Cell biology: More than a safety cap

Credit: A. SYRED/SPL

Science doi:10.1126/science.1147182 (2007)

Telomeres, the DNA 'caps' that protect the ends of chromosomes (pictured), produce RNA, according to Joachim Lingner of the Swiss Federal Institute of Technology in Lausanne and his colleagues.

The discovery comes as a surprise. Telomeres are believed to have a role in ageing — they shorten as cells grow old, and cancer cells achieve immortality by maintaining long telomeres — but their highly repetitive DNA sequences were not thought to yield RNA.

Lingner and his team report that some of the telomere RNA remains clustered around telomeres. This trend was enhanced when researchers lowered the expression of several proteins involved in stabilizing telomeres, indirectly suggesting that the RNA may be involved in regulation of telomere length. The RNA's precise function, however, remains unclear.

Biochemistry: Second signal

Nature Chem. Biol. doi:10.1038/nchembio.2007.33 (2007)

Researchers in Japan have found a previously unknown player in the pathway by which nitric oxide helps cells to communicate at a molecular level.

Nitric oxide is a poisonous gas, but in minuscule quantities it has a multitude of roles in biochemical processes ranging from neuronal and vascular signalling to immunity and the regulation of cell death. The nitric oxide pathway is targeted by some drugs meant to regulate blood flow, including Viagra.

Takaaki Akaike at Kumamoto University and his colleagues describe how a nucleic acid, guanosine 3′,5′-cyclic monophosphate (cGMP), is nitrated in the presence of nitric oxide, forming a 'second messenger' in the signal-transduction pathway: 8-nitrocGMP.The group also found that this second messenger chemically tags other proteins through a newly identified process known as S-guanylation.

Medicine: Every breath you take

Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0706533104 (2007)

Monitoring blood sugar is a matter of life and death for diabetics, but invasive needle pricks are a burden, especially to children. In search of an alternative, Pietro Galassetti and Sherwood Rowland at the University of California, Irvine, and their colleagues analysed the breath of children with diabetes for exhaled indicators of blood sugar.

Using a very sensitive technique involving gas chromatography and mass spectrometry, the team measured 100 exhaled compounds in vanishingly small quantities as the patients received insulin to lower blood sugar. Changes in methyl nitrate levels were most closely correlated with alterations in blood sugar.

The team hopes to find a suite of such volatile organic compounds that could serve as a signature for other important blood markers, including insulin and lipids.

Physics: Water that sticks

Phys. Rev. Lett. 99, 148301 (2007)

What drives hydrophobic molecules to stick together when they are immersed in water? In 1945, scientists suggested that water forms an ice-like cage around hydrophobic groups. According to this theory, aggregation of the hydrophobic groups would be favoured because it would set the immobilized water free, increasing the system's entropy.

Yves Rezus and Huib Bakker of the FOMInstitute for Atomic and Molecular Physics in Amsterdam, the Netherlands, find, with infrared spectroscopy, that water molecules around hydrophobic methyl groups on organic molecules rotate at least five times more slowly than they do in bulk water. Although not quite the ice cage originally proposed, this slowing down may help to explain the hydrophobic interaction.

Neuroscience: Hard to forget

Cell 131, 160–173 (2007)

Researchers have unpicked the mechanism by which memories tied to strong emotions are recalled with greater clarity. The effect has been linked to release of the neurotransmitter noradrenaline during emotional situations. Now, Roberto Malinow of Cold Spring Harbor Laboratory in New York and his colleagues have determined that noradrenaline acts by regulating a class of receptor, known as GluR1-containing AMPA receptors, that is involved in learning.

In mice, both the fear caused by exposure to fox urine and the experimental injection of adrenaline, which boosts noradrenaline, triggered the addition of phosphates to two sites in GluR1. This phosphorylation meant that GluR1 could be more easily incorporated into synapses, which improved the animals' learning in behavioural tests carried out immediately after adrenaline injection. Noradrenaline had no effect on learning in mice that contained a mutant GluR1 that lacked the phosphorylation sites.

Animal behaviour: An ear to the ground

Credit: M. WIKELSKI

Biol. Lett. doi:10.1098/rsbl.2007.0443 (2007)

The marine iguanas of the Galapagos eavesdrop on the warning cries of mockingbirds, report Maren Vitousek of Princeton University in New Jersey and her team. It's the first time that a non-vocal species has been spotted taking advantage of another animal's vocal communication.

Vitousek's team played recordings of different mockingbird calls to marine iguanas (Amblyrhynchus cristatus) on Santa Fe island, where both species are vulnerable to hawk attacks. In response to 'alarm' calls, about 45% of iguanas raised their heads or began to move away. Only 28% on average responded to playbacks of non-alarm birdsong. The tactic may give the iguanas — whose need to sunbathe can conflict with their need to keep watch — an early warning of the predators' presence. The picture (above) shows an iguana that didn't get away.

Chemical biology: Bittersweet reaction

Angew. Chem. Int. Edn 46, 7697–7699 (2007)

As those who take artificial sweeteners will know, saccharin isn't all sweetness — it leaves a bitter metallic aftertaste. Although this seems to be harmless, no one knows what causes it. Now Gerhard Klebe of the Philipps University of Marburg in Germany and his co-workers think they have a clue.

They have found that saccharin is a surprisingly potent inhibitor of certain carbonic anhydrases — enzymes that have various roles in metabolism, acidity regulation and other aspects of biochemistry. Nanomolar concentrations of saccharin deactivate several variants of the enzyme, including one present in saliva that is involved in olfaction and taste. Compounds used to inhibit these enzymes for clinical purposes also have bitter, metallic aftertastes, so this might be a general side effect of such inhibitory action.

Systems biology: Circadian ménage à trois

Science doi:10.1126/science.1148596 (2007)

Most organisms keep time with a circadian clock driven by changes in the expression of particular genes, but cyanobacteria do it differently. Erin O'Shea at Harvard University in Cambridge, Massachusetts, and her colleagues have devised a model that could explain how they tick.

The clock of the cyanobacterium Synechococcus elongatus centres on a protein, KaiC, that has different phosphorylation states. Over a roughly 24-hour period, a protein called KaiA functions with KaiC to add phosphates to two sites on KaiC, until another protein, KaiB, joins the complex and blocks KaiA's action. The phosphates then fall off.

Shea's team noticed an order to how the phosphates add and drop off that determines when KaiB can bind KaiC. This detail allowed them to explain how collections of these proteins maintain a cycle, even in a test-tube, instead of sitting in equilibrium.

Astronomy: Tidal stream

Credit: R. GENDLER

Astrophys. J. 668, 245–267 (2007)

Massive galaxies are thought to have formed through the merger of many smaller galaxies. In a new study, Karoline Gilbert at the University of California, Santa Cruz, and her colleagues identify a scar of such a process in the Andromeda galaxy (pictured), the nearest large galaxy to the Milky Way.

The researchers' survey of about 1,000 stars in Andromeda revealed a slow-moving stream of stars in the southeastern fringes of the galaxy. It is likely that this substructure is linked to the previously identified 'giant southern stream'. Computer simulations that explain the giant stream as the result of a galactic collision had predicted that such a feature should exist as an extended thread of debris.