Semaphorins in axon regeneration: developmental guidance molecules gone wrong?

Semaphorins are developmental axon guidance cues that continue to be expressed during adulthood and are regulated by neural injury. During the formation of the nervous system, repulsive semaphorins guide axons to their targets by restricting and channelling their growth. They affect the growth cone cytoskeleton through interactions with receptor complexes that are linked to a complicated intracellular signal transduction network. Following injury, regenerating axons stop growing when they reach the border of the glial-fibrotic scar, in part because they encounter a potent molecular barrier that inhibits growth cone extension. A number of secreted semaphorins are expressed in the glial-fibrotic scar and at least one transmembrane semaphorin is upregulated in oligodendrocytes surrounding the lesion site. Semaphorin receptors, and many of the signal transduction components required for semaphorin signalling, are present in injured central nervous system neurons. Here, we review evidence that supports a critical role for semaphorin signalling in axon regeneration, and highlight a number of challenges that lie ahead with respect to advancing our understanding of semaphorin function in the normal and injured adult nervous system.     

A flow-through fluorescence polarization detection system for measuring GPCR-mediated modulation of cAMP production

A flow-through fluorescence polarization (FP) detection system that makes use of a novel high-performance liquid chromatography (HPLC) fluorescence detector modified with polarization filters was developed. This flow-through FP detection system was evaluated by using a novel and very cost-effective bioassay for cyclic adenosine monophosphate (cAMP). The bioassay was first evaluated and optimized in an FP plate reader format and subsequently in a flow-through bioassay setup. The principle of the bioassay is based on the competition of cAMP and a fluorescent cAMP derivative for the cAMP binding domain of protein kinase A. cAMP could accurately be determined over a range of 0.8 to 30 pmol/well in the plate reader FP assay and over a range of 0.3 to 50 pmol/well in the flow-through FP assay setup. High Z' factors (i.e., 0.89 for the plate reader and 0.93 for the flow-through FP cAMP assay, respectively) indicated robust assays. Finally, functional cAMP signaling of the human histamine H(3) G-protein-coupled receptor (GPCR) in cell cultures was measured with both assay formats with good sensitivities and assay windows. The pEC(50) values obtained in both assay formats were in accordance with those obtained with standard methods. The flow-through FP detection system could thus be used as a cost-effective alternative to FP plate reader assays. Moreover, the novel flow-through FP detection system for cAMP constitutes a good analytical tool to be used in the GPCR research field as an alternative to the use of FP plate readers or radioactive laboratories nowadays used for cAMP measurements.     

Acetate Utilization in Lactococcus lactis Deficient in Lactate Dehydrogenase: a Rescue Pathway for Maintaining Redox Balance

Acetate was shown to improve glucose fermentation in Lactococcus lactis deficient in lactate dehydrogenase. 13C and 1H nuclear magnetic resonance studies using [2-13C]glucose and [2-(13)C]acetate as substrates demonstrated that acetate was exclusively converted to ethanol. This novel pathway provides an alternative route for NAD+ regeneration in the absence of lactate dehydrogenase.     

Paleoclimatic history and vicariant speciation in the "sand goby" group (Gobiidae, Teleostei)

Vicariant and climatic cycling speciation hypotheses of the 'sand gobies' belonging to the genera Pomatoschistus, Gobiusculus, Knipowitschia, and Economidichthys are tested using molecular phylogenies constructed of nuclear DNA (ITS1 locus) and mitochondrial DNA (12S and 16S fragments). These gobies are among the most abundant in the Eastern Atlantic-Mediterranean region, and play an important role in the ecosystem. Considerable ITS1 length differences, primarily due to the presence of several tandem repeats, were found between species and even within individuals. Therefore, phylogenetic analyses focused on fragments of the 12S and 16S mtDNA region that have been sequenced for 16 goby taxa. The 'sand gobies' clustered as a monophyletic group as proposed on morphological grounds. However, G. flavescens, E. pygmaeus, and K. punctatissima clustered within the Pomatoschistus species, pointing to a paraphyletic origin of these genera. Furthermore, the genetic divergence between P. minutus from the Adriatic Sea versus the Atlantic-Mediterranean region was as high as the divergence within the P. minutus complex, suggesting that P. minutus from the Adriatic Sea should be considered as a distinct species. The "star" phylogeny might suggest that these gobies evolved in a very short time period, possibly linked to the drastic alterations in the Mediterranean Sea during and immediately after the Messinian salinity crisis at the end of the Miocene. The freshwater life-style appeared monophyletic; equating its origin with the salinity crisis resulted in a molecular clock estimate of 1.4% divergence per million years. The last common ancestor probably occupied sandy bottoms and a coastal niche while several species subsequently adapted to new habitats (pelagic, freshwater or stenohaline). The origin of the shallowest clades dated back to the glacial cycling during the Pleistocene epoch.     

Mapping early fate determination in Lgr5+ crypt stem cells using a novel Ki67‐RFP allele

Cycling Lgr5⁺ stem cells fuel the rapid turnover of the adult intestinal epithelium. The existence of quiescent Lgr5⁺ cells has been reported, while an alternative quiescent stem cell population is believed to reside at crypt position +4. Here, we generated a novel Ki67^RFP knock-in allele that identifies dividing cells. Using Lgr5-GFP;Ki67^RFP mice, we isolated crypt stem and progenitor cells with distinct Wnt signaling levels and cell cycle features and generated their molecular signature using microarrays. Stem cell potential of these populations was further characterized using the intestinal organoid culture. We found that Lgr5^high stem cells are continuously in cell cycle, while a fraction of Lgr5^low progenitors that reside predominantly at +4 position exit the cell cycle. Unlike fast dividing CBCs, Lgr5^low Ki67⁻ cells have lost their ability to initiate organoid cultures, are enriched in secretory differentiation factors, and resemble the Dll1 secretory precursors and the label-retaining cells of Winton and colleagues. Our findings support the cycling stem cell hypothesis and highlight the cell cycle heterogeneity of early progenitors during lineage commitment.     

Effect of Antimicrobial Consumption and Production Type on Antibacterial Resistance in the Bovine Respiratory and Digestive Tract

The aim of this study was to investigate the relationship between antimicrobial use and the occurrence of antimicrobial resistance in the digestive and respiratory tract in three different production systems of food producing animals. A longitudinal study was set up in 25 Belgian bovine herds (10 dairy, 10 beef, and 5 veal herds) for a 2 year monitoring of antimicrobial susceptibilities in E. coli and Pasteurellaceae retrieved from the rectum and the nasal cavity, respectively. During the first year of observation, the antimicrobial use was prospectively recorded on 15 of these farms (5 of each production type) and transformed into the treatment incidences according to the (animal) defined daily dose (TI_ADD) and (actually) used daily dose (TI_UDD). Antimicrobial resistance rates of 4,174 E. coli (all herds) and 474 Pasteurellaceae (beef and veal herds only) isolates for 12 antimicrobial agents demonstrated large differences between intensively reared veal calves (abundant and inconstant) and more extensively reared dairy and beef cattle (sparse and relatively stable). Using linear mixed effect models, a strong relation was found between antimicrobial treatment incidences and resistance profiles of 1,639 E. coli strains (p<0.0001) and 309 Pasteurellaceae (p≤0.012). These results indicate that a high antimicrobial selection pressure, here found to be represented by low dosages of oral prophylactic and therapeutic group medication, converts not only the commensal microbiota from the digestive tract but also the opportunistic pathogenic bacteria in the respiratory tract into reservoirs of multi-resistance.     

Tomato Pto encodes a functional N-myristoylation motif that is required for signal transduction in Nicotiana benthamiana

Pto kinase of tomato (Lycopersicon esculentum) confers resistance to bacterial speck disease caused by Pseudomonas syringae pv. tomato expressing avrPto or avrPtoB. Pto interacts directly with these type-III secreted effectors, leading to induction of defence responses including the hypersensitive response (HR). Signalling by Pto requires the nucleotide-binding site-leucine-rich repeat (NBS-LRR) protein Prf. Little is known of how Pto is controlled prior to or during stimulation, although kinase activity is required for Avr-dependent activation. Here we demonstrate a role for the N-terminus in signalling by Pto. N-terminal residues outside the kinase domain were required for induction of the HR in Nicotiana benthamiana. The N-terminus also contributed to both AvrPto-binding and phosphorylation abilities. Pto residues 1-10 comprise a consensus motif for covalent attachment of myristate, a hydrophobic 14-carbon saturated fatty acid, to the Gly-2 residue. Several lines of evidence indicate that this motif is important for Pto function. A heterologous N-myristoylation motif complemented N-terminal deletion mutants of Pto for Prf-dependent signalling. Signalling by wild-type and mutant forms of Pto was strictly dependent on the Gly-2 residue. The N-myristoylation motif of Pto complemented the cognate motif of AvrPto for avirulence function and membrane association. Furthermore, Pto was myristoylated in vivo dependent on the presence of Gly-2. The subcellular localization of Pto was independent of N-myristoylation, indicating that N-myristoylation is required for some function other than membrane affinity. Consistent with this idea, AvrPtoB was also found to be a soluble protein. The data indicate an important role(s) for the myristoylated N-terminus in Pto signalling.