At the heart of DNA Improving research methods enable scientists to explore the genome in ever-greater detail, revealing unexpected forms of chromosome organization and gene regulation. Drosophila are model organisms widely used in biology, especially in genetics. Chromosomes tied up in knots ------------------------------------------------------------------------------------------------------------------------------------------- French researchers working in collaboration with a US team have discovered a new rule for the spatial organization of chromosomes, which are highly-condensed DNA structures found in cell nuclei. DNA in chromosomes is coiled up, forming a series of “balls of string” ranging in size from 100,000 to one million base pairs (known as A, C, G and T bases). Moreover, the balls of string isolate certain groups of genes that play a concerted role not only during key stages of embryo development but also at the adult age. In addition, these balls contain so-called regulatory sequences that, rather like switches, can control and coordinate the activity of the genes they are in contact with. This discovery sheds light on a genetic puzzle by showing how an alteration in one region of the genome can affect the expression of genes located several tens or even thousands of base pairs away. Nature April 2012 online 3D mapping of chromosomes For the first time, French and Israeli researchers have revealed the detailed three-dimensional architecture of chromosomes. By using an improved very-high-throughput genetic analysis technique, they have identified 118 million contact points between chromosomes in the Drosophila genome. They have also succeeded in producing highly-detailed interaction maps showing that chromosomes are organized into 1,169 either active or inactive domains, each containing one or more genes. This work should improve understanding of the impact of the 3D organization of chromosomes on genome expression. Cell January 2012 online 16 Sequencing a single DNA molecule by stretching it out A French-US experiment has demonstrated the feasibility of a novel DNA sequencing technique based on mechanical methods applied to the molecule. By pulling on both ends of a DNA fragment folded up in the form of a hairpin, it is possible to unzip the molecule and get it to hybridize with short sequences of complementary DNA, which temporarily prevents it from zipping up again. By measuring its length when it is blocked, the position of the hybrids can be determined. Nature Methods March 2012 A year at CNRS 2012
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