Midbrain dopaminergic axons are guided longitudinally through the diencephalon by Slit/Robo signals

Dopaminergic neurons from the ventral mesencephalon/diencephalon (mesodiencephalon) form vital pathways constituting the majority of the brain's dopamine systems. Mesodiencephalic dopaminergic (mdDA) neurons extend longitudinal projections anteriorly through the diencephalon, ascending toward forebrain targets. The mechanisms by which mdDA axons initially navigate through the diencephalon are poorly understood. Recently the Slit family of secreted axon guidance proteins, and their Robo receptors, have been identified as important guides for descending longitudinal axons. To test the potential roles of Slit/Robo guidance in ascending trajectories, we examined tyrosine hydroxylase-positive (TH+) projections from mdDA neurons in mutant mouse embryos. We found that mdDA axons grow out of and parallel to Slit-positive ventral regions within the diencephalon, and that subsets of the mdDA axons likely express Robo1 and possibly also Robo2. Slit2 was able to directly inhibit TH axon outgrowth in explant co-culture assays. The mdDA axons made significant pathfinding errors in Slit1/2 and Robo1/2 knockout mice, including spreading out in the diencephalon to form a wider tract. The wider tract resulted from a combination of invasion of the ventral midline, consistent with Slit repulsion, but also axons wandering dorsally, away from the ventral midline. Aberrant dorsal trajectories were prominent in Robo1 and Robo1/2 knockout mice, suggesting that an aspect of Robo receptor function is Slit-independent. These results indicate that Slit/Robo signaling is critical during the initial establishment of dopaminergic pathways, with roles in the dorsoventral positioning and precise pathfinding of these ascending longitudinal axons.     

Repulsive migration of schwann cells induced by slit‐2 through Ca2+‐dependent RhoA‐Myosin signaling

Schwann cells migrate along axons before initiating myelination during development and their migration facilitates peripheral nerve regeneration after injury. Axon guidance molecule Slit‐2 is highly expressed during peripheral development and nerve regeneration; however, whether Slit‐2 regulates the migration of Schwann cells remains a mystery. Here we show that Slit‐2 receptor Robo‐1 and Robo‐2 were highly expressed in Schwann cells in vitro and in vivo. Using three distinct migration assays, we found that Slit‐2 repelled the migration of cultured Schwann cells. Furthermore, frontal application of a Slit‐2 gradient to migrating Schwann cells first caused the collapse of leading front, and then reversed soma translocation of Schwann cells. The repulsive effects of Slit‐2 on Schwann cell migration depended on a Ca²⁺ signaling release from internal stores. Interestingly, in response to Slit‐2 stimulation, the collapse of leading front required the loss of F‐actin and focal adhesion, whereas the subsequent reversal of soma translocation depended on RhoA‐Rock‐Myosin signaling pathways. Taken together, we demonstrate that Slit‐2 repels the migration of cultured Schwann cells through RhoA‐Myosin signaling pathways in a Ca²⁺‐dependent manner.     

Dynamic expression of Slit1–3 and Robo1–2 in the mouse peripheral nervous system after injury

The Slit family of axon guidance cues act as repulsive molecules for precise axon pathfinding and neuronal migration during nervous system development through interactions with specific Robo receptors.Although we previously reported that Slit1–3 and their receptors Robo1 and Robo2 are highly expressed in the adult mouse peripheral nervous system,how this expression changes after injury has not been well studied.Herein,we constructed a peripheral nerve injury mouse model by transecting the right sciatic nerve.At 14 days after injury,quantitative real-time polymerase chain reaction was used to detect mRNA expression of Slit1–3 and Robo1–2 in L4–5 spinal cord and dorsal root ganglia,as well as the sciatic nerve.Immunohistochemical analysis was performed to examine Slit1–3,Robo1–2,neurofilament heavy chain,F4/80,and vimentin in L4–5 spinal cord,L4 dorsal root ganglia,and the sciatic nerve.Co-expression of Slit1–3 and Robo1–2 in L4 dorsal root ganglia was detected by in situ hybridization.In addition,Slit1–3 and Robo1–2 protein expression in L4–5 spinal cord,L4 dorsal root ganglia,and sciatic nerve were detected by western blot assay.The results showed no significant changes of Slit1–3 or Robo1–2 mRNA expression in the spinal cord within 14 days after injury.In the dorsal root ganglion,Slit1–3 and Robo1–2 mRNA expression were initially downregulated within 4 days after injury;however,Robo1–2 mRNA expression returned to the control level,while Slit1–3 mRNA expression remained upregulated during regeneration from 4–14 days after injury.In the sciatic nerve,Slit1–3 and their receptors Robo1–2 were all expressed in the proximal nerve stump;however,Slit1,Slit2,and Robo2 were barely detectable in the nerve bridge and distal nerve stump within 14 days after injury.Slit3 was highly ex-pressed in macrophages surrounding the nerve bridge and slightly downregulated in the distal nerve stump within 14 days after injury.Robo1 was upregulated in vimentin-positive cells and migrating Schwann cells inside the nerve bridge.Robo1 was also upregulated in Schwann cells of the distal nerve stump within 14 days after injury.Our findings indicate that Slit3 is the major ligand expressed in the nerve bridge and distal nerve stump during peripheral nerve regeneration,and Slit3/Robo signaling could play a key role in peripheral nerve repair after injury.This study was approved by Plymouth University Animal Welfare Ethical Review Board (approval No.30/3203) on April 12,2014.     

Intersectin1-s is involved in migration and invasion of human glioma cells

Malignant gliomas have a tendency to invade diffusely into surrounding healthy brain tissues, thereby precluding their successful surgical removal. Intersectin1 (ITSN1) as a molecular linker in the central nervous system is well known as an important regulator of endocytosis and exocytosis. ITSN1 has two isoforms: ITSN1-l and ITSN1-s. In this study, we show that siRNA-mediated down regulation of ITSN1-s inhibited migration and invasion of glioma cells. In addition, we demonstrate the possible mechanisms by which ITSN1-s functions in migration and invasion. Several key proteins, including cofilin, LIMK, PAK, FAK, integrin β1, and MMP-9, which are critical for cells migration and invasion, were probably involved in ITSN1-s signaling pathways. These results suggest that ITSN1-s contributes to glioma cells migration and invasion by regulating the formation of cytoskeleton, influencing adhesion and increasing expression of MMP-9. Our results indicate that ITSN1-s is a critical factor in gliomas invasion and identify that ITSN1-s is a new potentially antiinvasion target for therapeutic intervention in gliomas.     

Sonic Hedgehog/GLI1 signaling pathway inhibition restricts cell migration and invasion in human gliomas

Abstract

Recent studies have shown that aberrant activation of Sonic Hedgehog (SHH)/GLI1 signaling pathway is involved in many kinds of human malignancies. Both in vitro and in vivo experiments demonstrate that inhibiting the pathway results in tumor regression for a fraction of gliomas which harbor an active pathway. However, little is known about the linkage between the SHH/GLI1 signaling pathway and cell migration and invasion in gliomas. In this study, we showed that GLI1 expression closely correlates with pathological grades of human gliomas by immunohistochemistry analysis of 110 cases of surgically-resected glioma tissues. Moreover, we used cyclopamine and RNA interference technique to block the SHH/GLI1 signaling to investigate the in vitro changes of glioma cells. The result showed that suppression of the pathway markedly inhibited glioma cell migration and invasion. The following quantitative RT-PCR analysis showed that decreased expressions of Snail, MMP9, and increased E-cadherin expression coincided with GLI1 knockout. Collectively, our results raise the possibility that SHH/GLI1 is a potentially anti-invasive target for therapeutic intervention in human gliomas.     

Robo3.1A suppresses Slit‐mediated repulsion by triggering degradation of Robo2

Slits and Robos control the midline crossing of commissural axons, which are not sensitive to the midline repellent Slit before crossing but gain Slit responsiveness to exit the midline and avoid recrossing. Robo3.1A promotes midline crossing of commissural axons by suppressing the axonal responsiveness to the midline repellent Slit, but the underlying mechanism remains unclear. By using a cell surface binding assay and immunoprecipitation, we observed that Robo3.1A did not bind Slit on its own but prevented the specific binding of Slit to the cell surface when it was coexpressed with its close homologue Robo1 or Robo2 (Robo1/2), which are known to mediate the Slit repulsion. Cotransfection with Robo3.1A significantly reduced the protein level of Robo2 in HEK293 cells, and overexpression of Robo3.1A also significantly decreased Robo2 protein level in cerebellar granule cells. Downregulation of endogenous Robo3 by specific small interference RNA (siRNA) significantly increased Robo1 protein level, Slit binding to the cell surface was significantly elevated, and Slit‐triggered growth cone collapse appeared after downregulation of Robo3 in cultured cortical neurons. Immunocytochemical staining showed that Robo2 and Robo3 colocalized in intracellular vesicles positive for the marker of late endosomes and lysosomes, but not trans‐Golgi apparatus and early endosomes. Thus Robo3.1A may prevent the Slit responsiveness by recruiting Robo1/2 into a late endosome‐ and lysosome‐dependent degradation pathway. © 2014 Wiley Periodicals, Inc.     

Knockdown of annexin 2 decreases migration of human glioma cells in vitro

Diffuse invasion of brain tissue is a major reason for the poor prognosis of patients with glioblastoma. Annexin 2, a member of the large annexin family of Ca2+ and membrane-binding proteins, is expressed at high protein levels in human gliomas and has been proposed as a marker of glioma malignancy, while its functional role in these tumours is unknown so far. The ability of annexin 2 to interact with the actin cytoskeleton, as well as its potential to bind invasion-associated proteases, suggests that it could participate in invasion-associated processes in human gliomas. Therefore, we analysed here functional consequences of RNA interference-mediated silencing of annexin 2 in U87MG and U373MG human glioma cell lines. While no impact of annexin 2 downregulation on proliferation and adhesion was observed, our analyses revealed that migration of U87MG and U373MG cells was significantly inhibited following annexin 2 depletion. This effect was not related to a compensatory increase of the related annexins 1 or 6. Our findings identify annexin 2 as a potential candidate involved in glioma invasion and support the potential of RNA interference as powerful tool in the decryption of glioma invasion mechanisms.     

AMOG/β2 and glioma invasion: does loss of AMOG make tumour cells run amok?

The beta2 subunit of Na,K-ATPase, initially described as adhesion molecule on glia (AMOG), has been shown to mediate neurone-astrocyte adhesion as well as neural cell migration in vitro. We have investigated the expression of AMOG/beta2 in human gliomas and its effect on glioma cell adhesion and migration. Compared to normal astrocytes of human brain, AMOG/beta2 expression levels of neoplastic astrocytes were down-regulated in biopsy specimens and inversely related to the grade of malignancy. One rat and four human glioma cell lines showed complete loss of AMOG. To investigate the function of AMOG/beta2, its expression was re-established by transfecting an expression plasmid into AMOG/beta2-negative C6 rat glioma cells. In vitro assays revealed increased adhesion and decreased migration on matrigel of AMOG/beta2-positive cells as compared to their AMOG/beta2-negative counterparts. We conclude that increasing loss of AMOG/beta2 during malignant progression parallels and may underlie the extensive invasion pattern of malignant gliomas.     

Slit-Robo signals regulate pioneer axon pathfinding of the tract of the postoptic commissure in the mammalian forebrain

During early vertebrate forebrain development, pioneer axons establish a symmetrical scaffold descending longitudinally through the rostral forebrain, thus forming the tract of the postoptic commissure (TPOC). In mouse embryos, this tract begins to appear at embryonic day 9.5 (E9.5) as a bundle of axons tightly constrained at a specific dorsoventral level. We have characterized the participation of the Slit chemorepellants and their Robo receptors in the control of TPOC axon projection. In E9.5-E11.5 mouse embryos, Robo1 and Robo2 are expressed in the nucleus origin of the TPOC (nTPOC), and Slit expression domains flank the TPOC trajectory. These findings suggested that these proteins are important factors in the dorsoventral positioning of the TPOC axons. Consistently with this role, Slit2 inhibited TPOC axon growth in collagen gel cultures, and interfering with Robo function in cultured embryos induced projection errors in TPOC axons. Moreover, absence of both Slit1 and Slit2 or Robo1 and Robo2 in mutant mouse embryos revealed aberrant TPOC trajectories, resulting in abnormal spreading of the tract and misprojections into both ventral and dorsal tissues. These results reveal that Slit-Robo signaling regulates the dorsoventral position of this pioneer tract in the developing forebrain.     

HSP27 mediates SPARC-induced changes in glioma morphology, migration, and invasion

Secreted protein acidic and rich in cysteine (SPARC) regulates cell-extracellular matrix interactions that influence cell adhesion and migration. We have demonstrated that SPARC is highly expressed in human gliomas, and it promotes brain tumor invasion in vitro and in vivo. To further our understanding regarding SPARC function in glioma migration, we transfected SPARC-green fluorescent protein (GFP) and control GFP vectors into U87MG cells, and assessed the effects of SPARC on cell morphology, migration, and invasion after 24 h. The expression of SPARC was associated with elongated cell morphology, and increased migration and invasion. The effects of SPARC on downstream signaling were assessed from 0 to 6 h and 24 h. SPARC increased the levels of total and phosphorylated HSP27; the latter was preceded by activation of p38 MAPK and inhibited by the p38 MAPK inhibitor SB203580. Augmented expression of SPARC was correlated with increased levels of HSP27 mRNA. In a panel of glioma cell lines, increasing levels of SPARC correlated with increasing total and phosphorylated HSP27. SPARC and HSP27 were colocalized to invading cells in vivo. Inhibition of HSP27 mRNA reversed the SPARC-induced changes in cell morphology, migration, and invasion in vitro. These data indicate that HSP27, a protein that regulates actin polymerization, cell contraction, and migration, is a novel downstream effector of SPARC-regulated cell morphology and migration. As such, it is a potential therapeutic target to inhibit SPARC-induced glioma invasion.     

JAZF1对胶质母细胞瘤侵袭和迁徙的影响及分子机制研究

目的探讨JAZF1对脑胶质母细胞瘤（GBM）细胞侵袭、迁徙的作用及相关作用机制。 方法通过挖掘TCGA数据库中不同级别胶质瘤患者JAZF1的转录水平差异以及患者生存曲线差异,然后通过科内收集的胶质瘤样本提取总蛋白进行Western blot实验研究JAZF1蛋白水平在胶质瘤不同级别中的差异,通过Trans-well实验、细胞划痕实验研究JAZF1对胶质瘤细胞侵袭和迁移的影响,通过Western blot实验研究JAZF1对胶质瘤细胞侵袭和迁徙能力的关键分子的影响。 结果（1）Ⅳ级胶质瘤中JAZF1的mRNA、蛋白水平的表达上相较于Ⅱ级和Ⅲ级胶质瘤明显更高,差异具有统计学意义（P<0.05）;（2）JAZF1高表达组患者的中位生存期为13.0个月,而低表达组中位生存期为30.2个月,差异具有统计学意义（P<0.05）;（3）JAZF1表达下降后,U87M细胞的侵袭和迁徙能力均显著下降,差异具有统计学意义（P<0.05）;（4）干扰JAZF1的表达后,p-Akt、MMP9、MMP2的表达水平显著下调,差异均具有统计学意义（P<0.05）,而Akt的表达变化不明显,差异无统计学意义（P>0.05）。 结论JAZF1在GBM中高表达且显著缩短了患者的中位生存期,通过调控Akt的磷酸化水平进一步调控相应信号通路下游的MMP9、MMP2的表达影响GBM的侵袭和迁徙能力。     

FOXC2过表达通过激活Wnt/β-catenin信号通路促进胶质瘤U87细胞增殖、迁移

目的 探讨FOXC2过表达对胶质瘤U87细胞增殖、侵袭、迁移的影响及其机制.方法 体外培养人脑胶质瘤U87细胞和人脑胶质细胞HEB.U87细胞随机分为空白组(未转染任何质粒)、空载体组(转染pcDNA3.1空载体质粒)、FOXC2过表达组(转染pcDNA3.1-FOXC2过表达质粒)、FOXC2+抑制剂组[转染pcDN...     

下调RNA甲基化酶NSUN2表达对脑胶质瘤U87细胞增殖、侵袭、迁移的影响

目的 探讨下调NOP2/Sun RNA甲基转移酶家族成员2(NSUN2)表达对脑胶质瘤细胞增殖、侵袭、迁移的影响。方法体外培养正常胶质细胞HEB、胶质瘤细胞系（A172、U251、U87）,免疫印迹法检测NSUN2蛋白表达水平;用shNSUN2慢病毒（sh-NSUN2组）及shRNA scramble慢病毒（sh-CON组）感染U87细胞下调NSUN2表达,用CCK-8法检测细胞增殖活力,Transwell实验检测细胞侵袭和迁移。结果 与正常胶质细胞HEB相比,胶质瘤细胞系A172、U251、U87的NSUN2蛋白表达量均明显增高（P<0.05）。与sh-CON组比较,sh-NSUN2组NSUN2蛋白表达水平、细胞增殖活力、侵袭能力和迁移能力均明显降低（P<0.05）。结论 胶质瘤NSUN2呈高表达,下调其表达明显抑制胶质瘤细胞增殖、侵袭和迁移。     

Classic axon guidance molecules control correct nerve bridge tissue formation and precise axon regeneration

The peripheral nervous system has an astonishing ability to regenerate following a compression or crush injury;however,the potential for full repair following a transection injury is much less.Currently,the major clinical challenge for peripheral nerve repair come from long gaps between the proximal and distal nerve stumps,which prevent regenerating axons reaching the distal nerve.Precise axon targeting during nervous system development is controlled by families of axon guidance molecules including Netrins,Slits,Ephrins and Semaphorins.Several recent studies have indicated key roles of Netrin1,Slit3 and EphrinB2 signalling in controlling the formation of new nerve bridge tissue and precise axon regeneration after peripheral nerve transection injury.Inside the nerve bridge,nerve fibroblasts express EphrinB2 while migrating Schwann cells express the receptor EphB2.EphrinB2/EphB2 signalling between nerve fibroblasts and migrating Schwann cells is required for Sox2 upregulation in Schwann cells and the formation of Schwann cell cords within the nerve bridge to allow directional axon growth to the distal nerve stump.Macrophages in the outermost layer of the nerve bridge express Slit3 while migrating Schwann cells and regenerating axons express the receptor Robo1;within Schwann cells,Robo1 expression is also Sox2-dependent.Slit3/Robo1 signalling is required to keep migrating Schwann cells and regenerating axons inside the nerve bridge.In addition to the Slit3/Robo1 signalling system,migrating Schwann cells also express Netrin1 and regenerating axons express the DCC receptor.It appears that migrating Schwann cells could also use Netrin1 as a guidance cue to direct regenerating axons across the peripheral nerve gap.Engineered neural tissues have been suggested as promising alternatives for the repair of large peripheral nerve gaps.Therefore,understanding the function of classic axon guidance molecules in nerve bridge formation and their roles in axon regeneration could be highly beneficial in developing engineered neural tissue for more effective peripheral nerve repair.     

人脑膜瘤组织Slit2、Robo1的表达与术后复发的关系

目的 探讨人脑膜瘤Slit、Robo的表达与术后复发的关系。方法 收集2016年1月至2021年4月手术切除的脑膜瘤104例,另选取颅脑损伤内减压术切除的非肿瘤脑组织50例（对照组）,用免疫组织化学染色法检测Slit2、Robo1的表达水平。术后随访1年,判断肿瘤复发情况。结果 104例中,术后1年复发22例,复发率为21.15%。脑膜瘤组织Slit2低表达率[37.50%(39/104)]明显低于对照组[70.00%(35/50);P<0.05]。脑膜瘤组织Robo1高表达率[59.61%(62/104)]明显高于对照组[34.00%(17/50);P<0.05]。多因素logsitic回归分析显示,Slit2低表达、Robo1高表达是脑膜瘤术后复发的独立危险因素（P<0.05）。结论 脑膜瘤组织Slit2呈低表达,而Robo1呈高表达,二者均与术后复发有关。     

The adaptor protein Nck2 mediates Slit1-induced changes in cortical neuron morphology

Slits are multifunctional guidance cues, capable of triggering neurite repulsion, extension, or branching, depending on cell type and developmental context. While the Robo family of Slit receptors is a well-established mediator of axon repulsion, a role for Robos in Slit-mediated neurite growth and branching is not well defined, and the signaling molecules that link Robo to the cytoskeletal changes that drive neurite outgrowth are not well characterized in vertebrates. We show that Slit stimulates cortical dendrite branching, and we report that Slit also triggers a robust increase in the length of cortical axons in vitro. Moreover, neurons derived from Robo1; Robo2 deficient mice do not display an increase in neurite length, indicating that endogenous Robos mediate Slit's growth-promoting effects on both axons and dendrites. We also demonstrate that the SH2/SH3 adaptor proteins Nck1 and Nck2 bind to Robo via an atypical SH3-mediated mechanism. Furthermore, we show that only Nck2 is required for the Slit-induced changes in cortical neuron morphology in vitro. These findings indicate a specific role for Nck2 in linking Robo activation to the cytoskeleton rearrangements that shape cortical neuron morphology.     

神经导向因子Slit基因及其研究进展

神经导向因子Slit家族在调节神经元前体细胞定向迁移、定位和神经元轴突的定向生长中具有重要作用。Slit/Robo信号通路在调节肿瘤细胞转移、肿瘤血管生长、免疫细胞趋化、脉管系统生成和血管内皮细胞生长等方面的研究是近年关注的热点。本文对Slit因子及其Slit/Robo信号通路在神经细胞迁移、血管生成与神经修复等的作用及研究进展进行综述。     

Spatiotemporal expression patterns of slit and robo genes in the rat brain.

Diffusible chemorepellents play a major role in guiding developing axons toward their correct targets by preventing them from entering or steering them away from certain regions. Genetic studies in Drosophila revealed a repulsive guidance system that prevents inappropriate axons from crossing the central nervous system midline; this repulsive system is mediated by the secreted extracellular matrix protein Slit and its receptors Roundabout (Robo). Three distinct slit genes (slit1, slit2, and slit3) and three distinct robo genes (robo1, robo2, rig-1) have been cloned in mammals. However, to date, only Robo1 and Robo2 have been shown to be receptors for Slits. In rodents, Slits have been shown to function as chemorepellents for several classes of axons and migrating neurons. In addition, Slit can also stimulate the formation of axonal branches by some sensory axons. To identify Slit-responsive neurons and to help analyze Slit function, we have studied, by in situ hybridization, the expression pattern of slits and their receptors robo1 and robo2, in the rat central nervous system from embryonic stages to adult age. We found that their expression patterns are very dynamic: in most regions, slit and robo are expressed in a complementary pattern, and their expression is up-regulated postnatally. Our study confirms the potential role of these molecules in axonal pathfinding and neuronal migration. However, the persistence of robo and slit expression suggests that the couple slit/robo may also have an important function in the adult brain.