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Archive - Apr 11, 2012

Chromosomes Organize into “Yarns”

Chromosomes, the molecular basis of genetic heredity, remain enigmatic 130 years after their discovery in 1882 by Dr. Walther Flemming. New research published online on April 11, 2012 in Nature by the team of Edith Heard, Ph.D., from the Curie Institute and Job Dekker, Ph.D., from the University of Massachusetts Medical School (UMMS), reveals a new layer in the complex organization of chromosomes. The scientists have shown that chromosomes fold in a series of contiguous "yarns" that harbor groups of genes and regulatory elements, bringing them in contact with each other and allowing them to work in a coordinated manner during development. Chromosomes are relatively large molecules that, when spread out, can measure up to the length of an entire human arm. Despite their size, however, they are actually confined within the small space of the cell nucleus which is just a few micrometers in size. Furthermore, within each cell nucleus are multiple chromosomes. In humans, for example, there are 23 pairs of chromosomes. In order to fit all this material into this small area, chromosomes are folded, compacted, and mingled in the three-dimensional space of the nucleus. So do chromosomes fill the nucleus just like spaghetti fills a plate? "Not quite," said Elphege Nora, PhD, a post-doctoral fellow on the team of Dr. Heard, head of the Genetics and Developmental Biology Lab at the Curie Institute. "Chromosome folding follows a pattern, and this actually turns out to be important for ensuring their proper function." "We have known for decades that the DNA of individual genes is wrapped around nucleosomes to form the classical 'beads-on-a-string' structure," said Dr. Dekker, co-director of the Program in Systems Biology at UMMS.

Genes Identified for Common Childhood Obesity

Genetics researchers have identified at least two new gene variants that increase the risk of common childhood obesity. "This is the largest-ever genome-wide study of common childhood obesity, in contrast to previous studies that have focused on more extreme forms of obesity primarily connected with rare disease syndromes," said lead investigator Struan F.A. Grant, Ph.D., associate director of the Center for Applied Genomics at The Children's Hospital of Philadelphia. "As a consequence, we have definitively identified and characterized a genetic predisposition to common childhood obesity." The study, by an international collaborative group, the Early Growth Genetics (EGG) Consortium, appeared online on April 8, 2012 in Nature Genetics. As one of the major health issues affecting modern societies, obesity has increasingly received public attention, especially given a rising prevalence of the condition among children. Research indicates that obese adolescents tend to have higher risk of mortality as adults. Although environmental factors, such as food choices and sedentary habits, contribute to the increasing rates of obesity in childhood, twin studies and other family-based evidence have suggested a genetic component to the disease as well. Previous studies have identified gene variants contributing to obesity in adults and in children with extreme obesity, but relatively little is known about genes implicated in regular childhood obesity. "The Center for Applied Genomics at the Children's Hospital of Philadelphia has recruited and genotyped the world's largest collection of DNA from children with common obesity," said Dr. Grant.