PNAS highlights for the week of April 11 - 15


*Cloned Beef and Milk Meet Industry Standards

In a pilot study, scientists have shown that meat and milk from cloned bulls and cows, respectively, meet industry standards.

Xiangzhong Yang and colleagues cloned a Japanese Black beef bull and Holstein dairy cow, using somatic cell nuclear transfer (the same technique used to clone the sheep Dolly). The researchers compared the meat and milk from the clones to that of animals of similar age, genetics, and breed created through natural reproduction.

Analysis of protein, fat, and other variables routinely assessed by the dairy industry revealed no significant differences in the milk. The researchers also examined more than 100 meat quality criteria, of which 90% showed no noteworthy variations. But about 8 variables related to the amount of fat and fatty acids in the meat were significantly higher in the meat from the clones. The authors say these higher fat levels are within beef industry standards.

Animal food products from clones have yet to enter the food chain in any country, and this report lays groundwork for larger, more conclusive studies with cloned animals.

*Humans, Not Climate Change, Likely Cause of Elephant Extinctions

When early humans migrated out of Africa, they hunted elephants to extinction on five continents, archaeological evidence suggests.

A million years ago, elephants lived in most of Africa, Europe, Asia, and the Americas. Today, wild elephants are found only in portions of sub-Saharan Africa and South Asia. Whether these die-offs were due to climate change or human overkill has been a source of debate.

To investigate the question, Todd Surovell and colleagues examined 41 archaeology sites--ranging from 1.8 million years to 10,000 years ago, on five continents--that showed humans and elephants living together in the same place and time. By comparing age and location of the sites with early human migration trends, the researchers found that elephant-human interactions closely followed the successive waves of population expansion, then mostly disappeared.

Elephants might be particularly susceptible to overhunting because their size translates into fewer offspring and greater needs for roaming land. Furthermore, the authors point out, the elephant populations that have managed to survive live in areas where humans have never settled in large numbers.

*"Neural Cliques" Create Real-Time Memories


Typically, brain activity is measured in one or a few neurons at a time. But since complex behaviors, like learning and memory, depend on the actions of large sets of neurons, it becomes necessary to determine how these cells work together to allow memories to form.

Joe Tsien and colleagues simultaneously recorded the electrical activity of up to 260 individual neurons of the mouse hippocampus, the brain structure responsible for forming memories of places and events. The researchers recorded this activity in response to three different types of startling conditions.

The authors found that each startling episode produced different brain activity patterns and identified basic coding units in the hippocampus, neural cliques, that respond to the different stimuli. These neural cliques provide a plausible, real-time neural basis of memory formation. Furthermore, activation patterns of neural cliques can generate a set of brain codes that, like the genetic code, seem to be universal across different individuals and species.


*Cosmic Rays May Not Harm Sex Cells

Reproductive cell mutations arising from exposures to cosmic rays are not a significant hazard to astronauts, research suggests.

*Vegetation Affects Desert Water Cycle

Plant life appears to play an important role in controlling the water cycle in desert ecosystems, acting over time scales ranging from a year to a millennium.

*Color-Coded Laser Sequencing for Faster DNA Analysis

Laser sequencing of color-coded DNA stretches on a chip may lead to new methods for high-throughput DNA sequencing.

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