Amyloids are highly organized cross β-sheet-rich protein or peptide aggregates that are associated with pathological conditions including Alzheimer's disease and type II diabetes. However, amyloids may also have a normal biological function as demonstrated by fungal prions, which are involved in prion replication, and the amyloid protein Pmel17, which is involved in mammalian skin pigmentation. Here, we show that peptide and protein hormones in secretory granules of the endocrine system are stored in an amyloid-like cross β-sheet-rich conformation. Thus, in contrast to the original association of amyloids with diseases, functional amyloids in the pituitary and other organs can contribute to normal cell and tissue physiology.Cells transport newly synthesized secretory proteins and peptides in vesicles via the endoplasmic reticulum (ER) and Golgi for release into the extracellular space (1,2). Some secretory cells, such as neuroendocrine cells and exocrine cells, store secretory proteins and peptides for extended time periods in a highly concentrated form in membrane-enclosed electron-dense cores termed "secretory granules" (1,3,4), which are derived from the Golgi complex. The dense cores of these granules are made up of large, insoluble secretory protein and peptide aggregates that are formed by self-association (4-6). The granules are not amorphous, but possess a distinct molecular organization, possibly of crystalline structures (7) or large intermolecular aggregates (5,8).Amyloid fibrils are cross-β-sheet structures that are primarily associated with several neurodegenerative diseases including Alzheimer's disease. However, amyloid fibril formation also provides biologically functional entities termed functional amyloids (9) and are present in Escherichia coli (10), silkworm (11), fungi (12), and mammalian skin (13). The cross-β-sheet motif is composed of intermolecular β-sheets along the fibril axis with the β-strands aligned perpendicularly to the fibril axis. An amyloid-like structure of peptide and protein hormones in secretory granules could explain most of their properties.To address the question whether peptide and protein hormones are stored in secretory granules in an amyloid-like aggregation state, we first asked if a diverse set of peptide and protein hormones could form amyloids in vitro at granule-relevant pH 5.5. 42 peptide and protein hormones from multiple species and organs were selected randomly, some linear and some cyclic, with a variety of different three dimensional structures (Table S2). This set of hormones was assayed for a capacity to form amyloids by the amyloid-specific dyes thioflavin T (Thio T), congo red (CR), luminescent conjugated polyelectrolyte probes (LCP), by the conformational transition into β-sheet-rich structure measured by circular dichroism (CD), and by the presence of fibrils in electron microscopy (EM) images. Furthermore, x-ray fiber diffraction was measured for a subset of hormones (Table S1). Only 10 hormones out of the 42 showed significant formation of...

Autism spectrum disorders (ASD) are common, complex and heterogeneous neurodevelopmental disorders. Cellular and molecular mechanisms responsible for ASD pathogenesis have been proposed based on genetic studies, brain pathology, and imaging, but a major impediment to testing ASD hypotheses is the lack of human cell models. Here, we reprogrammed fibroblasts to generate induced pluripotent stem cells (iPSCs), neural progenitor cells (NPCs) and neurons from ASD individuals with early brain overgrowth and non-ASD controls with normal brain size. ASD-derived NPCs display increased cell proliferation due to dysregulation of a β-catenin/BRN2 transcriptional cascade. ASD-derived neurons display abnormal neurogenesis and reduced synaptogenesis leading to functional defects in neuronal networks. Interestingly, defects in neuronal networks could be rescued by IGF-1, a drug that is currently in clinical trials for ASD. This work demonstrates that selection of ASD subjects based on endophenotypes unraveled biologically relevant pathway disruption and revealed a potential cellular mechanism for the therapeutic effect of IGF-1.

Chemical modifications of histones can mediate diverse DNA-templated processes including gene transcription 1 – 3 . Here, we provide evidence for a new class of histone posttranslational modification (PTM), serotonylation of glutamine, which occurs at position 5 (Q5ser) on histone H3 in serotonin (5-hydroxytryptamine, 5-HT) producing organisms. We demonstrate that tissue Transglutaminase 2 (TGM2) can serotonylate histone H3 tri-methylated lysine 4 (H3K4me3) marked nucleosomes resulting in the presence of combinatorial H3K4me3Q5ser in vivo . H3K4me3Q5ser displays a ubiquitous pattern of tissue expression in mammals, with enrichment observed in brain and gut, two organ systems responsible for the bulk of 5-HT production. Genome-wide analyses of human serotonergic neurons, developing mouse brain and cultured serotonergic cells indicate that the mark is enriched in euchromatin, is sensitive to cellular differentiation and correlates with permissive gene expression, phenomena that are linked to the mark’s potentiation of TFIID 4 – 6 interactions with H3K4me3. Cells ectopically expressing an H3 mutant that cannot be serotonylated display significantly altered expression of H3K4me3Q5ser target loci leading to deficits in differentiation. Taken together, these data identify a direct role for 5-HT, independent from its contributions to neurotransmission and cellular signaling, in the mediation of permissive gene expression.

Neural stem cells (NSCs) generate new granule cells throughout life in the mammalian hippocampus. Canonical Wnt signaling regulates the differentiation of NSCs towards the neuronal lineage. Here we identified the prospero-related homeodomain transcription factor Prox1 as a target of β-catenin–TCF/LEF signaling in vitro and in vivo. Prox1 overexpression enhanced neuronal differentiation whereas shRNA-mediated knockdown of Prox1 impaired the generation of neurons in vitro and within the hippocampal niche. In contrast, Prox1 was not required for survival of adult-generated granule cells after they had matured, suggesting a role for Prox1 in initial granule cell differentiation but not in the maintenance of mature granule cells. The data presented here characterize a molecular pathway from Wnt signaling to a transcriptional target leading to granule cell differentiation within the adult brain and identify a stage-specific function for Prox1 in the process of adult neurogenesis.

Stress regulation of brain-derived neurotrophic factor (BDNF) is implicated in the hippocampal damage observed in depression. BDNF has a complex gene structure with four 5 0 untranslated exons (I-IV) with unique promoters, and a common 3 0 coding exon (V). To better understand the stress regulation of BDNF, we addressed whether distinct stressors differentially regulate exon-specific BDNF transcripts in the postnatal and adult hippocampus. The early life stress of maternal separation (MS) resulted in a time point-dependent differential upregulation of BDNF transcripts restricted to early postnatal life (P14-BDNF II, P21-BDNF IV, V). In adulthood, distinct stressors regulated BDNF transcripts in a signature manner. Immobilization stress, administered once, decreased all BDNF splice variants but had differing effects on BDNF I/II (increase) and III/IV (decrease) when administered chronically. Although immobilization stress reduced BDNF (V) mRNA, chronic unpredictable stress did not influence total BDNF despite altering specific BDNF transcripts. Furthermore, a prior history of MS altered the signature pattern in which adult-onset stress regulated specific BDNF transcripts. We also examined the expression of cyclic AMP response element-binding protein (CREB), an upstream transcriptional activator of BDNF, and observed a CREB induction in the postnatal hippocampus following MS. As a possible consequence of enhanced CREB and BDNF expression following MS, we examined hippocampal progenitor proliferation and observed a significant increase restricted to early life. These results suggest that alterations in CREB/BDNF may contribute to the generation of individual differences in stress neurocircuitry, providing a substrate for altered vulnerability to depressive disorders.

SummaryAstrocyte dysfunction and neuroinflammation are detrimental features in multiple pathologies of the CNS. Therefore, the development of methods that produce functional human astrocytes represents an advance in the study of neurological diseases. Here we report an efficient method for inflammation-responsive astrocyte generation from induced pluripotent stem cells (iPSCs) and embryonic stem cells. This protocol uses an intermediate glial progenitor stage and generates functional astrocytes that show levels of glutamate uptake and calcium activation comparable with those observed in human primary astrocytes. Stimulation of stem cell-derived astrocytes with interleukin-1β or tumor necrosis factor α elicits a strong and rapid pro-inflammatory response. RNA-sequencing transcriptome profiling confirmed that similar gene expression changes occurred in iPSC-derived and primary astrocytes upon stimulation with interleukin-1β. This protocol represents an important tool for modeling in-a-dish neurological diseases with an inflammatory component, allowing for the investigation of the role of diseased astrocytes in neuronal degeneration.

The brain's serotonergic system centrally regulates several physiological processes and its dysfunction has been implicated in the pathophysiology of several neuropsychiatric disorders. While in the past our understanding of serotonergic neurotransmission has come mainly from mouse models, the development of pluripotent stem cell and induced fibroblast-to-neuron (iN) transdifferentiation technologies has revolutionized our ability to generate human neurons in vitro. Utilizing these techniques and a novel lentiviral reporter for serotonergic neurons, we identified and overexpressed key transcription factors to successfully generate human serotonergic neurons. We found that overexpressing the transcription factors NKX2.2, FEV, GATA2 and LMX1B in combination with ASCL1 and NGN2 directly and efficiently generated serotonergic neurons from human fibroblasts. Induced serotonergic neurons (iSNs) showed increased expression of specific serotonergic genes that are known to be expressed in raphe nuclei. iSNs displayed spontaneous action potentials, released serotonin in vitro and functionally responded to selective serotonin reuptake inhibitors (SSRIs). Here, we demonstrate the efficient generation of functional human serotonergic neurons from human fibroblasts as a novel tool for studying human serotonergic neurotransmission in health and disease.

Comparative analyses of neuronal phenotypes in closely related species can shed light on neuronal changes occurring during evolution. The study of post-mortem brains of nonhuman primates (NHPs) has been limited and often does not recapitulate important species-specific developmental hallmarks. We utilize induced pluripotent stem cell (iPSC) technology to investigate the development of cortical pyramidal neurons following migration and maturation of cells grafted in the developing mouse cortex. Our results show differential migration patterns in human neural progenitor cells compared to those of chimpanzees and bonobos both in vitro and in vivo, suggesting heterochronic changes in human neurons. The strategy proposed here lays the groundwork for further comparative analyses between humans and NHPs and opens new avenues for understanding the differences in the neural underpinnings of cognition and neurological disease susceptibility between species.