Biomedical Beat Blog – National Institute of General Medical Sciences
Follow the process of discovery
This image of flowers visited by a bird is made of DNA, the molecule that provides the genetic instructions for making living organisms. It shows the latest capability of a technique called DNA origami to precisely twist and fold DNA into complex arrangements, which might find future use in biomedical applications.
Continue reading “Cool Image: DNA Origami”
DNA researcher Rosalind Franklin first described an unusual form of DNA called the A-form in the early 1950s (Franklin, who died in 1958, would have turned 95 next month). New research on a heat- and acid-loving virus has revealed surprising information about this DNA form, which is one of three known forms of DNA: A, B and Z.
“Many people have felt that this A-form of DNA is only found in the laboratory under very non-biological conditions, when DNA is dehydrated or dry,” says Edward Egelman 
in a University of Virginia news release about the recent study. But considered with earlier studies on bacteria by other researchers, the new findings suggest that the A-form “appears to be a general mechanism in biology for protecting DNA.”
Over the last two decades, exciting tools have emerged that allow researchers to cut and paste specific sequences of DNA within living cells, a process called gene editing. These tools, including one adapted from a bacterial defense system called CRISPR, have energized the research community with the possibility of using them to modify human genes associated with disease.
A major barrier to testing medical applications of gene editing has been getting the proteins that do the cutting into the cells of living animals. The main methods used in the laboratory take a roundabout route: Researchers push the DNA templates for making the proteins into cells, and then the cells’ own protein factories produce the editing proteins.
Researchers led by David Liu from Harvard University are trying to cut out the middleman, so to speak, by ferrying the editing proteins, not the DNA instructions, directly into cells. In a proof-of-concept study, their system successfully delivered three different types of editing proteins into cells in the inner ears of live mice. Continue reading “Delivering Gene-Editing Proteins to Living Cells”
Chemical tags that cells attach to DNA or to DNA-packaging proteins across the genome—called epigenetic marks—can alter gene activity, or expression, without changing the underlying DNA code. As a result, these epigenetic changes can influence health and disease. But it’s a matter of debate as to whether and how certain epigenetic changes on DNA-packaging proteins can be passed from parents to their offspring.
In studies with a model organism, the worm C. elegans, researchers led by Susan Strome of the University of California, Santa Cruz, have offered new details that help resolve the debate.
Strome’s team created worms with a genetic change that knocks out the enzyme responsible for making a particular methylation mark, a type of epigenetic mark that can turn off gene expression at certain points of an embryo’s development. Then the scientists bred the knockout worms with normal ones. Looking at the chromosomes from the resulting eggs, sperm and dividing cells of embryos after fertilization, the researchers found that the methylation marks are passed from both parents to offspring. The enzyme, however, is passed to the offspring just by the egg cell. For embryos with the enzyme, the epigenetic marks are passed faithfully through many cell divisions. For those without it, the epigenetic mark can be passed through a few cell divisions.
Because all animals use the same enzyme to create this particular methylation mark, the results have implications for parent-to-child epigenetic inheritance as well as cell-to-cell inheritance in other organisms.
This work was funded in part by NIH under grants R01GM034059, T32GM008646 and P40OD010440.
Learn more:
University of California, Santa Cruz News Release
Dynamic DNA Section from The New Genetics Booklet
Many of us have some Neanderthal genes. Before Neanderthals went extinct about 30,000 years ago, they interbred with humans living in Europe and Asia. Today’s descendants of those pairings inherited about 2 percent of their genomes from the big-brained hominids.
A research group led by David Reich at Harvard Medical School recently completed an analysis to determine the extent and identity of Neanderthal DNA in modern-day human populations. The group found that many traits in present-day people—including skin characteristics and susceptibility to various diseases—can be traced to Neanderthal DNA.
It also appears that, genetically speaking, Neanderthals and humans weren’t completely compatible. Based on the uneven distribution of Neanderthal DNA in today’s genomes, the scientists concluded that many of the male offspring of Neanderthal-human unions were infertile. In the animal world, this phenomenon is known as hybrid infertility, where the offspring of a male from one subspecies and a female from another have low or no fertility.
Studying human genes passed down through Neanderthals—as well as regions of the human genome notably devoid of Neanderthal DNA—provides an increasingly complete picture of the genetic landscape that contributed to health, disease and diversity among humans today.
Learn more:
Harvard Medical School News Release
Reich Lab 