Search

The Cre-loxP system is invaluable for spatial and temporal control of gene knockout, knockin, and reporter expression in the mouse nervous system. However, we report varying probabilities of unexpected germline recombination in distinct Cre driver lines designed for nervous system-specific recombination. Selective maternal or paternal germline recombination is showcased with sample Cre lines. Collated data reveal germline recombination in over half of 64 commonly used Cre driver lines, in most cases with a parental sex bias related to Cre expression in sperm or oocytes. Slight differences among Cre driver lines utilizing common transcriptional control elements affect germline recombination rates. Specific target loci demonstrated differential recombination; thus, reporters are not reliable proxies for another locus of interest. Similar principles apply to other recombinase systems and other genetically targeted organisms. We hereby draw attention to the prevalence of germline recombination and provide guidelines to inform future research for the neuroscience and broader molecular genetics communities.

The mechanisms utilized by neurons to regulate the efficacy of phasic and tonic inhibition and their impacts on synaptic plasticity and behavior are incompletely understood. Cleft lip and palate transmembrane protein 1 (Clptm1) is a membrane-spanning protein that interacts with multiple γ-aminobutyric acid type A receptor (GABAAR) subunits, trapping them in the endoplasmic reticulum and Golgi network. Overexpression and knock-down studies suggest that Clptm1 modulates GABAAR-mediated phasic inhibition and tonic inhibition as well as activity-induced inhibitory synaptic homeostasis in cultured hippocampal neurons. To investigate the role of Clptm1 in the modulation of GABAARs in vivo, we generated Clptm1 knock-out (KO) mice. Here, we show that genetic KO of Clptm1 elevated phasic and tonic inhibitory transmission in both male and female heterozygous mice. Although basal excitatory synaptic transmission was not affected, Clptm1 haploinsufficiency significantly blocked high-frequency stimulation-induced long–term potentiation (LTP) in hippocampal CA3→CA1 synapses. In the hippocampus-dependent contextual fear-conditioning behavior task, both male and female Clptm1 heterozygous KO mice exhibited impairment in contextual fear memory. In addition, LTP and contextual fear memory were rescued by application of L-655,708, a negative allosteric modulator of the extrasynaptic GABAAR α5 subunit. These results suggest that haploinsufficiency of Clptm1 contributes to cognitive deficits through altered synaptic transmission and plasticity by elevation of inhibitory neurotransmission, with tonic inhibition playing a major role. [ABSTRACT FROM AUTHOR]

Calsyntenin 3 (Cstn3 or Clstn3), a recently identified synaptic organizer, promotes the development of synapses. Cstn3 localizes to the postsynaptic membrane and triggers presynaptic differentiation. Calsyntenin members play an evolutionarily conserved role in memory and learning. Cstn3 was recently shown in cell-based assays to interact with neurexin 1α (n1α), a synaptic organizer that is implicated in neuropsychiatric disease. Interaction would permit Cstn3 and n1α to form a trans-synaptic complex and promote synaptic differentiation. However, it is contentious whether Cstn3 binds n1α directly. To understand the structure and function of Cstn3, we determined its architecture by electron microscopy and delineated the interaction between Cstn3 and n1α biochemically and biophysically. We show that Cstn3 ectodomains form monomers as well as tetramers that are stabilized by disulfide bonds and Ca(2+), and both are probably flexible in solution. We show further that the extracellular domains of Cstn3 and n1α interact directly and that both Cstn3 monomers and tetramers bind n1α with nanomolar affinity. The interaction is promoted by Ca(2+) and requires minimally the LNS domain of Cstn3. Furthermore, Cstn3 uses a fundamentally different mechanism to bind n1α compared with other neurexin partners, such as the synaptic organizer neuroligin 2, because Cstn3 does not strictly require the sixth LNS domain of n1α. Our structural data suggest how Cstn3 as a synaptic organizer on the postsynaptic membrane, particularly in tetrameric form, may assemble radially symmetric trans-synaptic bridges with the presynaptic synaptic organizer n1α to recruit and spatially organize proteins into networks essential for synaptic function.

Background: School nurses play a central role in assisting elementary school children in managing their asthma, especially those in higher-risk school districts that are at increased risk of uncontrolled asthma. Study purposes are to (1) identify barriers to asthma management by school nurses in higher-risk school districts; and (2) assess the extent to which National Asthma Education and Prevention Program (NAEPP) recommendations are followed in these districts. Methods: School districts containing at least one zipcode with high asthma hospitalization rates among children (0-14?years) in a New York State county were identified. Nurses in 44 elementary schools were surveyed about asthma management during 2008. Both quantitative and qualitative data were collected. Results: Study nurses learned of children with asthma mainly through school records and when students presented with symptoms rather than through parents. The major obstacles to asthma management were communication with parents and parental support. Reluctance of some physicians to diagnose asthma in these children presented a barrier and contributed to the nurses' ability to gain parental cooperation. Adherence to the NAEPP school recommendations was inconsistent. Conclusions: Improvement in the communication among parents, school nurses, and providers is critical to the improvement of asthma management for children in high-risk school districts.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tins.2005.11.002 Byline: Ann Marie Craig (a)(b), Ethan R. Graf (b), Michael W. Linhoff (a)(b) Abstract: Central neurons develop and maintain molecularly distinct synaptic specializations for excitatory and inhibitory transmitters, often only microns apart on their dendritic arbor. Progress towards understanding the molecular basis of synaptogenesis has come from several recent studies using a coculture system of non-neuronal cells expressing molecules that generate presynaptic or postsynaptic 'hemi-synapses' on contacting neurons. Together with molecular properties of these protein families, such studies have yielded interesting clues to how glutamatergic and GABAergic synapses are assembled. Other clues come from heterochronic cultures, manipulations of activity in subsets of neurons in a network, and of course many in vivo studies. Taking into account these data, we consider here how basic parameters of synapses - competence, placement, composition, size and longevity - might be determined. Author Affiliation: (a) Brain Research Centre and Department of Psychiatry, University of British Columbia, Vancouver, Canada V6T 2B5 (b) Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, MO 63110, USA

Synaptogenesis is a complex process involving the formation of functional synapses between neurons. Molecules derived from target neurons influence synaptic form, specificity and stability.

Studies were conducted to show that neurexins are sufficient to induce glutamate postsynaptic differentiation in contacting dendrites. These studies are relevant because the formation of synaptic connections is dependent on alignment of neurotransmitter receptors on postsynaptic dendrites.

A functionally significant relationship between N-methyl-D-aspartate (NMDA) receptors and the postsynaptic cytoskleton is indicated by the mechano-sensitivity of these receptors and by their dependence on the integrity of actin. There are indications that the localization of NMDA receptors and their moderation by Ca2+/calmodulin are influenced by actin-binding protein alpha-actinin-2.

A study using antibodies against the excitatory glutamate receptor subunit GluR1 and the inhibitory type A gamma-aminobutyric acid (GABA) receptor beta2/3 subunits reveals the preferential clustering of these receptors opposite terminals that release the related neurotansmitters. This clustering at postsynaptic sites on neurons involves complex mechanisms using nerve-terminal specific signals. GluR1 receptor clusters on dendrite spines and is related to glutamergic synapses, while GABA receptor subunits cluster on cell bodies and dendritic shafts opposite GABAergic terminals.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2007.08.020 Byline: Frederick Dobie (1), Ann Marie Craig (1) Abstract: The presynaptic scaffold molecule RIM1[alpha] is important for regulating neurotransmitter release. In this issue, show in mice that an E3 ubiquitin ligase, SCRAPPER, targets a set of presynaptic proteins including RIM1[alpha] for degradation by the ubiquitin-proteasome system. Their results identify protein degradation as a mechanism for holding rapid synaptic communication in check. Author Affiliation: (1) Brain Research Centre and Department of Psychiatry, University of British Columbia, Vancouver, BC, V6T 2B5, Canada

Abstract Background Neuronal output is shaped by a balance of excitation and inhibition. How this balance is attained in the central nervous system during development is not well understood, and is complicated by the fact that, in vivo, GABAergic and glycinergic synaptogenesis precedes that of glutamatergic synapses. Here, we determined the distributions of inhibitory postsynaptic sites on the dendritic arbors of individual neurons, and compared their developmental patterns with that of excitatory postsynaptic sites. We focused on retinal ganglion cells (RGCs), the output neurons of the retina, which receive excitatory input from bipolar cells and inhibitory input from amacrine cells. To visualize and map inhibitory postsynaptic sites, we generated transgenic mice in which RGCs express fluorescently tagged Neuroligin 2 (YFP-NL2) under the control of the Thy1 promoter. By labeling RGC dendrites biolistically in YFP-NL2-expressing retinas, we were able to map the spatial distribution and thus densities of inhibitory postsynaptic sites on the dendritic arbors of individual large-field RGCs across ages. Results We demonstrate that YFP-NL2 is present at inhibitory synapses in the inner plexiform layer by its co-localization with gephyrin, the γ2 subunit of the GABAA receptor and glycine receptors. YFP-NL2 puncta were apposed to the vesicular inhibitory transmitter transporter VGAT but not to CtBP2, a marker of presynaptic ribbons found at bipolar cell terminals. Similar patterns of co-localization with synaptic markers were observed for endogenous NL2. We also verified that expression of YFP-NL2 in the transgenic line did not significantly alter spontaneous inhibitory synaptic transmission onto RGCs. Using these mice, we found that, on average, the density of inhibitory synapses on individual arbors increased gradually until eye opening (postnatal day 15). A small centro-peripheral gradient in density found in mature arbors was apparent at the earliest age we examined (postnatal day 8). Unexpectedly, the adult ratio of inhibitory/excitatory postsynaptic sites was rapidly attained, shortly after glutamatergic synaptogenesis commenced (postnatal day 7). Conclusion Our observations suggest that bipolar and amacrine cell synaptogenesis onto RGCs appear coordinated to rapidly attain a balanced ratio of excitatory and inhibitory synapse densities prior to the onset of visual experience.