A three-tier mechanism involving distinct neurotrophin family ligand forms, different Toll receptors, and different adaptors regulates both cell survival and death. This rich mechanism confers cell number plasticity and could underlie structural plasticity in the nervous system and structural integrity, homeostasis, and regeneration in wider contexts.

Glial cells help central nervous system injury repair, but this is limited by the failure of newly produced glial cells to differentiate. Here, Losada-Perez et al. identify the NG2-dependent mechanism modulating glial proliferation and differentiation after damage to promote repair, in the central nervous system of Drosophila.

In the nematode C. elegans, insulin signaling regulates development and aging in response to the secretion of numerous insulin peptides. Here, we describe a novel, non-signaling isoform of the nematode insulin receptor (IR), DAF-2B, that modulates insulin signaling by sequestration of insulin peptides. DAF-2B arises via alternative splicing and retains the extracellular ligand binding domain but lacks the intracellular signaling domain. A daf-2b splicing reporter revealed active regulation of this transcript through development, particularly in the dauer larva, a diapause stage associated with longevity. CRISPR knock-in of mScarlet into the daf-2b genomic locus confirmed that DAF-2B is expressed in vivo and is likely secreted. Genetic studies indicate that DAF-2B influences dauer entry, dauer recovery and adult lifespan by altering insulin sensitivity according to the prevailing insulin milieu. Thus, in C. elegans alternative splicing at the daf-2 locus generates a truncated IR that fine-tunes insulin signaling in response to the environment.

Background: ␣-Catenin is a crucial link between adherens junctions and F-actin. Results: C-terminal amino acids in HMP-1/␣-catenin quantitatively modulate its ability to bind F-actin, but a putative vinculinbinding domain is not required in vivo. Conclusion: Key C-terminal residues in ␣-catenin modulate its ability to bind F-actin. Significance: This is the first genetic dissection of the ability of ␣-catenin to bind F-actin. Stable intercellular adhesions formed through the cadherincatenin complex are important determinants of proper tissue architecture and help maintain tissue integrity during morphogenetic movements in developing embryos. A key regulator of this stability is ␣-catenin, which connects the cadherin-catenin complex to the actin cytoskeleton. Although the C-terminal F-actin-binding domain of ␣-catenin has been shown to be crucial for its function, a more detailed in vivo analysis of discrete regions and residues required for actin binding has not been performed. Using Caenorhabditis elegans as a model system, we have characterized mutations in hmp-1/␣-catenin that identify HMP-1 residues 687-742 and 826-927, as well as amino acid 802, as critical to the localization of junctional proximal actin during epidermal morphogenesis. We also find that the S823F transition in a hypomorphic allele, hmp-1(fe4), decreases actin binding in vitro. Using hmp-1(fe4) animals in a mutagenesis screen, we were then able to identify 11 intragenic suppressors of hmp-1(fe4) that revert actin binding to wild-type levels. Using homology modeling, we show that these amino acids are positioned at key conserved sites within predicted ␣-helices in the C terminus. Through the use of transgenic animals, we also demonstrate that HMP-1 residues 315-494, which correspond to a putative mechanotransduction domain that binds vinculin in vertebrate ␣E-catenin, are not required during epidermal morphogenesis but may aid efficient recruitment of HMP-1 to the junction. Our studies are the first to identify key conserved amino acids in the C terminus of ␣-catenin that modulate F-actin binding in living embryos of a simple metazoan.

A disintegrin and metalloprotease 10 (ADAM10) is a transmembrane protein essential for embryonic development, and its dysregulation underlies disorders such as cancer, Alzheimer’s disease and inflammation.  ADAM10 is a “molecular scissor” that proteolytically cleaves the extracellular region from >100 substrates, including Notch, amyloid precursor protein, cadherins, growth factors, and chemokines.  ADAM10 has been recently proposed to function as six distinct scissors with different substrates, depending on its association with one of six regulatory tetraspanins, termed TspanC8s.  However, it remains unclear to what degree ADAM10 function critically depends on a TspanC8 partner, and a lack of monoclonal antibodies specific for most TspanC8s has hindered investigating this question.  To address this knowledge gap, here we designed an immunogen to generate the first monoclonal antibodies targeting Tspan15, a model TspanC8.  The immunogen was created in an ADAM10-knockout mouse cell line stably overexpressing human Tspan15, because we hypothesized that expression in this cell line would expose epitopes that are normally blocked by ADAM10.  Following immunization of mice, this immunogen strategy generated four Tspan15 antibodies.  Using these antibodies, we show that endogenous Tspan15 and ADAM10 co-localize on the cell surface, that ADAM10 is the principal Tspan15-interacting protein, that endogenous Tspan15 expression requires ADAM10 in cell lines and primary cells, and that a synthetic ADAM10/Tspan15 fusion protein is a functional scissor.  Furthermore, two of the four antibodies impaired ADAM10/Tspan15 activity.  These findings suggest that Tspan15 directly interacts with ADAM10 in a functional scissor complex.