New players tip the scales in the balance between excitatory and inhibitory synapses

Synaptogenesis is a highly controlled process, involving a vast array of players which include cell adhesion molecules, scaffolding and signaling proteins, neurotransmitter receptors and proteins associated with the synaptic vesicle machinery. These molecules cooperate in an intricate manner on both the pre- and postsynaptic sides to orchestrate the precise assembly of neuronal contacts. This is an amazing feat considering that a single neuron receives tens of thousands of synaptic inputs but virtually no mismatch between pre- and postsynaptic components occur in vivo. One crucial aspect of synapse formation is whether a nascent synapse will develop into an excitatory or inhibitory contact. The tight control of a balance between the types of synapses formed regulates the overall neuronal excitability, and is thus critical for normal brain function and plasticity. However, little is known about how this balance is achieved. This review discusses recent findings which provide clues to how neurons may control excitatory and inhibitory synapse formation, with focus on the involvement of the neuroligin family and PSD-95 in this process.     

Synaptic targeting of the postsynaptic density protein PSD-95 mediated by lipid and protein motifs

During synaptic development, proteins aggregate at specialized pre- and postsynaptic structures. Mechanisms that mediate protein clustering at these sites remain unknown. To investigate this process, we analyzed synaptic targeting of a postsynaptic density protein, PSD-95, by expressing green fluorescent protein- (GFP-) tagged PSD-95 in cultured hippocampal neurons. We find that postsynaptic clustering relies on three elements of PSD-95: N-terminal palmitoylation, the first two PDZ domains, and a C-terminal targeting motif. In contrast, disruptions of PDZ3, SH3, or guanylate kinase (GK) domains do not affect synaptic targeting. Palmitoylation is sufficient to target the diffusely expressed SAP-97 to synapses, and palmitoylation cannot be replaced with alternative membrane association motifs, suggesting that a specialized synaptic lipid environment mediates postsynaptic clustering. The requirements for PDZ domains and a C-terminal domain of PSD-95 indicate that protein-protein interactions cooperate with lipid interactions in synaptic targeting.     

A crystal-clear interaction: relating neuroligin/neurexin complex structure to function at the synapse

Neuronal circuits are maintained by homeostatic mechanisms controlling synapse maturation and signaling. Neuroligins (NLs) and neurexins (Nrxs) may regulate the fine balance between excitation and inhibition. In this issue of Neuron, Ara? et al. and Fabrichny et al. define crystal structures of NLs bound to beta-Nrx, providing insights into their synaptic actions and clarifying structural defects associated with autism-linked mutations.     

The eleventh reported case of Mulvihill-Smith syndrome in the literature

Background

The Mulvihill-Smith Syndrome was first recognized in 1975. After the recognition of the Mulvihill-Smith Syndrome, ten cases have been described.

Case presentation

This article describes the eleventh case of this syndrome in a male patient, 24 years-old with short stature and microcephaly with mild cognitive impairment, deafness and allergic conjunctivitis. The patient was hospitalized several times for repeated infections, and the presence of multiple melanocytic nevi on his skin was noticed.

Conclusions

Based on the entire set of signs and symptoms presented in our study, it was diagnosed the patient with Mulvihill-Smith Syndrome.     

Generation of “LYmph Node Derived Antibody Libraries” (LYNDAL) for selecting fully human antibody fragments with therapeutic potential

The development of efficient strategies for generating fully human monoclonal antibodies with unique functional properties that are exploitable for tailored therapeutic interventions remains a major challenge in the antibody technology field. Here, we present a methodology for recovering such antibodies from antigen-encountered human B cell repertoires. As the source for variable antibody genes, we cloned immunoglobulin G (IgG)-derived B cell repertoires from lymph nodes of 20 individuals undergoing surgery for head and neck cancer. Sequence analysis of unselected “LYmph Node Derived Antibody Libraries” (LYNDAL) revealed a naturally occurring distribution pattern of rearranged antibody sequences, representing all known variable gene families and most functional germline sequences. To demonstrate the feasibility for selecting antibodies with therapeutic potential from these repertoires, seven LYNDAL from donors with high serum titers against herpes simplex virus (HSV) were panned on recombinant glycoprotein B of HSV-1. Screening for specific binders delivered 34 single-chain variable fragments (scFvs) with unique sequences. Sequence analysis revealed extensive somatic hypermutation of enriched clones as a result of affinity maturation. Binding of scFvs to common glycoprotein B variants from HSV-1 and HSV-2 strains was highly specific, and the majority of analyzed antibody fragments bound to the target antigen with nanomolar affinity. From eight scFvs with HSV-neutralizing capacity in vitro, the most potent antibody neutralized 50% HSV-2 at 4.5 nM as a dimeric (scFv)₂. We anticipate our approach to be useful for recovering fully human antibodies with therapeutic potential.     

Recent advances in basic neurosciences and brain disease: from synapses to behavior

Understanding basic neuronal mechanisms hold the hope for future treatment of brain disease. The 1st international conference on synapse, memory, drug addiction and pain was held in beautiful downtown Toronto, Canada on August 21–23, 2006. Unlike other traditional conferences, this new meeting focused on three major aims: (1) to promote new and cutting edge research in neuroscience; (2) to encourage international information exchange and scientific collaborations; and (3) to provide a platform for active scientists to discuss new findings. Up to 64 investigators presented their recent discoveries, from basic synaptic mechanisms to genes related to human brain disease. This meeting was in part sponsored by Molecular Pain, together with University of Toronto (Faculty of Medicine, Department of Physiology as well as Center for the Study of Pain). Our goal for this meeting is to promote future active scientific collaborations and improve human health through fundamental basic neuroscience researches. The second international meeting on Neurons and Brain Disease will be held in Toronto (August 29–31, 2007).     

A monovalent streptavidin with a single femtomolar biotin binding site

Streptavidin and avidin are used ubiquitously because of the remarkable affinity of their biotin binding, but they are tetramers, which disrupts many of their applications. Making either protein monomeric reduces affinity by at least 10(4)-fold because part of the binding site comes from a neighboring subunit. Here we engineered a streptavidin tetramer with only one functional biotin binding subunit that retained the affinity, off rate and thermostability of wild-type streptavidin. In denaturant, we mixed a streptavidin variant containing three mutations that block biotin binding with wild-type streptavidin in a 3:1 ratio. Then we generated monovalent streptavidin by refolding and nickel-affinity purification. Similarly, we purified defined tetramers with two or three biotin binding subunits. Labeling of site-specifically biotinylated neuroligin-1 with monovalent streptavidin allowed stable neuroligin-1 tracking without cross-linking, whereas wild-type streptavidin aggregated neuroligin-1 and disrupted presynaptic contacts. Monovalent streptavidin should find general application in biomolecule labeling, single-particle tracking and nanotechnology.     

Patterns of MADS-box gene expression mark flower-type development in Gerbera hybrida (Asteraceae)

Background  

The inflorescence of the cut-flower crop Gerbera hybrida (Asteraceae) consists of two principal flower types, ray and disc, which form a tightly packed head, or capitulum. Despite great interest in plant morphological evolution and the tractability of the gerbera system, very little is known regarding genetic mechanisms involved in flower type specification. Here, we provide comparative staging of ray and disc flower development and microarray screening for differentially expressed genes, accomplished via microdissection of hundreds of coordinately developing flower primordia.