Parahippocampal latrophilin-2 (ADGRL2) expression controls topographical presubiculum to entorhinal cortex circuit connectivity

Single-nucleus profiling decoding the subcortical visual pathway evolution of vertebrates

During the evolution of vertebrates, significant transformations have occurred in the visual transmission and processing pathways. However, our understanding of the differences between two primary visual pathways in vertebrates and their evolutionary changes remains limited. The emerging technologies and comparative analysis have provided us with a more comprehensive way to decipher this process. Here, we applied single-nucleus RNA sequencing (snRNA-seq) onto the avian optic tectum, one of the key visual subcortical hubs in birds, to construct its cellular landscape. By integrating these data with mammalian snRNA-seq datasets, we revealed differences in the density of two types of thalamic-projecting excitatory neurons within the retinotectal pathway of birds and mammals. Additionally, a series of shared molecules were identified between two types of dominant visual pathways in vertebrates. Overall, this work provides a novel focus on the evolution of visual pathways and establishes a framework for their comparative analysis.

Expanding ligand-receptor interaction networks for axon guidance: Structural insights into signal crosstalk and specificity

Guidance of nascent axons to their targets is mediated by attractive and repulsive cues that activate receptors on the axonal growth cone. The number of ligand-receptor interactions implicated in axon pathfinding is still expanding, and large-scale cell-surface and extracellular protein interactome studies have revealed extensive crosstalk between signaling axes once thought to act independently. This raises the question how the apparent promiscuity of molecular interactions is compatible with specific signaling outcomes and effects on growth cone steering. Structural studies have provided insights into the modularity of binding interactions and shown the capacity of receptors to engage multiple ligands. Here, we review recent findings about the complexity of ligand-receptor interaction networks for axon guidance, and how structures of ligand-receptor complexes reveal mechanisms that may specify signaling output.

Differential Glutamatergic Inputs to Semilunar Granule Cells and Granule Cells Underscore Dentate Gyrus Projection Neuron Diversity

Semilunar Granule Cells (SGCs) are sparse dentate gyrus projection neurons whose role in the dentate circuit, including pathway specific inputs, remains unknown. We report that SGCs receive more frequent spontaneous excitatory synaptic inputs than granule cells (GCs). Dual GC-SGC recordings identified that SGCs receive stronger medial entorhinal cortex and associational synaptic drive but lack short-term facilitation of lateral entorhinal cortex inputs observed in GCs. SGCs dendritic spine density in proximal and middle dendrites was greater than in GCs. However, the strength of commissural inputs and dendritic input integration, examined in passive morphometric simulations, were not different between cell types. Activity dependent labeling identified an overrepresentation of SGCs among neuronal ensembles in both mice trained in a spatial memory task and task naïve controls. The divergence of modality specific inputs to SGCs and GCs can enable parallel processing of information streams and expand the computational capacity of the dentate gyrus.

Comprehensive Profiling of Genetic and Nongenetic Factors that Influence Skin Traits in Asian Women from 4 Countries

Brightness, pore size, wrinkles, color, elasticity, moisture, transepidermal water loss, pH, and sebum are traits that directly affect skin health and aesthetics, which vary substantially among ethnic groups and individuals. Although a complex combination of genetic and environmental factors influences these traits, an accurate estimation of skin phenotypic determination in individuals from Asian countries remains to be determined. In this study, we established the ASTAGR (Asian Skin Traits and Genetics Research) cohort, comprising 2762 female participants from 4 Asian countries (Korea, Vietnam, Thailand, and Indonesia). We documented 26 skin traits and conducted extensive skin-related surveys among the participants. Estimation of the quantitative contribution from whole-genome sequencing-based genotyping, combined with the survey findings, led to a comprehensive documentation of skin trait determination and its variation by country. This approach also revealed major variables affecting each skin trait. Our transethnic GWAS revealed 10 significant associations, 5 of which, to our knowledge, have not been previously reported. This study provides a comprehensive profile of skin traits and their regulation in the 4 Asian countries.

Autoencoder-based phenotyping of ophthalmic images highlights genetic loci influencing retinal morphology and provides informative biomarkers

MOTIVATION

Genome-wide association studies (GWAS) have been remarkably successful in identifying associations between genetic variants and imaging-derived phenotypes. To date, the main focus of these analyses has been on established, clinically-used imaging features. We sought to investigate if deep learning approaches can detect more nuanced patterns of image variability.

RESULTS

We used an autoencoder to represent retinal optical coherence tomography (OCT) images from 31 135 UK Biobank participants. For each subject, we obtained a 64-dimensional vector representing features of retinal structure. GWAS of these autoencoder-derived imaging parameters identified 118 statistically significant loci; 41 of these associations were also significant in a replication study. These loci encompassed variants previously linked with retinal thickness measurements, ophthalmic disorders, and/or neurodegenerative conditions. Notably, the generated retinal phenotypes were found to contribute to predictive models for glaucoma and cardiovascular disorders. Overall, we demonstrate that self-supervised phenotyping of OCT images enhances the discoverability of genetic factors influencing retinal morphology and provides epidemiologically informative biomarkers.

AVAILABILITY AND IMPLEMENTATION

Code and data links available at https://github.com/tf2/autoencoder-oct.

Synaptic Gα12/13 signaling establishes hippocampal PV inhibitory circuits

Combinatorial networks of cell adhesion molecules and cell surface receptors drive fundamental aspects of neural circuit establishment and function. However, the intracellular signals orchestrated by these cell surface complexes remain less understood. Here, we report that the Gα12/13 pathway lies downstream of several GPCRs with critical synaptic functions. Impairment of the Gα12/13 pathway in postnatal hippocampal neurons diminishes inhibitory inputs without altering neuronal morphology or excitatory transmission. Gα12/13 signaling in hippocampal CA1 neurons in vivo selectively regulates PV interneuron synaptic connectivity, supporting an inhibitory synapse subtype-specific function of this pathway. Our studies establish Gα12/13 as a signaling node that shapes inhibitory hippocampal circuitry.

Synaptic cell-adhesion molecule latrophilin-2 is differentially directed to dendritic domains of hippocampal neurons

Hippocampal pyramidal cells possess elaborate dendritic arbors with distinct domains that are targeted with input-specific synaptic sites. This synaptic arrangement is facilitated by synaptic cell-adhesion molecules that act as recognition elements to connect presynaptic and postsynaptic neurons. In this study, we investigate the organization of the synaptic recognition molecule latrophilin-2 at the surface of pyramidal neurons classified by spatial positioning and action potential firing patterns. Surveying two hippocampal neurons that highly express latrophilin-2, late-bursting CA1 pyramidal cells and early-bursting subiculum pyramidal cells, we found the molecule to be differentially positioned on their respective dendritic compartments. Investigating this latrophilin-2 positioning at the synaptic level, we found that the molecule is not present within either the pre- or postsynaptic terminal but rather is tightly coupled to synapses at a perisynaptic location. Together these findings indicate that hippocampal latrophilin-2 distribution patterning is cell-type specific, and requires multiple postsynaptic neurons for its synaptic localization.

Postnatal persistence of hippocampal Cajal-Retzius cells has a crucial role in the establishment of the hippocampal circuit

Cajal-Retzius (CR) cells are a transient neuron type that populate the postnatal hippocampus. To understand how the persistence of CR cells influences the maturation of hippocampal circuits, we combined a specific transgenic mouse line with viral vector injection to selectively ablate CR cells from the postnatal hippocampus. We observed layer-specific changes in the dendritic complexity and spine density of CA1 pyramidal cells. In addition, transcriptomic analysis highlighted significant changes in the expression of synapse-related genes across development. Finally, we were able to identify significant changes in the expression levels of latrophilin 2, a postsynaptic guidance molecule known for its role in the entorhinal-hippocampal connectivity. These findings were supported by changes in the synaptic proteomic content in CA1 stratum lacunosum-moleculare. Our results reveal a crucial role for CR cells in the establishment of the hippocampal network.

Context-dependent requirement of G protein coupling for Latrophilin-2 in target selection of hippocampal axons

The formation of neural circuits requires extensive interactions of cell-surface proteins to guide axons to their correct target neurons. Trans-cellular interactions of the adhesion G protein-coupled receptor latrophilin-2 (Lphn2) with its partner teneurin-3 instruct the precise assembly of hippocampal networks by reciprocal repulsion. Lphn2 acts as a repulsive receptor in distal CA1 neurons to direct their axons to the proximal subiculum, and as a repulsive ligand in the proximal subiculum to direct proximal CA1 axons to the distal subiculum. It remains unclear if Lphn2-mediated intracellular signaling is required for its role in either context. Here, we show that Lphn2 couples to Gα12/13 in heterologous cells; this coupling is increased by constitutive exposure of the tethered agonist. Specific mutations of Lphn2's tethered agonist region disrupt its G protein coupling and autoproteolytic cleavage, whereas mutating the autoproteolytic cleavage site alone prevents cleavage but preserves a functional tethered agonist. Using an in vivo misexpression assay, we demonstrate that wild-type Lphn2 misdirects proximal CA1 axons to the proximal subiculum and that Lphn2 tethered agonist activity is required for its role as a repulsive receptor in axons. By contrast, neither tethered agonist activity nor autoproteolysis were necessary for Lphn2's role as a repulsive ligand in the subiculum target neurons. Thus, tethered agonist activity is required for Lphn2-mediated neural circuit assembly in a context-dependent manner.

Hippocampal cells segregate positive and negative engrams

The hippocampus is involved in processing a variety of mnemonic computations specifically the spatiotemporal components and emotional dimensions of contextual memory. Recent studies have demonstrated cellular heterogeneity along the hippocampal axis. The ventral hippocampus has been shown to be important in the processing of emotion and valence. Here, we combine transgenic and all-virus based activity-dependent tagging strategies to visualize multiple valence-specific engrams in the vHPC and demonstrate two partially segregated cell populations and projections that respond to appetitive and aversive experiences. Next, using RNA sequencing and DNA methylation sequencing approaches, we find that vHPC appetitive and aversive engram cells display different transcriptional programs and DNA methylation landscapes compared to a neutral engram population. Additionally, optogenetic manipulation of tagged cell bodies in vHPC is not sufficient to drive appetitive or aversive behavior in real-time place preference, stimulation of tagged vHPC terminals projecting to the amygdala and nucleus accumbens (NAc), but not the prefrontal cortex (PFC), showed the capacity drive preference and avoidance. These terminals also were able to change their capacity to drive behavior. We conclude that the vHPC contains genetically, cellularly, and behaviorally segregated populations of cells processing appetitive and aversive memory engrams.