Specific gamma‐aminobutyrate chemotaxis in pseudomonads with different lifestyle

The PctC chemoreceptor of Pseudomonas aeruginosa mediates chemotaxis with high specificity to gamma‐aminobutyric acid (GABA). This compound is present everywhere in nature and has multiple functions, including being a human neurotransmitter or plant signaling compound. Because P. aeruginosa is ubiquitously distributed in nature and able to infect and colonize different hosts, the physiological relevance of GABA taxis is unclear, but it has been suggested that bacterial attraction to neurotransmitters may enhance virulence. We report the identification of McpG as a specific GABA chemoreceptor in non‐pathogenic Pseudomonas putida KT2440. As with PctC, GABA was found to bind McpG tightly. The analysis of chimeras comprising the PctC and McpG ligand‐binding domains fused to the Tar signaling domain showed very high GABA sensitivities. We also show that PctC inactivation does not alter virulence in Caenorhabditis elegans. Significant amounts of GABA were detected in tomato root exudates, and deletion of mcpG reduced root colonization that requires chemotaxis through agar. The C. elegans data and the detection of a GABA receptor in non‐pathogenic species indicate that GABA taxis may not be related to virulence in animal systems but may be of importance in the context of colonization and infection of plant roots by soil‐dwelling pseudomonads.     

Filtration is a time-efficient option to Histopaque,providing good-quality islets in mouse islet isolation

Pancreatic islet transplantation is a promising therapy for Type I Diabetes. For many years the method used worldwide for islet purification in both rodent and human islet isolation has been Ficoll-based density gradients, such as Histopaque. However, it is difficult to purify islets in laboratories with staff limitations when large scale isolations are required. We hypothesized that filtration could be a more simple and fast alternative to obtain good quality islets. Four separate islet isolations were performed per method, comparing filtration and Histopaque purification with handpicking as the gold standard method for islet purity. Different parameters of quality were assessed: yield in number of islets per pancreas, purity by dithizone staining, viability by Fluorescein Diacetate/Propidium Iodide vital staining and in vitro functionality assessed by Glucose Stimulated Insulin Secretion. Time efficiency and cost were also analyzed. The overall quality of the islets obtained both by Histopaque and filtration was good. Filtration saved almost 90 % of the time consumed by Histopaque purification, and was also cheaper. However, one-third of the islets were lost. Since human and rodent islets share similar size but different density, filtration appears as a purification method with potential interest in translation to clinic.     

Habitat‐specific demography,source‐sink dynamics,and the niche of a common shrub in a heterogeneous and fluctuating environment

The occurrence of a species in habitats of varying quality connected through migration can only be understood by detailed investigation of itsdemography. In the Chihuahuan Desert, the common shrub Flourensia cernua is found in both productive and unproductive areas. In the former, both growing and senescent populations are regularly found, while in the latter a low density scattered population persists indefinitely. While precipitation (and its annual stochastic variation) is the same in both habitats, their geomorphological differences produce a sharp difference in the availability of the limiting resource, water. This produces different population dynamics in F. cernua, but also radically different plant communities. Counterintuitively, the low‐resource habitat (LR) supports a scattered, slightly increasing or stable population that coexists with its neighbors and acts as exporter of seeds (source population). In contrast, the high‐resource habitat (HR) allows sporadic recruitment of locally dense patches that tend towards extinction (sink population). The latter is accounted for by the increasing dominance of the grass Pleuraphys mutica. The different dynamics and regulatory mechanisms in each habitat allow the species to occupy a wider distribution than it would have in their absence. The higher abundance of F. cernua in the sink habitat, together with its consequences on community composition and dynamics, questions the idea proposed in the literature that a sink population lives outside its fundamental niche. The study provides support to the notion that the ecological niche of a species cannot be completely characterized by its requirements (e.g. as they relate to physiology), but must also include the complex demographic responses to a spatially and temporally variable environment, which may often include substandard conditions. For the niche concept to retain its usefulness, it must incorporate the demographic response of populations to spatially and temporallyvariable resource supply.     

A BDNF loop-domain mimetic acutely reverses spontaneous apneas and respiratory abnormalities during behavioral arousal in a mouse model of Rett syndrome

Reduced levels of brain-derived neurotrophic factor (BDNF) are thought to contribute to the pathophysiology of Rett syndrome (RTT), a severe neurodevelopmental disorder caused by loss-of-function mutations in the gene encoding methyl-CpG-binding protein 2 (MeCP2). In Mecp2 mutant mice, BDNF deficits have been associated with breathing abnormalities, a core feature of RTT, as well as with synaptic hyperexcitability within the brainstem respiratory network. Application of BDNF can reverse hyperexcitability in acute brainstem slices from Mecp2-null mice, suggesting that therapies targeting BDNF or its receptor, TrkB, could be effective at acute reversal of respiratory abnormalities in RTT. Therefore, we examined the ability of LM22A-4, a small-molecule BDNF loop-domain mimetic and TrkB partial agonist, to modulate synaptic excitability within respiratory cell groups in the brainstem nucleus tractus solitarius (nTS) and to acutely reverse abnormalities in breathing at rest and during behavioral arousal in Mecp2 mutants. Patch-clamp recordings in Mecp2-null brainstem slices demonstrated that LM22A-4 decreases excitability at primary afferent synapses in the nTS by reducing the amplitude of evoked excitatory postsynaptic currents and the frequency of spontaneous and miniature excitatory postsynaptic currents. In vivo, acute treatment of Mecp2-null and -heterozygous mutants with LM22A-4 completely eliminated spontaneous apneas in resting animals, without sedation. Moreover, we demonstrate that respiratory dysregulation during behavioral arousal, a feature of human RTT, is also reversed in Mecp2 mutants by acute treatment with LM22A-4. Together, these data support the hypothesis that reduced BDNF signaling and respiratory dysfunction in RTT are linked, and establish the proof-of-concept that treatment with a small-molecule structural mimetic of a BDNF loop domain and a TrkB partial agonist can acutely reverse abnormal breathing at rest and in response to behavioral arousal in symptomatic RTT mice.KEY WORDS: Mecp2, Brain-derived neurotrophic factor (BDNF), Respiration, Brainstem, Arousal     

Sporadic naturally occurring melanoma in dogs as a preclinical model for human melanoma

Melanoma represents a significant malignancy in humans and dogs. Different from genetically engineered models, sporadic canine melanocytic neoplasms share several characteristics with human disease that could make dogs a more relevant preclinical model. Canine melanomas rarely arise in sun‐exposed sites. Most occur in the oral cavity, with a subset having intra‐epithelial malignant melanocytes mimicking the in situ component of human mucosal melanoma. The spectrum of canine melanocytic neoplasia includes benign lesions with some analogy to nevi, as well as invasive primary melanoma, and widespread metastasis. Growing evidence of distinct subtypes in humans, differing in somatic and predisposing germ‐line genetic alterations, cell of origin, epidemiology, relationship to ultraviolet radiation and progression from benign to malignant tumors, may also exist in dogs. Canine and human mucosal melanomas appear to harbor BRAF, NRAS, and c‐kit mutations uncommonly, compared with human cutaneous melanomas, although both species share AKT and MAPK signaling activation. We conclude that there is significant overlap in the clinical and histopathological features of canine and human mucosal melanomas. This represents opportunity to explore canine oral cavity melanoma as a preclinical model.     

The Synaptonemal Complex of Basal Metazoan Hydra:More Similarities to Vertebrate than Invertebrate Meiosis Model Organisms

The synaptonemal complex （SC） is an evolutionarily well-conserved structure that mediates chromosome synapsis during prophase of the first meiotic division. Although its structure is conserved, the characterized protein components in the current metazoan meiosis model systems （Drosophila melanogaster, Caenorhabditis elegans, and Mus musculus） show no sequence homology, challenging the question of a single evolutionary origin of the SC. However, our recent studies revealed the monophyletic origin of the mammalian SC protein components. Many of them being ancient in Metazoa and already present in the cnidarian Hydra. Remarkably, a comparison between different model systems disclosed a great similarity between the SC components of Hydra and mammals while the proteins of the ecdysozoan systems （D. rnelanogaster and C. elegans） differ significantly. In this review, we introduce the basal-branching metazoan species Hydra as a potential novel invertebrate model system for meiosis research and particularly for the investigation of SC evolution, function and assembly. Also, available methods for SC research in Hydra are summarized.     

Activation and identification of five clusters for secondary metabolites in Streptomyces albus J1074

Streptomyces albus J1074 is a streptomycete strain widely used as a host for expression of secondary metabolite gene clusters. Bioinformatic analysis of the genome of this organism predicts the presence of 27 gene clusters for secondary metabolites. We have used three different strategies for the activation of some of these silent/cryptic gene clusters in S. albus J1074: two hybrid polyketide-non-ribosomal peptides (PK-NRP) (antimycin and 6-epi-alteramides), a type I PK (candicidin), a non-ribosomal peptides (NRP) (indigoidine) and glycosylated compounds (paulomycins). By insertion of a strong and constitutive promoter in front of selected genes of two clusters, production of the blue pigment indigoidine and of two novel members of the polycyclic tetramate macrolactam family (6-epi-alteramides A and B) was activated. Overexpression of positive regulatory genes from the same organism also activated the biosynthesis of 6-epi-alteramides and heterologous expression of the regulatory gene pimM of the pimaricin cluster activated the simultaneous production of candicidins and antimycins, suggesting some kind of cross-regulation between both clusters. A cluster for glycosylated compounds (paulomycins) was also identified by comparison of the high-performance liquid chromatography profiles of the wild-type strain with that of a mutant in which two key enzymes of the cluster were simultaneously deleted.