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Individuals with obsessive-compulsive disorder (OCD) perform obsessive repetitive actions. Shahin Rafii and his colleagues show that mice lacking the gene Slitrk5 show OCD-like behavioral phenotypes and have deficits in corticostriatal communication in the brain. Obsessive-compulsive disorder (OCD) is a common psychiatric disorder defined by the presence of obsessive thoughts and repetitive compulsive actions, and it often encompasses anxiety and depressive symptoms 1 , 2 . Recently, the corticostriatal circuitry has been implicated in the pathogenesis of OCD 3 , 4 . However, the etiology, pathophysiology and molecular basis of OCD remain unknown. Several studies indicate that the pathogenesis of OCD has a genetic component 5 , 6 , 7 , 8 . Here we demonstrate that loss of a neuron-specific transmembrane protein, SLIT and NTRK-like protein-5 (Slitrk5), leads to OCD-like behaviors in mice, which manifests as excessive self-grooming and increased anxiety-like behaviors, and is alleviated by the selective serotonin reuptake inhibitor fluoxetine. Slitrk5 −/− mice show selective overactivation of the orbitofrontal cortex, abnormalities in striatal anatomy and cell morphology and alterations in glutamate receptor composition, which contribute to deficient corticostriatal neurotransmission. Thus, our studies identify Slitrk5 as an essential molecule at corticostriatal synapses and provide a new mouse model of OCD-like behaviors.

The cellular and molecular mechanisms by which a tumour cell undergoes metastasis to a predetermined location are largely unknown. Here we demonstrate that bone marrow-derived haematopoietic progenitor cells that express vascular endothelial growth factor receptor 1 (VEGFR1; also known as Flt1) home to tumour-specific pre-metastatic sites and form cellular clusters before the arrival of tumour cells. Preventing VEGFR1 function using antibodies or by the removal of VEGFR1 + cells from the bone marrow of wild-type mice abrogates the formation of these pre-metastatic clusters and prevents tumour metastasis, whereas reconstitution with selected Id3 (inhibitor of differentiation 3)-competent VEGFR1 + cells establishes cluster formation and tumour metastasis in Id3 knockout mice. We also show that VEGFR1 + cells express VLA-4 (also known as integrin α 4 β 1 ), and that tumour-specific growth factors upregulate fibronectin—a VLA-4 ligand—in resident fibroblasts, providing a permissive niche for incoming tumour cells. Conditioned media obtained from distinct tumour types with unique patterns of metastatic spread redirected fibronectin expression and cluster formation, thereby transforming the metastatic profile. These findings demonstrate a requirement for VEGFR1 + haematopoietic progenitors in the regulation of metastasis, and suggest that expression patterns of fibronectin and VEGFR1 + VLA-4 + clusters dictate organ-specific tumour spread. The ‘pre-metastatic’ niche Many tumours have a tendency towards metastasis to specific organs. The mechanisms that guide tumour cells to a specific tissue are largely unknown, but current thinking is that it may involve molecular differences inherent in the tumour cells themselves, modulated by the effects of immune cells and other tissues. New research suggests another possibility: haematopoietic precursor cells in the bone marrow expressing VEGFR1 appear to home in on specific sites before the tumour cells get there, paving the way for wandering metastatic cells by forming niches where they can locate and multiply. The concept of a pre-metastatic niche, in which non-cancer cells promote future metastasis, is a novel one that raises the possibility that targeting VEGFR1 and related molecules could have therapeutic value.

Stem cells make their mark Adult stem cells are an attractive alternative to embryonic stem cells for therapeutic use. As yet there is no standard method for obtaining such cells from adults and priming them to form different tissues, but a new system that generates large numbers of stem cells from the adult testicle shows promise. It makes use of a novel marker, an orphan receptor known as GPR125, found on the surface of spermatogonial stem cells. The use of specialized feeder cells to support stem cell growth allows stem cells once destined for spermatogenesis to become multipotent. This work also provides clues as to the minimal requirements for multipotency in adult cells. Adult stem cells are an ethically attractive alternative to embryonic stem cells for obtaining tissues for therapeutic purposes. However, no standardized methods exist to obtain such cells reliably from adults, and then convert them into different tissues. However, a system has been developed to generate large numbers of stem cells from the adult testicle, based on the presence of a novel marker (GPR125), specifically on the stem cell surface. Adult mammalian testis is a source of pluripotent stem cells 1 . However, the lack of specific surface markers has hampered identification and tracking of the unrecognized subset of germ cells that gives rise to multipotent cells 2 . Although embryonic-like cells can be derived from adult testis cultures after only several weeks in vitro 1 , it is not known whether adult self-renewing spermatogonia in long-term culture can generate such stem cells as well. Here, we show that highly proliferative adult spermatogonial progenitor cells (SPCs) can be efficiently obtained by cultivation on mitotically inactivated testicular feeders containing CD34 + stromal cells. SPCs exhibit testicular repopulating activity in vivo and maintain the ability in long-term culture to give rise to multipotent adult spermatogonial-derived stem cells (MASCs). Furthermore, both SPCs and MASCs express GPR125, an orphan adhesion-type G-protein-coupled receptor. In knock-in mice bearing a GPR125–β-galactosidase (LacZ) fusion protein under control of the native Gpr125 promoter (GPR125–LacZ), expression in the testis was detected exclusively in spermatogonia and not in differentiated germ cells. Primary GPR125–LacZ SPC lines retained GPR125 expression, underwent clonal expansion, maintained the phenotype of germline stem cells, and reconstituted spermatogenesis in busulphan-treated mice. Long-term cultures of GPR125 + SPCs (GSPCs) also converted into GPR125 + MASC colonies. GPR125 + MASCs generated derivatives of the three germ layers and contributed to chimaeric embryos, with concomitant downregulation of GPR125 during differentiation into GPR125 - cells. MASCs also differentiated into contractile cardiac tissue in vitro and formed functional blood vessels in vivo . Molecular bookmarking by GPR125 in the adult mouse and, ultimately, in the human testis could enrich for a population of SPCs for derivation of GPR125 + MASCs, which may be employed for genetic manipulation, tissue regeneration and revascularization of ischaemic organs.

The mechanisms through which hematopoietic cytokines accelerate revascularization are unknown. Here, we show that the magnitude of cytokine-mediated release of SDF-1 from platelets and the recruitment of nonendothelial CXCR4 + VEGFR1 + hematopoietic progenitors, 'hemangiocytes,' constitute the major determinant of revascularization. Soluble Kit-ligand (sKitL), thrombopoietin (TPO, encoded by Thpo ) and, to a lesser extent, erythropoietin (EPO) and granulocyte-macrophage colony-stimulating factor (GM-CSF) induced the release of SDF-1 from platelets, enhancing neovascularization through mobilization of CXCR4 + VEGFR1 + hemangiocytes. Although revascularization of ischemic hindlimbs was partially diminished in mice deficient in both GM-CSF and G-CSF ( Csf2 −/− Csf3 −/− ), profound impairment in neovascularization was detected in sKitL-deficient Mmp9 −/− as well as thrombocytopenic Thpo −/− and TPO receptor–deficient ( Mpl −/− ) mice. SDF-1–mediated mobilization and incorporation of hemangiocytes into ischemic limbs were impaired in Thpo −/− , Mpl −/− and Mmp9 −/− mice. Transplantation of CXCR4 + VEGFR1 + hemangiocytes into Mmp9 −/− mice restored revascularization, whereas inhibition of CXCR4 abrogated cytokine- and VEGF-A–mediated mobilization of CXCR4 + VEGFR1 + cells and suppressed angiogenesis. In conclusion, hematopoietic cytokines, through graded deployment of SDF-1 from platelets, support mobilization and recruitment of CXCR4 + VEGFR1 + hemangiocytes, whereas VEGFR1 is essential for their angiogenic competency for augmenting revascularization. Delivery of SDF-1 may be effective in restoring angiogenesis in individuals with vasculopathies.

Obsessive compulsive disorder (OCD) is substantially heritable, but few molecular genetic risk factors have been identified. Knockout mice lacking SLIT and NTRK-Like Family, Member 5 (SLITRK5) display OCD-like phenotypes including serotonin reuptake inhibitor-sensitive pathologic grooming, and corticostriatal dysfunction. Thus, mutations that impair SLITRK5 function may contribute to the genetic risk for OCD. We re-sequenced the protein-coding sequence of the human SLITRK5 gene (SLITRK5) in three hundred and seventy seven OCD subjects and compared rare non-synonymous mutations (RNMs) in that sample with similar mutations in the 1000 Genomes database. We also performed in silico assessments and in vitro functional synaptogenesis assays on the Slitrk5 mutations identified. We identified four RNM's among these OCD subjects. There were no significant differences in the prevalence or in silico effects of rare non-synonymous mutations in the OCD sample versus controls. Direct functional testing of recombinant SLITRK5 proteins found that all mutations identified in OCD subjects impaired synaptogenic activity whereas none of the pseudo-matched mutations identified in 1000 Genomes controls had significant effects on SLITRK5 function (Fisher's exact test P = 0.028). These results demonstrate that rare functional mutations in SLITRK5 contribute to the genetic risk for OCD in human populations. They also highlight the importance of biological characterization of allelic effects in understanding genotype-phenotype relationships as there were no statistical differences in overall prevalence or bioinformatically predicted effects of OCD case versus control mutations. Finally, these results converge with others to highlight the role of aberrant synaptic function in corticostriatal neurons in the pathophysiology of OCD.

Vascular cells contribute to organogenesis and tumorigenesis by producing unknown factors. Primary endothelial cells (PECs) provide an instructive platform for identifying factors that support stem cell and tumor homeostasis. However, long-term maintenance of PECs requires stimulation with cytokines and serum, resulting in loss of their angiogenic properties. To circumvent this hurdle, we have discovered that the adenoviral E4ORF1 gene product maintains long-term survival and facilitates organ-specific purification of PECs, while preserving their vascular repertoire for months, in serum/cytokine-free cultures. Lentiviral introduction of E4ORF1 into human PECs (E4ORF1⁺ ECs) increased the long-term survival of these cells in serum/cytokine-free conditions, while preserving their in vivo angiogenic potential for tubulogenesis and sprouting. Although E4ORF1, in the absence of mitogenic signals, does not induce proliferation of ECs, stimulation with VEGF-A and/or FGF-2 induced expansion of E4ORF1⁺ ECs in a contact-inhibited manner. Indeed, VEGF-A-induced phospho MAPK activation of E4ORF1⁺ ECs is comparable with that of naive PECs, suggesting that the VEGF receptors remain functional upon E4ORF1 introduction. E4ORF1⁺ ECs inoculated in implanted Matrigel plugs formed functional, patent, humanized microvessels that connected to the murine circulation. E4ORF1⁺ ECs also incorporated into neo-vessels of human tumor xenotransplants and supported serum/cytokine-free expansion of leukemic and embryonal carcinoma cells. E4ORF1 augments survival of PECs in part by maintaining FGF-2/FGF-R1 signaling and through tonic Ser-473 phosphorylation of Akt, thereby activating the mTOR and NF-κB pathways. Therefore, E4ORF1⁺ ECs establish an Akt-dependent durable vascular niche not only for expanding stem and tumor cells but also for interrogating the roles of vascular cells in regulating organ-specific vascularization and tumor neo-angiogenesis.

Colon cancer stem cells are believed to originate from a rare population of putative CD133+ intestinal stem cells. Recent publications suggest that a small subset of colon cancer cells expresses CD133, and that only these CD133+ cancer cells are capable of tumor initiation. However, the precise contribution of CD133+ tumor-initiating cells in mediating colon cancer metastasis remains unknown. Therefore, to temporally and spatially track the expression of CD133 in adult mice and during tumorigenesis, we generated a knockin lacZ reporter mouse (CD133lacZ/+), in which the expression of lacZ is driven by the endogenous CD133 promoters. Using this model and immunostaining, we discovered that CD133 expression in colon is not restricted to stem cells; on the contrary, CD133 is ubiquitously expressed on differentiated colonic epithelium in both adult mice and humans. Using Il10-/-CD133lacZ mice, in which chronic inflammation in colon leads to adenocarcinomas, we demonstrated that CD133 is expressed on a full gamut of colonic tumor cells, which express epithelial cell adhesion molecule (EpCAM). Similarly, CD133 is widely expressed by human primary colon cancer epithelial cells, whereas the CD133- population is composed mostly of stromal and inflammatory cells. Conversely, CD133 expression does not identify the entire population of epithelial and tumor-initiating cells in human metastatic colon cancer. Indeed, both CD133+ and CD133- metastatic tumor subpopulations formed colonospheres in in vitro cultures and were capable of long-term tumorigenesis in a NOD/SCID serial xenotransplantation model. Moreover, metastatic CD133- cells form more aggressive tumors and express typical phenotypic markers of cancer-initiating cells, including CD44 (CD44+CD24-), whereas the CD133+ fraction is composed of CD44lowCD24+ cells. Collectively, our data suggest that CD133 expression is not restricted to intestinal stem or cancer-initiating cells, and during the metastatic transition, CD133+ tumor cells might give rise to the more aggressive CD133(- )subset, which is also capable of tumor initiation in NOD/SCID mice.

Despite decades of clinical use and research, the mechanism of action (MOA) of antidepressant medications remains poorly understood. Selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) are the most commonly prescribed antidepressants—atypical antidepressants such as bupropion have also proven effective, while exhibiting a divergent clinical phenotype. The difference in phenotypic profiles presumably lies in the differences among the MOAs of SSRIs/SNRIs and bupropion. We integrated the ensemble of bupropion’s affinities for all its receptors with the expression levels of those targets in nervous system tissues. This “combined target tissue” profile of bupropion was compared to those of duloxetine, fluoxetine, and venlafaxine to isolate the unique target tissue effects of bupropion. Our results suggest that the three monoamines—serotonin, norepinephrine, and dopamine—all contribute to the common antidepressant effects of SSRIs, SNRIs, and bupropion. At the same time, bupropion is unique in its action on 5-HT3AR in the dorsal root ganglion and nicotinic acetylcholine receptors in the pineal gland. These unique tissue-specific activities may explain unique therapeutic effects of bupropion, such as pain management and smoking cessation, and, given melatonin’s association with nicotinic acetylcholine receptors and depression, highlight the underappreciated role of the melatonergic system in bupropion’s MOA.

Colon cancer stem cells are believed to originate from a rare population of putative [CD133.sup.+] intestinal stem cells. Recent publications suggest that a small subset of colon cancer cells expresses CD133, and that only these [CD133.sup.+] cancer cells are capable of tumor initiation. However, the precise contribution of [CD133.sup.+] tumor-initiating cells in mediating colon cancer metastasis remains unknown. Therefore, to temporally and spatially track the expression of CD133 in adult mice and during tumorigenesis, we generated a knockin lacZ reporter mouse ([CD133.sup.lacZ/+]), in which the expression of lacZ is driven by the endogenous CD133 promoters. Using this model and immunostaining, we discovered that CD133 expression in colon is not restricted to stem cells; on the contrary, CD133 is ubiquitously expressed on differentiated colonic epithelium in both adult mice and humans. Using Il10-/-[CD133.sup.lacZ] mice, in which chronic inflammation in colon leads to adenocarcinomas, we demonstrated that CD133 is expressed on a full gamut of colonic tumor cells, which express epithelial cell adhesion molecule (EpCAM). Similarly, CD133 is widely expressed by human primary colon cancer epithelial cells, whereas the [CD133.sup.-] population is composed mostly of stromal and inflammatory cells. Conversely, CD133 expression does not identify the entire population of epithelial and tumor-initiating cells in human metastatic colon cancer. Indeed, both [CD133.sup.+] and [CD133.sup.-] metastatic tumor subpopulations formed colonospheres in in vitro cultures and were capable of long-term tumorigenesis in a NOD/SCID serial xenotransplantation model. Moreover, metastatic [CD133.sup.-] cells form more aggressive tumors and express typical phenotypic markers of cancer-initiating cells, including CD44 ([CD44.sup.+][CD24.sup.-]), whereas the [CD133.sup.+] fraction is composed of [CD44.sup.low][CD24.sup.+] cells. Collectively, our data suggest that CD133 expression is not restricted to intestinal stem or cancer-initiating cells, and during the metastatic transition, [CD133.sup.+] tumor cells might give rise to the more aggressive [CD133.sup.-] subset, which is also capable of tumor initiation in NOD/SCID mice.