January 12 This dinosaur, most likely a stegosaur, was excavated last year from Early Cretaceous rocks in the Urho region of Xinjiang in northwestern China by paleontologists from the Natural History Museum of Los Angeles County and the National Geological Museum of China. Many joint teams are eagerly digging for fossils in China, which has become perhaps the hottest area in the world to prospect. An overview of recent discoveries–as well as stories about opportunities and problems facing paleontologists in China–begins on page 232. [Photo: Luis Chiappe]

January 19 In the plant Arabidopsis, light captured by the photoreceptive molecules cryptochrome and phytochrome regulates development through a signaling pathway containing SUB1, a calcium-binding protein. The SUB1 protein is enriched around the nucleus (dark blue) in plant cells transfected with a SUB1-GUS fusion protein. Cell nuclei are shown in turquoise (magnification, 1600). See page 487 [Image: H. Guo and T. Mockler]

February 16 The face of the human genome. A scientific milestone of enormous proportions, the sequencing of the human genome will impact all of us in diverse ways-from our views of ourselves as human beings to new paradigms in medicine. This entire issue is devoted to the scientific announcement of the sequencing of the human genome, initial analyses of the genome and genomic data, as well as Viewpoints and News features discussing the implications of the results and paths for the future.

March 9 Two neuronal axons on a two-dimensional substrate, visualized by fluorescent staining of filamentous actin. One axon originates from a cell body beyond the top right and extends diagonally downward. The other, originating from a cell body beyond the bottom, is turning upward. The expanded tip of each axon, the growth cone, extends protrusions, filopodia, in search of proteins such as netrin and Slit, which guide axons to their destinations in the developing nervous system. (Image width, 120 mm; bottom right, nonneuronal cell.) See page 1928 [Image: E. Stein and M. Tessier-Lavigne]

March 23 The cell surface landscape is richly decorated with oligosaccharides anchored to proteins or lipids within the plasma membrane. Cell surface oligosaccharides mediate the interactions of cells with each other and with extracellular matrix components. The important roles that carbohydrates play in biology and medicine have stimulated a rapid expansion of the field of glycobiology, the focus of the special section in this issue. See page 2357 [Illustration: Cameron Slayden]

April 13 Barn owls can pinpoint prey by sound in the dark. The differences in arrival time and intensity of sound between the two ears of the owl indicate the target’s position. Separate neural pathways process these two cues and converge on neurons that combine the time and intensity signals by multiplication. See page 249 [Photo: Ben Arthur]

May 11 The plague doctor in clothing worn to protect from contagion, circa 1656. We are haunted by images of the horrors of disease and death, but with the current influx of data from microbial genomes, we can expect some answers to questions about how microorganisms have evolved, causing much fear. Apart from using these data to design new drugs and vaccines, we can also explore what the molecular signature of a microorganism may mean to a host population and predict more precisely the effects of intervention. 1089 [Image: Stock Montage]

May 25 A reconstruction of Hadrocodium wui, an Early Jurassic fossil (about 195 million years old) found in Yunnan, China. This newly described mammaliaform is an extinct close relative of living mammals, with many advanced features despite its early age. On the basis of a subadult skull, the tiny insectivore is estimated to weigh approximately 2 grams. The reconstruction of this mammal is shown in comparison to a paper clip (32 millimeters). 1089 [Reconstruction artwork: Mark A. Klingler/Carnegie Museum of Natural History]

June 8 The enzyme RNA polymerase II in the act of transcribing a gene. X-ray crystal structure comprises the protein (gray, except for orange “clamp” and green “bridge” helix), DNA (blue template strand, green nontemplate strand), and RNA (red). The pink sphere is an active center Mg2+ ion. Double-stranded DNA enters from the right and unwinds before the active center. The unwound nontemplate DNA strand is obscured by motion or disorder. 1876 [Adapted from Fig. 2C of Gnatt et al.]

June 15 In algal cells, the chloroplast (red fluorescence) produces photosynthetically derived energy for cell growth. Through the introduction of a glucose transporter (green fluorescence), algal cells are able to import and then metabolize glucose for energy. These cells can now thrive without light, permitting culture by efficient fermentation technology. 2073 [Image: D. Ehrhardt]

June 29 Femtosecond optical pulses allow coherent operations to be performed on electron spins in semiconductors. A pump pulse excites spins whose precession about a magnetic field is recorded by a probe pulse. A third pulse tips the spins as they precess, inducing changes in the precession amplitude, shown here as a function of probe and tipping pulse time delay. Peaks occur when there is an effective torque between the tipping pulse and the electron spin. 2458 [Image: J. A. Gupta]

August 3 New restoration of the head of the sauropod dinosaur Diplodocus (left and bottom right), based on a study reflecting the forward position of the nostrils. Top right is the skull; middle right is the traditional view, refuted by the new research. 850 [Paintings by M. W. Skrepnick under the direction of L. M. Witmer]

August 24 A pollen tube (blue), 10 mm in diameter, thrusting into the embryo sac (haploid female gametophyte; orange) of the flowering plant Torenia. The pollen tube is precisely attracted to the embryo sac by two synergid cells in the sac, enabling successful fertilization. 1480 [Scanning electron microscope image: T. Higashiyama and T. Kuroiwa]

August 31 The undergraduate experience is recognizable the world over, and from generation to generation. Yet there are also many changes afoot in science education, from better mentoring, to improved assessment, to a growing presence online. A special section discusses these trends. 1607 [Photo: Sam Kittner]

September 7 Crystal structure of the multidrug resistance ABC transporter homolog MsbA from Escherichia coli as viewed from the plane of the lipid bilayer. This class of integral membrane proteins transports hydrophobic molecules such as lipids and drugs across the cell membrane bilayer. The structure of MsbA reveals three domains, which include the transmembrane (red), intracellular (dark blue), and nucleotide-binding (teal) domains. The structure can help elucidate the mechanism underlying multidrug resistance in the treatment of cancer and infectious diseases. 1793 [Image: G. Chang and C. B. Roth]

October 5 Sequencing genomes is only the first step to unlocking their secrets. This issue examines new ideas, approaches, and research related to genomic information. 81 [Art: C. Slayden]

October 12 Single-crystalline silver nanowires (width, 0.4 nm) grown inside the pores of self-assembled calix[4]hydroquinone nanotubes. Because these nanowires are coherently oriented as three-dimensional arrays of ultrahigh density, they could be used as model systems to investigate one-dimensional phenomena and as connectors in nanodevices. 348 [Image: K. S. Kim]

November 2 People who play the computer game Tetris often see intrusive images from the game in sleep-onset “hypnagogic” dreams. The special section in this issue focuses on the roles that sleep and dreams may play in processing memories. 1047 [Image: Christopher Davis]