648 research outputs found
Axons break in animals lacking β-spectrin
Axons and dendrites can withstand acute mechanical strain despite their small diameter. In this study, we demonstrate that β-spectrin is required for the physical integrity of neuronal processes in the nematode Caenorhabditis elegans. Axons in β-spectrin mutants spontaneously break. Breakage is caused by acute strain generated by movement because breakage can be prevented by paralyzing the mutant animals. After breaking, the neuron attempts to regenerate by initiating a new growth cone; this second round of axon extension is error prone compared with initial outgrowth. Because spectrin is a major target of calpain proteolysis, it is possible that some neurodegenerative disorders may involve the cleavage of spectrin followed by the breakage of neural processes
CAPS and syntaxin dock dense core vesicles to the plasma membrane in neurons
Docking to the plasma membrane prepares vesicles for rapid release. Here, we describe a mechanism for dense core vesicle docking in neurons. In Caenorhabditis elegans motor neurons, dense core vesicles dock at the plasma membrane but are excluded from active zones at synapses. We have found that the calcium-activated protein for secretion (CAPS) protein is required for dense core vesicle docking but not synaptic vesicle docking. In contrast, we see that UNC-13, a docking factor for synaptic vesicles, is not essential for dense core vesicle docking. Both the CAPS and UNC-13 docking pathways converge on syntaxin, a component of the SNARE (soluble N-ethyl-maleimideâsensitive fusion protein attachment receptor) complex. Overexpression of open syntaxin can bypass the requirement for CAPS in dense core vesicle docking. Thus, CAPS likely promotes the open state of syntaxin, which then docks dense core vesicles. CAPS function in dense core vesicle docking parallels UNC-13 in synaptic vesicle docking, which suggests that these related proteins act similarly to promote docking of independent vesicle populations
Rapid single nucleotide polymorphism mapping in C. elegans
BACKGROUND: In C. elegans, single nucleotide polymorphisms (SNPs) can function as silent genetic markers, with applications ranging from classical two- and three-factor mapping to measuring recombination across whole chromosomes. RESULTS: Here, we describe a set of 48 primer pairs that flank SNPs evenly spaced across the C. elegans genome and that work under identical PCR conditions. Each SNP in this set alters a DraI site, enabling rapid and parallel scoring. We describe a procedure using these reagents to quickly and reliably map mutations. We show that these techniques correctly map a known gene, dpy-5. We then use these techniques to map mutations in an uncharacterized strain, and show that its behavioral phenotype can be simultaneously mapped to three loci. CONCLUSION: Together, the reagents and methods described represent a significant advance in the accurate, rapid and inexpensive mapping of genes in C. elegans
Open Syntaxin Docks Synaptic Vesicles
Synaptic vesicles dock to the plasma membrane at synapses to facilitate rapid exocytosis. Docking was originally proposed to require the soluble N-ethylmaleimideâsensitive fusion attachment protein receptor (SNARE) proteins; however, perturbation studies suggested that docking was independent of the SNARE proteins. We now find that the SNARE protein syntaxin is required for docking of all vesicles at synapses in the nematode Caenorhabditis elegans. The active zone protein UNC-13, which interacts with syntaxin, is also required for docking in the active zone. The docking defects in unc-13 mutants can be fully rescued by overexpressing a constitutively open form of syntaxin, but not by wild-type syntaxin. These experiments support a model for docking in which UNC-13 converts syntaxin from the closed to the open state, and open syntaxin acts directly in docking vesicles to the plasma membrane. These data provide a molecular basis for synaptic vesicle docking
Translational aspects of blood-brain barrier transport and central nervous system effects of drugs: from discovery to patients
Pharmacolog
Delayed maximum northern European summer temperatures during the Last Interglacial as a result of Greenland Ice Sheet melt
This is the author accepted manuscript. The final version is available from the Geological Society of America via the DOI in this record.Here we report a new quantitative mean July temperature reconstruction using non-biting midges (chironomids) from the Danish Last Interglacial (LIG) site Hollerup (spanning 127â116 ka). We find that peak mean July temperatures of 17.5 °C, similar to those of the present day (1961â1990 CE), were reached shortly before the onset of the regional Carpinus pollen zone. Through comparison to terrestrial and marine sequences we demonstrate that peak summer warmth took place some three millennia after the onset of LIG warming in Europe, a marked delay in line with records from the North Atlantic. Crucially, the warmest northern European summer temperatures appear to follow maximum Greenland Ice Sheet mass loss, implying that meltwater substantially reduced Atlantic Meridional Overturning Circulation and depressed European temperatures during the early part of the interglacial.Turney and Fogwill thank the Australian Research Council (grants FL100100195, FT120100004,
LP120200724). Thanks to Bjørn Buchardt for providing the C:N data, Angela Self for help with statistical analysis, David Campbell and Alan Bedford for laboratory work, and three reviewers for their
constructive comments
The Sirius Passet Lagerstätte of North GreenlandâA geochemical window on early Cambrian lowâoxygen environments and ecosystems
The early Cambrian Sirius Passet fauna of northernmost Greenland (Cambrian Series 2, Stage 3) contains exceptionally preserved soft tissues that provide an important window to early animal evolution, while the surrounding sediment holds critical data on the palaeodepositional waterâcolumn chemistry. The present study combines palaeontological data with a multiproxy geochemical approach based on samples collected in situ at high stratigraphic resolution from Sirius Passet. After careful consideration of chemical alterations during burial, our results demonstrate that fossil preservation and biodiversity show significant correlation with iron enrichments (FeHR/FeT), trace metal behaviour (V/Al), and changes in nitrogen cycling (δ15N). These data, together with Mo/Al and the preservation of organic carbon (TOC), are consistent with a water column that was transiently low in oxygen concentration, or even intermittently anoxic. When compared with the biogeochemical characteristics of modern oxygen minimum zones (OMZs), geochemical and palaeontological data collectively suggest that oxygen concentrations as low as 0.2â0.4 ml/L restricted bioturbation but not the development of a largely nektobenthic community of predators and scavengers. We envisage for the Sirius Passet biota a depositional setting where anoxic water column conditions developed and passed over the depositional site, possibly in association with seaâlevel change, and where this early Cambrian biota was established in conditions with very low oxygen
Hypoxia inducible factorâ2Îą importance for migration, proliferation, and selfârenewal of trunk neural crest cells
Background: The neural crest is a transient embryonic stem cell population. Hypoxia inducible factor (HIF)â2Îą is associated with neural crest stem cell appearance and aggressiveness in tumors. However, little is known about its role in normal neural crest development.
Results: Here, we show that HIFâ2Îą is expressed in trunk neural crest cells of human, murine, and avian embryos. Knockdown as well as overexpression of HIFâ2Îą in vivo causes developmental delays, induces proliferation, and selfârenewal capacity of neural crest cells while decreasing the proportion of neural crest cells that migrate ventrally to sympathoadrenal sites. Reflecting the in vivo phenotype, transcriptome changes after loss of HIFâ2Îą reveal enrichment of genes associated with cancer, invasion, epithelialâtoâmesenchymal transition, and growth arrest.
Conclusions: Taken together, these results suggest that expression levels of HIFâ2Îą must be strictly controlled during normal trunk neural crest development and that dysregulated levels affects several important features connected to stemness, migration, and development
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