19.11.2019 | Physics and Astronomy
19.11.2019 | Health and Medicine