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<jats:p>The ventral premotor cortex in primates is thought to be involved in sensory-motor integration. Many of its neurons respond to visual stimuli in the space near the arms or face. In this study on the ventral premotor cortex of monkeys, an object was presented within the visual receptive fields of individual neurons, then the lights were turned off and the object was silently removed. A subset of the neurons continued to respond in the dark as if the object were still present and visible. Such cells exhibit “object permanence,” encoding the presence of an object that is no longer visible. These cells may underlie the ability to reach toward or avoid objects that are no longer directly visible.</jats:p>

<jats:p>Platelet-derived growth factor (PDGF)–B–deficient mouse embryos were found to lack microvascular pericytes, which normally form part of the capillary wall, and they developed numerous capillary microaneurysms that ruptured at late gestation. Endothelial cells of the sprouting capillaries in the mutant mice appeared to be unable to attract PDGF-Rβ–positive pericyte progenitor cells. Pericytes may contribute to the mechanical stability of the capillary wall. Comparisons made between PDGF null mouse phenotypes suggest a general role for PDGFs in the development of myofibroblasts.</jats:p>

<jats:p> In vertebrates, the presence of multiple heat shock transcription factors (HSFs) indicates that these factors may be regulated by distinct stress signals. HSF3 was specifically activated in unstressed proliferating cells by direct binding to the c- <jats:italic>myb</jats:italic> proto-oncogene product (c-Myb). These factors formed a complex through their DNA binding domains that stimulated the nuclear entry and formation of the transcriptionally active trimer of HSF3. Because c-Myb participates in cellular proliferation, this regulatory pathway may provide a link between cellular proliferation and the stress response. </jats:p>

<jats:p> Top predators and nutrient loading in lakes were manipulated to assess the influence of food web structure on carbon flux between lakes and the atmosphere. Nutrient enrichment increased primary production, causing lakes to become net sinks for atmospheric carbon (C <jats:sub>atm</jats:sub> ). Changes in top predators caused shifts in grazers. At identical nutrient loading, C <jats:sub>atm</jats:sub> invasion was greater to a lake with low grazing than to one with high grazing. Carbon stable-isotope distributions corroborated the drawdown of lake carbon dioxide and traced C <jats:sub>atm</jats:sub> transfer from algae to top predators. Thus, top predators altered ecosystem carbon fixation and linkages to the atmosphere. </jats:p>

<jats:p> Adenosine 3′,5′-monophosphate (cAMP) and cAMP-dependent protein kinase (PKA) are regulators of development in many organisms. <jats:italic>Dictyostelium</jats:italic> uses cAMP as an extracellular chemoattractant and as an intracellular signal for differentiation. Cells that are mutant in adenylyl cyclase do not develop. Moderate expression of the catalytic subunit of PKA in adenylyl cyclase–null cells led to near-normal development without detectable accumulation of cAMP. These results suggest that all intracellular cAMP signaling is effected through PKA and that signals other than extracellular cAMP coordinate morphogenesis in <jats:italic>Dictyostelium.</jats:italic> </jats:p>

<jats:p> The organizer of the amphibian gastrula provides the neurectoderm with both neuralizing and posteriorizing (transforming) signals. In zebrafish, transplantations show that a spatially distinct transformer signal emanates from tissues other than the organizer. Cells of the germring (nonaxial mesendoderm) posteriorized forebrain progenitors when grafted nearby, resulting in an ectopic hindbrain-like structure; in contrast, cells of the organizer (axial mesendoderm) caused no posterior transformation. Local application of basic fibroblast growth factor, a candidate transformer in <jats:italic>Xenopus</jats:italic> , caused malformation but not hindbrain transformation in the forebrain. Thus, the zebrafish gastrula may integrate spatially distinct signals from the organizer and the germring to pattern the neural axis. </jats:p>