St. Jude Children's Research Hospital scientists have rewritten the job description of the protein TopBP1 after demonstrating that it guards early brain cells from DNA damage. Such damage might foreshadow later problems, including cancer.
Researchers showed that cells in the developing brain require TopBP1 to prevent DNA strands from breaking as the molecule is copied prior to cell division. Investigators also reported that stem cells and immature cells known as progenitor cells involved at the beginning of brain development are more sensitive to unrepaired DNA damage than progenitor cells later in the process. Although more developmentally advanced than stem cells, progenitor cells retain the ability to become one of a variety of more specialized neurons.
"Such DNA strand breaks have great potential for creating mutations that push a normal cell toward malignancy," said Peter McKinnon, Ph.D., a St. Jude Department of Genetics member and the paper's senior author. "When we selectively knocked out TopBP1 in mice, the amount of DNA damage we saw suggests that TopBP1 is likely to be a tumor suppressor. We are exploring that question now."
The work appeared in the April 22 online edition of the scientific journal Nature Neuroscience. The research builds on McKinnon's interest in DNA repair systems, including the enzymes ATM and ATR, which are associated with a devastating cancer-prone neurodegenerative disease in children called ataxia telangiectasia, and a neurodevelopmental disorder called Seckel syndrome.
TopBP1 was known to activate ATR. Previous laboratory research by other investigators also suggested that activation made TopBP1 indispensable for DNA replication and cell proliferation. This study, however, showed that was not the case. Most progenitor cells in the embryonic mouse brain kept dividing after investigators switched off the TopBP1 gene.
"We showed that rather than being fundamentally important for building the machinery of replication, TopBP1's role is to monitor DNA damage and act when DNA damage occurs during replication," McKinnon said. The results offer insight into normal brain development, DNA damage repair mechanisms and cancer biology.
For this study, researchers tracked the impact of TopBP1 loss in progenitor cells at different stages in the developing mouse brain. The damage was most severe when the protein was knocked out in early progenitor cells. These rapidly dividing cells yield the next generations of progenitor cells that give rise to structures in the cortex involved in memory, vision, movement and sensation. When TopBP1 was silenced in the early progenitor cells, the cortex never developed. When TopBP1 was knocked out a day or two later in progenitor cells responsible for completing brain and nervous system development, the defects were present but less severe.
The progenitor cells that were created following the loss of TopBP1 were equally riddled with broken strands of DNA. In both the early and later progenitor cells, unrepaired DNA damage switched on the p53 gene that activated the cell's suicide pathway.
Researchers used low-dose radiation to show that early progenitor cells were more sensitive to the DNA strand breaks than were progenitor cells created a day or two later. Although the cells suffered comparable damage, the damage was more likely to induce cell suicide in the earliest progenitor cells. "This raises the likelihood that there is a different threshold to DNA damage in the early-born progenitors," researchers noted.
McKinnon added: "These early progenitor cells give rise to the cells that go on to make various brain structures, so it is really important that there are no errors in the blueprint of these starting cells. These findings show that TopBP1 plays a critical role in maintaining the integrity of the genome."
TopBP1 is not the only protein responsible for repairing broken DNA strands, but this study suggests it plays a unique role. When researchers turned off two other key repair factors, the proteins Lig4 and Xrcc1, in the cortex of developing mice, the loss resulted in much less severe defects than when TopBP1 was lost.
The study's first author is Youngsoo Lee of St. Jude. The other authors are Sachin Katyal, Susanna Downing, Jingfeng Zhao and Helen Russell, also of St. Jude.
The work was supported in part by the National Institutes of Health and ALSAC. Katyal is a Neoma Boadway AP Endowed Fellow.
St. Jude Children's Research Hospital
Since opening 50 years ago, St. Jude Children's Research Hospital has changed the way the world treats childhood cancer and other life-threatening diseases. No family ever pays St. Jude for the care their child receives and, for every child treated here, thousands more have been saved worldwide through St. Jude discoveries. The hospital has played a pivotal role in pushing U.S. pediatric cancer survival rates from 20 to 80 percent overall, and is the first and only National Cancer Institute-designated Comprehensive Cancer Center devoted solely to children. It is also a leader in the research and treatment of blood disorders and infectious diseases in children. St. Jude was founded by the late entertainer Danny Thomas, who believed that no child should die in the dawn of life. To learn more, visit www.stjude.org. Follow us on Twitter @StJudeResearch.
Summer Freeman | EurekAlert!
23.03.2017 | Technische Universität München
How prenatal maternal infections may affect genetic factors in Autism spectrum disorder
22.03.2017 | University of California - San Diego
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
23.03.2017 | Life Sciences
23.03.2017 | Power and Electrical Engineering
23.03.2017 | Earth Sciences