Direct interaction enables cross-talk between ionotropic and group I metabotropic glutamate receptors

Functional interplay between ionotropic and metabotropic receptors frequently involves complex intracellular signaling cascades. The group I metabotropic glutamate receptor mGlu5a co-clusters with the ionotropic N-methyl-d-aspartate (NMDA) receptor in hippocampal neurons. In this study, we report that a more direct cross-talk can exist between these types of receptors. Using bioluminescence resonance energy transfer in living HEK293 cells, we demonstrate that mGlu5a and NMDA receptor clustering reflects the existence of direct physical interactions. Consequently, the mGlu5a receptor decreased NMDA receptor current, and reciprocally, the NMDA receptor strongly reduced the ability of the mGlu5a receptor to release intracellular calcium. We show that deletion of the C terminus of the mGlu5a receptor abolished both its interaction with the NMDA receptor and reciprocal inhibition of the receptors. This direct functional interaction implies a higher degree of target-effector specificity, timing, and subcellular localization of signaling than could ever be predicted with complex signaling pathways.     

Experimental Infections with Mycoplasma agalactiae Identify Key Factors Involved in Host-Colonization

Mechanisms underlying pathogenic processes in mycoplasma infections are poorly understood, mainly because of limited sequence similarities with classical, bacterial virulence factors. Recently, large-scale transposon mutagenesis in the ruminant pathogen Mycoplasma agalactiae identified the NIF locus, including nifS and nifU, as essential for mycoplasma growth in cell culture, while dispensable in axenic media. To evaluate the importance of this locus in vivo, the infectivity of two knock-out mutants was tested upon experimental infection in the natural host. In this model, the parental PG2 strain was able to establish a systemic infection in lactating ewes, colonizing various body sites such as lymph nodes and the mammary gland, even when inoculated at low doses. In these PG2-infected ewes, we observed over the course of infection (i) the development of a specific antibody response and (ii) dynamic changes in expression of M. agalactiae surface variable proteins (Vpma), with multiple Vpma profiles co-existing in the same animal. In contrast and despite a sensitive model, none of the knock-out mutants were able to survive and colonize the host. The extreme avirulent phenotype of the two mutants was further supported by the absence of an IgG response in inoculated animals. The exact role of the NIF locus remains to be elucidated but these data demonstrate that it plays a key role in the infectious process of M. agalactiae and most likely of other pathogenic mycoplasma species as many carry closely related homologs.     

Anzygina, a new genus for some Australasian microleafhopper species formerly placed in the genus Zygina Fieber (Cicadellidae: Typhlocybinae: Erythroneurini)

Species of Erythroneurini (Cicadellidae: Typhlocybinae) currently placed in the genus Zygina and found in Australia, New Zealand and some neighbouring islands are transferred to the new genus Anzygina , type species Erythroneura sidnica Kirkaldy, following comparison with the type species of the genus: Typhlocyba nivea Mulsant and Rey. New combinations are Anzygina sidnica (Kirkaldy), Anzygina honiloa (Kirkaldy), Anzygina melanogaster (Kirkaldy) and Anzygina sativae (Evans) from Australia, Anzygina toetoe (Cumber), Anzygina agni (Knight), Anzygina dumbletoni (Ghauri) and Anzygina ramsayi (Knight) from New Zealand, Anzygina zealandica (Myers) from Australia and New Zealand, Anzygina jowettae (Knight) from Norfolk Island and Anzygina medioborealis (Ghauri) from Papua New Guinea. Lectotypes are designated for Erythroneura honiloa Kirkaldy and E. sidnica Kirkaldy. Anzygina billi sp.n. is described from SE Qld, and Anzygina barrattae sp.n. is described from the South Island of New Zealand. A. agni is a new record for Australia and is presumed to be Australian in origin. A. dumbletoni has a distribution which suggests that it also is introduced to New Zealand although its origins are not known. A. ramsayi, A. barrattae and A. toetoe , all of which appear to be New Zealand endemics, show affinity with each other based on aedeagal structure. A key to these species, based on males, is provided. The lack of male syntypes for Erythroneura honiala Kirkaldy and Erythroneura lubra Kirkaldy precludes establishment of their identities relative to other species of the genus, and both names are regarded as having nomen dubium status. Australian species not transferred to Anzygina are Zygina evansi (Ross) and Zygina ipoloa (Kirkaldy), both of which belong elsewhere.     

Social Agonistic Distress in Male and Female Mice: Changes of Behavior and Brain Monoamine Functioning in Relation to Acute and Chronic Challenges

Stressful events promote several neuroendocrine and neurotransmitter changes that might contribute to the provocation of psychological and physical pathologies. Perhaps, because of its apparent ecological validity and its simple application, there has been increasing use of social defeat (resident-intruder) paradigms as a stressor. The frequency of stress-related psychopathology is much greater in females than in males, but the typical resident-intruder paradigm is less useful in assessing stressor effects in females. An alternative, but infrequently used procedure in females involves exposing a mouse to a lactating dam, resulting in threatening gestures being expressed by the resident. In the present investigation we demonstrated the utility of this paradigm, showing that the standard resident-intruder paradigm in males and the modified version in females promoted elevated anxiety in a plus-maze test. The behavioral effects that reflected anxiety were more pronounced 2 weeks after the stressor treatment than they were 2 hr afterward, possibly reflecting the abatement of the stress-related of hyper-arousal. These treatments, like a stressor comprising physical restraint, increased plasma corticosterone and elicited variations of norepinephrine and serotonin levels and turnover within the prefrontal cortex, hippocampus and central amygdala. Moreover, the stressor effects were exaggerated among mice that had been exposed to a chronic or subchronic-intermittent regimen of unpredictable stressors. Indeed, some of the monoamine changes were more pronounced in females than in males, although it is less certain whether this represented compensatory changes to deal with chronic stressors that could result in excessive strain on biological systems (allostatic overload).     

The Dystrophin Glycoprotein Complex Regulates the Epigenetic Activation of Muscle Stem Cell Commitment

1. Download high-res image (270KB)
2. Download full-size image

     

Identification and characterization of a novel chemically induced allele at the planar cell polarity gene Vangl2

Planar cell polarity (PCP) signaling controls a number of morphogenetic processes including convergent extension during gastrulation and neural tube formation. Defects in this pathway cause neural tube defects (NTD), the most common malformations of the central nervous system. The Looptail (Lp) mutant mouse was the first mammalian mutant implicating a PCP gene (Vangl2) in the pathogenesis of NTD. We report on a novel chemically induced mutant allele at Vangl2 called Curly Bob that causes a missense mutation p.Ile268Asn (I268N) in the Vangl2 protein. This mutant segregates in a semi-dominant fashion with heterozygote mice displaying a looped tail appearance, bobbing head, and a circling behavior. Homozygote mutant embryos suffer from a severe form of NTD called craniorachischisis, severe PCP defects in the inner hair cells of the cochlea and posterior cristae, and display a distinct defect in retinal axon guidance. This mutant genetically interacts with the Lp allele (Vangl2 ^S464N) in neural tube development and inner ear hair cell polarity. The Vangl2^I268N protein variant is expressed at very low levels in affected neural and retinal tissues of mutant homozygote embryos. Biochemical studies show that Vangl2^I268N exhibits impaired targeting to the plasma membrane and accumulates in the endoplasmic reticulum. The Vangl2^I268N variant no longer physically interacts with its PCP partner DVL3 and has a reduced protein half-life. This mutant provides an important model for dissecting the role of Vangl2 in the development of the neural tube, establishment of polarity of sensory cells of the auditory and vestibular systems, and retinal axon guidance.

     

Characterization and inhibition of aminopeptidase A by α-mercapto-β-amino acyl dipeptides

Summary In order to study the physiological role of aminopeptidase A(APA), several α-mercapto-β-amino acyl dipeptides were synthesized to obtain compounds having a high affinity for APA and a high selectivity versus aminopeptidase N (APN). Sulfornamide and carboxylate moieties which have been shown to be recognized by the S₁ subsite of the enzyme were introduced on the side chain of the α-mercapto-β-amino acyl sub-unit, the latter being coupled to dipeptides optimized to interact with the S'₁ and S'₂ subsites by means of combinatorial chemistry. Good affinities (16nM) were obtained, the selectivity factors being up to 160-fold versus APN.     

Allosteric-type control of synaptobrevin cleavage by protect tetanus toxin light chain

Summary The light chain of tetanus neurotoxin (TeNTL chain) has been shown to be endowed with zine endopeptidase activity, selectively directed towards the Gln⁷⁶-Phe⁷⁷ bond of synaptobrevin, a vesicle-associated membrane protein critically involved in neuroexocytosis. In previous reports, truncations at the NH₂- and COOH-terminus of synaptobrevin have shown that the sequence 39–88 of synaptobrevin is the minimum substrate of TeNT, suggesting either the requirement of a well-defined three-dimensional structure of synaptobrevin or a role in the mechanism of substrate hydrolysis for residues distal from the cleavage site. In this study, the addition of NH₂- and COOH-terminal peptides of synaptobrevin, S 27–55 (S₁) and S 82–93 (S₂), to the synaptobrevin fragment S 56–81 allowed the cleavage of this latter peptide by TeNT to occur. This appears to result from an activation process mediated by the simultaneous binding of S₁ and S₂ with complementary sites present on TeNT as shown by surface plasmon resonance experiments. All these results favor an exosite-controlled hydrolysis of synaptobrevin by TeNT probably involving a conformational change of the toxin. This could accound for the high degree of substrate specificity of TeNT and, probably, botulinum neurotoxins.