Glowing from Within
A new fluorescent marker illuminates tissue deep within living animals

SOURCE: “Bright Far-Red Fluorescent Protein for Whole-Body Imaging”
Dmitriy Chudakov et al.
Nature Methods 4: 741-746

RESULTS: Using genetic-­engineering techniques, scientists have altered a red protein found in sea anemones to create a fluorescent marker that can be used to study living tissue deep in the body.

WHY IT MATTERS: The light from existing fluorescent markers is difficult to detect through layers of tissue, so the use of such markers has been limited to dissected or surface tissue or to transparent animals, such as worms. This new marker emits light in the far-red part of the spectrum, which can better pass through living tissue. That means the marker can be used in live animals to help researchers track molecular and cellular activity, such as the rapid division of cancer cells, in real time.

METHODS: By inducing both random and directed mutations in the anemone protein, scientists altered it to create new compounds that are brighter than the original one. They then tested the new proteins both in frogs and in human cells, showing that they shine much more brightly than those previously available.

NEXT STEPS: Collaborators of the scientists will soon begin testing the proteins in mice. Although the markers aren’t bright enough for whole-body imaging of humans, they might eventually be used to image human tumors that are near the surface of the skin, such as melanoma and breast cancer.

The First Diploid Sequence of an Individual Human
The highly accurate sequence suggests that our genetic code is five times as variable as we thought

SOURCE: “The Diploid Genome Sequence of an Individual Human”
Samuel Levy et al.
PLoS Biology 5: e254

RESULTS: Genomics pioneer Craig Venter and his colleagues have generated a highly accurate sequence of Venter’s genome, one that includes the DNA sequences inherited from both his mother and his father.

WHY IT MATTERS: The genome sequence generated by the Human Genome Project, the massive, distributed effort to sequence human DNA that was completed in 2003, was a milestone in the history of biology. But the DNA sequence produced by the project represented just one set of chromosomes (every human has two sets, one inherited from each parent), and it drew on DNA samples from many individuals. As a result, it didn’t reflect some of the variability between individuals. ­Venter’s diploid genome suggests that genetic variation between individuals is approximately 0.5 percent, not the 0.1 percent that earlier sequencing projects suggested.

METHODS: In the new study, researchers used a method of gene sequencing called Sanger sequencing. The method is more expensive than newer approaches, but it generates longer strings of DNA that are easier to assemble into a complete genome.

NEXT STEPS: Venter and his colleagues plan to add phenotypic information, such as medical records and physical characteristics, to the database housing his genome. This will allow scientists to begin analyzing an individual’s genomic information in the context of his or her actual traits.