#2 Decoding mental illness. Disorders such as schizophrenia, depression, and bipolar disorder often run in families, but researchers have only begun to unravel how genes can nudge someone into mental illness. This year, progress was made on several fronts.
Antidepressant drugs work by targeting a receptor important for signaling via the chemical messenger serotonin. The gene for this receptor comes in two common versions, or alleles, one of which had been tenuously linked to an increased risk of depression. This year, researchers revealed why the link had been so elusive: The allele increases the risk of depression only when combined with stress. Among people who had suffered bereavement, romantic rejection, or job loss in their early 20s, those who carried the vulnerability allele were more likely to be depressed than those with the other variant.
New insights also came for schizophrenia. Two years ago, a version of a gene called COMT was shown to muddle the prefrontal cortex, which is necessary for planning and problem-solving skills that are impaired by schizophrenia. Even healthy people who carry the schizophrenia risk allele have extra activity in the prefrontal cortex when doing relatively simple tasks. This year, the non-schizophrenia allele, which allows more efficient activity in the prefrontal cortex, was reported to increase the risk of anxiety, suggesting that the two diseases lie at opposite ends of a spectrum.
#3 Is it warm in here? A century's worth of temperature measurements show that the globe has been warming. New work shows that the planet has taken notice. The stream of studies suggesting global warming's impact on Earth and its inhabitants surged to a flood in 2003 with reports on melting ice, droughts, decreased plant productivity, and altered plant and animal behavior.
Among the findings this year, climate modelers linked a now fading, years-long, globe-girdling drought to unusually warm waters in the western Pacific and Indian oceans (ScienceNOW, 10 October). That warm water looks to be a product of greenhouse gases. In the Arctic, river monitoring showed a 7% increase since 1936 in the flows of the six largest Eurasian rivers that empty into the Arctic Ocean (ScienceNOW, 13 December, 2002). That fits climate model predictions of increased high-latitude precipitation and follows the observed warming and atmospheric circulation trends. Life has taken notice of warming, too. Plants and animals around the globe have shifted their geographic ranges or changed behaviors--such as when they bloom or lay eggs--in ways consistent with reacting to global warming. Climate change also seems to depress both corn and soybean productivity in the U.S. Midwest (ScienceNOW, 13 February) and plant productivity in Africa's great Lake Tanganyika (ScienceNOW, 15 August).
#4 Mini RNAs still hot. Science's breakthrough of 2002 kept scientists on the edge of their seats in 2003. Having sketched out the role played by miniature RNA molecules in modulating gene expression, this year biologists dove into the details.
MicroRNAs, the runts of the RNA litter at about 22 nucleotides in length, were found to guide early development in plants and animals. RNA interference (RNAi), which shuts down gene expression, is also critical. Mice lacking an RNAi protein called Dicer lost swaths of stem cells and died before birth. Also this year, certain microRNAs in mice were found to help direct stem cells that create the embryo's immune system. Humans, meanwhile, are now thought to harbor as many as 255 genes that encode microRNAs--nearly 1% of the genes in the entire genome.
RNAi also proved its worth this year in genetic screening (ScienceNOW, 28 March), and RNA enthusiasts have begun recruiting small interfering RNAs (siRNAs) in the fight against disease (ScienceNOW, 10 February; 12 May).
#5 Single molecules groove and glow. Biologists and physicists are detailing the busy lives of single molecules, in real time, as they buzz about in the cell. Work this year captured molecular motors in motion. So-called optical tweezers exploit a laser light beam to manipulate single particles. This year, biologists learned how to adapt them to measure the stepwise motion of individual kinesin proteins--part of the cell's transportation machinery--as they chug along cellular tracks called microtubules. Kinesins move with a hand-over-hand action, it appears, rather than an inchworm gait as an earlier report suggested. Also seen in detail was the hand-over-hand motion of another motor protein called myosin.
Perhaps the most exciting new technique to emerge is quantum dots. These tiny semiconductor nanocrystals glow in myriad colors when excited by laser light. This year, researchers tracked the movements of individual glycine receptors within nerve cell membranes using quantum dots attached to antibodies.
#6 Cosmic blasts. Several discoveries this year lifted veils that had shrouded the most energetic explosions in the universe: titanic blasts of energy called gamma ray bursts (GRBs). Most notably, in March, astronomers confirmed the connection between GRBs and supernovas--the death throes of massive stars--when they spotted the unmistakable imprints of a supernova in the glow of a bright GRB (ScienceNOW, 12 April). Astrophysicists now believe that the burst's jets of energy spewed into space when a star's core imploded, forming a black hole or--in a minority view--a rapidly spinning neutron star with a crushing magnetic field.
#7 Spontaneous generation. At least one observer called the surprise discovery an "ethical earthquake": Mouse embryonic stem cells can develop into both sperm and egg cells in culture dishes (ScienceNOW, 1 May; 16 September). The work hatched both scientific and ethical questions. In the short term, the discoveries should help reveal how germ cells develop. If the feat can be reproduced in human cells, it could provide a renewable source of human eggs or sperm for research. But it also opens a Pandora's box of ethical questions: Could a child be born whose genetic parent is a cell line?
#8 About-face. Work this year confirmed that certain oddball materials can bend light in the wrong direction. In 1964, a Russian physicist theorized that researchers could tailor materials to reverse the way they manipulate passing electromagnetic radiation. Two years ago, researchers created such "left-handed" materials. They beamed microwaves at a composite of copper rings and wires, which steered microwaves out at a negative instead of positive angle. Last year other teams challenged those results, but this year definitive proof came from multiple camps. Another team, meanwhile, snapped the first-ever image with a flat lens made from a left-handed material. Ultimately, such lenses promise to generate far less distortion than standard optics.
#9 The little Y that could. A sequencing tour de force revealed the genetic code of the Y chromosome this year and in the process earned new respectability for the stubby hunk of DNA that makes a man a man (ScienceNOW, 18 June). Half of the 59 million bases in this chromosome are jumbled, possibly useless, and virtually impossible to decipher. This “junk” suggested that the Y is slowly fading as a chromosome. But the new sequence of the other half of Y's DNA, which contains the genes, shows that it has evolved an unusual, but effective, way to take care of itself.
#10 Starving cancer. It's been a roller-coaster ride for researchers working on anticancer drugs that block development of the blood vessels that feed tumor growth, a process called angiogenesis. But this year, they've finally begun to see their efforts pay off.
This June, researchers announced that an antiangiogenesis drug, given with conventional chemotherapy drugs in a large clinical trial, prolonged the lives of patients with advanced colon cancer. The drug had failed a similar test with breast cancer patients, possibly because advanced breast tumors produce more angiogenesis-promoting factors than colon tumors do and are thus harder to control. This suggests that antiangiogenesis therapies will have to be tailored to their targets to be effective. Researchers have also learned that antiangiogenesis drugs work most effectively in combination, either with each other or with conventional chemotherapeutic drugs or radiation.