Mouse ten-m/Odz is a new family of dimeric type II transmembrane proteins expressed in many tissues

Odz4 upregulates SAN-specific genes to promote differentiation into cardiac pacemaker-like cells

Cardiac arrhythmias stemming from abnormal sinoatrial node (SAN) function can lead to sudden death. Developing a biological pacemaker device for treating sick sinus syndrome (SSS) could offer a potential cure. Understanding SAN differentiation is crucial, yet its regulatory mechanism remains unclear. We reanalyzed published RNA-seq data and identified Odz4 as a SAN-specific candidate. In situ hybridization revealed Odz4 expression in the cardiac crescent and throughout the cardiac conduction system (CCS). To assess the role of Odz4 in CCS differentiation, we utilized a Tet-Off inducible system for its intracellular domain (ICD). Embryonic bodies (EBs) exogenously expressing Odz4-ICD exhibited an increased propensity to develop into pacemaker-like cells with enhanced automaticity and upregulated expression of SAN-specific genes. CellChat and GO analyses unveiled SAN-specific enrichment of ligand-receptor sets, especially Ptn-Ncl, and extracellular matrix components in the group exogenously expressing Odz4-ICD. Our findings underscore the significance of Odz4 in SAN development and offer fresh insights into biological pacemaker establishment.

Reconstitution of synaptic junctions orchestrated by teneurin-latrophilin complexes

Synapses are organized by trans-synaptic adhesion molecules that coordinate assembly of pre- and postsynaptic specializations, which, in turn, are composed of scaffolding proteins forming liquid-liquid phase-separated condensates. Presynaptic teneurins mediate excitatory synapse organization by binding to postsynaptic latrophilins; however, the mechanism of action of teneurins, driven by extracellular domains evolutionarily derived from bacterial toxins, remains unclear. In this work, we show that only the intracellular sequence, a dimerization sequence, and extracellular bacterial toxin-derived latrophilin-binding domains of Teneurin-3 are required for synapse organization, suggesting that teneurin-induced latrophilin clustering mediates synaptogenesis. Intracellular Teneurin-3 sequences capture liquid-liquid phase-separated presynaptic active zone scaffolds, enabling us to reconstitute an entire synaptic junction from purified proteins in which trans-synaptic teneurin-latrophilin complexes recruit phase-separated pre- and postsynaptic specializations.

Alternative splicing controls teneurin-3 compact dimer formation for neuronal recognition

Neuronal network formation is facilitated by recognition between synaptic cell adhesion molecules at the cell surface. Alternative splicing of cell adhesion molecules provides additional specificity in forming neuronal connections. For the teneurin family of cell adhesion molecules, alternative splicing of the EGF-repeats and NHL domain controls synaptic protein-protein interactions. Here we present cryo-EM structures of the compact dimeric ectodomain of two teneurin-3 isoforms that harbour the splice insert in the EGF-repeats. This dimer is stabilised by an EGF8-ABD contact between subunits. Cryo-EM reconstructions of all four splice variants, together with SAXS and negative stain EM, reveal compacted dimers for each, with variant-specific dimeric arrangements. This results in specific trans-cellular interactions, as tested in cell clustering and stripe assays. The compact conformations provide a structural basis for teneurin homo- and heterophilic interactions. Altogether, our findings demonstrate how alternative splicing results in rearrangements of the dimeric subunits, influencing neuronal recognition and likely circuit wiring.

Skeletal muscle metabolism and contraction performance regulation by teneurin C-terminal-associated peptide-1

Skeletal muscle regulation is responsible for voluntary muscular movement in vertebrates. The genes of two essential proteins, teneurins and latrophilins (LPHN), evolving in ancestors of multicellular animals form a ligand-receptor pair, and are now shown to be required for skeletal muscle function. Teneurins possess a bioactive peptide, termed the teneurin C-terminal associated peptide (TCAP) that interacts with the LPHNs to regulate skeletal muscle contractility strength and fatigue by an insulin-independent glucose importation mechanism in rats. CRISPR-based knockouts and siRNA-associated knockdowns of LPHN-1 and-3 in the C2C12 mouse skeletal cell line shows that TCAP stimulates an LPHN-dependent cytosolic Ca2+ signal transduction cascade to increase energy metabolism and enhance skeletal muscle function via increases in type-1 oxidative fiber formation and reduce the fatigue response. Thus, the teneurin/TCAP-LPHN system is presented as a novel mechanism that regulates the energy requirements and performance of skeletal muscle.

Teneurin paralogues are able to localise synaptic sites driven by the intracellular domain and have the potential to form cis-heterodimers

Synaptic specificity during neurodevelopment is driven by combinatorial interactions between select cell adhesion molecules expressed at the synaptic membrane. These protein-protein interactions are important for instructing the correct connectivity and functionality of the nervous system. Teneurins are one family of synaptic adhesion molecules, highly conserved and widely expressed across interconnected areas during development. These type-II transmembrane glycoproteins are involved in regulating key neurodevelopmental processes during the establishment of neural connectivity. While four teneurin paralogues are found in vertebrates, their subcellular distribution within neurons and interaction between these different paralogues remains largely unexplored. Here we show, through fluorescently tagging teneurin paralogues, that true to their function as synaptic adhesion molecules, all four paralogues are found in a punctate manner and partially localised to synapses when overexpressed in neurons in vitro. Interestingly, each paralogue is differentially distributed across different pre- and post-synaptic sites. In organotypic cultures, Tenm3 is similarly localised to dendritic spines in CA1 neurons, particularly to spine attachment points. Furthermore, we show that the intracellular domain of teneurin plays an important role for synaptic localisation. Finally, while previous studies have shown that the extracellular domain of teneurins allows for active dimer formation and transsynaptic interactions, we find that all paralogues are able to form the full complement of homodimers and cis-heterodimers. This suggests that the combinatorial power to generate distinct molecular teneurin complexes underlying synaptic specificity is even higher than previously thought. The emerging link between teneurin with cancers and neurological disorders only serves to emphasise the importance of further elucidating the molecular mechanisms of teneurin function and their relation to human health and disease.

Cryo-electron Microscopic Analysis of Single-Pass Transmembrane Receptors

Single-pass transmembrane receptors (SPTMRs) represent a diverse group of integral membrane proteins that are involved in many essential cellular processes, including signal transduction, cell adhesion, and transmembrane transport of materials. Dysregulation of the SPTMRs is linked with many human diseases. Despite extensive efforts in past decades, the mechanisms of action of the SPTMRs remain incompletely understood. One major hurdle is the lack of structures of the full-length SPTMRs in different functional states. Such structural information is difficult to obtain by traditional structural biology methods such as X-ray crystallography and nuclear magnetic resonance (NMR). The recent rapid development of single-particle cryo-electron microscopy (cryo-EM) has led to an exponential surge in the number of high-resolution structures of integral membrane proteins, including SPTMRs. Cryo-EM structures of SPTMRs solved in the past few years have tremendously improved our understanding of how SPTMRs function. In this review, we will highlight these progresses in the structural studies of SPTMRs by single-particle cryo-EM, analyze important structural details of each protein involved, and discuss their implications on the underlying mechanisms. Finally, we also briefly discuss remaining challenges and exciting opportunities in the field.

Immunomodulatory Properties of Human Breast Milk: MicroRNA Contents and Potential Epigenetic Effects

Infants who are exclusively breastfed in the first six months of age receive adequate nutrients, achieving optimal immune protection and growth. In addition to the known nutritional components of human breast milk (HBM), i.e., water, carbohydrates, fats and proteins, it is also a rich source of microRNAs, which impact epigenetic mechanisms. This comprehensive work presents an up-to-date overview of the immunomodulatory constituents of HBM, highlighting its content of circulating microRNAs. The epigenetic effects of HBM are discussed, especially those regulated by miRNAs. HBM contains more than 1400 microRNAs. The majority of these microRNAs originate from the lactating gland and are based on the remodeling of cells in the gland during breastfeeding. These miRNAs can affect epigenetic patterns by several mechanisms, including DNA methylation, histone modifications and RNA regulation, which could ultimately result in alterations in gene expressions. Therefore, the unique microRNA profile of HBM, including exosomal microRNAs, is implicated in the regulation of the genes responsible for a variety of immunological and physiological functions, such as FTO, INS, IGF1, NRF2, GLUT1 and FOXP3 genes. Hence, studying the HBM miRNA composition is important for improving the nutritional approaches for pregnancy and infant's early life and preventing diseases that could occur in the future. Interestingly, the composition of miRNAs in HBM is affected by multiple factors, including diet, environmental and genetic factors.

Teneurins assemble into presynaptic nanoclusters that promote synapse formation via postsynaptic non-teneurin ligands

Extensive studies concluded that homophilic interactions between pre- and postsynaptic teneurins, evolutionarily conserved cell-adhesion molecules, encode the specificity of synaptic connections. However, no direct evidence is available to demonstrate that teneurins are actually required on both pre- and postsynaptic neurons for establishing synaptic connections, nor is it known whether teneurins are localized to synapses. Using super-resolution microscopy, we demonstrate that Teneurin-3 assembles into presynaptic nanoclusters of approximately 80 nm in most excitatory synapses of the hippocampus. Presynaptic deletions of Teneurin-3 and Teneurin-4 in the medial entorhinal cortex revealed that they are required for assembly of entorhinal cortex-CA1, entorhinal cortex-subiculum, and entorhinal cortex-dentate gyrus synapses. Postsynaptic deletions of teneurins in the CA1 region, however, had no effect on synaptic connections from any presynaptic input. Our data suggest that different from the current prevailing view, teneurins promote the establishment of synaptic connections exclusively as presynaptic cell-adhesion molecules, most likely via their nanomolar-affinity binding to postsynaptic latrophilins.

Teneurin4 dimer structures reveal a calcium‐stabilized compact conformation supporting homomeric trans‐interactions

Establishment of correct synaptic connections is a crucial step during neural circuitry formation. The Teneurin family of neuronal transmembrane proteins promotes cell–cell adhesion via homophilic and heterophilic interactions, and is required for synaptic partner matching in the visual and hippocampal systems in vertebrates. It remains unclear how individual Teneurins form macromolecular cis‐ and trans‐synaptic protein complexes. Here, we present a 2.7 Å cryo‐EM structure of the dimeric ectodomain of human Teneurin4. The structure reveals a compact conformation of the dimer, stabilized by interactions mediated by the C‐rich, YD‐shell, and ABD domains. A 1.5 Å crystal structure of the C‐rich domain shows three conserved calcium binding sites, and thermal unfolding assays and SAXS‐based rigid‐body modeling demonstrate that the compactness and stability of Teneurin4 dimers are calcium‐dependent. Teneurin4 dimers form a more extended conformation in conditions that lack calcium. Cellular assays reveal that the compact cis‐dimer is compatible with homomeric trans‐interactions. Together, these findings support a role for teneurins as a scaffold for macromolecular complex assembly and the establishment of cis‐ and trans‐synaptic interactions to construct functional neuronal circuits.

Role and Involvement of TENM4 and miR-708 in Breast Cancer Development and Therapy

Teneurin 4 (TENM4) is a transmembrane protein that is codified by the ODZ4 gene and is involved in nervous system development, neurite outgrowth, and neuronal differentiation. In line with its involvement in the nervous system, TENM4 has also been implicated in several mental disorders such as bipolar disorder, schizophrenia, and autism. TENM4 mutations and rearrangements have recently been identified in a number of tumors. This, combined with impaired expression in tumors, suggests that it may potentially be involved in tumorigenesis. Most of the TENM4 mutations that are observed in tumors occur in breast cancer, in which TENM4 plays a role in cells’ migration and stemness. However, the functional role that TENM4 plays in breast cancer still needs to be better evaluated, and further studies are required to better understand the involvement of TENM4 in breast cancer progression. Herein, we review the currently available data for TENM4′s role in breast cancer and propose its use as both a novel target with which to ameliorate patient prognosis and as a potential biomarker. Moreover, we also report data on the tumorigenic role of miR-708 deregulation and the possible use of this miRNA as a novel therapeutic molecule, as miR-708 is spliced out from TENM4 mRNA.

Teneurins: Role in Cancer and Potential Role as Diagnostic Biomarkers and Targets for Therapy

Teneurins have been identified in vertebrates as four different genes (TENM1-4), coding for membrane proteins that are mainly involved in embryonic and neuronal development. Genetic studies have correlated them with various diseases, including developmental problems, neurological disorders and congenital general anosmia. There is some evidence to suggest their possible involvement in cancer initiation and progression, and drug resistance. Indeed, mutations, chromosomal alterations and the deregulation of teneurins expression have been associated with several tumor types and patient survival. However, the role of teneurins in cancer-related regulatory networks is not fully understood, as both a tumor-suppressor role and pro-tumoral functions have been proposed, depending on tumor histotype. Here, we summarize and discuss the literature data on teneurins expression and their potential role in different tumor types, while highlighting the possibility of using teneurins as novel molecular diagnostic and prognostic biomarkers and as targets for cancer treatments, such as immunotherapy, in some tumors.

Identification of TENM4 as a Novel Cancer Stem Cell-Associated Molecule and Potential Target in Triple Negative Breast Cancer

Simple Summary

Patients with triple negative breast cancer (TNBC) experience shorter overall survival compared to non-TNBC patients because of the high incidence of recurrences and metastases. This is due to the capacity of aggressive cancer cell subpopulations named cancer stem cells (CSC) to resist current therapies. To design more effective therapeutic strategies for TNBC patients, in this study we sought to identify functional targets expressed on CSC. Our analyses led us to propose teneurin 4 (TENM4) as a promising candidate for drug- and immune-based therapies due to its role in CSC self-renewal and migratory capacity and the inverse correlation between its expression and survival of TNBC patients. In addition, TENM4 detection in the plasma of tumor-bearing patients endorses its potentiality as a disease detection marker.

Abstract

Triple-negative breast cancer (TNBC) is insensitive to endocrine and Her2-directed therapies, making the development of TNBC-targeted therapies an unmet medical need. Since patients with TNBC frequently show a quicker relapse and metastatic progression compared to other breast cancer subtypes, we hypothesized that cancer stem cells (CSC) could have a role in TNBC. To identify putative TNBC CSC-associated targets, we compared the gene expression profiles of CSC-enriched tumorspheres and their parental cells grown as monolayer. Among the up-regulated genes coding for cell membrane-associated proteins, we selected Teneurin 4 (TENM4), involved in cell differentiation and deregulated in tumors of different histotypes, as the object for this study. Meta-analysis of breast cancer datasets shows that TENM4 mRNA is up-regulated in invasive carcinoma specimens compared to normal breast and that high expression of TENM4 correlates with a shorter relapse-free survival in TNBC patients. TENM4 silencing in mammary cancer cells significantly impaired tumorsphere-forming ability, migratory capacity and Focal Adhesion Kinase (FAK) phosphorylation. Moreover, we found higher levels of TENM4 in plasma from tumor-bearing mice and TNBC patients compared to the healthy controls. Overall, our results indicate that TENM4 may act as a novel biomarker and target for the treatment of TNBC.

Alternative splicing controls teneurin-latrophilin interaction and synapse specificity by a shape-shifting mechanism

The trans-synaptic interaction of the cell-adhesion molecules teneurins (TENs) with latrophilins (LPHNs/ADGRLs) promotes excitatory synapse formation when LPHNs simultaneously interact with FLRTs. Insertion of a short alternatively-spliced region within TENs abolishes the TEN-LPHN interaction and switches TEN function to specify inhibitory synapses. How alternative-splicing regulates TEN-LPHN interaction remains unclear. Here, we report the 2.9 Å resolution cryo-EM structure of the TEN2-LPHN3 complex, and describe the trimeric TEN2-LPHN3-FLRT3 complex. The structure reveals that the N-terminal lectin domain of LPHN3 binds to the TEN2 barrel at a site far away from the alternatively spliced region. Alternative-splicing regulates the TEN2-LPHN3 interaction by hindering access to the LPHN-binding surface rather than altering it. Strikingly, mutagenesis of the LPHN-binding surface of TEN2 abolishes the LPHN3 interaction and impairs excitatory but not inhibitory synapse formation. These results suggest that a multi-level coincident binding mechanism mediated by a cryptic adhesion complex between TENs and LPHNs regulates synapse specificity.

The trans-synaptic interaction of the cell-adhesion molecules teneurins (TENs) with latrophilins (LPHNs) promotes excitatory synapse formation. Here authors report the high resolution cryo-EM structure of the TEN2-LPHN3 complex, describe the trimeric TEN2-LPHN3-FLRT3 complex and show how alternative-splicing regulates the TEN2-LPHN3 interaction.

Synthetic Peptides as Therapeutic Agents: Lessons Learned From Evolutionary Ancient Peptides and Their Transit Across Blood-Brain Barriers

Peptides play a major role in the transmission of information to and from the central nervous system. However, because of their structural complexity, the development of pharmacological peptide-based therapeutics has been challenged by the lack of understanding of endogenous peptide evolution. The teneurin C-terminal associated peptides (TCAP) possess many of the required attributes of a practical peptide therapeutic. TCAPs, associated with the teneurin transmembrane proteins that bind to the latrophilins, members of the Adhesion family of G-protein-coupled receptors (GPCR). Together, this ligand-receptor unit plays an integral role in synaptogenesis, neurological development, and maintenance, and is present in most metazoans. TCAP has structural similarity to corticotropin-releasing factor (CRF), and related peptides, such as calcitonin and the secretin-based peptides and inhibits the (CRF)-associated stress response. Latrophilins are structurally related to the secretin family of GPCRs. TCAP is a soluble peptide that crosses the blood-brain barrier and regulates glucose transport into the brain. We posit that TCAP represents a phylogenetically older peptide system that evolved before the origin of the CRF-calcitonin-secretin clade of peptides and plays a fundamental role in the regulation of cell-to-cell energy homeostasis. Moreover, it may act as a phylogenetically older peptide system that evolved as a natural antagonist to the CRF-mediated stress response. Thus, TCAP's actions on the CNS may provide new insights into the development of peptide therapeutics for the treatment of CNS disorders.

An LRR Receptor-Teneurin System Directs Planar Polarity at Compartment Boundaries

Epithelial cells dynamically self-organize in response to extracellular spatial cues relayed by cell-surface receptors. During convergent extension in Drosophila, Toll-related receptors direct planar polarized cell rearrangements that elongate the head-to-tail axis. However, many cells establish polarity in the absence of Toll receptor activity, indicating the presence of additional spatial cues. Here we demonstrate that the leucine-rich-repeat receptor Tartan and the teneurin Ten-m provide critical polarity signals at epithelial compartment boundaries. The Tartan and Ten-m extracellular domains interact in vitro, and Tartan promotes Ten-m localization to compartment boundaries in vivo. We show that Tartan and Ten-m are necessary for the planar polarity and organization of compartment boundary cells. Moreover, ectopic stripes of Tartan and Ten-m are sufficient to induce myosin accumulation at stripe boundaries. These results demonstrate that the Tartan/Ten-m and Toll receptor systems together create a high-resolution network of spatial cues that guides cell behavior during convergent extension.

Teneurin Structure: Splice Variants of a Bacterial Toxin Homolog Specifies Synaptic Connections

Teneurins are a conserved family of cell-surface adhesion molecules that mediate cellular communication, and play key roles in embryonic and neural development. Their mechanisms of action remained unclear due in part to their unknown structures. In recent years, the structures of teneurins have been reported at atomic resolutions and revealed a clear homology to bacterial Tc toxins with no similarity to other eukaryotic proteins. Another surprising observation was that alternatively spliced variants of teneurins interact with distinct ligands, and thus specify excitatory vs. inhibitory synapses. In this review, we discuss teneurin structures that together with structure-guided biochemical and functional analyses, provide insights for the mechanisms of trans-cellular communication at the synapse and other cell-cell contact sites.

Teneurins and latrophilins: two giants meet at the synapse

Teneurins and latrophilins are both conserved families of cell adhesion proteins that mediate cellular communication and play critical roles in embryonic and neural development. However, their mechanisms of action remain poorly understood. In the past several years, three-dimensional structures of teneurins and latrophilins have been reported at atomic resolutions and revealed distinct protein folds and unique structural features. In this review, we discuss these structures which, together with structure-guided biochemical and functional analyses, provide hints for the mechanisms of trans-cellular communication at the synapse and other cell-cell contact sites.

Catching Latrophilin With Lasso: A Universal Mechanism for Axonal Attraction and Synapse Formation

Latrophilin-1 (LPHN1) was isolated as the main high-affinity receptor for α-latrotoxin from black widow spider venom, a powerful presynaptic secretagogue. As an adhesion G-protein-coupled receptor, LPHN1 is cleaved into two fragments, which can behave independently on the cell surface, but re-associate upon binding the toxin. This triggers intracellular signaling that involves the Gαq/phospholipase C/inositol 1,4,5-trisphosphate cascade and an increase in cytosolic Ca²⁺, leading to vesicular exocytosis. Using affinity chromatography on LPHN1, we isolated its endogenous ligand, teneurin-2/Lasso. Both LPHN1 and Ten2/Lasso are expressed early in development and are enriched in neurons. LPHN1 primarily resides in axons, growth cones and presynaptic terminals, while Lasso largely localizes on dendrites. LPHN1 and Ten2/Lasso form a trans-synaptic receptor pair that has both structural and signaling functions. However, Lasso is proteolytically cleaved at multiple sites and its extracellular domain is partially released into the intercellular space, especially during neuronal development, suggesting that soluble Lasso has additional functions. We discovered that the soluble fragment of Lasso can diffuse away and bind to LPHN1 on axonal growth cones, triggering its redistribution on the cell surface and intracellular signaling which leads to local exocytosis. This causes axons to turn in the direction of spatio-temporal Lasso gradients, while LPHN1 knockout blocks this effect. These results suggest that the LPHN1-Ten2/Lasso pair can participate in long- and short-distance axonal guidance and synapse formation.

Discovery of Teneurins

Teneurins were first discovered and published in 1993 and 1994, in Drosophila melanogaster as Ten-a and Ten-m. They were initially described as cell surface proteins, and as pair-rule genes. Later, they proved to be type II transmembrane proteins, and not to be pair-rule genes. Ten-m might nonetheless have had an ancestral function in clock-based segmentation as a Ten-m oscillator. The turn of the millennium saw a watershed of vertebrate Teneurin discovery, which was soon complemented by Teneurin protein annotations from whole genome sequence publications. Teneurins encode proteins with essentially invariant domain order and size. The first years of Teneurin studies in many experimental systems led to key insights, and a unified picture, of Teneurin proteins.

Latrophilins and Teneurins in Invertebrates: No Love for Each Other?

Transsynaptic connections enabling cell–cell adhesion and cellular communication are a vital part of synapse formation, maintenance and function. A recently discovered interaction between the Adhesion GPCRs Latrophilins and the type II single transmembrane proteins Teneurins at mammalian synapses is vital for synapse formation and dendrite branching. While the understanding of the effects and the molecular interplay of this Latrophilin-Teneurin partnership is not entirely understood, its significance is highlighted by behavioral and neurological phenotypes in various animal models. As both groups of molecules, Latrophilins and Teneurins, are generally highly conserved, have overlapping expression and often similar functions across phyla, it can be speculated that this interaction, which has been proven essential in mammalian systems, also occurs in invertebrates to control shaping of synapses. Knowledge of the generality of this interaction is especially of interest due to its possible involvement in neuropathologies. Further, several invertebrates serve as model organisms for addressing various neurobiological research questions. So far, an interaction of Latrophilins and Teneurins has not been observed in invertebrates, but our knowledge on both groups of molecules is by far not complete. In this review, we give an overview on existing experimental evidence arguing for as well as against a potential Latrophilin-Teneurin interaction beyond mammals. By combining these insights with evolutionary aspects on each of the interaction partners we provide and discuss a comprehensive picture on the functions of both molecules in invertebrates and the likeliness of an evolutionary conservation of their interaction.

Teneurins and Teneurin C-Terminal Associated Peptide (TCAP) in Metabolism: What's Known in Fish?

Teneurins have well established roles in function and maintenance of the central nervous systems of vertebrates. In addition, teneurin c-terminal associated peptide (TCAP), a bioactive peptide found on the c-terminal portion of teneurins, has been shown to regulate glucose metabolism. Although, the majority of research conducted on the actions of teneurins and TCAPs has strictly focused on neurological systems in rodents, TCAP was first identified in rainbow trout after screening trout hypothalamic cDNA. This suggests a conserved functional role of TCAP across vertebrates, however, the current depth of literature on teneurins and TCAPs in fish is limited. In addition, the overall function of TCAP in regulating metabolism is unclear. This review will highlight work that has been conducted specifically in fish species in relation to the teneurin system and metabolism in order to identify areas of research that are needed for future work.

Structural Basis for Teneurin Function in Circuit-Wiring: A Toxin Motif at the Synapse

Teneurins (TENs) are cell-surface adhesion proteins with critical roles in tissue development and axon guidance. Here, we report the 3.1-Å cryoelectron microscopy structure of the human TEN2 extracellular region (ECR), revealing a striking similarity to bacterial Tc-toxins. The ECR includes a large β barrel that partially encapsulates a C-terminal domain, which emerges to the solvent through an opening in the mid-barrel region. An immunoglobulin (Ig)-like domain seals the bottom of the barrel while a β propeller is attached in a perpendicular orientation. We further show that an alternatively spliced region within the β propeller acts as a switch to regulate trans-cellular adhesion of TEN2 to latrophilin (LPHN), a transmembrane receptor known to mediate critical functions in the central nervous system. One splice variant activates trans-cellular signaling in a LPHN-dependent manner, whereas the other induces inhibitory postsynaptic differentiation. These results highlight the unusual structural organization of TENs giving rise to their multifarious functions.

Teneurins: Domain Architecture, Evolutionary Origins, and Patterns of Expression

Disruption of teneurin expression results in abnormal neural networks, but just how teneurins support the development of the central nervous system remains an area of active research. This review summarizes some of what we know about the functions of the various domains of teneurins, the possible evolution of teneurins from a bacterial toxin, and the intriguing patterns of teneurin expression. Teneurins are a family of type-2 transmembrane proteins. The N-terminal intracellular domain can be processed and localized to the nucleus, but the significance of this nuclear localization is unknown. The extracellular domain of teneurins is largely composed of tyrosine-aspartic acid repeats that fold into a hollow barrel, and the C-terminal domains of teneurins are stuffed, and least partly, into the barrel. A 6-bladed beta-propeller is found at the other end of the barrel. The same arrangement-6-bladed beta-propeller, tyrosine-aspartic acid repeat barrel, and the C-terminal domain inside the barrel-is seen in toxic proteins from bacteria, and there is evidence that teneurins may have evolved from a gene encoding a prokaryotic toxin via horizontal gene transfer into an ancestral choanoflagellate. Patterns of teneurin expression are often, but not always, complementary. In the central nervous system, where teneurins are best studied, interconnected populations of neurons often express the same teneurin. For example, in the chicken embryo neurons forming the tectofugal pathway express teneurin-1, whereas neurons forming the thalamofugal pathway express teneurin-2. In Drosophila melanogaster, Caenorhabditis elegans, zebrafish and mice, misexpression or knocking out teneurin expression leads to abnormal connections in the neural networks that normally express the relevant teneurin. Teneurins are also expressed in non-neuronal tissue during development, and in at least some regions the patterns of non-neuronal expression are also complementary. The function of teneurins outside the nervous system remains unclear.

Teneurins: An Integrative Molecular, Functional, and Biomedical Overview of Their Role in Cancer

Teneurins are large transmembrane proteins originally identified in Drosophila. Their essential role in development of the central nervous system is conserved throughout species, and evidence supports their involvement in organogenesis of additional tissues. Homophilic and heterophilic interactions between Teneurin paralogues mediate cellular adhesion in crucial processes such as neuronal pathfinding and synaptic organization. At the molecular level, Teneurins are proteolytically processed into distinct subdomains that have been implicated in extracellular and intracellular signaling, and in transcriptional regulation. Phylogenetic studies have shown a high degree of intra- and interspecies conservation of Teneurin genes. Accordingly, the occurrence of genetic variants has been associated with functional and phenotypic alterations in experimental systems, and with some inherited or sporadic conditions. Recently, tumor-related variations in Teneurin gene expression have been associated with patient survival in different cancers. Although these findings were incidental and molecular mechanisms were not addressed, they suggested a potential utility of Teneurin transcript levels as biomarkers for disease prognosis. Mutations and chromosomal alterations affecting Teneurin genes have been found occasionally in tumors, but literature remains scarce. The analysis of open-access molecular and clinical datasets derived from large oncologic cohorts provides an invaluable resource for the identification of additional somatic mutations. However, Teneurin variants have not been classified in terms of pathogenic risk and their phenotypic impact remains unknown. On this basis, is it plausible to hypothesize that Teneurins play a role in carcinogenesis? Does current evidence support a tumor suppressive or rather oncogenic function for these proteins? Here, we comprehensively discuss available literature with integration of molecular evidence retrieved from open-access databases. We show that Teneurins undergo somatic changes comparable to those of well-established cancer genes, and discuss their involvement in cancer-related signaling pathways. Current data strongly suggest a functional contribution of Teneurins to human carcinogenesis.

Proteolytically released Lasso/teneurin-2 induces axonal attraction by interacting with latrophilin-1 on axonal growth cones

A presynaptic adhesion G-protein-coupled receptor, latrophilin-1, and a postsynaptic transmembrane protein, Lasso/teneurin-2, are implicated in trans-synaptic interaction that contributes to synapse formation. Surprisingly, during neuronal development, a substantial proportion of Lasso is released into the intercellular space by regulated proteolysis, potentially precluding its function in synaptogenesis. We found that released Lasso binds to cell-surface latrophilin-1 on axonal growth cones. Using microfluidic devices to create stable gradients of soluble Lasso, we show that it induces axonal attraction, without increasing neurite outgrowth. Using latrophilin-1 knockout in mice, we demonstrate that latrophilin-1 is required for this effect. After binding latrophilin-1, Lasso causes downstream signaling, which leads to an increase in cytosolic calcium and enhanced exocytosis, processes that are known to mediate growth cone steering. These findings reveal a novel mechanism of axonal pathfinding, whereby latrophilin-1 and Lasso mediate both short-range interaction that supports synaptogenesis, and long-range signaling that induces axonal attraction.

The brain is a complex mesh of interconnected neurons, with each cell making tens, hundreds, or even thousands of connections. These links can stretch over long distances, and establishing them correctly during development is essential. Developing neurons send out long and thin structures, called axons, to reach distant cells. To guide these growing axons, neurons release molecules that work as traffic signals: some attract axons whilst others repel them, helping the burgeoning structures to twist and turn along their travel paths.

When an axon reaches its target cell, the two cells join to each other by forming a structure called a synapse. To make the connection, surface proteins on the axon latch onto matching proteins on the target cell, zipping up the synapse. There are many different types of synapses in the brain, but we only know a few of the surface molecules involved in their creation – not enough to explain synaptic variety.

Two of these surface proteins are latrophilin-1, which is produced by the growing axon, and Lasso, which sits on the membrane of the target cell. The two proteins interact strongly, anchoring the axon to the target cell and allowing the synapse to form. However, a previous recent discovery by Vysokov et al. has revealed that an enzyme can also cut Lasso from the membrane of the target cell. The ‘free’ protein can still interact with latrophilin-1, but as it is shed by the target cell, it can no longer serve as an anchor for the synapse. Could it be that free Lasso acts as a traffic signal instead?

Here, Vysokov et al. tried to answer this by growing neurons from a part of the brain called the hippocampus in a special labyrinth dish. When free Lasso was gradually introduced in the culture through microscopic channels, it interacted with latrophilin-1 on the surface of the axons. This triggered internal changes that led the axons to add more membrane where they had sensed Lasso, making them grow towards the source of the signal.

The results demonstrate that a target cell can both carry and release Lasso, using this duplicitous protein to help attract growing axons as well as anchor them. The work by Vysokov et al. contributes to our knowledge of how neurons normally connect, which could shed light on how this process can go wrong. This may be relevant to understand conditions such as schizophrenia and ADHD, where patients’ brains often show incorrect wiring.

The teneurin C-terminal domain possesses nuclease activity and is apoptogenic

Teneurins are type 2 transmembrane proteins expressed by developing neurons during periods of synaptogenesis and apoptosis. Neurons expressing teneurin-1 synapse with other teneurin-1-expressing neurons, and neurons expressing teneurin-2 synapse with other teneurin-2-expressing neurons. Knockdowns and mutations of teneurins lead to abnormal neuronal connections, but the mechanisms underlying teneurin action remain unknown. Teneurins appear to have evolved via horizontal gene transfer from prokaryotic proteins involved in bacterial self-recognition. The bacterial teneurin-like proteins contain a cytotoxic C-terminal domain that is encapsulated in a tyrosine-aspartic acid repeat barrel. Teneurins are likely to be organized in the same way, but it is unclear if the C-terminal domains of teneurins have cytotoxic properties. Here we show that expression of teneurin C-terminal domains or the addition of purified teneurin C-terminal domains leads to an increase in apoptosis in vitro. The C-terminal domains of teneurins are most similar to bacterial nucleases, and purified C-terminal domains of teneurins linearize pcDNA3 and hydrolyze mitochondrial DNA. We hypothesize that yet to be identified stimuli lead to the release of the encapsulated teneurin C-terminal domain into the intersynaptic region, resulting in programmed cell death or the disruption of mitochondrial DNA and the subsequent pruning of inappropriate contacts.

Summary: Teneurins are transmembrane proteins found in the developing nervous system that are related to bacterial toxins. Teneurins also have cytotoxic properties that may help regulate apoptosis or pruning.

Structures of Teneurin adhesion receptors reveal an ancient fold for cell-cell interaction

Teneurins are ancient cell–cell adhesion receptors that are vital for brain development and synapse organisation. They originated in early metazoan evolution through a horizontal gene transfer event when a bacterial YD-repeat toxin fused to a eukaryotic receptor. We present X-ray crystallography and cryo-EM structures of two Teneurins, revealing a ~200 kDa extracellular super-fold in which eight sub-domains form an intricate structure centred on a spiralling YD-repeat shell. An alternatively spliced loop, which is implicated in homophilic Teneurin interaction and specificity, is exposed and thus poised for interaction. The N-terminal side of the shell is ‘plugged’ via a fibronectin-plug domain combination, which defines a new class of YD proteins. Unexpectedly, we find that these proteins are widespread amongst modern bacteria, suggesting early metazoan receptor evolution from a distinct class of proteins, which today includes both bacterial proteins and eukaryotic Teneurins.

Teneurins are cell-cell adhesion receptors that evolved through horizontal gene transfer in which a bacterial YD-repeat protein fused to a eukaryotic receptor. Here the authors present crystallographic and cryo-EM structures of two Teneurins, revealing an ancient YD-repeat protein super-fold.

Teneurin-3 controls topographic circuit assembly in the hippocampus

Brain functions rely on specific patterns of connectivity. Teneurins are evolutionarily conserved transmembrane proteins that instruct synaptic partner matching in Drosophila and are required for vertebrate visual system development. The roles of vertebrate teneurins in connectivity beyond the visual system remain largely unknown and their mechanisms of action have not been demonstrated. Here we show that mouse teneurin-3 is expressed in multiple topographically interconnected areas of the hippocampal region, including proximal CA1, distal subiculum, and medial entorhinal cortex. Viral-genetic analyses reveal that teneurin-3 is required in both CA1 and subicular neurons for the precise targeting of proximal CA1 axons to distal subiculum. Furthermore, teneurin-3 promotes homophilic adhesion in vitro in a splicing isoform-dependent manner. These findings demonstrate striking genetic heterogeneity across multiple hippocampal areas and suggest that teneurin-3 may orchestrate the assembly of a complex distributed circuit in the mammalian brain via matching expression and homophilic attraction.

Molecular guidance cues in the development of visual pathway

70%–80% of our sensory input comes from vision. Light hit the retina at the back of our eyes and the visual information is relayed into the dorsal lateral geniculate nuclei (dLGN) and primary visual cortex (V1) thereafter, constituting the image-forming visual circuit. Molecular cues are one of the key factors to guide the wiring and refinement of the image-forming visual circuit during pre- and post-embryonic stages. Distinct molecular cues are involved in different developmental stages and nucleus, suggesting diverse guidance mechanisms. In this review, we summarize molecular guidance cues throughout the image-forming visual circuit, including chiasm determination, eye-specific segregation and refinement in the dLGN, and at last the reciprocal connections between the dLGN and V1.

The Mechanism of Regulated Release of Lasso/Teneurin-2

Teneurins are large cell-surface receptors involved in axon guidance. Teneurin-2 (also known as latrophilin-1-associated synaptic surface organizer (Lasso)) interacts across the synaptic cleft with presynaptic latrophilin-1, an adhesion G-protein-coupled receptor that participates in regulating neurotransmitter release. Lasso-latrophilin-1 interaction mediates synapse formation and calcium signaling, highlighting the important role of this trans-synaptic receptor pair. However, Lasso is thought to be proteolytically cleaved within its ectodomain and released into the medium, making it unclear whether it acts as a proper cell-surface receptor or a soluble protein. We demonstrate here that during its intracellular processing Lasso is constitutively cleaved at a furin site within its ectodomain. The cleaved fragment, which encompasses almost the entire ectodomain of Lasso, is potentially soluble; however, it remains anchored on the cell surface via its non-covalent interaction with the transmembrane fragment of Lasso. Lasso is also constitutively cleaved within the intracellular domain (ICD). Finally, Lasso can be further proteolytically cleaved within the transmembrane domain. The third cleavage is regulated and releases the entire ectodomain of Lasso into the medium. The released ectodomain of Lasso retains its functional properties and binds latrophilin-1 expressed on other cells; this binding stimulates intracellular Ca²⁺ signaling in the target cells. Thus, Lasso not only serves as a bona fide cell-surface receptor, but also as a partially released target-derived signaling factor.

Systems genetic analysis of hippocampal neuroanatomy and spatial learning in mice

Variation in hippocampal neuroanatomy correlates well with spatial learning ability in mice. Here, we have studied both hippocampal neuroanatomy and behavior in 53 isogenic BXD recombinant strains derived from C57BL/6J and DBA/2J parents. A combination of experimental, neuroinformatic and systems genetics methods was used to test the genetic bases of variation and covariation among traits. Data were collected on seven hippocampal subregions in CA3 and CA4 after testing spatial memory in an eight-arm radial maze task. Quantitative trait loci were identified for hippocampal structure, including the areas of the intra- and infrapyramidal mossy fibers (IIPMFs), stratum radiatum and stratum pyramidale, and for a spatial learning parameter, error rate. We identified multiple loci and gene variants linked to either structural differences or behavior. Gpc4 and Tenm2 are strong candidate genes that may modulate IIPMF areas. Analysis of gene expression networks and trait correlations highlight several processes influencing morphometrical variation and spatial learning.

MicroRNAs in Breastmilk and the Lactating Breast: Potential Immunoprotectors and Developmental Regulators for the Infant and the Mother

Human milk (HM) is the optimal source of nutrition, protection and developmental programming for infants. It is species-specific and consists of various bioactive components, including microRNAs, small non-coding RNAs regulating gene expression at the post-transcriptional level. microRNAs are both intra- and extra-cellular and are present in body fluids of humans and animals. Of these body fluids, HM appears to be one of the richest sources of microRNA, which are highly conserved in its different fractions, with milk cells containing more microRNAs than milk lipids, followed by skim milk. Potential effects of exogenous food-derived microRNAs on gene expression have been demonstrated, together with the stability of milk-derived microRNAs in the gastrointestinal tract. Taken together, these strongly support the notion that milk microRNAs enter the systemic circulation of the HM fed infant and exert tissue-specific immunoprotective and developmental functions. This has initiated intensive research on the origin, fate and functional significance of milk microRNAs. Importantly, recent studies have provided evidence of endogenous synthesis of HM microRNA within the human lactating mammary epithelium. These findings will now form the basis for investigations of the role of microRNA in the epigenetic control of normal and aberrant mammary development, and particularly lactation performance.

On the Teneurin track: a new synaptic organization molecule emerges

To achieve proper synaptic development and function, coordinated signals must pass between the pre- and postsynaptic membranes. Such transsynaptic signals can be comprised of receptors and secreted ligands, membrane associated receptors, and also pairs of synaptic cell adhesion molecules. A critical open question bridging neuroscience, developmental biology, and cell biology involves identifying those signals and elucidating how they function. Recent work in Drosophila and vertebrate systems has implicated a family of proteins, the Teneurins, as a new transsynaptic signal in both the peripheral and central nervous systems. The Teneurins have established roles in neuronal wiring, but studies now show their involvement in regulating synaptic connections between neurons and bridging the synaptic membrane and the cytoskeleton. This review will examine the Teneurins as synaptic cell adhesion molecules, explore how they regulate synaptic organization, and consider how some consequences of human Teneurin mutations may have synaptopathic origins.

Characterization of the teneurin C-terminal associated peptide (TCAP) in the vase tunicate, Ciona intestinalis: A novel peptide system associated with energy metabolism and reproduction

The vase tunicate, Ciona intestinalis, is a protochordate and is considered a sister lineage to the chordates. The recent sequencing of its genome has made this species a particularly important model to understand the genetic basis of vertebrate evolution. However, C. intestinalis is also a highly invasive species along the Atlantic coast of North America and other regions of the world which have caused considerable economic stress due to its biofouling actions and, in particular, negative impacts on the mussel- and oyster-based aquaculture industry. Despite this background, little is known about C. intestinalis physiology. The teneurin C-terminal associated peptides (TCAP) are a family of highly conserved peptide hormones found in most metazoans. Moreover, these peptides have been implicated in the inhibition of stress and stimulation of feeding-based metabolism. We have, therefore, identified this peptide using an in silico approach and characterized its immunological expression in tissues using a mouse polyclonal antiserum. These data indicate that its primary structure is more similar to invertebrate TCAPs relative to vertebrate TCAPs. Immunological expression indicates that it is highly expressed in the digestive tract and gonads consistent with findings in vertebrates. Synthetic mouse TCAP-1 administered into the brachial basket significantly increases the incidence of non-stress contractile behaviors. These findings support the hypothesis that TCAP is a bioactive peptide in C. intestinalis. Thus, C. intestinalis and tunicates in general may offer a simple model to investigate peptide interaction while providing information on how to control this invasive species.

Ancient interaction between the teneurin C-terminal associated peptides (TCAP) and latrophilin ligand-receptor coupling: a role in behavior

Teneurins are multifunctional transmembrane proteins that are found in all multicellular animals and exist as four paralogous forms in vertebrates. They are highly expressed in the central nervous system, where they exert their effects, in part, by high-affinity binding to latrophilin (LPHN), a G-protein coupled receptor (GPCR) related to the adhesion and secretin GPCR families. The teneurin C-terminal associated peptides (TCAPs) are encoded by the terminal exon of all four teneurins, where TCAPs 1 and 3 are independently transcribed as soluble peptides, and TCAPs 2 and 4 remain tethered to their teneurin proprotein. Synthetic TCAP-1 interacts with LPHN, with an association with β-dystroglycan, to induce a tissue-dependent signal cascade to modulate cytoskeletal dynamics. TCAP-1 reduces stress-induced behaviors associated with anxiety, addiction and depression in a variety of models, in part, by regulating synaptic plasticity. Therefore, the TCAP-1-teneurin-LPHN interaction represents a novel receptor-ligand model and may represent a key mechanism underlying the association of behavior and neurological conditions.

The intracellular domain of teneurin-1 induces the activity of microphthalmia-associated transcription factor (MITF) by binding to transcriptional repressor HINT1

Teneurins are large type II transmembrane proteins that are necessary for the normal development of the CNS. Although many studies highlight the significance of teneurins, especially during development, there is only limited information known about the molecular mechanisms of function. Previous studies have shown that the N-terminal intracellular domain (ICD) of teneurins can be cleaved at the membrane and subsequently translocates to the nucleus, where it can influence gene transcription. Because teneurin ICDs do not contain any intrinsic DNA binding sequences, interaction partners are required to affect transcription. Here, we identified histidine triad nucleotide binding protein 1 (HINT1) as a human teneurin-1 ICD interaction partner in a yeast two-hybrid screen. This interaction was confirmed in human cells, where HINT1 is known to inhibit the transcription of target genes by directly binding to transcription factors at the promoter. In a whole transcriptome analysis of BS149 glioblastoma cells overexpressing the teneurin-1 ICD, several microphthalmia-associated transcription factor (MITF) target genes were found to be up-regulated. Directly comparing the transcriptomes of MITF versus TEN1-ICD-overexpressing BS149 cells revealed 42 co-regulated genes, including glycoprotein non-metastatic b (GPNMB). Using real-time quantitative PCR to detect endogenous GPNMB expression upon overexpression of MITF and HINT1 as well as promoter reporter assays using GPNMB promoter constructs, we could demonstrate that the teneurin-1 ICD binds HINT1, thus switching on MITF-dependent transcription of GPNMB.

The teneurins: new players in the generation of visual topography

A functionally critical feature of the nervous system is the precision of its connectivity. An emerging molecular mediator of this process is the teneurin/ten-m/odz family of transmembrane proteins. A number of recent studies have provided compelling evidence that teneurins have homophilic adhesive properties which, together with their corresponding expression patterns in interconnected groups of neurons, enables them to promote appropriate patterns of connectivity. Particularly important roles have been demonstrated in the visual, olfactory and motor systems. This review attempts to relate new insights into the complex biology of these molecules to their roles in the establishment of functional neural circuits.

Retinal overexpression of Ten-m3 alters ipsilateral retinogeniculate projections in the wallaby (Macropus eugenii)

The dorsal lateral geniculate nucleus (dLGN) contains a retinotopic map where input from the two eyes map in register to provide a substrate for binocular vision. Ten-m3, a transmembrane protein, mediates homophilic interactions and has been implicated in the patterning of ipsilateral visual projections. Ease of access to early developmental stages in a marsupial wallaby has been used to manipulate levels of Ten-m3 during the development of retinogeniculate projections. In situ hybridisation showed a high dorsomedial to low ventrolateral gradient of Ten-m3 in the developing dLGN, matching retinotopically with the previously reported high ventral to low dorsal retinal gradient. Overexpression of Ten-m3 in ventronasal but not dorsonasal retina resulted in an extension of ipsilateral projections beyond the normal binocular zone. These results demonstrate that Ten-m3 influences ipsilateral projections and support a role for it in binocular mapping.

Latrophilins function as heterophilic cell-adhesion molecules by binding to teneurins: regulation by alternative splicing

Latrophilin-1, -2, and -3 are adhesion-type G protein-coupled receptors that are auxiliary α-latrotoxin receptors, suggesting that they may have a synaptic function. Using pulldowns, we here identify teneurins, type II transmembrane proteins that are also candidate synaptic cell-adhesion molecules, as interactors for the lectin-like domain of latrophilins. We show that teneurin binds to latrophilins with nanomolar affinity and that this binding mediates cell adhesion, consistent with a role of teneurin binding to latrophilins in trans-synaptic interactions. All latrophilins are subject to alternative splicing at an N-terminal site; in latrophilin-1, this alternative splicing modulates teneurin binding but has no effect on binding of latrophilin-1 to another ligand, FLRT3. Addition to cultured neurons of soluble teneurin-binding fragments of latrophilin-1 decreased synapse density, suggesting that latrophilin binding to teneurin may directly or indirectly influence synapse formation and/or maintenance. These observations are potentially intriguing in view of the proposed role for Drosophila teneurins in determining synapse specificity. However, teneurins in Drosophila were suggested to act as homophilic cell-adhesion molecules, whereas our findings suggest a heterophilic interaction mechanism. Thus, we tested whether mammalian teneurins also are homophilic cell-adhesion molecules, in addition to binding to latrophilins as heterophilic cell-adhesion molecules. Strikingly, we find that although teneurins bind to each other in solution, homophilic teneurin-teneurin binding is unable to support stable cell adhesion, different from heterophilic teneurin-latrophilin binding. Thus, mammalian teneurins act as heterophilic cell-adhesion molecules that may be involved in trans-neuronal interaction processes such as synapse formation or maintenance.

C-terminal region of teneurin-1 co-localizes with the dystroglycan complex in adult mouse testes and regulates testicular size and testosterone production

Testicular size is directly proportional to fertility potential and is dependent on the integration of developmental proteins, trophic factors, and sex steroids. The teneurins are transmembrane glycoproteins that function as signaling and cell adhesion molecules in the establishment and maintenance of the somatic gonad, gametogenesis, and basement membrane. Moreover, teneurins are thought to function redundantly to the extracellular matrix protein, dystroglycan. Encoded on the last exon of the teneurin genes is a family of bioactive peptides termed the teneurin C-terminal-associated peptides (TCAPs). One of these peptides, TCAP-1, functionally interacts with β-dystroglycan to act as a neuromodulatory peptide with trophic characteristics independent from the teneurins. However, little is known about the localization and relationship between the teneurin-TCAP-1 system and the dystroglycans in the gonad. In the adult mouse testis, immunoreactive TCAP-1 was localized to spermatogonia and spermatocytes and co-localized with β-dystroglycan. However, teneurin-1 was localized to the peritubular myoid cell layer of seminiferous tubules and tubules within the epididymis, and co-localized with α-dystroglycan and α-smooth muscle actin. TCAP-1-binding sites were identified in the germ cell layers and adluminal compartment of the seminiferous tubules, and epithelial cells of the epididymis. In vivo, TCAP-1 administration to adult mice for 9 days increased testicular size, seminiferous and epididymal tubule short-diameter and elevated testosterone levels. TCAP-1-treated mice also showed increased TCAP-1 immunoreactivity in the caput and corpa epididymis. Our data provide novel evidence of TCAP-1 localization in the testes that is distinct from teneurin-1, but is integrated through an association with the dystroglycan complex.

Ten-m2 is required for the generation of binocular visual circuits

Functional binocular vision requires that inputs arising from the two retinae are integrated and precisely organized within central visual areas. Previous studies have demonstrated an important role for one member of the Ten-m/Odz/teneurin family, Ten-m3, in the mapping of ipsilateral retinal projections. Here, we have identified a distinct role for another closely related family member, Ten-m2, in the formation of the ipsilateral projection in the mouse visual system. Ten-m2 expression was observed in the retina, dorsal lateral geniculate nucleus (dLGN), superior colliculus (SC), and primary visual cortex (V1) of the developing mouse. Anterograde and retrograde tracing experiments in Ten-m2 knock-out (KO) mice revealed a specific decrease in ipsilateral retinal ganglion cells projecting to dLGN and SC. This reduction was most prominent in regions corresponding to ventral retina. No change in the topography of ipsilateral or contralateral projections was observed. While expression of a critical ipsilateral fate determinant, Zic2, appeared unaltered, a notable reduction in one of its downstream targets, EphB1, was observed in ventral retina, suggesting that Ten-m2 may interact with this molecular pathway. Immunohistochemistry for c-fos, a neural activity marker, revealed that the area of V1 driven by ipsilateral inputs was reduced in KOs, while the ratio of ipsilateral-to-contralateral responses contributing to binocular activation during visually evoked potential recordings was also diminished. Finally, a novel two-alternative swim task revealed specific deficits associated with dorsal visual field. These data demonstrate a requirement for Ten-m2 in the establishment of ipsilateral projections, and thus the generation of binocular circuits, critical for mammalian visual function.

Origin of chordate peptides by horizontal protozoan gene transfer in early metazoans and protists: evolution of the teneurin C-terminal associated peptides (TCAP)

The teneurin C-terminal associated peptides (TCAP) are found at the extracellular face in C-terminal region of the teneurin transmembrane proteins. One of these peptides, TCAP-1 is independently transcribed as a smaller bioactive peptide that possesses a number of stress response-attenuating activities. The teneurin-TCAP system appears to be the result of a horizontal gene transfer from a prokaryotic proteinaceous polymorphic toxin to a choanoflagellate. In a basal metazoan, the TCAP region has been modified from a toxin to a soluble intercellular signaling system. New studies indicate that the teneurin-TCAP system form a complex signaling system associated with adhesion, cytoskeletal regulation and intracellular signaling. TCAP-1 is highly conserved in all vertebrates and in mammals, inhibits corticotropin-releasing factor (CRF)-associated stress. Using the TCAP-teneurin system as a model, it is likely that numerous peptide systems in the Chordata began as a result of horizontal gene transfer from prokaryotes early in metazoan ancestry.

Deciphering teneurin domains that facilitate cellular recognition, cell-cell adhesion, and neurite outgrowth using atomic force microscopy-based single-cell force spectroscopy

Teneurins are evolutionarily conserved transmembrane receptors that function as axon guidance and target selection molecules in the developing nervous system. How teneurins recognize each other, whether they establish neuronal adhesion, and which teneurin specific interactions guide neurons remains to be determined. To reveal insight into these pertinent questions we combine atomic force microscopy-based single-cell force spectroscopy with genetic engineering and quantify the interactions teneurins establish between animal cells. Using a combinatorial approach of deletions and swaps of teneurin-1 and teneurin-2 domains, we unravel that teneurins use their NHL (NCL-1, HT2A, and Lin-41) domain to select homophilic teneurins from adjacent cells. This homophilic recognition of teneurins initiates cell-cell adhesion that, dependent on the intracellular domain, strengthens over time. Neurite outgrowth assays show that establishing and strengthening of teneurin-mediated homophilic cell-cell adhesion is required to stop outgrowth. On the basis of the results, we introduce a molecular model of teneurin domains that specify cellular recognition, adhesion strengthening, and neuronal pathfinding. The combined force spectroscopy and genetic approach can be applied to quantitatively decipher the contribution of any neuronal receptor domain and more generally of a given cell surface receptor domain to cell-cell recognition and adhesion.

Overexpression of Ten-m3 in the retina alters ipsilateral retinocollicular projections in the wallaby (Macropus eugenii)

Retinal projections to the superior colliculus are organised into retinotopic maps. Binocular vision requires that inputs from the two eyes map in register with each other. Studies in mice lacking Ten-m3, a homophilic transmembrane protein, indicate that it plays a key role in this process by influencing ipsilateral projections. The postnatal, ex utero development of the wallaby allows the targeted manipulation of molecules of interest during development. The distribution of mRNA for Ten-m3 in the retina and superior colliculus of the wallaby, and the effects of its spatiotemporally restricted retinal overexpression was investigated, in particular on the mapping of ipsilateral projections. Quantitative polymerase chain reaction found that Ten-m3 mRNA is expressed at relatively higher levels in the retina and colliculus early in development. Further, it is higher in ventral than dorsal retina, and increased in the retinotopically corresponding medial compared to lateral superior colliculus. In situ hybridisation demonstrated an increasing dorsoventral gradient in retinal ganglion cells was matched to an increasing lateromedial gradient in the superior colliculus. Overexpression of Ten-m3 by in vivo retinal electroporation produced an increase in ipsilateral projections to the binocular rostromedial colliculus, fitting with the proposal that Ten-m3 mediates mapping by attractant homophilic interactions. Retrograde labelling of the projection from this region suggested that overexpression produces a shift in the axons of existing ipsilaterally projecting ganglion cells rather than a rerouting of the axons of contralaterally projecting cells. Retinal manipulation of Ten-m3 levels produces changes in ipsilateral mapping, supporting a role for it in binocular mapping.

Mouse Tenm4 is required for mesoderm induction

Background

Tenm4 is a mouse homolog of the Drosophila gene Tenascin-m (Ten-m (Odd oz)), which functions in motor neuron routing. Recently, a genome-wide association analysis for bipolar disorder identified a new susceptibility locus at TENM4 increasing the importance of understanding Tenm4. A series of Tenm4 mouse alleles showing a broad range of phenotypes were isolated after ENU mutagenesis. Here, we examine the timing and features of gastrulation failure in a loss of function allele.

Results

Embryonic mesoderm did not form in loss of function Tenm4^m1/m1 mutant embryos. Genes normally expressed in embryonic mesoderm were not expressed in the mutant, the primitive streak did not form, and markers of the anteroposterior axis were not expressed or were mislocalized. The lack of embryonic mesoderm could not be attributed to poor proliferation of the epiblast, as normal numbers of dividing cells were observed. Epiblast cells maintained expression of Pou5f1 suggesting that they remain pluripotent, but they did not have the capacity to form any germ layer derivatives in teratomas, showing that the inability to induce mesoderm is cell autonomous. Misexpression of E-cadherin and N-cadherin suggest that the embryos did not undergo an epithelial-to-mesenchymal transition. In addition, Wnt signaling did not occur in the mutants, as assessed by the TOPGAL reporter assay, while a GSK3β inhibitor partially rescued the mutant embryos, and rescued TOPGAL reporter expression.

Conclusions

These data demonstrate that Tenm4 mutants fail to form a primitive streak and to induce embryonic mesoderm. Markers of anterior posterior patterning fail to be expressed or are mislocalized. Further, Tenm4 mutants lack the ability to differentiate in a cell autonomous manner. Together, our data suggest that embryos become impaired prior to E6.5 and as a result, Wnt signaling fails to occur; however, the involvement of other signaling pathways remains to be examined.

Transcriptome profiling of microRNA by Next-Gen deep sequencing reveals known and novel miRNA species in the lipid fraction of human breast milk

While breast milk has unique health advantages for infants, the mechanisms by which it regulates the physiology of newborns are incompletely understood. miRNAs have been described as functioning transcellularly, and have been previously isolated in cell-free and exosomal form from bodily liquids (serum, saliva, urine) and tissues, including mammary tissue. We hypothesized that breast milk in general, and milk fat globules in particular, contain significant numbers of known and limited novel miRNA species detectable with massively parallel sequencing. Extracted RNA from lactating mothers before and following short-term treatment with recombinant human growth hormone (rhGH) was smRNA-enriched. smRNA-Seq was performed to generate 124,110,646 36-nt reads. Of these, 31,102,927 (25%) exactly matched known human miRNAs; with relaxing of stringency, 74,716,151 (60%) matched known miRNAs including 308 of the 1018 (29%) mature miRNAs (miRBase 16.0). These miRNAs are predicted to target 9074 genes; the 10 most abundant of these predicted to target 2691 genes with enrichment for transcriptional regulation of metabolic and immune responses. We identified 21 putative novel miRNAs, of which 12 were confirmed in a large validation set that included cohorts of lactating women consuming enriched diets. Of particular interest, we observed that expression of several novel miRNAs were altered by the perturbed maternal diet, notably following a high-fat intake (p<0.05). Our findings suggest that known and novel miRNAs are enriched in breast milk fat globules, and expression of several novel miRNA species is regulated by maternal diet. Based on robust pathway mapping, our data supports the notion that these maternally secreted miRNAs (stable in the milk fat globules) play a regulatory role in the infant and account in part for the health benefits of breast milk. We further speculate that regulation of these miRNA by a high fat maternal diet enables modulation of fetal metabolism to accommodate significant dietary challenges.

C-terminal processing of the teneurin proteins: independent actions of a teneurin C-terminal associated peptide in hippocampal cells

Many neuropsychiatric conditions have a common set of neurological substrates associated with the integration of sensorimotor processing. The teneurins are a recently described family of proteins that play a significant role in visual and auditory development. Encoded on the terminal exon of the teneurin genes is a family of bioactive peptides, termed teneurin C-terminal associated peptides (TCAP), which regulate mood-disorder associated behaviors. Thus, the teneurin-TCAP system could represent a novel neurological system underlying the origins of a number of complex neuropsychiatric conditions. However, it is not known if TCAP-1 exerts its effects as part of a direct teneurin function, whereby TCAP represents a functional region of the larger teneurin protein, or if it has an independent role, either as a splice variant or post-translational proteolytic cleavage product of teneurin. In this study, we show that TCAP-1 can be transcribed as a smaller mRNA transcript. After translation, further processing yields a smaller 15 kDa protein containing the TCAP-1 region. In the mouse hippocampus, immunoreactive (ir) TCAP-1 is exclusively localized to the pyramidal layers of the CA1, CA2 and CA3 regions. Although the localization of TCAP and teneurin in hippocampal regions is similar, they are distinct within the cell as most ir-teneurin is found at the plasma membrane, whereas ir-TCAP-1 is predominantly found in the cytosol. Moreover, in mouse embryonic hippocampal cell culture, FITC-labeled TCAP-1 binds to the plasma membrane and is taken up into the cytosol via dynamin-dependent caveolae-mediated endocytosis. Our data provides novel evidence that TCAP-1 is structurally and functionally distinct from the larger teneurins.