Slit and robo: expression patterns in lung development

Overexpression of miR-25 Downregulates the Expression of ROBO2 in Idiopathic Intellectual Disability

Idiopathic intellectual disability (IID) encompasses the cases of intellectual disability (ID) without a known cause and represents approximately 50% of all cases. Neural progenitor cells (NPCs) from the olfactory neuroepithelium (NEO) contain the same information as the cells found in the brain, but they are more accessible. Some miRNAs have been identified and associated with ID of known etiology. However, in idiopathic ID, the effect of miRNAs is poorly understood. The aim of this study was to determine the miRNAs regulating the expression of mRNAs that may be involved in development of IID. Expression profiles were obtained using NPC-NEO cells from IID patients and healthy controls by microarray. A total of 796 miRNAs and 28,869 mRNAs were analyzed. Several miRNAs were overexpressed in the IID patients compared to controls. miR-25 had the greatest expression. In silico analysis showed that ROBO2 was the target for miR-25, with the highest specificity and being the most down-regulated. In vitro assay showed an increase of miR-25 expression induced a decrease in ROBO2 expression. In neurodevelopment, ROBO2 plays a crucial role in episodic learning and memory, so its down-regulation, caused by miR-25, could have a fundamental role in the intellectual disability that, until now, has been considered idiopathic.

Morphologically intact airways in lung fibrosis have an abnormal proteome

Honeycombing is a histological pattern consistent with Usual Interstitial Pneumonia (UIP). Honeycombing refers to cystic airways located at sites of dense fibrosis with marked mucus accumulation. Utilizing laser capture microdissection coupled mass spectrometry (LCM-MS), we interrogated the fibrotic honeycomb airway cells and fibrotic uninvolved airway cells (distant from honeycomb airways and morphologically intact) in specimens from 10 patients with UIP. Non-fibrotic airway cell specimens from 6 patients served as controls. Furthermore, we performed LCM-MS on the mucus plugs found in 6 patients with UIP and 6 patients with mucinous adenocarcinoma. The mass spectrometry data were subject to both qualitative and quantitative analysis and validated by immunohistochemistry. Surprisingly, fibrotic uninvolved airway cells share a similar protein profile to honeycomb airway cells, showing deregulation of the slit and roundabout receptor (Slit and Robo) pathway as the strongest category. We find that (BPI) fold-containing family B member 1 (BPIFB1) is the most significantly increased secretome-associated protein in UIP, whereas Mucin-5AC (MUC5AC) is the most significantly increased in mucinous adenocarcinoma. We conclude that fibrotic uninvolved airway cells share pathological features with fibrotic honeycomb airway cells. In addition, fibrotic honeycomb airway cells are enriched in mucin biogenesis proteins with a marked derangement in proteins essential for ciliogenesis. This unbiased spatial proteomic approach generates novel and testable hypotheses to decipher fibrosis progression.

Abnormal expression of SLIT3 induces intravillous vascularization dysplasia in ectopic pregnancy

Objective

To investigate whether the morphology, capillary number, and transcriptome expression profiles of ectopic pregnancy (EP) villi differ from those of normal pregnancy (NP) villi.

Methods

Hematoxylin-eosin (HE) and immunohistochemistry (IHC) staining for CD31 were conducted to compare differences in morphology and capillary number between EP and NP villi. Differentially expressed (DE) miRNAs and mRNAs were determined from transcriptome sequencing of both types of villi and used to construct a miRNA-mRNA network, from which hub genes were identified. Candidate DE-miRNAs and DE-mRNAs were validated by quantitative reverse transcription (qRT)-PCR. Correlations were identified between the number of capillaries and serum beta human chorionic gonadotropin (β-HCG) levels and between the expression levels of hub genes associated with angiogenesis and β-HCG levels.

Results

The mean and total cross-sectional areas of placental villi were significantly increased in EP compared with NP villi. Capillary density was greatly reduced in EP villi and was positively correlated with β-HCG levels. A total of 49 DE-miRNAs and 625 DE-mRNAs were identified from the sequencing data. An integrated analysis established a miRNA-mRNA network containing 32 DE-miRNAs and 103 DE-mRNAs. Based on the validation of hub mRNAs and miRNAs in the network, a regulatory pathway involving miR-491-5p-SLIT3 was discovered, which may have a role in the development of villous capillaries.

Conclusion

Villus morphology, capillary number, and miRNA/mRNA expression profiles in villous tissues were aberrant in EP placentas. Specifically, SLIT3, which is regulated by miR-491-5p, may contribute to the regulation of villous angiogenesis and was established as a putative predictor of chorionic villus development, providing a basis for future research.

The expression of Slit2 and Robo1 increased during retinoic acid syndrome in acute promyelocytic leukemia and impacted differentiated cell migration

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The upregulation of Robo1 and Slit2 was first found in APL patients.

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The positive correlation between Robo1/Slit2 and retinoic acid syndrome was first demonstrated.

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It was demonstrated for the first time that Slit2 induces the migration of differentiated cells.

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Slit2 did not inhibit il8-induced differentiated cell migration.

Retinoic acid syndrome (RAS) is a serious complication developed during the induction therapy of acute promyelocytic leukemia (APL). Cytokines and differentiated cells migration play important roles in the development of RAS. Slit guidance ligand 2 (Slit2) and roundabout 1 (Robo1) involve in cell migration. Our study aimed to investigate the expression of Slit2 and Robo1 in APL and check whether they affected promyelocytes migration. 62 cases of newly diagnosed APL patients were involved and received all-trans retinoic acid (ATRA) and arsenic trioxide as induction therapy. Bone marrow cells (BMCs) were obtained on days 0 and 28, and promyelocytes and plasma were collected from day 1 to day 21. The expression of Robo1 in promyelocytes, and that of Slit2 and cytokines, including IL-8,IL-1β and others, in serum were monitored. 20 healthy individuals donated their cells as control. Of the 62 APL patients, 16 (25.81%) patients developed RAS. The expression of Robo1, Slit2 and IL-8 increased significantly with the development of RAS. In the 16 patients with RAS, levels of Slit2, Robo1 and IL-8 were higher during the development of RAS than before or after the RAS (P < 0.05). RhSlit2-N and rhIL-8 induced cells migration, and the migration induced by IL-8 was not inhibited by rhSlit2-N. Elevated Slit2 and Robo1 levels might be useful markers for the diagnosis and treatment of RAS. The levels of Slit2, Robo1 and IL-8 showed a positive correlation with the severity of RAS. Slit2 and IL-8 promoted the migration of differentiated cells.

Integrative analysis of lncRNAs, miRNAs, and mRNAs-associated ceRNA network in a neonatal mouse model of bronchopulmonary dysplasia

OBJECTIVE

To elucidate the potential roles of the lncRNA-mediated competitive endogenous RNA (ceRNA) network in the pathogenesis of bronchopulmonary dysplasia (BPD), we performed an integrated bioinformatics analysis based on miRNA and mRNA microarray datasets between BPD and normal samples.

STUDY DESIGN

The mRNA and miRNA expression profiles of BPD were downloaded from the Gene Expression Omnibus (GEO) database to perform an integrated analysis. The limma package was used to identify differentially expressed genes (DEGs) and differentially expressed miRNA (DEmiRs), followed by functional enrichment analysis of DEGs. DEmiR-DEG and DEmiRNA-lncRNA interactions were predicted. Subsequently, the lncRNA-related ceRNA network was structured. Finally, a newborn BPD mouse model was established, and quantitative real-time PCR (qPCR) was used to validate the expression of the selected mRNAs, miRNAs, and lncRNAs.

RESULTS

A total of 445 DEGs and 155 DEmiRs were obtained by comparing BPD samples and normal samples. Functional enrichment analysis showed that DEGs were primarily enriched in GO terms such as cell division and inflammatory response; and DEGs were mainly involved in the p53 signaling pathway. The miR17hg-miR-130b-3p-roundabout guidance receptor 2 (Robo2) and GM20455-miR-34a-5p-BMP/retinoic acid-inducible neural specific 1 (Brinp1) ceRNA axes were obtained by constructing the ceRNA network. In addition, the upregulation of Robo2 and miR17hg while the downregulation of miR-130b-3p; as well as the upregulation of Brinp1 and GM20455 but the downregulation of miR-34a-5p were validated by qPCR.

CONCLUSION

The miR17hg-miR-130b-3p-Robo2 and GM20455-miR-34a-5p-Brinp1 axes may serve important role in the development of BPD. These findings might provide novel insight for a comprehensive understanding of molecular mechanisms in BPD, and genes in the ceRNA network might be considered as potential biomarkers and therapeutic targets against BPD.

Expression patterns of Slit and Robo family members in adult mouse spinal cord and peripheral nervous system

The secreted glycoproteins, Slit1-3, are classic axon guidance molecules that act as repulsive cues through their well characterised receptors Robo1-2 to allow precise axon pathfinding and neuronal migration. The expression patterns of Slit1-3 and Robo1-2 have been most characterized in the rodent developing nervous system and the adult brain, but little is known about their expression patterns in the adult rodent peripheral nervous system. Here, we report a detailed expression analysis of Slit1-3 and Robo1-2 in the adult mouse sciatic nerve as well as their expression in the nerve cell bodies within the ventral spinal cord (motor neurons) and dorsal root ganglion (sensory neurons). Our results show that, in the adult mouse peripheral nervous system, Slit1-3 and Robo1-2 are expressed in the cell bodies and axons of both motor and sensory neurons. While Slit1 and Robo2 are only expressed in peripheral axons and their cell bodies, Slit2, Slit3 and Robo1 are also expressed in satellite cells of the dorsal root ganglion, Schwann cells and fibroblasts of peripheral nerves. In addition to these expression patterns, we also demonstrate the expression of Robo1 in blood vessels of the peripheral nerves. Our work gives important new data on the expression patterns of Slit and Robo family members within the peripheral nervous system that may relate both to nerve homeostasis and the reaction of the peripheral nerves to injury.

Understanding the developmental pathways pulmonary fibroblasts may follow during alveolar regeneration

Although pulmonary alveolar interstitial fibroblasts are less specialized than their epithelial and endothelial neighbors, they play essential roles during development and in response to lung injury. At birth, they must adapt to the sudden mechanical changes imposed by the onset of respiration and to a higher ambient oxygen concentration. In diseases such as bronchopulmonary dysplasia and interstitial fibrosis, their adaptive responses are overwhelmed leading to compromised gas-exchange function. Thus, although fibroblasts do not directly participate in gas-exchange, they are essential for creating and maintaining an optimal environment at the alveolar epithelial-endothelial interface. This review summarizes new information and concepts about the ontogeny differentiation, and function of alveolar fibroblasts. Alveolar development will be emphasized, because the development of strategies to evoke alveolar repair and regeneration hinges on thoroughly understanding the way that resident fibroblasts populate specific locations in which extracellular matrix must be produced and remodeled. Other recent reviews have described the disruption that diseases cause to the fibroblast niche and so my objective is to illustrate how the unique developmental origins and differentiation pathways could be harnessed favorably to augment certain fibroblast subpopulations and to optimize the conditions for alveolar regeneration.

Fibroblasts secrete Slit2 to inhibit fibrocyte differentiation and fibrosis

Monocytes leave the blood and enter tissues. In healing wounds and fibrotic lesions, some of the monocytes differentiate into fibroblast-like cells called fibrocytes. In healthy tissues, even though monocytes enter the tissue, for unknown reasons, very few monocytes differentiate into fibrocytes. In this report, we show that fibroblasts from healthy human tissues secrete the neuronal guidance protein Slit2 and that Slit2 inhibits human fibrocyte differentiation. In mice, injections of Slit2 inhibit bleomycin-induced lung fibrosis. In lung tissue from pulmonary fibrosis patients with relatively normal lung function, Slit2 has a widespread distribution whereas, in patients with advanced disease, there is less Slit2 in the fibrotic lesions. These data may explain why fibrocytes are rarely observed in healthy tissues, may suggest that the relative levels of Slit2 present in healthy tissue and at sites of fibrosis may have a significant effect on the decision of monocytes to differentiate into fibrocytes, and may indicate that modulating Slit2 signaling may be useful as a therapeutic for fibrosis.

An association between genetic variation in the roundabout, axon guidance receptor, homolog 2 gene and immunity traits in chickens

The roundabout, axon guidance receptor, homolog 2 (ROBO2) gene is one member of the roundabout (ROBO) family, which belongs to the immunoglobulin superfamily. The ROBO molecules are known to function in axon guidance and cell migration and are involved in SLIT/ROBO signaling. In this study, we obtained the full-length cDNA sequence of the chicken ROBO2 gene. Sequence analysis indicated that 3 SNP (1418G > A, 1421C > A and 2462T > C) exist in exons 5 and 12 of the ROBO2 gene. Genotyping results revealed that the allele frequency of SNP 1421C > A was similar in all tested breeds, but the allele frequencies of the other 2 SNP were different between White Leghorn and Chinese indigenous chickens. Allele G of 1418G > A and allele T of 2462T > C predominated in the Chinese indigenous breed, whereas alleles A and C predominated in the White Leghorn breed. Association analyses revealed that birds with the GG genotype of SNP 1418G > A or the TT genotype of SNP 2462T > C had significantly higher antibody responses to Newcastle disease virus (NDV_S/P; P < 0.01) than carriers of the A allele (GA and AA) or the C allele (TC), respectively. Real-time PCR further revealed that ROBO2 expression in the spleens of the birds with higher antibody responses (GG and TT genotypes at SNP 1418 and 2462, respectively) was significantly higher than in the spleens of birds with the AA and AG genotypes at SNP 1418 or the TC genotype at SNP 2462 (P < 0.01). The results demonstrated that genetic variation at the ROBO2 gene plays a key role in the immune response to Newcastle disease virus, and SNP 1418G > A and 2462T > C can be used as genetic markers for the selection of chickens with stronger immune responses to Newcastle disease virus.

Roundabout receptors are critical for foregut separation from the body wall

In mammals, precise placement of organs is essential for survival. We show here that inactivation of Roundabout (Robo) receptors 1 and 2 in mice leads to mispositioning of the stomach in the thoracic instead of the abdominal cavity, which likely contributes to poor lung inflation and lethality at birth, reminiscent of congenital diaphragmatic hernia (CDH) cases in humans. Unexpectedly, in Robo mutant mice, the primary defect preceding organ misplacement and diaphragm malformation is a delayed separation of foregut from the dorsal body wall. Foregut separation is a rarely considered morphogenetic event, and our data indicate that it occurs via repulsion of Robo-expressing foregut cells away from the Slit ligand source. In humans, genomic lesions containing Robo genes have been documented in CDH. Our findings suggest that separation of the foregut from the body wall is genetically controlled and that defects in this event may contribute to CDH.

Guidance for life, cell death, and colorectal neoplasia by netrin dependence receptors

This review is focusing on a critical mediator of embryonic and postnatal development with multiple implications in inflammation, neoplasia, and other pathological situations in brain and peripheral tissues. These morphogenetic guidance and dependence processes are involved in several malignancies targeting the epithelial and immune systems including the progression of human colorectal cancers. We consider the most important findings and their impact on basic, translational, and clinical cancer research. Expected information can bring new cues for innovative, efficient, and safe strategies of personalized medicine based on molecular markers, protagonists, signaling networks, and effectors inherent to the Netrin axis in pathophysiological states.

GSK3 temporally regulates neurogenin 2 proneural activity in the neocortex

The neocortex is comprised of six neuronal layers that are generated in a defined temporal sequence. While extrinsic and intrinsic cues are known to regulate the sequential production of neocortical neurons, how these factors interact and function in a coordinated manner is poorly understood. The proneural gene Neurog2 is expressed in progenitors throughout corticogenesis, but is only required to specify early-born, deep-layer neuronal identities. Here, we examined how neuronal differentiation in general and Neurog2 function in particular are temporally controlled during murine neocortical development. We found that Neurog2 proneural activity declines in late corticogenesis, correlating with its phosphorylation by GSK3 kinase. Accordingly, GSK3 activity, which is negatively regulated by canonical Wnt signaling, increases over developmental time, while Wnt signaling correspondingly decreases. When ectopically activated, GSK3 inhibits Neurog2-mediated transcription in cultured cells and Neurog2 proneural activities in vivo. Conversely, a reduction in GSK3 activity promotes the precocious differentiation of later stage cortical progenitors without influencing laminar fate specification. Mechanistically, we show that GSK3 suppresses Neurog2 activity by influencing its choice of dimerization partner, promoting heterodimeric interactions with E47 (Tcfe2a), as opposed to Neurog2-Neurog2 homodimer formation, which occurs when GSK3 activity levels are low. At the functional level, Neurog2-E47 heterodimers have a reduced ability to transactivate neuronal differentiation genes compared with Neurog2-Neurog2 homodimers, both in vitro and in vivo. We thus conclude that the temporal regulation of Neurog2-E47 heterodimerization by GSK3 is a central component of the neuronal differentiation "clock" that coordinates the timing and tempo of neocortical neurogenesis in mouse.

Human placental expression of SLIT/ROBO signaling cues: effects of preeclampsia and hypoxia

Preeclampsia is characterized by dysfunctional endothelium and impaired angiogenesis. Recent studies suggest that the neuronal guidance SLIT/ROBO system regulates tumor angiogenesis. This study investigated if SLIT and ROBO are differentially expressed in healthy term and preeclamptic placentas and if hypoxia regulates SLIT and ROBO expression in placental trophoblast and endothelial cells. Total RNA and protein were extracted from placental tissues of healthy term (n = 5) and preeclamptic (n = 6) pregnancies and used for SLIT/ROBO expression analyses with reverse transcription-polymerase chain reaction (RT-PCR), real-time quantitative-PCR, and immunoblotting. Paraffin-embedded tissues were processed to localize SLIT/ROBO proteins in placental villi by immunohistochemistry. BeWo choriocarcinoma cells and human umbilical vein endothelial cells (HUVEC) were treated with 2% or 10% oxygen or the hypoxia mimetic deferoxamine mesylate (100 μM) to test if hypoxia regulates SLIT/ROBO expression. SLIT2, SLIT3, ROBO1, and ROBO4 mRNA and proteins were detected in the placenta. SLIT2 and ROBO1 proteins localized in the syncytiotrophoblast, and SLIT3, ROBO1, and ROBO4 in capillary endothelium of the placental villi. Levels of ROBO1 and ROBO4 as well as sFLT1 (soluble fms-like tyrosine kinase-1) proteins were significantly greater in preeclamptic placentas compared to normal controls. Hypoxia significantly increased both mRNA and protein levels of SLIT2 in BeWo cells and of SLIT3, ROBO1, and ROBB4 in HUVEC. Thus, trophoblast and endothelial coexpression of SLIT/ROBO suggests an autocrine/paracrine regulatory system for regulating placental function. Differential expression of SLITs and ROBOs in healthy term and preeclamptic placentas and hypoxia regulation of their expressions in placental cells implicate a potential pathophysiological role for this system in preeclampsia.

Slit2-N inhibits PDGF-induced migration in rat airway smooth muscle cells: WASP and Arp2/3 involved

BACKGROUND

Slit2 has been reported to be implicated in many kinds of cell migration. However little is known about the effect of Slit2 on airway smooth muscle cell migration. This study was to detect the expression of Slit2 in rat airway smooth muscle (RASM) cells stimulated by platelet-derived growth factor (PDGF) and characterized the effect of Slit2-N on PDGF-induced migration of RASM cells in vitro.

METHODS

mRNAs of Slit-Robo in RASM cells were examined by RT-PCR, and the effect of exogenous Slit2-N at different doses on PDGF-induced migration of RASM cells were examined by transwell and scrape-wound assays. Actin filaments (F-actin) were stained with rhodamine-conjugated phalloidin and the levels of protein expression were detected by western blot.

RESULTS

RASM cells were identified to express Slit2, Slit3, Robo1, Robo2 and Robo4 in vitro. Slit2-N caused a time- and dose-dependent inhibition of cell proliferation, while had no significantly effect on cell apoptosis. Slit2-N pretreatment attenuated the elongated morphologic characteristics, reduced lamellipodia formation, inhibited actin rearrangement and cell migration induced by PDGF. PDGF-induced increase of WASP and Arp2/3 proteins were dramatically inhibited by 100 ng/ml Slit2-N.

CONCLUSION

Slit2-N inhibits RASM cells migration at least partly through attenuating the expressions of WASP and Arp2/3, inhibiting actin rearrangement in vitro. The results contribute to provide new insights into the pathogenesis of airway remodeling in asthma and may be helpful for development of effective treatments.

Slit2 regulates attractive eosinophil and repulsive neutrophil chemotaxis through differential srGAP1 expression during lung inflammation

Directional migration of leukocytes is an essential step in leukocyte trafficking during inflammatory responses. However, the molecular mechanisms governing directional chemotaxis of leukocytes remain poorly understood. The Slit family of guidance cues has been implicated for inhibition of leuocyte migration. We report that Clara cells in the bronchial epithelium secreted Slit2, whereas eosinophils and neutrophils expressed its cell-surface receptor, Robo1. Compared to neutrophils, eosinophils exhibited a significantly lower level of Slit-Robo GTPase-activating protein 1 (srGAP1), leading to activation of Cdc42, recruitment of PI3K to Robo1, enhancment of eotaxin-induced eosinophil chemotaxis, and exaggeration of allergic airway inflammation. Notably, OVA sensitization elicited a Slit2 gradient at so-called bronchus-alveoli axis, with a higher level of Slit2 in the bronchial epithelium and a lower level in the alveolar tissue. Aerosol administration of rSlit2 accelerated eosinophil infiltration, whereas i.v. administered Slit2 reduced eosinophil deposition. In contrast, Slit2 inactivated Cdc42 and suppressed stromal cell-derived factor-1α-induced chemotaxis of neutrophils for inhibiting endotoxin-induced lung inflammation, which were reversed by blockade of srGAP1 binding to Robo1. These results indicate that the newly identified Slit2 gradient at the bronchus-alveoli axis induces attractive PI3K signaling in eosinophils and repulsive srGAP1 signaling in neutrophils through differential srGAP1 expression during lung inflammation.

Guidance molecules in lung cancer

Guidance molecules were first described in the nervous system to control axon outgrowth direction. They are also widely expressed outside the nervous system where they control cell migration, tissue development and establishment of the vascular network. In addition, they are involved in cancer development, tumor angiogenesis and metastasis. This review is primarily focused on their functions in lung cancer and their involvement in lung development is also presented. Five guidance molecule families and their corresponding receptors are described, including the semaphorins/neuropilins/plexins, ephrins and Eph receptors, netrin/DCC/UNC5, Slit/Robo and Notch/Delta. In addition, the possibility to target these molecules as a therapeutic approach in cancer is discussed.

Lung organogenesis

Developmental lung biology is a field that has the potential for significant human impact: lung disease at the extremes of age continues to cause major morbidity and mortality worldwide. Understanding how the lung develops holds the promise that investigators can use this knowledge to aid lung repair and regeneration. In the decade since the "molecular embryology" of the lung was first comprehensively reviewed, new challenges have emerged-and it is on these that we focus the current review. Firstly, there is a critical need to understand the progenitor cell biology of the lung in order to exploit the potential of stem cells for the treatment of lung disease. Secondly, the current familiar descriptions of lung morphogenesis governed by growth and transcription factors need to be elaborated upon with the reinclusion and reconsideration of other factors, such as mechanics, in lung growth. Thirdly, efforts to parse the finer detail of lung bud signaling may need to be combined with broader consideration of overarching mechanisms that may be therapeutically easier to target: in this arena, we advance the proposal that looking at the lung in general (and branching in particular) in terms of clocks may yield unexpected benefits.

Novel regulated expression of the SLIT/ROBO pathway in the ovary: possible role during luteolysis in women

The human corpus luteum (CL) undergoes luteolysis, associated with marked tissue and vascular remodeling, unless conception occurs and the gland is rescued by human chorionic gonadotropin (hCG). In Drosophila the Slit gene product, a secreted glycoprotein, acts as a ligand for the roundabout (robo) transmembrane receptor. Together they influence the guidance and migration of neuronal and nonneuronal cells. In vertebrates three Slit (Slit1, Slit2, Slit3) and four Robo (Robo1, Robo2, Robo3/Rig-1, Robo4/Magic Robo) genes have been identified. ROBO1, SLIT2, and SLIT3 are also inactivated in human cancers and may regulate apoptosis and metastasis. Because processes such as apoptosis and tissue remodeling occur during the regression of the CL, the aim of this study was to investigate the expression, regulation, and effects of the SLIT and ROBO genes in human luteal cells. Immunohistochemistry and RT-PCR revealed that SLIT2, SLIT3, ROBO1, and ROBO2 are expressed in luteal steroidogenic cells and fibroblast-like cells of the human CL. Furthermore, using real-time quantitative PCR, expression of SLIT2, SLIT3, and ROBO2 was maximal in the late-luteal phase and significantly reduced after luteal rescue in vivo with exogenous hCG (P<0.05). Additionally, hCG significantly inhibited SLIT2, SLIT3, and ROBO2 expression in cultured luteinized granulosa cells (P<0.05). Blocking SLIT-ROBO activity increased migration and significantly decreased levels of apoptosis in primary cultures of luteal cells (P<0.05). Overall, these results suggest the SLIT/ROBO pathway could play an important role in luteolysis in women.

Slit-2 induces a tumor-suppressive effect by regulating beta-catenin in breast cancer cells

SLIT-2 is considered as a candidate tumor suppressor gene, because it is frequently inactivated in various cancers due to hypermethylation of its promoter region and allelic loss. However, the exact mechanism of its tumor-suppressive effect has not been elucidated. Here, we observed that Slit-2-overexpressing breast cancer cells exhibited decreased proliferation and migration capabilities compared with control cells under in vitro conditions. These results were confirmed in vivo in mouse model systems. Mice injected with MCF-7/Slit-2 cells showed a 60-70% reduction in tumor size compared with mice injected with MCF-7/VC cells both in the absence and presence of estrogen. Upon further elucidation, we observed that Slit-2 mediates the tumor-suppressive effect via a coordinated regulation of the beta-catenin and PI3K signaling pathways and by enhancing beta-catenin/E-cadherin-mediated cell-cell adhesion. Our study for the first time reveals that Slit-2-overexpressing breast cancer cells exhibit tumor suppressor capabilities through the novel mechanism of beta-catenin modulation.

Robo2-Slit1 dependent cell-cell interactions mediate assembly of the trigeminal ganglion

Vertebrate cranial sensory ganglia, responsible for sensation of touch, taste and pain in the face and viscera, are composed of both ectodermal placode and neural crest cells. The cellular and molecular interactions allowing generation of complex ganglia remain unknown. Here, we show that proper formation of the trigeminal ganglion, the largest of the cranial ganglia, relies on reciprocal interactions between placode and neural crest cells in chick, as removal of either population resulted in severe defects. We demonstrate that ingressing placode cells express the Robo2 receptor and early migrating cranial neural crest cells express its cognate ligand Slit1. Perturbation of this receptor-ligand interaction by blocking Robo2 function or depleting either Robo2 or Slit1 using RNA interference disrupted proper ganglion formation. The resultant disorganization mimics the effects of neural crest ablation. Thus, our data reveal a novel and essential role for Robo2-Slit1 signaling in mediating neural crest-placode interactions during trigeminal gangliogenesis.

Basic helix-loop-helix transcription factors cooperate to specify a cortical projection neuron identity

Several transcription factors are essential determinants of a cortical projection neuron identity, but their mode of action (instructive versus permissive) and downstream genetic cascades remain poorly defined. Here, we demonstrate that the proneural basic helix-loop-helix (bHLH) gene Ngn2 instructs a partial cortical identity when misexpressed in ventral telencephalic progenitors, inducing ectopic marker expression in a defined temporal sequence, including early (24 h; Nscl2), intermediate (48 h; BhlhB5), and late (72 h; NeuroD, NeuroD2, Math2, and Tbr1) target genes. Strikingly, cortical gene expression was much more rapidly induced by Ngn2 in the dorsal telencephalon (within 12 to 24 h). We identify the bHLH gene Math3 as a dorsally restricted Ngn2 transcriptional target and cofactor, which synergizes with Ngn2 to accelerate target gene transcription in the cortex. Using a novel in vivo luciferase assay, we show that Ngn2 generates only approximately 60% of the transcriptional drive in ventral versus dorsal telencephalic domains, an activity that is augmented by Math3, providing a mechanistic basis for regional differences in Ngn2 function. Cortical bHLH genes thus cooperate to control transcriptional strength, thereby temporally coordinating downstream gene expression.

Slit-2/Robo-1 modulates the CXCL12/CXCR4-induced chemotaxis of T cells

Slit, which mediates its function by binding to the Roundabout (Robo) receptor, has been shown to regulate neuronal, dendritic, and leukocyte migration. However, the molecular mechanism by which the Slit/Robo complex inhibits the migration of cells is not well defined. Here, we showed that Slit-2 can inhibit the CXCL12-induced chemotaxis and transendothelial migration of T cells and monocytes. We observed that CXCR4 associates with Robo-1 and that Slit-2 treatment enhances this association with the Robo-1 receptor. Robo-1 is a single-pass transmembrane receptor whose intracellular region contains four conserved motifs designated as CC0, CC1, CC2, and CC3. Structural and functional analyses of Robo receptors revealed that interaction of the CC3 motif with the CXCR4 receptor may regulate the CXCL12-induced chemotaxis of T cells. We further characterized Slit-2-mediated inhibition of the CXCL12/CXCR4 chemotactic pathway and found that Slit-2 can block the CXCL12-induced activation of the Src and Lck kinases but not Lyn kinase. Although Slit-2 did not inhibit the CXCL12-induced activation of MAPKs, it did inhibit the Akt phosphorylation and Rac activation induced by this chemokine. Altogether, our studies indicate a novel mechanism by which the Slit/Robo complex may inhibit the CXCR4/CXCL12-mediated chemotaxis of T cells.

New cell surface markers for murine fetal hepatic stem cells identified through high density complementary DNA microarrays

Isolation of hepatic stem cells from the adult liver (AL) has not yet been achieved due to the lack of specific cell surface markers. To identify new surface markers for hepatic stem cells, we analyzed differences in the gene expression profile of embryonic day (ED) 13.5 fetal liver stem/progenitor cells (FLSPC) versus AL by complementary DNA (cDNA) microarray technology. Using FLSPC purified to >90% by immunomagnetic selection for E-cadherin and high density (27k) mouse cDNA microarrays, we identified 474 genes that are more strongly expressed in FLSPC (FLSPC-up genes) and 818 genes that are more strongly expressed in AL (AL-up genes). The most highly overrepresented gene ontology (GO) categories for FLSPC-up genes are nucleus, cellular proliferation, and cell cycle control. AL-up genes are overrepresented for genes in metabolic pathways for specific hepatic functions. We identified 24 FLSPC-up gene surface markers and 69 AL-up gene surface markers. Western blot studies confirmed the expression of the FLSPC-up gene neighbor of Punc E11 (Nope) in fetal liver, but expression was not detectable in AL. Immunohistochemistry, confocal microscopy, and fluorescence-activated cell sorting (FACS) analysis of fetal liver demonstrated that Nope is specifically expressed on the surface of FLSPC within the fetal liver.

CONCLUSION

This is the first microarray study to analyze the specific gene expression profile of purified murine FLSPC. Our analysis identified 24 new/potential cell surface markers for murine fetal hepatic stem cells, of which Nope may be particularly useful in future studies to identify, characterize and isolate hepatic stem cells from the AL.

Congenital diaphragmatic hernia (CDH) etiology as revealed by pathway genetics

Congenital diaphragmatic hernia (CDH) is a common birth defect with high mortality and morbidity. Two hundred seventy CDH patients were ascertained, carefully phenotyped, and classified as isolated (diaphragm defects alone) or complex (with additional anomalies) cases. We established different strategies to reveal CDH-critical chromosome loci and genes in humans. Candidate genes for sequencing analyses were selected from CDH animal models, genetic intervals of recurrent chromosomal aberration in humans, such as 15q26.1-q26.2 or 1q41-q42.12, as well as genes in the retinoic acid and related pathways and those known to be involved in embryonic lung development. For instance, FOG2, GATA4, and COUP-TFII are all needed for both normal diaphragm and lung development and are likely all in the same genetic and molecular pathway. Linkage analysis was applied first in a large inbred family and then in four multiplex families with Donnai-Barrow syndrome (DBS) associated with CDH. 10K SNP chip and microsatellite markers revealed a DBS locus on chromosome 2q23.3-q31.1. We applied array-based comparative genomic hybridization (aCGH) techniques to over 30, mostly complex, CDH patients and found a de novo microdeletion in a patient with Fryns syndrome related to CDH. Fluorescence in situ hybridization (FISH) and multiplex ligation-dependent probe amplification (MLPA) techniques allowed us to further define the deletion interval. Our aim is to identify genetic intervals and, in those, to prioritize genes that might reveal molecular pathways, mutations in any step of which, might contribute to the same phenotype. More important, the elucidation of pathways may ultimately provide clues to treatment strategies.

Congenital diaphragmatic hernia associated with duplication of 11q23-qter

Congenital diaphragmatic hernia (CDH) is a relatively common birth defect with a high mortality. Although little is known about its etiology, there is increasing evidence for a strong genetic contribution. Both numerical and structural chromosomal abnormalities have been described in patients with CDH. Partial trisomy 11q and partial trisomy 22 associated with the common t(11;22) has been reported in several cases of CDH. It has been assumed that the diaphragmatic defect seen in these individuals was primarily due to duplication of material from chromosome 22q11. However, in this report we describe a family with a t(11;12) in which one of two brothers with partial trisomy 11q has a left sided posterolateral CDH. This is the second case of CDH in partial trisomy 11q due to an unbalanced translocation other than t(11;22). Using array-based comparative genomic hybridization and fluorescent in situ hybridization, we mapped the breakpoints in both brothers and their mother who is a balanced translocation carrier. Our results suggest that duplication of one or more genes on a approximately 19 Mb region of 11q23.3-qter predisposes to the development of CDH. These effects may be the primary cause of CDH in individuals t(11;22) or may be additive to effects from the duplication of chromosome 22 material. We also conclude that the partial trisomy 11q syndrome has a variable phenotype and that CDH should be added to the spectrum of anomalies that can be present in this syndrome.

Alternatively spliced Robo2 isoforms in zebrafish and rat

Robo2, a member of the robo gene family, functions as a repulsive axon guidance receptor as well as a regulator of cell migration and tissue morphogenesis in different taxa. In this study, a novel isoform of the zebrafish robo2 (robo2_tv2), which included an otherwise alternatively spliced exon (CAE), has been characterized. Robo2_tv2 is expressed differentially in most non-neuronal tissues of adult zebrafish whereas robo2_tv1 expression to a great extent is restricted to the brain and eye. In zebrafish, robo2_tv2 exhibits a very-low-level basal expression starting from 1 day post fertilization until the mid-larval stages, at which time its expression increases dramatically and could be detected throughout adulthood. Our findings demonstrate that the amino acid sequence coded by CAE of the robo2 gene is highly conserved between zebrafish and mammals, and also contains conserved motifs shared with robo1 and robo4 but not with robo3. Furthermore, we provide an account of differential transcription of the CAE homolog in various tissues of the adult rat. These results suggest that the alternatively spliced robo2 isoforms may exhibit tissue specificity.

Early postnatal exposure to allergen and ozone leads to hyperinnervation of the pulmonary epithelium

Airway injury in infant monkeys exposed to ozone and/or house dust mite allergen (HDMA) is associated with a loss of epithelial innervation. In this study, we evaluated for persistence/recovery of the altered epithelial innervation. Thirty-day-old rhesus monkeys were exposed to repeated episodes of HDMA and/or ozone from 1 to 6 months of age and subsequently allowed to recover for 6 months in the absence of further ozone exposure and/or minimal HDMA challenge (sufficient to maintain allergen sensitization). At 1 year of age, nerve density in intrapulmonary airways was immunohistochemically evaluated using antibodies directed against protein gene product 9.5. Hyperinnervation and irregular epithelial nerve distribution was observed in both HDMA- and ozone-exposed groups; most prominent alterations were observed in animals exposed to HDMA plus ozone. Therefore, while adaptive mechanisms exist that re-establish epithelial innervation following cessation or diminution of exposure to HDMA and/or ozone, the recovery is associated with persistent proliferative mechanisms that result in hyperinnervation of the airways.

Netrin-1 and slit-2 regulate and direct neurite growth of ventral midbrain dopaminergic neurons

We investigated the roles of netrin-1 and slit-2 in regulation and navigation of dopamine (DA) axon growth using an explant culture preparation of embryonic ventral midbrain (embryonic day 14) and a co-culture system. We found that netrin-1 protein significantly enhanced DA axonal outgrowth and promoted DA axonal outgrowth in a co-culture system of netrin-1 expressing cells. Such effects were mediated by the receptor DCC as demonstrated by antibody perturbation of the DCC receptor. In contrast, slit-2 inhibited DA neuron extensions and repelled DA neurite growth. These slit-2 activities required robo receptors since the reduced neurite extension was abolished by addition of excess robo receptors. In this system, netrin-1 stimulated and slit-2 opposed DA neurite growth. Such regulation may be important for DA axonal maintenance, regeneration, and phenotypic target recognition.

The transcription factor gene Nfib is essential for both lung maturation and brain development

The phylogenetically conserved nuclear factor I (NFI) gene family encodes site-specific transcription factors essential for the development of a number of organ systems. We showed previously that Nfia-deficient mice exhibit agenesis of the corpus callosum and other forebrain defects, whereas Nfic-deficient mice have agenesis of molar tooth roots and severe incisor defects. Here we show that Nfib-deficient mice possess unique defects in lung maturation and exhibit callosal agenesis and forebrain defects that are similar to, but more severe than, those seen in Nfia-deficient animals. In addition, loss of Nfib results in defects in basilar pons formation and hippocampus development that are not seen in Nfia-deficient mice. Heterozygous Nfib-deficient animals also exhibit callosal agenesis and delayed lung maturation, indicating haploinsufficiency at the Nfib locus. The similarity in brain defects in Nfia- and Nfib-deficient animals suggests that these two genes may cooperate in late fetal forebrain development, while Nfib is essential for late fetal lung maturation and development of the pons.

The Versatile Roles of “Axon Guidance” Cues in Tissue Morphogenesis

The Netrin, Slit, Semaphorin, and Ephrin families of secreted proteins were originally characterized in the nervous system as guidance cues for axons; however, recent studies demonstrate that many members of these families contribute to the development of a variety of organs. Here, the current knowledge of their roles is discussed with a focus on four tissues: lung, mammary, cardiovascular, and kidney. While many studies indicate a role for "axon guidance" cues in regulating cell-cell and cell-extracellular matrix (ECM) interactions during organogenesis, there is accumulating evidence that they also contribute to tissue development by regulating the transcription and translation of genes encoding key morphogenetic factors.

Novel role for Netrins in regulating epithelial behavior during lung branching morphogenesis

The development of many organs, including the lung, depends upon a process known as branching morphogenesis, in which a simple epithelial bud gives rise to a complex tree-like system of tubes specialized for the transport of gas or fluids. Previous studies on lung development have highlighted a role for fibroblast growth factors (FGFs), made by the mesodermal cells, in promoting the proliferation, budding, and chemotaxis of the epithelial endoderm. Here, by using a three-dimensional culture system, we provide evidence for a novel role for Netrins, best known as axonal guidance molecules, in modulating the morphogenetic response of lung endoderm to exogenous FGFs. This effect involves inhibition of localized changes in cell shape and phosphorylation of the intracellular mitogen-activated protein kinase(s) (ERK1/2, for extracellular signal-regulated kinase-1 and -2), elicited by exogenous FGFs. The temporal and spatial expression of netrin 1, netrin 4, and Unc5b genes and the localization of Netrin-4 protein in vivo suggest a model in which Netrins in the basal lamina locally modulate and fine-tune the outgrowth and shape of emergent epithelial buds.

Two divergent slit1 genes in zebrafish

Members of the Slit family regulate axon guidance and cell migration. To date, three vertebrate slit1 genes have been identified in mammals and orthologs of two, slit2 and slit3, have been identified in zebrafish. Here, we describe the cloning of full-length cDNAs for two zebrafish slit orthologs, slit1a and slit1b. Both predicted proteins contain the conserved motifs that characterize other vertebrate Slits. slit1a and slit1b are both expressed in the midline, hypochord, telencephalon, and hindbrain. Apart from these shared expression domains, however, their expression patterns largely differ. Whereas slit1a is expressed broadly in the central nervous system (CNS) and in the somites, pectoral fin buds, tail bud, and caudal fin folds, slit1b is expressed in the olfactory system throughout embryonic and larval development, and in the retina during larval stages. Their expression patterns, particularly that of slit1a, suggest that Slit proteins may have roles in tissue morphogenesis in addition to their established roles in axon guidance and cell migration.

Slit and robo expression in the developing mouse lung

Mammalian lung development is mediated through complex interactions between foregut endoderm and surrounding mesenchyme. As airway branching progresses, the mesenchyme undergoes dramatic remodeling and differentiation. Little is understood about the mechanisms that direct mesenchymal organization during lung development. A screen for candidate genes mediating this process identified Slit, a ligand for the Roundabout (Robo) receptor previously associated with guidance of axonal projections during central nervous system development. Here, we demonstrate by in situ hybridization that two Slit genes (Slit-2 and Slit-3) and two Robo genes (Robo-1 and Robo-2) are expressed in fetal lung mesenchyme. Slit-2 and Robo-1 expression is present throughout mesenchyme at midgestation and is not detectable by newborn day 1. Slit-3 and Robo-2 expression is restricted to specific, complementary subsets of mesenchyme. Robo-2 is expressed in mesenchymal cells immediately adjacent to large airways, whereas Slit-3 expression predominates in mesenchyme remote from airway epithelium. The temporal and spatial distribution of Slit and Robo mRNAs indicate that these genes may direct the functional organization and differentiation of fetal lung mesenchyme.