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<jats:p>The 1992 and 1995 basaltic eruptions of Cerro Negro volcano, Nicaragua, had contrasting eruptive styles. Although they were nearly identical in composition, the 1992 eruption was explosive, producing a 7-kilometer-high sustained ash column, whereas the 1995 eruption was essentially effusive. The differences in water and carbon dioxide contents of melt inclusions from the two eruptions define minimum saturation pressures and show how decompression of initially similar magmas influences eruptive style. Before eruption, the explosive 1992 magma retained water and carbon dioxide while ascending to a moderate crustal level (about 6 kilometers), whereas the nonexplosive 1995 magma lost all carbon dioxide by degassing during ascent to shallow crustal levels (about 1 to 2 kilometers).</jats:p>

<jats:p>A previously unsampled outcrop of gently dipping or flat-lying Upper Cretaceous sedimentary strata in the Vancouver Island region, which contains unaltered aragonitic mollusk fossils, yielded a stable remanent magnetization that is biostratigraphically consistent with Cretaceous magnetochrons 33R, 33N, and 32R. These results, characterized by shallow inclinations, indicate an Upper Cretaceous paleolatitude of about 25 ± 3 degrees north, which is equivalent to that of modern-day Baja California. These findings are consistent with the Baja–British Columbia hypothesis, which puts the Insular Superterrane well south of the Oregon-California border in the Late Cretaceous.</jats:p>

<jats:p> Small globular fossils known as <jats:italic>Olivooides</jats:italic> and <jats:italic>Markuelia</jats:italic> from basal Cambrian rocks in China and Siberia, respectively, contain directly developing embryos of metazoans. Fossilization is due to early diagenetic phosphatization. A nearly full developmental sequence of <jats:italic>Olivooides</jats:italic> can be observed, from late embryonic stages still within an egg membrane, to hatched specimens belonging to several ontogenetic stages. Earlier cleavage stages also occur, but cannot be identified to taxon. <jats:italic>Olivooides</jats:italic> shows similarities to coronate scyphozoans and to their probable Paleozoic representatives, the conulariids. <jats:italic>Markuelia</jats:italic> eggs contain looped embryos of a segmented worm with short, conical processes covering the body. </jats:p>

<jats:p>A sodium-layer laser guide star beacon with high-order adaptive optics at Lick Observatory (Mount Hamilton, California) produced a factor of 2.4 intensity increase and a factor of 2 decrease in full width at half maximum for an astronomical point source, compared with image motion compensation alone. The image full widths at half maximum were identical for laser and natural guide stars (0.3 arc second). The Strehl ratio with the laser guide star was 65 percent of that with a natural guide star. This technique should allow ground-based telescopes to attain the diffraction limit, by correcting for atmospheric distortions.</jats:p>

<jats:p> Gangliosides participate in development and tissue differentiation. Cross-linking of the apoptosis-inducing CD95 protein (also called Fas or APO-1) in lymphoid and myeloid tumor cells triggered GD3 ganglioside synthesis and transient accumulation. CD95-induced GD3 accumulation depended on integral receptor “death domains” and on activation of a family of cysteine proteases called caspases. Cell-permeating ceramides, which are potent inducers of apoptosis, also triggered GD3 synthesis. GD3 disrupted mitochondrial transmembrane potential (ΔΨ <jats:sub>m</jats:sub> ), and induced apoptosis, in a caspase-independent fashion. Transient overexpression of the GD3 synthase gene directly triggered apoptosis. Pharmacological inhibition of GD3 synthesis and exposure to GD3 synthase antisense oligodeoxynucleotides prevented CD95-induced apoptosis. Thus, GD3 ganglioside mediates the propagation of CD95-generated apoptotic signals in hematopoietic cells. </jats:p>

<jats:p>Kaposi's sarcoma–associated herpesvirus encodes a chemokine called vMIP-II. This protein displayed a broader spectrum of receptor activities than any mammalian chemokine as it bound with high affinity to a number of both CC and CXC chemokine receptors. Binding of vMIP-II, however, was not associated with the normal, rapid mobilization of calcium from intracellular stores; instead, it blocked calcium mobilization induced by endogenous chemokines. In freshly isolated human monocytes the virally encoded vMIP-II acted as a potent and efficient antagonist of chemotaxis induced by chemokines. Because vMIP-II could inhibit cell entry of human immunodeficiency virus (HIV) mediated through CCR3 and CCR5 as well as CXCR4, this protein may serve as a lead for development of broad-spectrum anti-HIV agents.</jats:p>

<jats:p> Variations in maternal care affect the development of individual differences in neuroendocrine responses to stress in rats. As adults, the offspring of mothers that exhibited more licking and grooming of pups during the first 10 days of life showed reduced plasma adrenocorticotropic hormone and corticosterone responses to acute stress, increased hippocampal glucocorticoid receptor messenger RNA expression, enhanced glucocorticoid feedback sensitivity, and decreased levels of hypothalamic corticotropin-releasing hormone messenger RNA. Each measure was significantly correlated with the frequency of maternal licking and grooming (all <jats:italic>r</jats:italic> 's &gt; −0.6). These findings suggest that maternal behavior serves to “program” hypothalamic-pituitary-adrenal responses to stress in the offspring. </jats:p>

<jats:p>An essential step in retrovirus infection is the binding of the virus to its receptor on a target cell. The structure of the receptor-binding domain of the envelope glycoprotein from Friend murine leukemia virus was determined to 2.0 angstrom resolution by x-ray crystallography. The core of the domain is an antiparallel β sandwich, with two interstrand loops forming a helical subdomain atop the sandwich. The residues in the helical region, but not in the β sandwich, are highly variable among mammalian C-type retroviruses with distinct tropisms, indicating that the helical subdomain determines the receptor specificity of the virus.</jats:p>

<jats:p>Late Pleistocene glaciations have been ascribed a dominant role in sculpting present-day diversity and distributions of North American vertebrates. Molecular comparisons of recently diverged sister species now permit a test of this assertion. The Late Pleistocene Origins model predicts a mitochondrial DNA divergence value of less than 0.5 percent for avian sister species of Late Pleistocene origin. Instead, the average mitochondrial DNA sequence divergence for 35 such songbird species pairs is 5.1 percent, which exceeds the predicted value by a factor of 10. Molecular data suggest a relatively protracted history of speciation events among North American songbirds over the past 5 million years.</jats:p>

<jats:p>Cytotrophoblasts, specialized placental cells, proliferate early in pregnancy and then differentiate into tumor-like cells that establish blood flow to the placenta by invading the uterus and its vasculature. In this study, cytotrophoblasts cultured under hypoxic conditions (2 percent oxygen), mimicking the environment near the uterine surface before 10 weeks of gestation, continued proliferating and differentiated poorly. When cultured in 20 percent oxygen, mimicking the environment near uterine arterioles, the cells stopped proliferating and differentiated normally. Thus, oxygen tension determines whether cytotrophoblasts proliferate or invade, thereby regulating placental growth and cellular architecture.</jats:p>