Mycalolide B dissociates dynactin and abolishes retrograde axonal transport of dense-core vesicles

Axonal transport is critical for maintaining synaptic transmission. Of interest, anterograde and retrograde axonal transport appear to be interdependent, as perturbing one directional motor often impairs movement in the opposite direction. Here live imaging of Drosophila and hippocampal neuron dense-core vesicles (DCVs) containing a neuropeptide or brain-derived neurotrophic factor shows that the F-actin depolymerizing macrolide toxin mycalolide B (MB) rapidly and selectively abolishes retrograde, but not anterograde, transport in the axon and the nerve terminal. Latrunculin A does not mimic MB, demonstrating that F-actin depolymerization is not responsible for unidirectional transport inhibition. Given that dynactin initiates retrograde transport and that amino acid sequences implicated in macrolide toxin binding are found in the dynactin component actin-related protein 1, we examined dynactin integrity. Remarkably, cell extract and purified protein experiments show that MB induces disassembly of the dynactin complex. Thus imaging selective retrograde transport inhibition led to the discovery of a small-molecule dynactin disruptor. The rapid unidirectional inhibition by MB suggests that dynactin is absolutely required for retrograde DCV transport but does not directly facilitate ongoing anterograde DCV transport in the axon or nerve terminal. More generally, MB''s effects bolster the conclusion that anterograde and retrograde axonal transport are not necessarily interdependent.     

The Micronesia Challenge: Assessing the Relative Contribution of Stressors on Coral Reefs to Facilitate Science-to-Management Feedback

Fishing and pollution are chronic stressors that can prolong recovery of coral reefs and contribute to ecosystem decline. While this premise is generally accepted, management interventions are complicated because the contributions from individual stressors are difficult to distinguish. The present study examined the extent to which fishing pressure and pollution predicted progress towards the Micronesia Challenge, an international conservation strategy initiated by the political leaders of 6 nations to conserve at least 30% of marine resources by 2020. The analyses were rooted in a defined measure of coral-reef-ecosystem condition, comprised of biological metrics that described functional processes on coral reefs. We report that only 42% of the major reef habitats exceeded the ecosystem-condition threshold established by the Micronesia Challenge. Fishing pressure acting alone on outer reefs, or in combination with pollution in some lagoons, best predicted both the decline and variance in ecosystem condition. High variances among ecosystem-condition scores reflected the large gaps between the best and worst reefs, and suggested that the current scores were unlikely to remain stable through time because of low redundancy. Accounting for the presence of marine protected area (MPA) networks in statistical models did little to improve the models’ predictive capabilities, suggesting limited efficacy of MPAs when grouped together across the region. Yet, localized benefits of MPAs existed and are expected to increase over time. Sensitivity analyses suggested that (i) grazing by large herbivores, (ii) high functional diversity of herbivores, and (iii) high predator biomass were most sensitive to fishing pressure, and were required for high ecosystem-condition scores. Linking comprehensive fisheries management policies with these sensitive metrics, and targeting the management of pollution, will strengthen the Micronesia Challenge and preserve ecosystem services that coral reefs provide to societies in the face of climate change.     

Identification of a monocyte-derived factor which regulates synthesis of insulin receptors on activated T-lymphocytes (MIRRF)

The regulation of the insulin receptor on the activated T-lymphocyte was studied. It has been previously shown that the monocyte with its constitutive insulin receptor can signal the quiescent T-lymphocyte with respect to ambient insulin concentration which regulates the copies of insulin receptors synthesized during the lymphocyte activation event. In this communication it is shown that the vehicle by which the monocyte signals the T-lymphocyte is a soluble, small molecular weight protein. Initially a bioassay was established to test the putative monocyte-derived factor in which freshly prepared purified populations of monocytes were incubated with insulin, extensively washed, and replated with lymphocytes in microwells or across a 3 microns filter from lymphocytes using the appearance of insulin receptors on T lymphocytes responding to lectin as measured by a radioligand binding assay as the outcome variable. Dose response and time course relationships were established to develop the ideal conditions for the bioassay. It was shown that the monocyte-derived insulin receptor regulatory factor (MIRRF) could be readily detected in conditioned medium of insulin-incubated and then washed monocytes as a starting point for attempts at later purification. Using rats fed an essential fatty acid deficient diet (EFAD), incapable of generating standard prostanoids, it was demonstrated that the MIRRF was readily detectable in our standard bioassay revealing that the factor was not a member of the arachidonic acid family. Lastly, it was shown that MIRRF is cycloheximide sensitive and either is a protein or requires protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preproenkephalin mRNA and Methionine-Enkephalin Content Are Increased in Mouse Striatum After Treatment with Nicotine

Abstract: A single dose of nicotine increased methionine-enkephalin (Met-Enk) immunoreactivity in the striatum of mice in a time-dependent manner. Met-Enk content reached a maximum by ∼1 h after nicotine and returned to control values by 6 h. The response to nicotine was blocked by pretreating animals with the nicotinic receptor antagonist mecamylamine. In contrast, pretreating mice with the muscarinic receptor antagonist atropine or the dopamine receptor antagonist haloperidol did not block the response. A single dose of nicotine also increased mRNA for the precursor peptide preproenkephalin (PPE). The increase of PPE mRNA preceded that of Met-Enk and reached a maximum by ∼30 min after nicotine. PPE mRNA levels returned to near normal by ∼3 h and increased again by 6 h after nicotine. Daily administration of nicotine for 14 days increased Met-Enk content and PPE mRNA in the striatum of mice as well. Taken together, our results suggest that nicotinic receptors modulate Met-Enk content and PPE mRNA in the mouse striatum.     

A close relationship between cytotoxic T lymphocytes generated in the mixed lymphocyte culture and insulin receptor-bearing lymphocytes: enrichment by density gradient centrifugation.

In contrast to liver, fat, muscle, the fibroblast, and the monocyte, the lymphocyte does not bear insulin receptors unless it is activated by antigen or mitogen. Antigen stimulation by skin graft or in the mixed lymphocyte culture (MLC) generates a population of T lymphocytes, the effector function of which can be augmented by insulin. In the same pool of cells are found T lymphocytes with newly emergent insulin receptors capable of supporting this augmentation. This study demonstrates the close relationship between the augmentable effector T cell and the insulin receptor-bearing cell and strongly suggests that these cells are identical. Splenic lymphocytes from unidirectional murine MLCs were separated into light and heavy fractions by discrete density gradient eentrifugation daily and assayed for cellular-mediated cytotoxicity and for insulin receptors. Receptor-bearing and cytotoxic lymphocytes waxed and waned together primarily in the light fraction. Receptor-positive cells preceded effectors by 24 hr and the two characteristics were highly correlated over time (r ≥ 0.95). T-Cell depletion by specific antisera or by immunoabsorbent column chromatography demonstrated that most, but not all, receptor-bearing cells were T cells and that virtually all effectors were also receptor positive. When the insulin receptor was functionally removed from the lymphocyte membrane by trypsin proteolysis, effector function ceased. The return of cytotoxicity was accompanied by return of the lymphocyte insulin receptor. Receptor-bearing cells were predominantly of the Ly 2⁺3⁺ pedigree but Ly 1⁺ cells were also induced to bear the insulin receptor along with a few non-T cells. These data show that the emergence of a lymphocyte insulin receptor is not just a fortuitous marker event of cellular activation but provides a structure capable of supporting lymphocyte effector function. The appearance of Ly 1⁺ receptor-bearing cells suggests the alloactivation of T helpers and their participation in a T-T cooperative event.     

Streptococcus mutans and dental caries in humans: a bacteriological and immunological study

Plaque samples from caries-active subjects showed a higher incidence of S. mutans than plaque samples from caries-free subjects. This was especially evident in approximal incisor plaque. S. mutans serotype d was almost exclusively present in approximal plaque obtained from caries-active subjects. Tooth surfaces infected with S. mutans still harbored this micro-organism 10 months later, while uninfected tooth surfaces remained free of S. mutans.Caries development predominantly occurs on those tooth surfaces which harbor relatively high percentages of S. mutans (> 5%). It is unlikely that serum or saliva antibodies against S. mutans play a major role in the protection against dental caries in these caries-free subjects since subjects with the greatest number of decayed surfaces showed the highest antibody titre as measured by haemagglutination or by the enzyme-linked immuno sorbent assay (ELISA).The present investigation shows that serum or salivary antibodies against S. mutans do not seem to play a role in caries resistance in young adults. However, this does not preclude a role of antibodies, prior to infection with S. mutans, in man.     

Differential habitat use by Acadian Nelson's sharp-tailed sparrows: implications for regional conservation

ABSTRACT.   Nelson's Sharp-tailed Sparrows ( Ammodramus nelsoni ) that breed along the Atlantic coast of North America (Acadian subspecies subvirgatus ) are considered saltmarsh specialists. However, these sparrows occasionally use upland habitats, such as hayfields. To evaluate the importance of hayfields as breeding habitat, we studied populations of A. n. subvirgatus in saltmarsh and hayfields in Nova Scotia, Canada, in 2004 and 2005. We monitored relative abundance and breeding phenology at 64 point-count stations (48 in hayfields and 16 in saltmarsh) and used an ordinal (0–5) observational index to quantify reproductive activity. A. n. subvirgatus showed more evidence of reproductive activity in saltmarsh (44% of point-count stations) than hayfields (28%; P = 0.07). However, there was no difference in either mean reproductive activity (saltmarsh = 0.83, hayfields = 0.53; P = 0.69) or mean relative abundance (saltmarsh = 0.27, hayfields = 0.26; P = 0.93). Although A. n. subvirgatus apparently breeds primarily in saltmarsh, hayfields appear to be an alternative breeding habitat. Use of hayfield habitat by A. n. subvirgtus , however, seems to vary between southern Maine and eastern Canada, suggesting that management plans will require approaches uniquely tailored to specific regions.     

Influence of liquid-layer thickness on pulmonary surfactant spreading and collapse

Pulmonary surfactant spreads on the thin ( approximately 0.1 microm) liquid layer that lines the alveoli, forming a film that reduces surface tension and allows normal respiration. Pulmonary surfactant deposited in vitro on liquid layers that are several orders of magnitude thicker, however, does not reach the low surface tensions ( approximately 0.001 N/m) achieved in the lungs during exhalation when the surfactant film compresses. This is due to collapse, a surface phase transition during which the surfactant film, rather than decreasing surface tension by increasing its surface density, becomes thicker at constant surface tension ( approximately 0.024 N/m). Formation of the collapse phase requires transport of surfactant to collapse sites, and this transport can be hindered in thinner liquid layers by viscous resistance to motion. Our objective is to determine the effect of the liquid-layer thickness on surfactant transport, which might affect surfactant collapse. To this end, we developed a mathematical model that accounts for the effect of the liquid-layer thickness on surfactant transport, and focused on surfactant spreading and collapse. Model simulations showed a marked decrease in collapse rates for thinner liquid layers, but this decrease was not enough to completely explain differences in surfactant film behavior between in vitro and in situ experiments.