(Press-News.org) Researchers at the University of California, Davis have discovered a key tool that helps sperm and eggs develop exactly 23 chromosomes each. The work, which could lead to insights into fertility, spontaneous miscarriages, cancer and developmental disorders, is published April 13 in the journal Cell.
Healthy humans have 46 chromosomes, 23 from the sperm and 23 from the egg. An embryo with the wrong number of chromosomes is usually miscarried, or develops disorders such as Down's syndrome, which is caused by an extra copy of chromosome 21.
During meiosis, the cell division process that creates sperm and eggs, matching chromosomes pair up and become connected by "crossing over" with each other, said Neil Hunter, a professor of microbiology at UC Davis and senior author of the new study.
These connections are essential for precise chromosome sorting and the formation of sperm and eggs with exactly the right numbers of chromosomes. Crossovers also play a fundamental role in evolution by allowing the chromosomes to swap chunks of DNA, introducing some variety into the next generation.
Each pair of chromosomes must contain at least one crossover. But there shouldn't be more than about two crossovers per pair, or the genome could be destabilized.
In their paper, Hunter and his colleagues describe a "missing tool" that explains how crossovers are regulated.
"There must be enzymes that ensure at least one crossover, but not too many," said Hunter, who is also a member of the UC Davis Comprehensive Cancer Center research program.
Hunter, graduate students Kseniya Zakharyevich and Shangming Tang and research associate Yunmei Ma, looked for enzymes that could cut DNA to form crossovers in yeast, which form sexual gametes, or spores, in much the same way that humans and other mammals form sperm and eggs.
"There were several good candidates, but none turned out to play a major role," Hunter said.
Then they discovered the missing tool for crossing-over: three yeast enzymes, Mlh1, Mlh3 and Sgs1, which work together to cut DNA and make crossovers.
It turns out that the human equivalents of these enzymes are well known for their role in suppressing tumors. Human MLH1 and MLH3 are mutated in an inherited form of colon cancer. BLM, the human equivalent of Sgs1, is mutated in a cancer-prone disease called Bloom's Syndrome.
"Sgs1 was the biggest surprise," Hunter said. "We previously knew it as an enzyme that unwinds DNA to prevent crossovers. Its role in making crossovers had been hidden by other enzymes that can step in when it is absent."
"While other enzymes cut DNA randomly, Mlh1-Mlh3-Sgs1 only makes crossovers. This unique activity is essential for meiosis and its discovery is a huge step forward," he said.
INFORMATION:
The work was supported by the National Institutes of Health. Hunter is an Early Career Scientist of the Howard Hughes Medical Institute.
Sex, tools and chromosomes
2012-04-13
[Attachments] See images for this press release:
ELSE PRESS RELEASES FROM THIS DATE:
Lilitab iPad Kiosk Featured at Macy's With New NBC Reality Series "Fashion Star"
2012-04-13
Who will win the big prize? Fans of the new reality series "Fashion Star" on NBC can hardly wait to find out. This unique design show offers merchandizing contracts to each week's winners, with a $6,000,000 contract as the grand prize. The winning designs are available the next day in stores, using the Lilitab iPad kiosk at select Macy's.
Supermodel Elle Macpherson hosts the program with a panel of fashion mentors: Jessica Simpson, Nicole Richie and John Varvatos. Viewers get instant gratification, and the hottest new styles, by being able to purchase their ...
Research teams discover cellular system for detecting and responding to poisons and pathogens
2012-04-13
Two Massachusetts General Hospital (MGH)-based research teams, along with a group from the University of California at San Diego, have discovered that animals have a previously unknown system for detecting and responding to pathogens and toxins. In three papers published in the journals Cell and Cell Host & Microbe, the investigators describe finding evidence that disruptions to the core functions of animal cells trigger immune and detoxification responses, along with behavioral changes.
"Viewing many diseases through the prism of this newly discovered system will eventually ...
Kinase test may yield big gains for drug-resistant cancers
2012-04-13
Chapel Hill, NC – In a paper published today in the journal Cell, a team from the University of North Carolina at Chapel Hill unveils the first broad-based test for activation of protein kinases "en masse", enabling measurement of the mechanism behind drug-resistant cancer and rational prediction of successful combination therapies.
Kinases are proteins expressed in human tissues that play a key role in cell growth, particularly in cancer. Of the 518 known human kinases, about 400 are expressed in cancers, but which ones and how many are actually active in tumors has ...
High levels of phthalates can lead to greater risk for type-2 diabetes
2012-04-13
There is a connection between phthalates found in cosmetics and plastics and the risk of developing diabetes among seniors. Even at a modest increase in circulating phthalate levels, the risk of diabetes is doubled. This conclusion is drawn by researchers at Uppsala University in a study published in the journal Diabetes Care.
"Although our results need to be confirmed in more studies, they do support the hypothesis that certain environmental chemicals can contribute to the development of diabetes," says Monica Lind, associate professor of environmental medicine at the ...
Drastic changes needed to curb most potent greenhouse gas
2012-04-13
Meat consumption in the developed world needs to be cut by 50 per cent per person by 2050 if we are to meet the most aggressive strategy, set out by the Intergovernmental Panel on Climate Change (IPCC), to reduce one of the most important greenhouse gases, nitrous oxide (N2O).
This is the finding from a new study, published today, 13 April, in IOP Publishing's Environmental Research Letters, which also claims that N2O emissions from the industrial and agricultural sectors will also need to be cut by 50 per cent if targets are to be met.
The findings have been made ...
Breakthrough discovery unveils 'master switches' in colon cancer
2012-04-13
A team of researchers at Case Western Reserve University School of Medicine have identified a new mechanism by which colon cancer develops. By focusing on segments of DNA located between genes, or so-called "junk DNA," the team has discovered a set of master switches, i.e., gene enhancer elements, that turn "on and off" key genes whose altered expression is defining for colon cancers. They have coined the term Variant Enhancer Loci or "VELs," to describe these master switches.
Importantly, VELs are not mutations in the actual DNA sequence, but rather are changes in proteins ...
Researchers call for a new direction in oil spill research
2012-04-13
Inadequate knowledge about the effects of deepwater oil well blowouts such as the Deepwater Horizon event of 2010 threatens scientists' ability to help manage and assess comparable events in future, according to an article that a multi-author group of specialists will publish in the May issue of BioScience. Even federal "rapid response" grants awarded to study the Deepwater Horizon event were far more focused on near-surface effects than on the deepwater processes that the BioScience authors judge to be most in need of more research.
The article, by a team led by Charles ...
Pride and prejudice: Pride impacts racism and homophobia
2012-04-13
A new University of British Columbia study finds that the way individuals experience the universal emotion of pride directly impacts how racist and homophobic their attitudes toward other people are.
The study, published in the April issue of Personality and Social Psychology Bulletin, offers new inroads in the fight against harmful prejudices such as racism and homophobia, and sheds important new light on human psychology.
"These studies show that how we feel about ourselves directly influences how we feel about people who are different from us," says Claire Ashton-James, ...
Determining a stem cell's fate
2012-04-13
PASADENA, Calif.—What happens to a stem cell at the molecular level that causes it to become one type of cell rather than another? At what point is it committed to that cell fate, and how does it become committed? The answers to these questions have been largely unknown. But now, in studies that mark a major step forward in our understanding of stem cells' fates, a team of researchers from the California Institute of Technology (Caltech) has traced the stepwise developmental process that ensures certain stem cells will become T cells—cells of the immune system that help ...
New research puts focus on earthquake, tsunami hazard for southern California
2012-04-13
San Francisco, April 12, 2012 -- Scientists will convene in San Diego to present the latest seismological research at the annual conference of the Seismological Society of America (SSA), April 17-19.
This year's meeting is expected to draw a record number of registrants, with more than 630 scientists in attendance, and will feature 292 oral presentations and 239 poster presentations.
"For over 100 years the Annual Meeting of SSA has been the forum of excellence for presenting and discussing exciting new developments in seismology research and operations in the U.S. ...