Rapid Plasma Membrane Anchoring of Newly Synthesized p59 fyn: Selective Requirement for NH2-Terminal Myristoylation and Palmitoylation at Cysteine-3

The trafficking of Src family proteins after biosynthesis is poorly defined. Here we studied the role of dual fatty acylation with myristate and palmitate in biosynthetic transport of p59^fyn. Metabolic labeling of transfected COS or NIH 3T3 cells with [³⁵S]methionine followed by analysis of cytosolic and total membrane fractions showed that Fyn became membrane bound within 5 min after biosynthesis. Newly synthesized Src, however, accumulated in the membranes between 20– 60 min. Northern blotting detected Fyn mRNA specifically in soluble polyribosomes and soluble Fyn protein was only detected shortly (1–2 min) after radiolabeling. Use of chimeric Fyn and Src constructs showed that rapid membrane targeting was mediated by the myristoylated NH₂-terminal sequence of Fyn and that a cysteine at position 3, but not 6, was essential. Examination of Gα_o-, Gα_s-, or GAP43-Fyn fusion constructs indicated that rapid membrane anchoring is exclusively conferred by the combination of N-myristoylation plus palmitoylation of cysteine-3. Density gradient analysis colocalized newly synthesized Fyn with plasma membranes. Interestingly, a 10–20-min lag phase was observed between plasma membrane binding and the acquisition of non-ionic detergent insolubility. We propose a model in which synthesis and myristoylation of Fyn occurs on soluble ribosomes, followed by rapid palmitoylation and plasma membrane anchoring, and a slower partitioning into detergent-insoluble membrane subdomains. These results serve to define a novel trafficking pathway for Src family proteins that are regulated by dual fatty acylation.     

Host versus in vitro signals and intrastrain allelic differences in the expression of a Candida albicans virulence gene

The yeast Candida albicans is a harmless colonizer of mucosal surfaces in healthy people but can become a serious pathogen in immunocompromised patients, causing superficial as well as systemic infections. The evolution of gene families encoding pathogenicity-related functions, like adhesins and secreted aspartic proteinases (Saps), which are differentially induced by host signals at various stages of colonization and infection, may have allowed C. albicans an optimal adaptation to many different host niches. We found that even the two alleles of a single gene can be differentially regulated in the diploid C. albicans. In the model strain SC5314, the in vitro expression of one of the two SAP2 alleles, SAP2-1, depended on the presence of a functional SAP2-2 allele. In contrast, inactivation of SAP2-1 did not in-fluence the expression of SAP2-2. The proteinase encoded by the SAP2-2 allele serves as a signal sensor and amplifier to enhance its own expression as well as to induce the SAP2-1 allele to achieve maximal proteolytic activity under appropriate conditions. Using in vivo expression technology, we could demonstrate that the SAP2-1 allele is significantly activated only in the late stages of systemic candidiasis in mice, whereas the SAP2-2 allele is induced much earlier. The differential regulation of the two SAP2 alleles was due to differences in their pro-moters, which contained a variable number of two pentameric nucleotide repeats. Mutations that reduced or increased the copy number of these repeats diminished the inducibility of the SAP2 promoter during infection but not in vitro, suggesting that the mutations affected interactions of regulatory factors that are necessary for SAP2 activation in vivo but dispensable for its induction in vitro. Therefore, the signals and signal transduction pathways that mediate SAP2 expression within certain host niches may differ from those that activate the gene in vitro. In addition to the generation of gene families whose members exhibit functional and regulatory diversification, C. albicans seems to use its diploid genome to create further variability and host adaptation by differential evolution of even the two alleles of a single gene.     

The crystal structure of the Physarum polycephalum actin-fragmin kinase: an atypical protein kinase with a specialized substrate-binding domain.

Coordinated temporal and spatial regulation of the actin cytoskeleton is essential for diverse cellular processes such as cell division, cell motility and the formation and maintenance of specialized structures in differentiated cells. In plasmodia of Physarum polycephalum, the F-actin capping activity of the actin-fragmin complex is regulated by the phosphorylation of actin. This is mediated by a novel type of protein kinase with no sequence homology to eukaryotic-type protein kinases. Here we present the crystal structure of the catalytic domain of the first cloned actin kinase in complex with AMP at 2.9 A resolution. The three-dimensional fold reveals a catalytic module of approximately 160 residues, in common with the eukaryotic protein kinase superfamily, which harbours the nucleotide binding site and the catalytic apparatus in an inter-lobe cleft. Several kinases that share this catalytic module differ in the overall architecture of their substrate recognition domain. The actin-fragmin kinase has acquired a unique flat substrate recognition domain which is supposed to confer stringent substrate specificity.     

No evidence for melatonin-linked immunoenhancement over the annual cycle of an avian species

The winter immunoenhancement hypothesis associates long nights and increased exposure to melatonin with enhanced immune function in winter when resource availability is low and the chances of becoming ill are high. Thus, increased exposure to melatonin in the winter could be adaptive for species facing difficult winter conditions. This idea has found some support in studies of resident mammals. In birds, the link between day length and melatonin over the annual cycle is weaker, and contributions of melatonin to seasonal timing are unclear. Furthermore, many species, especially migrants, do not experience the most difficult conditions of their annual cycle in winter. In this study, we tested whether the winter immunoenhancement hypothesis holds in an avian species, the red knot Calidris canutus. We found that melatonin duration and amplitude varied significantly over the annual cycle with the highest values occurring in winter. However, peaks did not correspond to the winter solstice or with annual variation in immune function. Our findings do not support the winter immunoenhancement hypothesis in knots and question whether the idea that immune function should be bolstered in winter can be generalized to systems where winter is not the most difficult time of the year.     

Future Climate Change Will Favour Non-Specialist Mammals in the (Sub)Arctics

Arctic and subarctic (i.e., [sub]arctic) ecosystems are predicted to be particularly susceptible to climate change. The area of tundra is expected to decrease and temperate climates will extend further north, affecting species inhabiting northern environments. Consequently, species at high latitudes should be especially susceptible to climate change, likely experiencing significant range contractions. Contrary to these expectations, our modelling of species distributions suggests that predicted climate change up to 2080 will favour most mammals presently inhabiting (sub)arctic Europe. Assuming full dispersal ability, most species will benefit from climate change, except for a few cold-climate specialists. However, most resident species will contract their ranges if they are not able to track their climatic niches, but no species is predicted to go extinct. If climate would change far beyond current predictions, however, species might disappear. The reason for the relative stability of mammalian presence might be that arctic regions have experienced large climatic shifts in the past, filtering out sensitive and range-restricted taxa. We also provide evidence that for most (sub)arctic mammals it is not climate change per se that will threaten them, but possible constraints on their dispersal ability and changes in community composition. Such impacts of future changes in species communities should receive more attention in literature.     

Exceptional Evolutionary Divergence of Human Muscle and Brain Metabolomes Parallels Human Cognitive and Physical Uniqueness

Metabolite concentrations reflect the physiological states of tissues and cells. However, the role of metabolic changes in species evolution is currently unknown. Here, we present a study of metabolome evolution conducted in three brain regions and two non-neural tissues from humans, chimpanzees, macaque monkeys, and mice based on over 10,000 hydrophilic compounds. While chimpanzee, macaque, and mouse metabolomes diverge following the genetic distances among species, we detect remarkable acceleration of metabolome evolution in human prefrontal cortex and skeletal muscle affecting neural and energy metabolism pathways. These metabolic changes could not be attributed to environmental conditions and were confirmed against the expression of their corresponding enzymes. We further conducted muscle strength tests in humans, chimpanzees, and macaques. The results suggest that, while humans are characterized by superior cognition, their muscular performance might be markedly inferior to that of chimpanzees and macaque monkeys.     

Ontogeny of the opioidergic regulation of LH and prolactin secretion in lactating sows. II: Interaction between suckling and morphine administration

Administration of morphine to ten suckled and nine zero-weaned (piglets removed immediately after farrowing) sows was used to investigate the apparent absence of opioid regulation of LH and prolactin secretion in early lactation. Blood samples were collected at 10 min intervals at 24-30, 48-54, 72-78 h post partum, and for a 12 h period from 08:00 to 20:00 on day 10 after farrowing. Morphine (0.1 mg kg-1) was administered as three i.v. bolus injections at intervals of 1 h during the last 3 h of each of the 6 h sampling periods, and at 6, 7 and 8 h after the beginning of sampling on day 10. There were significant (P < 0.001) group (zero-weaned versus suckled), time and morphine effects on LH secretion. Plasma LH concentrations increased (P < 0.001) within 48 h of farrowing in zero-weaned sows. Long-term trends of an increase in mean plasma LH in the sampling periods before treatment were attenuated in both groups by morphine treatment. Morphine also significantly inhibited (P < 0.05) prolactin secretion in suckled sows. In zero-weaned sows, plasma prolactin was already low at the start of sampling and did not change with time or in response to morphine treatment. Therefore, the inability to demonstrate an opioidergic involvement in the suckling-induced inhibition of LH secretion during the early post-partum period in sows is not due to a lack of opioid receptors. Furthermore, in suckled sows, morphine is stimulatory to systems that have an inhibitory effect on prolactin secretion.     

Molecular and Cellular Evidence for an Oligodendrocyte Abnormality in Schizophrenia

Our previous analyses in postmortem prefrontal cortex samples from a well-characterized cohort of severely affected schizophrenics and in matched controls demonstrated decreased expression of myelin and oligodendrocyte-related genes in the disease state. This decreased expression, now replicated in independent studies, suggests that there is a disruption of oligodendrocyte function and/or a loss of oligodendrocytes in schizophrenia. In the current report, we review expression studies in schizophrenia and present data demonstrating consistently fewer oligodendrocytes in schizophrenics compared to controls. The decrease in density reached 22% (p < 0.01) in layer III of area 9 and 20% (p < 0.02) in the white matter of the superior frontal gyrus. These data, when taken together with expression studies carried out by us and by other groups, and by imaging and other microscopic studies, point to a major involvement of oligodendrocyte abnormalities in schizophrenia. Therapies modulating oligodendrocyte survival and differentiation may therefore be beneficial in schizophrenia.