Cell biology: Drug resistance lies within

Mol. Biol. Cell doi:10.1091/mbc.E02-11-0704 (2003)

When tumours become drug-resistant they often ramp up the production of so-called multidrug-resistance transporters — thought to thrust the toxin out of the tumour's cells. In fact, these pumps might be working inside the cells instead.

Asha Rajagopal and Sanford M. Simon genetically engineered cells in culture so that they made a fluorescent version of one of a family of pumps, such as multidrug-resistance protein 1 and breast-cancer-resistance protein. They then tracked the fate of chemotherapy drug doxorubicin on the basis of its natural fluorescence. They found that the pumps prevent doxorubicin from reaching its target, the nucleus, and killing cells. Instead, the drug is diverted into small compartments called lysosomes, which break down cellular trash.

The transporters sit in the membrane of lysosomes and probably pump in the drugs, rendering them useless against the cell. The authors say that this could affect the design of treatments aimed at quashing drug-resistance proteins.

Helen Pearson

Environmental science: Shades of China

Glob. Biogeochem. Cycles 17, 1034–1052 (2003)

An analysis of historical tree coverage in China suggests that the country was a net source of atmospheric carbon well before its industrialization, before becoming a carbon sink in the past decade or so. Attempts at such analyses have previously been stymied by a lack of historical information: the first national inventory of forests was not published until 1983, for example. But by examining these data, and augmenting them with agricultural archives and inferring forest cover from historical accounts and pollen records, R. A. Houghton and J. L. Hackler have been able to produce estimates of land-use change in China between 1700 and 2000.

Pollen records indicate that by 1700 China had already lost between 19% and 48% of its estimated prehistoric forest cover. Continued deforestation led to the loss of a further 180 million hectares between 1700 and 2000, with the concomitant release of some 17–33 billion tonnes of carbon into the atmosphere.

Between the 1950s and 1970s, emissions of carbon due to land-use change peaked at 0.2 to 0.5 billion tonnes annually. But more recently the picture has changed: because of the implementation of nationwide re-forestation programmes, and a 1998 moratorium on logging, during the 1990s China has on average become a sink for atmospheric carbon.

Tom Clarke

Ecology: News of chews

Funct. Ecol. 17, 201–212 (2003)

Differences in jaw power might help different bat species coexist, say L. F. Aguirre and colleagues. They looked at the diets and jaw strengths of 23 bat species living on the Bolivian savanna, and found that the diet of each species seems to be limited by the strength of their bites.

Analyses of stomach contents revealed that each species specialized in either fruit or insects. For both fruit and insects, bigger food items tended to be harder. And the maximum size of food item in each species' diet tended to match the strength of its jaws, as estimated by force measurements of its bite. Food hardness probably limits the diet of small bat species; only a few large species are able to crunch their way through the bigger beetles or toughest fruits. Bats are known to chew their food well, so the time and energy taken to process tough foodstuffs are probably an important determinant of what they can eat — and so how different species divide up the food resources in their environment.

John Whitfield

Microscopy: Nanoscience in ribbons

Appl. Phys. Lett. 82, 2886–2888 (2003)

The sensitivity of an atomic force microscope (AFM) depends on the thin ribbon of material that connects the needle-like probe tip to the body of the device. This cantilever should be thin and stiff, and is typically made of a hard, strong substance such as silicon nitride, giving it a large spring constant and the ability to detect very small forces. William L. Hughes and Zhong L. Wang claim that it should be possible to make vastly improved AFM cantilevers from 'nanobelts' of metal oxides and sulphides.

Nanobelts are tiny ribbons that form spontaneously when the materials are deposited by high-temperature evaporation of a fine powder — an example of the 'bottom-up' approach to nanofabrication, contrasting with the way that cantilevers are traditionally made by carving them from bigger chunks of material. Wang and co-workers first made nanobelts two years ago. The ribbons are typically 20–1,000 nm wide — up to 1,800 times smaller than conventional cantilevers.

Now Hughes and Wang have developed methods for cutting the ribbons into shorter sections: for example, using the electron beam of a transmission electron microscope, or chiselling through a nanobelt using a conventional AFM tip. They then use an AFM to pick up a section of the ribbon and position it on a silicon wafer. If a fine tip could be attached to the end of a ribbon, it would serve as a peerless cantilever: the increase in force sensitivity might realize such alluring goals as single-atom magnetic-resonance spectroscopy.

Philip Ball

Animal behaviour: A dog's dinner

Curr. Biol. 13, 763–766 (2003)

Dogs readily understand human gestures that direct them to food. Pointing, a nod of the head, or simply gazing in the direction of a hidden treat can get them going. How did dogs obtain this skill? From their comparison of wolves and dogs, Ádám Miklósi et al. propose that it has to do with centuries of domestication.

Miklósi et al. discovered that teaching wolves to find a piece of meat hidden in a pot wasn't easy, even when the wolves were reared as if they were dogs. Touching the pot containing the meat, or pointing at it from nearby, helped a little, but only after many trials did the wolves respond to pointing from a distance.

In order to spot direction in a distant gesture, an animal must look at the trainer, and the wolves seemed to avoid just that. When confronted with an insoluble task — retrieving meat from a locked pot, for example — the dogs immediately looked back at their owners, and gazed at their face as if to ask for help. But the wolves never looked back.

Domestication may have selected for the tendency of dogs to look at the human face in situations of uncertainty. Miklósi et al. suggest that this simple change in behaviour may have opened the door to our long and productive relationship with dogs.

Marie-Thérèse Heemels