The WAGR syndrome gene PRRG4 is a functional homologue of the commissureless axon guidance gene

PRRG4 regulates mitochondrial function and promotes migratory behaviors of breast cancer cells through the Src-STAT3-POLG axis

BACKGROUND

Breast cancer is the leading cause of cancer death for women worldwide. Most of the breast cancer death are due to disease recurrence and metastasis. Increasingly accumulating evidence indicates that mitochondria play key roles in cancer progression and metastasis. Our recent study revealed that transmembrane protein PRRG4 promotes the metastasis of breast cancer. However, it is not clear whether PRRG4 can affect the migration and invasion of breast cancer cells through regulating mitochondria function.

METHODS

RNA-seq analyses were performed on breast cancer cells expressing control and PRRG4 shRNAs. Quantitative PCR analysis and measurements of mitochondrial ATP content and oxygen consumption were carried out to explore the roles of PRRG4 in regulating mitochondrial function. Luciferase reporter plasmids containing different lengths of promoter fragments were constructed. Luciferase activities in breast cancer cells transiently transfected with these reporter plasmids were analyzed to examine the effects of PRRG4 overexpression on promoter activity. Transwell assays were performed to determine the effects of PRRG4-regulated pathway on migratory behaviors of breast cancer cells.

RESULTS

Analysis of the RNA-seq data revealed that PRRG4 knockdown decreased the transcript levels of all the mitochondrial protein-encoding genes. Subsequently, studies with PRRG4 knockdown and overexpression showed that PRRG4 expression increased mitochondrial DNA (mtDNA) content. Mechanistically, PRRG4 via Src activated STAT3 in breast cancer cells. Activated STAT3 in turn promoted the transcription of mtDNA polymerase POLG through a STAT3 DNA binding site present in the POLG promoter region, and increased mtDNA content as well as mitochondrial ATP production and oxygen consumption. In addition, PRRG4-mediated activation of STAT3 also enhanced filopodia formation, migration, and invasion of breast cancer cells. Moreover, PRRG4 elevated migratory behaviors and mitochondrial function of breast cancer cells through POLG.

CONCLUSION

Our results indicate that PRRG4 via the Src-STAT3-POLG axis enhances mitochondrial function and promotes migratory behaviors of breast cancer cells.

Comprehensive Analysis of a Competing Endogenous RNA Co-Expression Network in Chronic Obstructive Pulmonary Disease

Purpose

Chronic obstructive pulmonary disease (COPD) is the main cause of mortality world widely. Non-coding RNAs (lncRNAs) and associated competitive endogenous RNAs (ceRNAs) networks were recently proved to lead to mRNA gene expression downregulation but were still unclear in COPD. This study aims to investigate and elucidate the mechanisms underlying the involvement of ceRNA co-expression networks in COPD pathogenesis.

Methods

Obtained expression signature of data from the Gene Expression Omnibus database and compared the differentially expression of mRNAs and miRNAs between COPD patients and healthy smokers. Predicted the miRNA-lncRNA and miRNA-mRNA interaction using online library and employed CIBERSORT to measure the proportions of the 22 immune cells in the COPD and control groups.

Results

Established a ceRNA-network comprising 11 lncRNAs, 5 miRNAs, and 16 mRNAs. Using the weighted correlation network analysis method, we identified hub genes and hub miRNAs and obtained one core sub-network, XIST, FGD5-AS1, KCNQ1OT1, HOXA11-AS, LINC00667, H19, PRKCQ-AS1, NUTM2A-AS1/has-mir-454-3p/ZNF678, PRRG4. COPD patients had different proportions of immune cells than controls, and these variations were associated with the magnitude of pulmonary function parameters.

Conclusion

The ceRNA-network, particularly the core sub-network, may be a putative goal for COPD, in which specific immune cells were involved.

Single-cell transcriptomics illuminates regulatory steps driving anterior-posterior patterning of Drosophila embryonic mesoderm

Single-cell technologies promise to uncover how transcriptional programs orchestrate complex processes during embryogenesis. Here, we apply a combination of single-cell technology and genetic analysis to investigate the dynamic transcriptional changes associated with Drosophila embryo morphogenesis at gastrulation. Our dataset encompassing the blastoderm-to-gastrula transition provides a comprehensive single-cell map of gene expression across cell lineages validated by genetic analysis. Subclustering and trajectory analyses revealed a surprising stepwise progression in patterning to transition zygotic gene expression and specify germ layers as well as uncovered an early role for ecdysone signaling in epithelial-to-mesenchymal transition in the mesoderm. We also show multipotent progenitors arise prior to gastrulation by analyzing the transcription trajectory of caudal mesoderm cells, including a derivative that ultimately incorporates into visceral muscles of the midgut and hindgut. This study provides a rich resource of gastrulation and elucidates spatially regulated temporal transitions of transcription states during the process.

Commissureless acts as a substrate adapter in a conserved Nedd4 E3 ubiquitin ligase pathway to promote axon growth across the midline

In both vertebrates and invertebrates, commissural neurons prevent premature responsiveness to the midline repellant Slit by downregulating surface levels of its receptor Roundabout1 (Robo1). In Drosophila, Commissureless (Comm) plays a critical role in this process; however, there is conflicting data on the underlying molecular mechanism. Here, we demonstrate that the conserved PY motifs in the cytoplasmic domain of Comm are required allow the ubiquitination and lysosomal degradation of Robo1. Disruption of these motifs prevents Comm from localizing to Lamp1 positive late endosomes and to promote axon growth across the midline in vivo. In addition, we conclusively demonstrate a role for Nedd4 in midline crossing. Genetic analysis shows that nedd4 mutations result in midline crossing defects in the Drosophila embryonic nerve cord, which can be rescued by introduction of exogenous Nedd4. Biochemical evidence shows that Nedd4 incorporates into a three-member complex with Comm and Robo in a PY motif-dependent manner. Finally, we present genetic evidence that Nedd4 acts with Comm in the embryonic nerve cord to downregulate Robo1 levels. Taken together, these findings demonstrate that Comm promotes midline crossing in the nerve cord by facilitating Robo ubiquitination by Nedd4, ultimately leading to its degradation.

Intracellular Trafficking Mechanisms that Regulate Repulsive Axon Guidance

Friedrich Bonhoeffer made seminal contributions to the study of axon guidance in the developing nervous system. His discoveries of key cellular and molecular mechanisms that dictate wiring specificity laid the foundation for countless investigators who have followed in his footsteps. Perhaps his most significant contribution was the cloning and characterization of members of the conserved ephrin family of repulsive axon guidance cues. In this review, we highlight the major contributions that Bonhoeffer and his colleagues made to the field of axon guidance, and discuss ongoing investigations into the diverse array of mechanisms that ensure that axon repulsion is precisely regulated to allow for accurate pathfinding. Specifically, we focus our discussion on the post-translational regulation of two major families of repulsive axon guidance factors: ephrin ligands and their Eph receptors, and slit ligands and their Roundabout (Robo) receptors. We will give special emphasis to the ways in which regulated endocytic trafficking events allow navigating axons to adjust their responses to repellant signals and how these trafficking events are intimately related to receptor signaling. By highlighting parallels and differences between the regulation of these two important repulsive axon guidance pathways, we hope to identify key outstanding questions for future investigation.

Different temporal requirements for tartan and wingless in the formation of contractile interfaces at compartmental boundaries

Compartmental boundaries physically separate developing tissues into distinct regions, which is fundamental for the organisation of the body plan in both insects and vertebrates. In many examples, this physical segregation is caused by a regulated increase in contractility of the actomyosin cortex at boundary cell-cell interfaces, a property important in developmental morphogenesis beyond compartmental boundary formation. We performed an unbiased screening approach to identify cell surface receptors required for actomyosin enrichment and polarisation at parasegmental boundaries (PSBs) in early Drosophila embryos, from the start of germband extension at gastrulation and throughout the germband extended stages (stages 6 to 11). First, we find that Tartan is required during germband extension for actomyosin enrichment at PSBs, confirming an earlier report. Next, by following in real time the dynamics of loss of boundary straightness in tartan mutant embryos compared with wild-type and ftz mutant embryos, we show that Tartan is required during germband extension but not beyond. We identify candidate genes that could take over from Tartan at PSBs and confirm that at germband extended stages, actomyosin enrichment at PSBs requires Wingless signalling.

Novel dominant and recessive variants in human ROBO1 cause distinct neurodevelopmental defects through different mechanisms

The Roundabout (Robo) receptors, located on growth cones of neurons, induce axon repulsion in response to the extracellular ligand Slit. The Robo family of proteins controls midline crossing of commissural neurons during development in flies. Mono- and bi-allelic variants in human ROBO1 (HGNC: 10249) have been associated with incomplete penetrance and variable expressivity for a breath of phenotypes, including neurodevelopmental defects such as strabismus, pituitary defects, intellectual impairment, as well as defects in heart and kidney. Here, we report two novel ROBO1 variants associated with very distinct phenotypes. A homozygous missense p.S1522L variant in three affected siblings with nystagmus; and a monoallelic de novo p.D422G variant in a proband who presented with early-onset epileptic encephalopathy. We modeled these variants in Drosophila and first generated a null allele by inserting a CRIMIC T2A-GAL4 in an intron. Flies that lack robo1 exhibit reduced viability but have very severe midline crossing defects in the central nervous system. The fly wild-type cDNA driven by T2A-Gal4 partially rescues both defects. Overexpression of the human reference ROBO1 with T2A-GAL4 is toxic and reduces viability, whereas the recessive p.S1522L variant is less toxic, suggesting that it is a partial loss-of-function allele. In contrast, the dominant variant in fly robo1 (p.D413G) affects protein localization, impairs axonal guidance activity and induces mild phototransduction defects, suggesting that it is a neomorphic allele. In summary, our studies expand the phenotypic spectrum associated with ROBO1 variant alleles.

The Largest Germline Heterozygous Deletion Encompassing Potocki-Shaffer and WAGR Syndromes Loci to Date: A Case Report

Potocki-Schaffer syndrome includes multiple exostoses, parietal foramina, and variable developmental delay/intellectual disability. It is associated with a heterozygous deletion of the 11p12p11.2 region. In some cases, the deletion extends to the WAGR locus (11p13p12). We describe here a 9-month-old girl harboring the largest germline heterozygous deletion characterized so far. Oligohydramnios and parietal foramina were noticed during pregnancy. No patient has been diagnosed before with concomitance of these two syndromes during the prenatal period. Cytogenetic diagnosis was anticipated on basis of clinical and radiological signs. Postnatal conventional karyotype confirmed an interstitial 11p deletion: 46,XX,del(11)(p11.2p15.1). Array-comparative genomic hybridization characterized a 29.6 Mb deletion. Our case illustrates the interest of high-resolution genomic approaches to correlate adequately clinical phenotypes with specific genes in suspected contiguous gene deletion syndromes.

Conserved and divergent aspects of Robo receptor signaling and regulation between Drosophila Robo1 and C. elegans SAX-3

The evolutionarily conserved Roundabout (Robo) family of axon guidance receptors control midline crossing of axons in response to the midline repellant ligand Slit in bilaterian animals including insects, nematodes, and vertebrates. Despite this strong evolutionary conservation, it is unclear whether the signaling mechanism(s) downstream of Robo receptors are similarly conserved. To directly compare midline repulsive signaling in Robo family members from different species, here we use a transgenic approach to express the Robo family receptor SAX-3 from the nematode Caenorhabditis elegans in neurons of the fruit fly, Drosophila melanogaster. We examine SAX-3's ability to repel Drosophila axons from the Slit-expressing midline in gain of function assays, and test SAX-3's ability to substitute for Drosophila Robo1 during fly embryonic development in genetic rescue experiments. We show that C. elegans SAX-3 is properly translated and localized to neuronal axons when expressed in the Drosophila embryonic CNS, and that SAX-3 can signal midline repulsion in Drosophila embryonic neurons, although not as efficiently as Drosophila Robo1. Using a series of Robo1/SAX-3 chimeras, we show that the SAX-3 cytoplasmic domain can signal midline repulsion to the same extent as Robo1 when combined with the Robo1 ectodomain. We show that SAX-3 is not subject to endosomal sorting by the negative regulator Commissureless (Comm) in Drosophila neurons in vivo, and that peri-membrane and ectodomain sequences are both required for Comm sorting of Drosophila Robo1.

Calcineurin-dependent regulation of endocytosis by a plasma membrane ubiquitin ligase adaptor, Rcr1

Rsp5, the Nedd4 family member in yeast, is an E3 ubiquitin ligase involved in numerous cellular processes, many of which require Rsp5 to interact with PY-motif containing adaptor proteins. Here, we show that two paralogous transmembrane Rsp5 adaptors, Rcr1 and Rcr2, are sorted to distinct cellular locations: Rcr1 is a plasma membrane (PM) protein, whereas Rcr2 is sorted to the vacuole. Rcr2 is delivered to the vacuole using ubiquitin as a sorting signal. Rcr1 is delivered to the PM by the exomer complex using a newly uncovered PM sorting motif. Further, we show that Rcr1, but not Rcr2, is up-regulated via the calcineurin/Crz1 signaling pathway. Upon exogenous calcium treatment, Rcr1 ubiquitinates and down-regulates the chitin synthase Chs3. We propose that the PM-anchored Rsp5/Rcr1 ubiquitin ligase-adaptor complex can provide an acute response to degrade unwanted proteins under stress conditions, thereby maintaining cell integrity.

Circular RNA hsa_circ_0000700 promotes cell proliferation and migration in Esophageal Squamous Cell Carcinoma by sponging miR-1229

Accumulating evidence has demonstrated that circular RNAs (circRNAs) are involved in the pathogenesis of cancer, including that of esophageal squamous cell carcinoma (ESCC). The current study aimed to investigate the role of hsa_circ_0000700 in ESCC. hsa_circ_0000700, miR-1229, and related functional gene expression was measured by RT-qPCR. To characterize the functions of hsa_circ_0000700 and miR-1229, ESCC cells were infected with hsa_circ_0000700-specific siRNA, miR-1229 mimics, and an inhibitor alone or in combination. Cell Counting Kit-8 (CCK8), colony formation, EdU, flow cytometry, and Transwell assays were employed to evaluate cell proliferation, apoptosis, and migration. Luciferase reporter and RNA immunoprecipitation assays were used to confirm the targeting relationship between hsa_circ_0000700 and miR-1229. Finally, a competing endogenous RNAs (ceRNA) network was built for hsa_circ_0000700, and miR-1229 targets were analyzed by bioinformatics. circ_0000700 expression was significantly upregulated in ESCC cell lines. Actinomycin D and RNase R treatment confirmed that circ_0000700 was more stable than its linear CDH9 mRNA form. Moreover, a cytoplasmic and nuclear fractionation assay suggested that circ_0000700 was mainly distributed in the cytoplasm of ECA-109 and TE-1 cells. In vitro, the proliferative and migratory capacities of ECA-109 and TE-1 cells were inhibited by knocking down circ_0000700 expression. Additionally, miR-1229 silencing reversed the circ_0000700-specific siRNA-induced attenuation of malignant phenotypes. Mechanistically, circ_0000700 was identified as a sponge of miR-1229 and could activate PRRG4, REEP5, and PSMB5 indirectly to promote ESCC progression. In summary, our results suggest that hsa_circ_0000700 functions as an oncogenic factor by sponging miR-1229 in ESCC.

Adaptors as the regulators of HECT ubiquitin ligases

The HECT (homologous to E6AP C-terminus) ubiquitin ligases (E3s) are a small family of highly conserved enzymes involved in diverse cellular functions and pathological conditions. Characterised by a C-terminal HECT domain that accepts ubiquitin from E2 ubiquitin conjugating enzymes, these E3s regulate key signalling pathways. The activity and functional regulation of HECT E3s are controlled by several factors including post-translational modifications, inter- and intramolecular interactions and binding of co-activators and adaptor proteins. In this review, we focus on the regulation of HECT E3s by accessory proteins or adaptors and discuss various ways by which adaptors mediate their regulatory roles to affect physiological outcomes. We discuss common features that are conserved from yeast to mammals, regardless of the type of E3s as well as shed light on recent discoveries explaining some existing enigmas in the field.

Results From the WAGR Syndrome Patient Registry: Characterization of WAGR Spectrum and Recommendations for Care Management

WAGR syndrome is a rare genetic disorder characterized by Wilms tumor, Aniridia, Genitourinary anomalies, and Range of developmental delays. In addition to the classic features, patients affected by WAGR syndrome can develop obesity and kidney failure, and a wide variety of non-classical manifestations have also been described. This suggests that a broader phenotypic spectrum beyond the classic syndrome exists and here we demonstrate that spectrum using data from the WAGR Syndrome Patient Registry. In the present study, we collected information from 91 individuals enrolled in the registry to explore self-reported health issues in this patient population. A wide variety of common clinical issues not classically associated with the disorder were found, prompting the redefinition from WAGR syndrome to WAGR spectrum disorder to incorporate the phenotypic variations that occur. A comprehensive care management approach is needed to address the wide range of clinical issues and we propose a care model for patients affected by WAGR spectrum disorder. Further research is needed to solidify the breath of the phenotype and confirm the observations in this study to advance individualized patient care in this population.

Commissural axon guidance in the developing spinal cord: from Cajal to the present day

During neuronal development, the formation of neural circuits requires developing axons to traverse a diverse cellular and molecular environment to establish synaptic contacts with the appropriate postsynaptic partners. Essential to this process is the ability of developing axons to navigate guidance molecules presented by specialized populations of cells. These cells partition the distance traveled by growing axons into shorter intervals by serving as intermediate targets, orchestrating the arrival and departure of axons by providing attractive and repulsive guidance cues. The floor plate in the central nervous system (CNS) is a critical intermediate target during neuronal development, required for the extension of commissural axons across the ventral midline. In this review, we begin by giving a historical overview of the ventral commissure and the evolutionary purpose of decussation. We then review the axon guidance studies that have revealed a diverse assortment of midline guidance cues, as well as genetic and molecular regulatory mechanisms required for coordinating the commissural axon response to these cues. Finally, we examine the contribution of dysfunctional axon guidance to neurological diseases.

Temporal regulation of axonal repulsion by alternative splicing of a conserved microexon in mammalian Robo1 and Robo2

Proper connectivity of the nervous system requires temporal and spatial control of axon guidance signaling. As commissural axons navigate across the CNS midline, ROBO-mediated repulsion has traditionally been thought to be repressed before crossing, and then to become upregulated after crossing. The regulation of the ROBO receptors involves multiple mechanisms that control protein expression, trafficking, and activity. Here, we report that mammalian ROBO1 and ROBO2 are not uniformly inhibited precrossing and are instead subject to additional temporal control via alternative splicing at a conserved microexon. The NOVA splicing factors regulate the developmental expression of ROBO1 and ROBO2 variants with small sequence differences and distinct guidance activities. As a result, ROBO-mediated axonal repulsion is activated early in development to prevent premature crossing and becomes inhibited later to allow crossing. Postcrossing, the ROBO1 and ROBO2 isoforms are disinhibited to prevent midline reentry and to guide postcrossing commissural axons to distinct mediolateral positions.

The Effect of Genetic Variation on the Placental Transcriptome in Humans

The knowledge of genetic variants shaping human placental transcriptome is limited and they are not cataloged in the Genotype-Tissue Expression project. So far, only one whole genome analysis of placental expression quantitative trait loci (eQTLs) has been published by Peng et al. (2017) with no external independent validation. We report the second study on the landscape of placental eQTLs. The study aimed to generate a high-confidence list of placental cis-eQTLs and to investigate their potential functional implications. Analysis of cis-eQTLs (±100 kbp from the gene) utilized 40 placental RNA sequencing and respective whole genome genotyping datasets. The identified 199 placental cis-eSNPs represented 88 independent eQTL signals (FDR < 5%). The most significant placental eQTLs (FDR < 10-5) modulated the expression of ribosomal protein RPL9, transcription factor ZSCAN9 and aminopeptidase ERAP2. The analysis confirmed 50 eSNP-eGenes pairs reported by Peng et al. (2017) and thus, can be claimed as robust placental eQTL signals. The study identified also 13 novel placental eGenes. Among these, ZSCAN9 is modulated by several eSNPs (experimentally validated: rs1150707) that have been also shown to affect the methylation level of genes variably escaping X-chromosomal inactivation. The identified 63 placental eGenes exhibited mostly mixed or ubiquitous expression. Functional enrichment analysis highlighted 35 Gene Ontology categories with the top ranking pathways "ruffle membrane" (FDR = 1.81 × 10-2) contributing to the formation of motile cell surface and "ATPase activity, coupled" (FDR = 2.88 × 10-2), critical for the membrane transport. Placental eGenes were also significantly enriched in pathways implicated in development, signaling and immune function. However, this study was not able to confirm a significant overrepresentation of genome-wide association studies top hits among the placental eSNP and eGenes, reported by Peng et al. (2017). The identified eSNPs were further analyzed in association with newborn and pregnancy traits. In the discovery step, a suggestive association was detected between the eQTL of ALPG (rs11678251) and reduced placental, newborn's and infant's weight. Meta-analysis across REPROMETA, HAPPY PREGNANCY, ALSPAC cohorts (n = 6830) did not replicate these findings. In summary, the study emphasizes the role of genetic variation in driving the transcriptome profile of the human placenta and the importance to explore further its functional implications.

Transcriptome and Proteome Profiling of Neural Induced Pluripotent Stem Cells from Individuals with Down Syndrome Disclose Dynamic Dysregulations of Key Pathways and Cellular Functions

Down syndrome (DS) or trisomy 21 (T21) is a leading genetic cause of intellectual disability. To gain insights into dynamics of molecular perturbations during neurogenesis in DS, we established a model using induced pluripotent stem cells (iPSC) with transcriptome profiles comparable to that of normal fetal brain development. When applied on iPSCs with T21, transcriptome and proteome signatures at two stages of differentiation revealed strong temporal dynamics of dysregulated genes, proteins and pathways belonging to 11 major functional clusters. DNA replication, synaptic maturation and neuroactive clusters were disturbed at the early differentiation time point accompanied by a skewed transition from the neural progenitor cell stage and reduced cellular growth. With differentiation, growth factor and extracellular matrix, oxidative phosphorylation and glycolysis emerged as major perturbed clusters. Furthermore, we identified a marked dysregulation of a set of genes encoded by chromosome 21 including an early upregulation of the hub gene APP, supporting its role for disturbed neurogenesis, and the transcription factors OLIG1, OLIG2 and RUNX1, consistent with deficient myelination and neuronal differentiation. Taken together, our findings highlight novel sequential and differentiation-dependent dynamics of disturbed functions, pathways and elements in T21 neurogenesis, providing further insights into developmental abnormalities of the DS brain.

Ndfip Proteins Target Robo Receptors for Degradation and Allow Commissural Axons to Cross the Midline in the Developing Spinal Cord

Commissural axons initially respond to attractive signals at the midline, but once they cross, they become sensitive to repulsive cues. This switch prevents axons from re-entering the midline. In insects and mammals, negative regulation of Roundabout (Robo) receptors prevents premature response to the midline repellant Slit. In Drosophila, the endosomal protein Commissureless (Comm) prevents Robo1 surface expression before midline crossing by diverting Robo1 into late endosomes. Notably, Comm is not conserved in vertebrates. We identified two Nedd-4-interacting proteins, Ndfip1 and Ndfip2, that act analogously to Comm to localize Robo1 to endosomes. Ndfip proteins recruit Nedd4 E3 ubiquitin ligases to promote Robo1 ubiquitylation and degradation. Ndfip proteins are expressed in commissural axons in the developing spinal cord and removal of Ndfip proteins results in increased Robo1 expression and reduced midline crossing. Our results define a conserved Robo1 intracellular sorting mechanism between flies and mammals to avoid premature responsiveness to Slit.

A crucial role for Arf6 in the response of commissural axons to Slit

A switch in the response of commissural axons to the repellent Slit is crucial for ensuring that they cross the ventral midline only once. However, the underlying mechanisms remain to be elucidated. We have found that both endocytosis and recycling of Robo1 receptor are crucial for modulating Slit sensitivity in vertebrate commissural axons. Robo1 endocytosis and its recycling back to the cell surface maintained the stability of axonal Robo1 during Slit stimulation. We identified Arf6 guanosine triphosphatase and its activators, cytohesins, as previously unknown components in Slit-Robo1 signalling in vertebrate commissural neurons. Slit-Robo1 signalling activated Arf6. The Arf6-deficient mice exhibited marked defects in commissural axon midline crossing. Our data showed that a Robo1 endocytosis-triggered and Arf6-mediated positive-feedback strengthens the Slit response in commissural axons upon their midline crossing. Furthermore, the cytohesin-Arf6 pathways modulated this self-enhancement of the Slit response before and after midline crossing, resulting in a switch that reinforced robust regulation of axon midline crossing. Our study provides insights into endocytic trafficking-mediated mechanisms for spatiotemporally controlled axonal responses and uncovers new players in the midline switch in Slit responsiveness of commissural axons.

Structure and Function of Roundabout Receptors

The creation of complex neuronal networks relies on ligand-receptor interactions that mediate attraction or repulsion towards specific targets. Roundabouts comprise a family of single-pass transmembrane receptors facilitating this process upon interaction with the soluble extracellular ligand Slit protein family emanating from the midline. Due to the complexity and flexible nature of Robo receptors , their overall structure has remained elusive until now. Recent structural studies of the Robo 1 and Robo 2 ectodomains have provided the basis for a better understanding of their signalling mechanism. These structures reveal how Robo receptors adopt an auto-inhibited conformation on the cell surface that can be further stabilised by cis and/or trans oligmerisation arrays. Upon Slit -N binding Robo receptors must undergo a conformational change for Ig4 mediated dimerisation and signaling, probably via endocytosis. Furthermore, it's become clear that Robo receptors do not only act alone, but as large and more complex cell surface receptor assemblies to manifest directional and growth effects in a concerted fashion. These context dependent assemblies provide a mechanism to fine tune attractive and repulsive signals in a combinatorial manner required during neuronal development. While a mechanistic understanding of Slit mediated Robo signaling has advanced significantly further structural studies on larger assemblies are required for the design of new experiments to elucidate their role in cell surface receptor complexes. These will be necessary to understand the role of Slit -Robo signaling in neurogenesis, angiogenesis, organ development and cancer progression. In this chapter, we provide a review of the current knowledge in the field with a particular focus on the Roundabout receptor family.

ADP-ribosylation factor-like 4A interacts with Robo1 to promote cell migration by regulating Cdc42 activation

Cell migration is a highly regulated event that is initiated by cell membrane protrusion and actin reorganization. Robo1, a single-pass transmembrane receptor, is crucial for neuronal guidance and cell migration. ADP-ribosylation factor (Arf)-like 4A (Arl4A), an Arf small GTPase, functions in cell morphology, cell migration, and actin cytoskeleton remodeling; however, the molecular mechanisms of Arl4A in cell migration are unclear. Here, we report that the binding of Arl4A to Robo1 modulates cell migration by promoting Cdc42 activation. We found that Arl4A interacts with Robo1 in a GTP-dependent manner and that the Robo1 amino acid residues 1394-1398 are required for this interaction. The Arl4A-Robo1 interaction is essential for Arl4A-induced cell migration and Cdc42 activation but not for the plasma membrane localization of Robo1. In addition, we show that the binding of Arl4A to Robo1 decreases the association of Robo1 with the Cdc42 GTPase-activating protein srGAP1. Furthermore, Slit2/Robo1 binding down-regulates the Arl4A-Robo1 interaction in vivo, thus attenuating Cdc42-mediated cell migration. Therefore, our study reveals a novel mechanism by which Arl4A participates in Slit2/Robo1 signaling to modulate cell motility by regulating Cdc42 activity.

Long Noncoding RNA PRRG4-4 Promotes Viability, Cell Cycle, Migration, and Invasion in Lung Cancer Cells

There is a perception that long noncoding RNA (lncRNA) has relationship with carcinogenesis. Many studies have previously identified and validated that the section of chromosome 11p13 is associated with high incidence of tumor. In this study, we investigated a new lncRNA, named lncPRRG4-4, mapped to 11p13 and suspected that lncPRRG4-4 was a potential lung cancer-related gene. To explore its role in carcinogenesis, we first demonstrated that lncPRRG4-4 was upregulated in lung cancer tissues compared with adjacent nontumor tissues and functioned as an oncogene in lung cancer cells. The lncPRRG4-4 was significantly upregulated in lung cancer tissues compared with adjacent normal counterparts (mean ± standard deviation: 0.12 ± 0.84 vs. 0.05 ± 0.22; p < 0.001). Patients with metastasis exhibited high levels of lncPRRG4-4 expression than those without metastasis in both the southern samples (p = 0.045) and eastern samples (p = 0.030), total samples (p = 0.004). In addition, downregulation of lncPRRG4-4 expression inhibited lung cancer proliferation, viability, migration, and invasion ability, arrested cell cycle, facilitated apoptosis, and vice versa. Taken together, these observations suggested that the lncPRRG4-4 functions as an oncogene in lung cancer cells.

Clinical, molecular genetics and therapeutic aspects of syndromic obesity

Obesity has become a major health problem worldwide. To date, more than 25 different syndromic forms of obesity are known in which one (monogenic) or multiple (polygenic) genes are involved. This review gives an overview of these forms and focuses more in detail on 6 syndromes: Prader Willi Syndrome and Prader Willi like phenotype, Bardet Biedl Syndrome, Alström Syndrome, Wilms tumor, Aniridia, Genitourinary malformations and mental Retardation syndrome and 16p11.2 (micro)deletions. Years of research provided plenty of information on the molecular genetics of these disorders and the obesity phenotype leading to a more individualized treatment of the symptoms, however, many questions still remain unanswered. As these obesity syndromes have different signs and symptoms in common, it makes it difficult to accurately diagnose patients which may result in inappropriate treatment of the disease. Therefore, the big challenge for clinicians and scientists is to more clearly differentiate all syndromic forms of obesity to provide conclusive genetic explanations and eventually deliver accurate genetic counseling and treatment. In addition, further delineation of the (functions of the) underlying genes with the use of array- or next-generation sequencing-based technology will be helpful to unravel the mechanisms of energy metabolism in the general population.

Midline axon guidance in the Drosophila embryonic central nervous system

Studies in the fruit fly Drosophila melanogaster have provided many fundamental insights into the genetic regulation of neural development, including the identification and characterization of evolutionarily conserved axon guidance pathways and their roles in important guidance decisions. Due to its highly organized and fast-developing embryonic nervous system, relatively small number of neurons, and molecular and genetic tools for identifying, labeling, and manipulating individual neurons or small neuronal subsets, studies of axon guidance in the Drosophila embryonic CNS have allowed researchers to dissect these genetic mechanisms with a high degree of precision. In this review, we discuss the major axon guidance pathways that regulate midline crossing of axons and the formation and guidance of longitudinal axon tracts, two processes that contribute to the development of the precise three-dimensional structure of the insect nerve cord. We focus particularly on recent insights into the roles and regulation of canonical midline axon guidance pathways, and on additional factors and pathways that have recently been shown to contribute to axon guidance decisions at and near the midline.