The related neuronal endosomal proteins NEEP21 (Nsg1) and P19 (Nsg2) have divergent expression profiles in vivo

Knockout of AMPA receptor binding protein Neuron-specific gene 2 (NSG2) enhances associative learning and cognitive flexibility

The vast majority of gene mutations and/or gene knockouts result in either no observable changes, or significant deficits in molecular, cellular, or organismal function. However, in a small number of cases, mutant animal models display enhancements in specific behaviors such as learning and memory. To date, most gene deletions shown to enhance cognitive ability generally affect a limited number of pathways such as NMDA receptor- and translation-dependent plasticity, or GABA receptor- and potassium channel-mediated inhibition. While endolysosomal trafficking of AMPA receptors is a critical mediator of synaptic plasticity, mutations in genes that affect AMPAR trafficking either have no effect or are deleterious for synaptic plasticity, learning and memory. NSG2 is one of the three-member family of Neuron-specific genes (NSG1-3), which have been shown to regulate endolysosomal trafficking of a number of proteins critical for neuronal function, including AMPAR subunits (GluA1-2). Based on these findings and the largely universal expression throughout mammalian brain, we predicted that genetic knockout of NSG2 would result in significant impairments across multiple behavioral modalities including motor, affective, and learning/memory paradigms. However, in the current study we show that loss of NSG2 had highly selective effects on associative learning and memory, leaving motor and affective behaviors intact. For instance, NSG2 KO animals performed equivalent to wild-type C57Bl/6n mice on rotarod and Catwalk motor tasks, and did not display alterations in anxiety-like behavior on open field and elevated zero maze tasks. However, NSG2 KO animals demonstrated enhanced recall in the Morris water maze, accelerated reversal learning in a touch-screen task, and accelerated acquisition and enhanced recall on a Trace Fear Conditioning task. Together, these data point to a specific involvement of NSG2 on multiple types of associative learning, and expand the repertoire of pathways that can be targeted for cognitive enhancement.

Neuron-Specific Gene Family Member 1 is a Potential New Therapeutic Target Associated with Immune Cell Infiltration for Breast Cancer

Background

Breast cancer (BC) is the most common cancer and is highly morphologically and molecularly heterogeneous. Neuron-specific gene family member 1 (NSG1) is a small single-channel transmembrane protein that consists of 185 amino acids and has been reported in a variety of tumours in recent years. However, the role of NSG1 in BC is unclear.

Objective

This study aimed to explore the role of NSG1 in the pathogenesis and development of BC and its potential as a prognostic marker for BC.

Methods

This study analysed data from The Cancer Genome Atlas database and the Gene Expression Omnibus database to determine the expression level and prognostic value of NSG1 messenger ribonucleic acid in BC. Using this data, we constructed a clinical risk model. Immunohistochemistry was performed in combination with a clinical cohort of 192 patients with BC to explore the NSG1 protein expression in BC. Enrichment analysis was used to predict the biological function of NSG1 in BC. To analyse the correlation between NSG1 and the BC immune microenvironment, a single-cell analysis of NSG1 expression and cells in BC was performed. Kaplan‒Meier curves and Cox regression analysis were utilised to identify the relationship between the expression of NSG1 protein and clinicopathological features and prognosis.

Results

Neuron-specific gene family member 1 is highly expressed in patients with early BC, and its expression suggests a good prognosis for patients with BC. Neuron-specific gene family member 1 is involved in the T-cell receptor complex in BC and is associated with CD8 T cells in the BC immune microenvironment and may induce M1 polarisation of macrophages.

Conclusion

Neuron-specific gene family member 1 is a biomarker of good prognosis in BC. It is associated with the immune microenvironment of BC and may be a potential therapeutic target.

Knockout of AMPA receptor binding protein Neuron-Specific Gene 2 (NSG2) enhances associative learning and cognitive flexibility

The vast majority of gene mutations and/or gene knockouts result in either no observable changes, or significant deficits in molecular, cellular, or organismal function. However, in a small number of cases, mutant animal models display enhancements in specific behaviors such as learning and memory. To date, most gene deletions shown to enhance cognitive ability generally affect a limited number of pathways such as NMDA receptor- and translation-dependent plasticity, or GABA receptor- and potassium channel-mediated inhibition. While endolysosomal trafficking of AMPA receptors is a critical mediator of synaptic plasticity, mutations in genes that affect AMPAR trafficking either have no effect or are deleterious for synaptic plasticity, learning and memory. NSG2 is one of the three-member family of Neuron-specific genes (NSG1-3), which have been shown to regulate endolysosomal trafficking of a number of proteins critical for neuronal function, including AMPAR subunits (GluA1-2). Based on these findings and the largely universal expression throughout mammalian brain, we predicted that genetic knockout of NSG2 would result in significant impairments across multiple behavioral modalities including motor, affective, and learning/memory paradigms. However, in the current study we show that loss of NSG2 had highly selective effects on associative learning and memory, leaving motor and affective behaviors intact. For instance, NSG2 KO animals performed equivalent to wild-type C57Bl/6n mice on rotarod and Catwalk motor tasks, and did not display alterations in anxiety-like behavior on open field and elevated zero maze tasks. However, NSG2 KO animals demonstrated enhanced recall in the Morris water maze, accelerated reversal learning in a touch-screen task, and accelerated acquisition and enhanced recall on a Trace Fear Conditioning task. Together, these data point to a specific involvement of NSG2 on multiple types of associative learning, and expand the repertoire of pathways that can be targeted for cognitive enhancement.

MIF-Modulated Spinal Proteins Associated with Persistent Bladder Pain: A Proteomics Study

Bladder pain is a prominent symptom in Interstitial Cystitis/Bladder Pain Syndrome (IC/BPS). We studied spinal mechanisms of bladder pain in mice using a model where repeated activation of intravesical Protease Activated Receptor-4 (PAR4) results in persistent bladder hyperalgesia (BHA) with little or no bladder inflammation. Persistent BHA is mediated by spinal macrophage migration inhibitory factor (MIF), and is associated with changes in lumbosacral proteomics. We investigated the contribution of individual spinal MIF receptors to persistent bladder pain as well as the spinal proteomics changes associated with relief of persistent BHA by spinal MIF antagonism. Female mice with persistent BHA received either intrathecal (i.t.) MIF monoclonal antibodies (mAb) or mouse IgG1 (isotype control antibody). MIF antagonism temporarily reversed persistent BHA (peak effect: 2 h), while control IgG1 had no effect. Moreover, i.t. antagonism of the MIF receptors CD74 and C-X-C chemokine receptor type 4 (CXCR4) partially reversed persistent BHA. For proteomics experiments, four separate groups of mice received either repeated intravesical scrambled peptide and sham i.t. injection (control, no pain group) or repeated intravesical PAR4 and: sham i.t.; isotype IgG1 i.t. (15 μg); or MIF mAb (15 μg). L6-S1 spinal segments were excised 2 h post-injection and examined for proteomics changes using LC-MS/MS. Unbiased proteomics analysis identified and relatively quantified 6739 proteins. We selected proteins that showed significant changes compared to control (no pain group) after intravesical PAR4 (sham or IgG i.t. treatment) and showed no significant change after i.t. MIF antagonism. Six proteins decreased during persistent BHA (V-set transmembrane domain-containing protein 2-like confirmed by immunohistochemistry), while two proteins increased. Spinal MIF antagonism reversed protein changes. Therefore, spinal MIF and MIF receptors mediate persistent BHA and changes in specific spinal proteins. These novel MIF-modulated spinal proteins represent possible new targets to disrupt spinal mechanisms that mediate persistent bladder pain.

Prenatal delta-9-tetrahydrocannabinol exposure is associated with changes in rhesus macaque DNA methylation enriched for autism genes

BACKGROUND

With the growing availability of cannabis and the popularization of additional routes of cannabis use beyond smoking, including edibles, the prevalence of cannabis use in pregnancy is rapidly increasing. However, the potential effects of prenatal cannabis use on fetal developmental programming remain unknown.

RESULTS

We designed this study to determine whether the use of edible cannabis during pregnancy is deleterious to the fetal and placental epigenome. Pregnant rhesus macaques consumed a daily edible containing either delta-9-tetrahydrocannabinol (THC) (2.5 mg/7 kg/day) or placebo. DNA methylation was measured in 5 tissues collected at cesarean delivery (placenta, lung, cerebellum, prefrontal cortex, and right ventricle of the heart) using the Illumina MethylationEPIC platform and filtering for probes previously validated in rhesus macaque. In utero exposure to THC was associated with differential methylation at 581 CpGs, with 573 (98%) identified in placenta. Loci differentially methylated with THC were enriched for candidate autism spectrum disorder (ASD) genes from the Simons Foundation Autism Research Initiative (SFARI) database in all tissues. The placenta demonstrated greatest SFARI gene enrichment, including genes differentially methylated in placentas from a prospective ASD study.

CONCLUSIONS

Overall, our findings reveal that prenatal THC exposure alters placental and fetal DNA methylation at genes involved in neurobehavioral development that may influence longer-term offspring outcomes. The data from this study add to the limited existing literature to help guide patient counseling and public health polices focused on prenatal cannabis use in the future.

Phosphatidylinositol (3,5)-bisphosphate machinery regulates neurite thickness through neuron-specific endosomal protein NSG1/NEEP21

Phosphatidylinositol (3,5)-bisphosphate [PtdIns(3,5)P₂] is a critical signaling phospholipid involved in endolysosome homeostasis. It is synthesized by a protein complex composed of PIKfyve, Vac14, and Fig4. Defects in PtdIns(3,5)P₂ synthesis underlie a number of human neurological disorders, including Charcot-Marie-Tooth disease, child onset progressive dystonia, and others. However, neuron-specific functions of PtdIns(3,5)P₂ remain less understood. Here, we show that PtdIns(3,5)P₂ pathway is required to maintain neurite thickness. Suppression of PIKfyve activities using either pharmacological inhibitors or RNA silencing resulted in decreased neurite thickness. We further find that the regulation of neurite thickness by PtdIns(3,5)P₂ is mediated by NSG1/NEEP21, a neuron-specific endosomal protein. Knockdown of NSG1 expression also led to thinner neurites. mCherry-tagged NSG1 colocalized and interacted with proteins in the PtdIns(3,5)P₂ machinery. Perturbation of PtdIns(3,5)P₂ dynamics by overexpressing Fig4 or a PtdIns(3,5)P₂-binding domain resulted in mislocalization of NSG1 to nonendosomal locations, and suppressing PtdIns(3,5)P₂ synthesis resulted in an accumulation of NSG1 in EEA1-positive early endosomes. Importantly, overexpression of NSG1 rescued neurite thinning in PtdIns(3,5)P₂-deficient CAD neurons and primary cortical neurons. Our study uncovered the role of PtdIns(3,5)P₂ in the morphogenesis of neurons, which revealed a novel aspect of the pathogenesis of PtdIns(3,5)P₂-related neuropathies. We also identified NSG1 as an important downstream protein of PtdIns(3,5)P₂, which may provide a novel therapeutic target in neurological diseases.

Aberrant NSG1 Expression Promotes Esophageal Squamous Cell Carcinoma Cell EMT by the Activation of ERK Signaling Pathway

BACKGROUND

Neuron-specific gene family member 1 (NSG1) is a 21 kDa endosomal protein that is specifically expressed in neurons.

AIMS

This study was to explore the expression of NSG1 and possible mechanism in Esophageal Squamous Cell Carcinoma (ESCC).

METHODS

The Cancer Genome Atlas (TCGA) database was consulted to analyze the expression of NSG1 in ESCC. Immunohistochemistry (IHC) staining was used to evaluate NSG1 expression in ESCC cancerous tissues and matched paracancerous tissues. The CCK-8 assay, wound-healing assay, and transwell assay were used to detect the cell viability, migration, and invasion of ESCC cells. Western blot was used to assay epithelial-mesenchymal transition (EMT)-related proteins and ERK signaling pathway protein expression.

RESULTS

The results showed that the expression of NSG1 in ESCC cancerous tissues was higher than noncancerous tissues. Compared with negative control (NC) group, cell viability, migration. and invasion significantly increased, the expression of p-ERK in ERK signaling pathway was significantly upregulated, the expressions of mesenchymal marker Vimentin and EMT-related transcription factors including snail and slug were significantly upregulated, and the expression of epithelial marker E-cadherin was significantly downregulated in KYSE-150 cells with NSG1 overexpression. However, these effects were reversed by the ERK signaling pathway inhibitor U0126. On the other hand, TE-1 cells with NSG1 knockdown had the changes contrary to that in KYSE-150 cells with NSG1 overexpression.

CONCLUSION

NSG1 plays a potential carcinogenic role on the occurrence and progression of ESCC, and aberrant NSG1 expression might promote ESCC cell EMT by the activation of ERK signaling pathway.

Global loss of Neuron-specific gene 1 causes alterations in motor coordination, increased anxiety, and diurnal hyperactivity in male mice

The Neuron-specific gene family (NSG1-3) consists of small endolysosomal proteins that are critical for trafficking multiple receptors and signaling molecules in neurons. NSG1 has been shown to play a critical role in AMPAR recycling from endosomes to plasma membrane during synaptic plasticity. However, to date nothing is known about whether NSG1 is required for normal behavior at an organismal level. Here we performed a battery of behavioral tests to determine whether loss of NSG1 would affect motor, cognitive, and/or affective behaviors, as well as circadian-related activity. Consistent with unique cerebellar expression of NSG1 among family members, we found that NSG1 was obligatory for motor coordination but not for gross motor function or learning. NSG1 knockout (KO) also altered performance across other behavioral modalities including anxiety-related and diurnal activity paradigms. Surprisingly, NSG1 KO did not cause significant impairments across all tasks within a given modality, but had specific effects within each modality. For instance, we found increases in anxiety-related behaviors in tasks with multiple stressors (e.g., elevation and exposure), but not those with a single main stressor (e.g., exposure). Interestingly, NSG1 KO animals displayed a significant increase in locomotor activity during subjective daytime, suggesting a possible impact on diurnal activity rhythms or vigilance. Surprisingly, loss of NSG1 had no effect on hippocampal-dependent learning despite previous studies showing deficits in CA1 long-term potentiation. Together, these findings do not support a role of NSG1 in hippocampal-dependent learning, but support a role in mediating proper neuronal function across amygdalar and cerebellar circuits.

Schizophrenia-Linked Protein tSNARE1 Regulates Endosomal Trafficking in Cortical Neurons

TSNARE1, which encodes the protein tSNARE1, is a high-confidence gene candidate for schizophrenia risk, but nothing is known about its cellular or physiological function. We identified the major gene products of TSNARE1 and their cytoplasmic localization and function in endosomal trafficking in cortical neurons. We validated three primary isoforms of TSNARE1 expressed in human brain, all of which encode a syntaxin-like Qa SNARE domain. RNA-sequencing data from adult and fetal human brain suggested that the majority of tSNARE1 lacks a transmembrane domain that is thought to be necessary for membrane fusion. Biochemical data demonstrate that tSNARE1 can compete with Stx12 for incorporation into an endosomal SNARE complex, supporting its possible role as an inhibitory SNARE. Live-cell imaging in cortical neurons from mice of both sexes demonstrated that brain tSNARE1 isoforms localized to the endosomal network. The most abundant brain isoform, tSNARE1c, localized most frequently to Rab7+ late endosomes, and endogenous tSNARE1 displayed a similar localization in human neural progenitor cells and neuroblastoma cells. In mature rat neurons from both sexes, tSNARE1 localized to the dendritic shaft and dendritic spines, supporting a role for tSNARE1 at the postsynapse. Expression of either tSNARE1b or tSNARE1c, which differ only in their inclusion or exclusion of an Myb-like domain, delayed the trafficking of the dendritic endosomal cargo Nsg1 into late endosomal and lysosomal compartments. These data suggest that tSNARE1 regulates endosomal trafficking in cortical neurons, likely by negatively regulating early endosomal to late endosomal trafficking.SIGNIFICANCE STATEMENT Schizophrenia is a severe and polygenic neuropsychiatric disorder. Understanding the functions of high-confidence candidate genes is critical toward understanding how their dysfunction contributes to schizophrenia pathogenesis. TSNARE1 is one of the high-confidence candidate genes for schizophrenia risk, yet nothing was known about its cellular or physiological function. Here we describe the major isoforms of TSNARE1 and their cytoplasmic localization and function in the endosomal network in cortical neurons. Our results are consistent with the hypothesis that the majority of brain tSNARE1 acts as a negative regulator to endolysosomal trafficking.

Development of a panel of autoantibody against NSG1 with CEA, CYFRA21-1, and SCC-Ag for the diagnosis of esophageal squamous cell carcinoma

OBJECTIVE

Development of a panel of serum autoantibody against Neuron specific gene family member 1 (NSG1) with traditional tumor biomarkers of esophageal squamous cell carcinoma (ESCC) to further improve the diagnostic efficiency for ESCC patients.

METHODS

Immunohistochemistry (IHC) staining was used to detect the expression of NSG1 protein in 40 pairs of ESCC tissues and matched paracancerous tissues. Serum anti-NSG1 levels of 203 patients with early ESCC, 103 patients with advanced ESCC, 135 patients with esophageal benign lesion (EBL), and 155 healthy controls (HCs) were detected by ELISA. The diagnostic performances of all possible combinations of serum anti-NSG1with CEA, CYFRA21-1 and SCC-Ag were assessed to develop an optimal panel for ESCC diagnosis.

RESULTS

NSG1 protein expression in ESCC tissues was significantly higher than that in matched paracancerous tissues (p < 0.001). Serum anti-NSG1 expression in ESCC group was significantly higher than that in EBL group and HC group (p < 0.001). The AUC of serum anti-NSG1 for ESCC was 0.706, with 49.7% sensitivity at 93.5% specificity, superior to that of CEA, CYFRA21-1 and SCC-Ag. Of all possible combinations, serum anti-NSG1 combined with CEA, CYFRA21-1 and SCC-Ag showed the highest AUC of 0.758 and 67.3% sensitivity at 88.3% specificity for ESCC, with the highest NPV of 71.9% and the lowest NLR of 0.37.

CONCLUSION

Aberrant NSG1 protein expression in ESCC tissues might be responsible for massive releases of autoantibody anginst NSG1 in sera of ESCC. A panel of anti-NSG1 with CEA, CYFRA21-1 and SCC-Ag contributes to further improving the diagnostic efficiency for ESCC.

Neural innervation as a potential trigger of morphological color change and sexual dimorphism in cichlid fish

Many species change their coloration during ontogeny or even as adults. Color change hereby often serves as sexual or status signal. The cellular and subcellular changes that drive color change and how they are orchestrated have been barely understood, but a deeper knowledge of the underlying processes is important to our understanding of how such plastic changes develop and evolve. Here we studied the color change of the Malawi golden cichlid (Melanchromis auratus). Females and subordinate males of this species are yellow and white with two prominent black stripes (yellow morph; female and non-breeding male coloration), while dominant males change their color and completely invert this pattern with the yellow and white regions becoming black, and the black stripes becoming white to iridescent blue (dark morph; male breeding coloration). A comparison of the two morphs reveals that substantial changes across multiple levels of biological organization underlie this polyphenism. These include changes in pigment cell (chromatophore) number, intracellular dispersal of pigments, and tilting of reflective platelets (iridosomes) within iridophores. At the transcriptional level, we find differences in pigmentation gene expression between these two color morphs but, surprisingly, 80% of the genes overexpressed in the dark morph relate to neuronal processes including synapse formation. Nerve fiber staining confirms that scales of the dark morph are indeed innervated by 1.3 to 2 times more axonal fibers. Our results might suggest an instructive role of nervous innervation orchestrating the complex cellular and ultrastructural changes that drive the morphological color change of this cichlid species.

Neuron-Specific Gene 2 (NSG2) Encodes an AMPA Receptor Interacting Protein That Modulates Excitatory Neurotransmission

Neurons have evolved a number of unique protein-coding genes that regulate trafficking of protein complexes within small organelles throughout dendrites and axons. Neuron-specific gene 2 (NSG2) encodes for one of the most abundant proteins in the nervous system during perinatal development. NSG2 belongs to a family of small neuronal endosomal proteins but its function has remained uncharacterized to date. Here, we show that NSG2 is found in discrete punctae restricted to the somatodendritic arbors of developing mouse and human neurons, and a significant proportion of NSG2 punctae colocalize with postsynaptic HOMER1 and surface-expressed AMPA-type glutamate receptors (AMPARs) at excitatory synapses. Immunoprecipitation revealed that NSG2 physically interacts with both the GluA1 and GluA2 AMPAR subunits in mouse brain. Knock-out of NSG2 in mouse hippocampal neurons selectively impaired the frequency of miniature EPSCs (mEPSCs) and caused alterations in PSD95 expression at postsynaptic densities (PSDs). In contrast, NSG2 overexpression caused a significant increase in the amplitude of mEPSCs as well as GluA2 surface expression. Thus, NSG2 functions as an AMPAR-binding protein that is required for normal synapse formation and/or maintenance, and has unique functions compared with other NSG family members.

Degradation of dendritic cargos requires Rab7-dependent transport to somatic lysosomes

Neurons are large and long lived, creating high needs for regulating protein turnover. Disturbances in proteostasis lead to aggregates and cellular stress. We characterized the behavior of the short-lived dendritic membrane proteins Nsg1 and Nsg2 to determine whether these proteins are degraded locally in dendrites or centrally in the soma. We discovered a spatial heterogeneity of endolysosomal compartments in dendrites. Early EEA1-positive and late Rab7-positive endosomes are found throughout dendrites, whereas the density of degradative LAMP1- and cathepsin (Cat) B/D-positive lysosomes decreases steeply past the proximal segment. Unlike in fibroblasts, we found that the majority of dendritic Rab7 late endosomes (LEs) do not contain LAMP1 and that a large proportion of LAMP1 compartments do not contain CatB/D. Second, Rab7 activity is required to mobilize distal predegradative LEs for transport to the soma and terminal degradation. We conclude that the majority of dendritic LAMP1 endosomes are not degradative lysosomes and that terminal degradation of dendritic cargos such as Nsg1, Nsg2, and DNER requires Rab7-dependent transport in LEs to somatic lysosomes.

Temporally restricted death and the role of p75NTR as a survival receptor in the developing sensory nervous system

The peripheral somatosensory system overproduces neurons early in development followed by a period of cell death during final target innervation. The decision to survive or die in somatosensory neurons of the dorsal root ganglion (DRG) is mediated by target-derived neurotrophic factors and their cognate receptors. Subsets of peripheral somatosensory neurons can be crudely defined by the neurotrophic receptors that they express: peptidergic nociceptors (TrkA+), nonpeptidergic nociceptors (Ret+), mechanoreceptors (Ret+ or TrkB+), and proprioceptors (TrkC+). A direct comparison of early developmental timing between these subsets has not been performed. Here we characterized the accumulation and death of TrkA, B, C, and Ret+ neurons in the DRG as a function of developmental time. We find that TrkB, TrkC, and Ret-expressing neurons in the DRG complete developmental cell death prior to TrkA-expressing neurons. Given the broadly defined roles of the neurotrophin receptor p75NTR in augmenting neurotrophic signaling in sensory neurons, we investigated its role in supporting the survival of these distinct subpopulations. We find that TrkA+, TrkB+, and TrkC+ sensory neuron subpopulations require p75NTR for survival, but proliferating progenitors do not. These data demonstrate how diverging sensory neurons undergo successive waves of cell death and how p75NTR represses the magnitude, but not developmental window of this culling. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 78: 701-717, 2018.

Transcytosis of TrkA leads to diversification of dendritic signaling endosomes

The development of the peripheral nervous system relies on long-distance signaling from target organs back to the soma. In sympathetic neurons, this long-distance signaling is mediated by target derived Nerve Growth Factor (NGF) interacting with its axonal receptor, TrkA. This ligand receptor complex internalizes into what is commonly referred to as the signaling endosome which is transported retrogradely to the soma and dendrites to mediate survival signaling and synapse formation, respectively. The molecular identity of signaling endosomes in dendrites has not yet been determined. Here, we perform a detailed analysis of TrkA endosomal compartments and trafficking patterns. We find that signaling endosomes are not uniform but molecularly diversified into Rab7 (late endosome) and Rab11 (recycling endosome) populations in axons and dendrites in vitro and in the soma in vivo. Surprisingly, TrkA-NGF signaling endosomes in dendrites undergo dynamic trafficking events, including putative fusion and fission. Overall, we find that signaling endosomes do not remain as a singular endosomal subtype but instead exist in multiple populations that undergo dynamic endosomal trafficking events. These dynamic events might drive functional diversification of the signaling endosome.

The endosomal neuronal proteins Nsg1/NEEP21 and Nsg2/P19 are itinerant, not resident proteins of dendritic endosomes

Membrane traffic critically regulates most aspects of neuronal function. Neurons express many neuronal-specific proteins that regulate membrane traffic, including the poorly understood small transmembrane proteins neural-specific gene 1 and 2 (Nsg1/NEEP21 and Nsg2/P19). Nsg1 has been implicated in regulating endosomal recycling and sorting of several important neuronal receptors. Nsg2 is largely unstudied. At steady-state, Nsg1 and Nsg2 only partially co-localize with known endosomal compartments, and it was suggested that they mark a neuronal-specific endosome. Since Nsg1 localizes to and functions in the dendritic endosome, we set out to discover how Nsg1 and Nsg2 localization to endosomes is regulated in primary rat hippocampal neurons, using quadruple immunolocalization against endogenous proteins, live imaging of dendritic endosomes, and interference approaches against the endosomal regulators Rab5 and Rab7. In contrast to previous conclusions, we now show that Nsg1 and Nsg2 are not resident endosomal proteins, but traffic rapidly from the cell surface to lysosomes and have a half-life of less than two hours. Their partial co-localization with canonical endosomal markers thus reflects their rapid flux towards degradation rather than specific targeting to a singular compartment. These findings will require rethinking of how this class of endosomal proteins regulates trafficking of much longer-lived receptors.