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Distinct neuronal types connect in complex ways to generate functional neural circuits. The molecular diversity required to specify this connectivity could be supplied by multigene families of synaptic recognition molecules, but most studies to date have assessed just one or a few members at a time. Here, we analyze roles of cadherins (Cdhs) in formation of retinal circuits comprising eight neuronal types that inform the brain about motion in four directions. We show that at least 15 classical Cdhs are expressed by neurons in these circuits and at least 6 (Cdh6-10 and 18) act individually or in combinations to promote specific connectivity among the cells. They act in part by directing the processes of output neurons and excitatory interneurons to a cellular scaffold formed by inhibitory interneurons. Because Cdhs are expressed combinatorially by many central neurons, similar interactions could be involved in patterning circuits throughout the brain.

Thus far, optical recording of neuronal activity in freely behaving animals has been limited to a thin axial range. We present a head-mounted miniaturized light-field microscope (MiniLFM) capable of capturing neuronal network activity within a volume of 700 × 600 × 360 µm3 at 16 Hz in the hippocampus of freely moving mice. We demonstrate that neurons separated by as little as ~15 µm and at depths up to 360 µm can be discriminated.

Classical cadherins, a set of ~20 related recognition and signaling molecules, have been implicated in many aspects of neural development, including the formation and remodeling of synapses. Mechanisms underlying some of these steps have been studied by expressing N-cadherin (cdh2), a Type 1 cadherin, in heterologous cells, but analysis is complicated because widely used lines express cdh2 endogenously. We used CRISPR-mediated gene editing to generate a Human embryonic kidney (HEK)293 variant lacking Cdh2, then compared the behavior of rodent cortical and hippocampal neurons co-cultured with parental, cdh2 mutant and cdh2-rescued 293 lines. The comparison demonstrated that Cdh2 promotes neurite branching and that it is required for three synaptic organizers, neurologin1 (NLGL1), leucine-rich repeat transmembrane protein 2 (LRRtm2), and Cell Adhesion Molecule 1 (Cadm1/SynCAM) to stimulate presynaptic differentiation, assayed by clustering of synaptic vesicles at sites of neurite-293 cell contact. Similarly, Cdh2 is required for a presynaptic organizing molecule, Neurexin1β, to promote postsynaptic differentiation in dendrites. We also show that another Type I cadherin, Cdh4, and a Type II cadherin, Cdh6, can substitute for Cdh2 in these assays. Finally, we provide evidence that the effects of cadherins require homophilic interactions between neurites and the heterologous cells. Together, these results indicate that classical cadherins act together with synaptic organizers to promote synaptic differentiation, perhaps in part by strengthening the intracellular adhesion required for the organizers to act efficiently. We propose that cadherins promote high affinity contacts between appropriate partners, which then enable synaptic differentiation.

Hippocampal CA3 neurons form synapses with CA1 neurons in two layers, stratum oriens (SO) and stratum radiatum (SR). Each layer develops unique synaptic properties but molecular mechanisms that mediate these differences are unknown. Here, we show that SO synapses normally have significantly more mushroom spines and higher-magnitude long-term potentiation (LTP) than SR synapses. Further, we discovered that these differences require the Type II classic cadherins, cadherins-6, -9, and -10. Though cadherins typically function via trans-cellular homophilic interactions, our results suggest presynaptic cadherin-9 binds postsynaptic cadherins-6 and -10 to regulate mushroom spine density and high-magnitude LTP in the SO layer. Loss of these cadherins has no effect on the lower-magnitude LTP typically observed in the SR layer, demonstrating that cadherins-6, -9, and -10 are gatekeepers for high-magnitude LTP. Thus, Type II cadherins may uniquely contribute to the specificity and strength of synaptic changes associated with learning and memory.

Intercellular protein-protein interactions (PPIs) enable communication between cells in diverse biological processes, including cell proliferation, immune responses, infection, and synaptic transmission, but they are challenging to visualize because existing techniques have insufficient sensitivity and/or specificity. Here we report a split horseradish peroxidase (sHRP) as a sensitive and specific tool for the detection of intercellular PPIs. The two sHRP fragments, engineered through screening of 17 cut sites in HRP followed by directed evolution, reconstitute into an active form when driven together by an intercellular PPI, producing bright fluorescence or contrast for electron microscopy. Fusing the sHRP fragments to the proteins neurexin (NRX) and neuroligin (NLG), which bind each other across the synaptic cleft, enabled sensitive visualization of synapses between specific sets of neurons, including two classes of synapses in the mouse visual system. sHRP should be widely applicable to studying mechanisms of communication between a variety of cell types.

SynBio is a journal that focuses on synthetic biology, a field that uses engineering principles to design and build new biological systems. It has the potential to address global challenges such as food production, developing new therapies, regulating the environment, and generating renewable energy. The journal covers various cutting-edge techniques used in synthetic biology, including genetic engineering, informatics, systems biology, and computational modeling. The first issue of SynBio includes articles on topics such as the production of acrylic acid, biofuel from non-food biomass, cutinases, phenylnaphthacenoid polyketides, programmable proteins, and the treatment of rheumatoid arthritis and periodontitis. The journal aims to publish high-quality research in the field and is committed to maintaining a transparent editorial policy. [Extracted from the article]

In the mammalian retina, processes of approximately 70 types of interneurons form specific synapses on roughly 30 types of retinal ganglion cells (RGCs) in a neuropil called the inner plexiform layer. Each RGC type extracts salient features from visual input, which are sent deeper into the brain for further processing (1-4). The specificity and stereotypy of synapses formed in the inner plexiform layer account for the feature-detecting ability of RGCs. Here we analyse the development and function of synapses on one mouse RGC type, called the W3B-RGC (5,6). These cells have the remarkable property of responding when the timing of the movement of a small object differs from that of the background, but not when they coincide (6). Such cells, known as local edge detectors or object motion sensors, can distinguish moving objects from a visual scene that is also moving (6-12). We show that W3B-RGCs receive strong and selective input from an unusual excitatory amacrine cell type known as VG3-AC (vesicular glutamate transporter 3). Both W3BRGCs and VG3-ACs express the immunoglobulin superfamily recognition molecule sidekick 2 (Sdk2) (13,14), and both loss- and gain-of-function studies indicate that Sdk2-dependent homophilic interactions are necessary for the selectivity of the connection. The Sdk2-specified synapse is essential for visual responses of W3BRGCs: whereas bipolar cells relay visual input directly to most RGCs, the W3B-RGCs receive much of their input indirectly, via the VG3-ACs. This non-canonical circuit introduces a delay into the pathway from photoreceptors in the centre of the receptive field to W3B-RGCs, which could improve their ability to judge the synchrony of local and global motion., In situ hybridization revealed that both Sdkl and Sdk2 were expressed in subsets of mouse retinal neurons (Fig. 1a-c). Sdkl- and Sdk2-positive cells were largely non-overlapping, as shown previously in [...]

Programmable proteins to detect, visualize, modulate, or eliminate proteins of selection in vitro and in vivo are essential to study the targets recognized and the biology that follows. The specificity of programmable proteins can be easily altered by designing their sequences and structures. The flexibility and modularity of these proteins are currently pivotal for synthetic biology and various medical applications. There exist numerous reviews of the concept and application of individual programmable proteins, such as programmable nucleases, single-domain antibodies, and other protein scaffolds. This review proposes an expanded conceptual framework of such programmable proteins based on their programmable principle and target specificity to biomolecules (nucleic acids, proteins, and glycans) and overviews their advantages, limitations, and future directions. [ABSTRACT FROM AUTHOR]

The retina contains complex circuits of neurons that extract salient information from visual inputs. Signals from photoreceptors are processed by retinal interneurons, integrated by retinal ganglion cells (RGCs) and sent [...]

Author(s): Masahito Yamagata [1]; Joshua R. Sanes (corresponding author) [1] Synaptic circuits in the retina transform visual input gathered by photoreceptors into messages that retinal ganglion cells (RGCs) send to [...]

Results reveal that the homologous transmembrane immunoglobulin superfamily molecules, Sidekick-1 and -2, are involved in homophilic adhesion in vitro as well as direct neurites to lamina in vivo. The Sidekick proteins are concentrated at synaptic sites and participate in the lamina-specific synaptic connectivity.

Misexpression of two transcriptional regulators, topographically expressed along the nasotemporal axis in the embryonic chicken retina, leads to misprojection on the tectum along the rostrocaudal axis. These regulators belong to the winged-helix family, and their topographical expression determines the formation of the retinotectal map. This evidence supports the chemoaffinity theory, according to which, topographical arrangement of molecules determines the orderly retinotectal projection.

Replication-defective adenoviral vectors are efficient in transferring genes to chick embryos. In vivo or in vitro infection of the embryonic cells with a recombinant adenoviral vector results in the expression of Escherichia coli beta-galactosidase in the cells. The infection of a limited subset of embryonic cells at specific stages reveals the complex regulation of the infectivity of the adenovirus.