Dishevelled, a Wnt signalling component, is involved in mitotic progression in cooperation with Plk1

Meru co-ordinates spindle orientation with cell polarity and cell cycle progression

Correct mitotic spindle alignment is essential for tissue architecture and plays an important role in cell fate specification through asymmetric cell division. Spindle tethering factors such as Drosophila Mud (NuMA in mammals) are recruited to the cell cortex and capture astral microtubules, pulling the spindle in the correct orientation. However, how spindle tethering complexes read the cell polarity axis and how spindle attachment is coupled to mitotic progression remains poorly understood. We explore these questions in Drosophila sensory organ precursors (SOPs), which divide asymmetrically to give rise to epidermal mechanosensory bristles. We show that the scaffold protein Meru, which is enriched at the posterior cortex by the Frizzled/Dishevelled planar cell polarity complex, in turn recruits Mud, linking the spindle tethering and polarity machineries. Furthermore, Cyclin A/Cdk1 associates with Meru at the posterior cortex, promoting the formation of the Mud/Meru/Dsh complex via Meru and Dsh phosphorylation. Thus, Meru couples spindle orientation with cell polarity and provides a cell cycle-dependent cue for spindle tethering.

Genetic Markers of Spina Bifida: Enrichment of Pathogenic Variants and Variants of Uncertain Significance

Introduction

The genetic diversity of the population in India, shaped by its unique history of migrations and varied ethnic landscape, suggests the possibility of genetic profiles distinct from the western populations.

Objective

The objective is to investigate the genetic basis of spina bifida in the Indian cohort through whole-exome sequencing and pathway enrichment.

Methods

The variants of uncertain significance (VUS) of spina bifida were identified through whole-exome sequencing in the study cohort (n = 3). The pathogenic, likely pathogenic, and VUS were analyzed for protein-protein interactions and functional associations with genes implicated in spina bifida using tools such as STRING and KEGG pathways, which were validated through a literature review. The study was focused on the Wnt/planar cell polarity signaling pathway, which is crucial for neural tube closure.

Results

The study-cohort was collectively represented through 40 common VUS, including eight deleterious SNPs related to genes AP3D1, NLRP9, PCDHGA11, PRSS3, MTSS2, ENDOV, C9, and NSD3. These genes were functionally linked to neural development, immune response, and cellular processes critical for neural tube closure. Notably, interactions were observed between four genes (NLGN2, PKD1, PRSS3, and PLK1) and CTNNB1 (Wnt signaling pathway) crucial for embryonic neural tube formation.

Conclusions

This study has identified novel genetic variants and pathways potentially contributing to the etiopathogenesis of spina bifida in the Indian population. Future research with larger cohorts and functional studies is necessary to validate these findings and explore their potential for clinical applications in spina bifida.

Cilia as Wnt signaling organelles

Cilia and Wnt signaling have a complex relationship, wherein Wnt regulates cilia and, conversely, cilia may affect Wnt signaling. Recently, it was shown that Wnt receptors are present in flagella, primary cilia, and multicilia, where they transmit an intraciliary signal that is independent of β-catenin. Intraciliary Wnt signaling promotes ciliogenesis, affecting male fertility, adipogenesis, and mucociliary clearance. Wnt also stimulates the beating of motile cilia, highlighting that these nanomotors, too, are chemosensory. Intraciliary Wnt signaling employs a Wnt-protein phosphatase 1 (PP1) signaling axis, involving the canonical Wnt pathway's inhibition of glycogen synthase kinase 3 (GSK3) to repress PP1 activity. Collectively, these findings support that cilia are Wnt signaling organelles, with implications for ciliopathies and cancer.

A comparative analysis of paxillin and Hic-5 proximity interactomes

Focal adhesions serve as structural and signaling hubs, facilitating bidirectional communication at the cell-extracellular matrix interface. Paxillin and the related Hic-5 (TGFβ1i1) are adaptor/scaffold proteins that recruit numerous structural and regulatory proteins to focal adhesions, where they perform both overlapping and discrete functions. In this study, paxillin and Hic-5 were expressed in U2OS osteosarcoma cells as biotin ligase (BioID2) fusion proteins and used as bait proteins for proximity-dependent biotinylation in order to directly compare their respective interactomes. The fusion proteins localized to both focal adhesions and the centrosome, resulting in biotinylation of components of each of these structures. Biotinylated proteins were purified and analyzed by mass spectrometry. The list of proximity interactors for paxillin and Hic-5 comprised numerous shared core focal adhesion proteins that likely contribute to their similar functions in cell adhesion and migration, as well as proteins unique to paxillin and Hic-5 that have been previously localized to focal adhesions, the centrosome, or the nucleus. Western blotting confirmed biotinylation and enrichment of FAK and vinculin, known interactors of Hic-5 and paxillin, as well as several potentially unique proximity interactors of Hic-5 and paxillin, including septin 7 and ponsin, respectively. Further investigation into the functional relationship between the unique interactors and Hic-5 or paxillin may yield novel insights into their distinct roles in cell migration.

Structural and Functional Insights into Dishevelled-Mediated Wnt Signaling

Dishevelled (DVL) proteins precisely control Wnt signaling pathways with many effectors. While substantial research has advanced our understanding of DVL's role in Wnt pathways, key questions regarding its regulatory mechanisms and interactions remain unresolved. Herein, we present the recent advances and perspectives on how DVL regulates signaling. The experimentally determined conserved domain structures of DVL in conjunction with AlphaFold-predicted structures are used to understand the DVL's role in Wnt signaling regulation. We also summarize the role of DVL in various diseases and provide insights into further directions for research on the DVL-mediated signaling mechanisms. These findings underscore the importance of DVL as a pharmaceutical target or biological marker in diseases, offering exciting potential for future biomedical applications.

Carboxy-terminal polyglutamylation regulates signaling and phase separation of the Dishevelled protein

Polyglutamylation is a reversible posttranslational modification that is catalyzed by enzymes of the tubulin tyrosine ligase-like (TTLL) family. Here, we found that TTLL11 generates a previously unknown type of polyglutamylation that is initiated by the addition of a glutamate residue to the free C-terminal carboxyl group of a substrate protein. TTLL11 efficiently polyglutamylates the Wnt signaling protein Dishevelled 3 (DVL3), thereby changing the interactome of DVL3. Polyglutamylation increases the capacity of DVL3 to get phosphorylated, to undergo phase separation, and to act in the noncanonical Wnt pathway. Both carboxy-terminal polyglutamylation and the resulting reduction in phase separation capacity of DVL3 can be reverted by the deglutamylating enzyme CCP6, demonstrating a causal relationship between TTLL11-mediated polyglutamylation and phase separation. Thus, C-terminal polyglutamylation represents a new type of posttranslational modification, broadening the range of proteins that can be modified by polyglutamylation and providing the first evidence that polyglutamylation can modulate protein phase separation.

Developmental signals control chromosome segregation fidelity during pluripotency and neurogenesis by modulating replicative stress

Human development relies on the correct replication, maintenance and segregation of our genetic blueprints. How these processes are monitored across embryonic lineages, and why genomic mosaicism varies during development remain unknown. Using pluripotent stem cells, we identify that several patterning signals-including WNT, BMP, and FGF-converge into the modulation of DNA replication stress and damage during S-phase, which in turn controls chromosome segregation fidelity in mitosis. We show that the WNT and BMP signals protect from excessive origin firing, DNA damage and chromosome missegregation derived from stalled forks in pluripotency. Cell signalling control of chromosome segregation declines during lineage specification into the three germ layers, but re-emerges in neural progenitors. In particular, we find that the neurogenic factor FGF2 induces DNA replication stress-mediated chromosome missegregation during the onset of neurogenesis, which could provide a rationale for the elevated chromosomal mosaicism of the developing brain. Our results highlight roles for morphogens and cellular identity in genome maintenance that contribute to somatic mosaicism during mammalian development.

The interplay between Wnt signaling pathways and microtubule dynamics

Wnt signaling pathways represent an evolutionarily highly conserved, intricate network of molecular interactions that regulates various aspects of cellular behavior, including embryonic development and tissue homeostasis. Wnt signaling pathways share the β-catenin-dependent (canonical) and the multiple β-catenin-independent (non-canonical) pathways. These pathways collectively orchestrate a wide range of cellular processes through distinct mechanisms of action. Both the β-catenin-dependent and β-catenin-independent pathways are closely intertwined with microtubule dynamics, underscoring the complex crosstalk between Wnt signaling and the cellular cytoskeleton. This interplay involves several mechanisms, including how the components of Wnt signaling can influence the stability, organization, and distribution of microtubules. The modulation of microtubule dynamics by Wnt signaling plays a crucial role in coordinating cellular behaviors and responses to external signals. In this comprehensive review, we discussed the current understanding of how Wnt signaling and microtubule dynamics intersect in various aspects of cellular behavior. This study provides insights into our understanding of these crucial cellular processes.

Investigation of iso-propylchaetominine anticancer activity on apoptosis, cell cycle and Wnt signaling pathway in different cancer models

Dysregulation of the Wnt signaling pathway contributes to the development of many cancer types. Natural compounds produced with biotechnological systems have been the focus of research for being a new drug candidate both with unlimited resources and cost-effective production. In this study, it was aimed to reveal the effects of isopropylchaetominine on cytotoxic, cytostatic, apoptotic and Wnt signaling pathways in brain, pancreatic and prostate cancer. The IC50 values of isopropylchaetominine in U-87 MG, PANC1, PC3 and LNCaP cells were calculated as 91.94 μM, 41.68 μM, 54.54 μM and 7.86 μM in 72nd h, respectively. The metabolite arrests the cell cycle in G0/G1 phase in each cancer cells. Iso-propylchaetominine induced a 4.3-fold and 1.9-fold increase in apoptosis in PC3 and PANC1 cells, respectively. The toxicity of isopropylchaetominine in healthy fibroblast cells was assessed using the annexin V method, and no significant apoptotic activity was observed between the groups treated with the active substance and untreated. In U-87 MG, PANC1, PC3, and LNCaP cells under treatment with isopropylchaetominin, the expression levels of DKK3, TLE1, AES, DKK1, FRZB, DAB2, AXIN1/2, PPARD, SFRP4, APC and SOX17 tumor suppressor genes increased significantly. Decreases in expression of Wnt1, Wnt2, Wnt3, Wnt4, Wnt5, Wnt6, Wnt10, Wnt11, FRZ2, FRZ3, FRZ7, TCF7L1, BCL9, PYGO, CCND2, c-MYC, WISP1 and CTNNB1 oncogenic genes were detected. All these result shows that isopropylchaetominine can present promising new treatment strategy in different cancer types.

WNT5A regulates the proliferation, apoptosis and stemness of human stem Leydig cells via the β-catenin signaling pathway

Stem Leydig cells (SLCs) are essential for maintaining normal spermatogenesis as the significant component of testis microenvironment and gonadal aging. Although progress has been achieved in the regulation of male germ cells in mammals and humans, it remains unknown about the genes and signaling pathways of human SLCs. Here we have demonstrated, for the first time, that WNT5A (Wnt family member 5a) mediates the proliferation, apoptosis, and stemness of human SLCs, namely NGFR+ Leydig cells. We revealed that NGFR+ Leydig cells expressed NGFR, PDGFRA, NES, NR2F2, and THY1, hallmarks for SLCs. RNA-sequencing showed that WNT5A was expressed at a higher level in human SLCs than non-SLCs, while immunohistochemistry and Western blots further illustrated that WNT5A was predominantly expressed in human SLCs. Notably, CCK-8, EdU and Western blots displayed that WNT5A enhanced the proliferation and DNA synthesis and retained stemness of human SLCs, whereas flow cytometry and TUNEL analyses demonstrated that WNT5A inhibited the apoptosis of these cells. WNT5A knockdown caused an increase in LC lineage differentiation of human SLCs and reversed the effect of WNT5A overexpression on fate decisions of human SLCs. In addition, WNT5A silencing  resulted in the decreases in nuclear translocation of β-catenin and expression levels of c-Myc, CD44, and Cyclin D1. Collectively, these results implicate that WNT5A regulates the proliferation, apoptosis and stemness of human SLCs through the activation of the β-catenin signaling pathway. This study thus provides a novel molecular mechanism underlying the fate determinations of human SLCs, and it offers a new insight into the niche regulation of human testis.

Inhibition of WNT signaling by conjugated microRNA nano-carriers: A new therapeutic approach for treating triple-negative breast cancer a perspective review

Triple-Negative Breast Cancer is the most aggressive form and accounts the 15%-25% of all breast cancer. Receptors are absent in triple-negative breast cancer, which makes them unresponsive to the current hormonal therapies. The patients with TNBC are left with the option of cytotoxic chemotherapy. The Wnt pathways are connected to cancer, and when activated, they result in mammary hyperplasia and tumors. The tumor suppressor microRNAs can block tumor cell proliferation, invasion, and migration, lead to cancer cell death, and are also known to down-regulate the WNT signaling. Nanoparticles with microRNA have been seen to be more effective when compared with their single release. In this review, we have tried to understand how Wnt signaling plays a crucial role in TNBC, EMT, metastasis, anti-drug resistance, and regulation of Wnt by microRNA. The role of nano-carriers in delivering micro-RNA. The clinical biomarkers, including the present state-of-the-art, involve novel pathways of Wnt.

Wnt signalling in cell division: from mechanisms to tissue engineering

Wnt signalling is an essential player in tissue formation, notably in the regulation of stem cell function. Wnt signalling is best known for its roles in G1/S progression. However, a complex Wnt programme that also mediates mitotic progression and asymmetric cell division (ACD) is emerging. Recent developments in this area have provided mechanistic insights as well as tools to engineer or target Wnt signalling for translational and therapeutic purposes. Here, we discuss the bidirectional relationship between Wnt activity and mitosis. We emphasise how various Wnt-dependent mechanisms control spindle dynamics, chromosome segregation, and ACD. Finally, we illustrate how knowledge about these mechanisms has been successfully employed in tissue engineering for regenerative medicine applications.

Superresolution microscopy localizes endogenous Dvl2 to Wnt signaling-responsive biomolecular condensates

Wnt signaling governs cell fate and tissue polarity across species. The Dishevelled proteins are central to Wnt signaling cascades. Wnt-mediated multiprotein complexes such as the “signalosome” and the “destruction complex” have been proposed to represent biomolecular condensates. These nonmembranous, specialized compartments have been suggested to form through liquid–liquid phase separation and ensure correctly proceeding physiological reactions. Although biomolecular condensates have increasingly been studied, key questions remain regarding, for example, their architecture and physiological regulation. Here, superresolution microscopy after endogenous labeling of Dishevelled-2 gives insights into protein functions and Wnt signaling at physiological levels. It reveals the distinct molecular architecture of endogenous Wnt condensates at single-molecule resolution and illustrates close interactions at the centrosome.

During organismal development, homeostasis, and disease, Dishevelled (Dvl) proteins act as key signaling factors in beta-catenin–dependent and beta-catenin–independent Wnt pathways. While their importance for signal transmission has been genetically demonstrated in many organisms, our mechanistic understanding is still limited. Previous studies using overexpressed proteins showed Dvl localization to large, punctate-like cytoplasmic structures that are dependent on its DIX domain. To study Dvl’s role in Wnt signaling, we genome engineered an endogenously expressed Dvl2 protein tagged with an mEos3.2 fluorescent protein for superresolution imaging. First, we demonstrate the functionality and specificity of the fusion protein in beta-catenin–dependent and beta-catenin–independent signaling using multiple independent assays. We performed live-cell imaging of Dvl2 to analyze the dynamic formation of the supramolecular cytoplasmic Dvl2_mEos3.2 condensates. While overexpression of Dvl2_mEos3.2 mimics the previously reported formation of abundant large “puncta,” supramolecular condensate formation at physiological protein levels is only observed in a subset of cells with approximately one per cell. We show that, in these condensates, Dvl2 colocalizes with Wnt pathway components at gamma-tubulin and CEP164-positive centrosomal structures and that the localization of Dvl2 to these condensates is Wnt dependent. Single-molecule localization microscopy using photoactivated localization microscopy (PALM) of mEos3.2 in combination with DNA-PAINT demonstrates the organization and repetitive patterns of these condensates in a cell cycle–dependent manner. Our results indicate that the localization of Dvl2 in supramolecular condensates is coordinated dynamically and dependent on cell state and Wnt signaling levels. Our study highlights the formation of endogenous and physiologically regulated biomolecular condensates in the Wnt pathways at single-molecule resolution.

Cortical Cyclin A controls spindle orientation during asymmetric cell divisions in Drosophila

The coordination between cell proliferation and cell polarity is crucial to orient the asymmetric cell divisions to generate cell diversity in epithelia. In many instances, the Frizzled/Dishevelled planar cell polarity pathway is involved in mitotic spindle orientation, but how this is spatially and temporally coordinated with cell cycle progression has remained elusive. Using Drosophila sensory organ precursor cells as a model system, we show that Cyclin A, the main Cyclin driving the transition to M-phase of the cell cycle, is recruited to the apical-posterior cortex in prophase by the Frizzled/Dishevelled complex. This cortically localized Cyclin A then regulates the orientation of the division by recruiting Mud, a homologue of NuMA, the well-known spindle-associated protein. The observed non-canonical subcellular localization of Cyclin A reveals this mitotic factor as a direct link between cell proliferation, cell polarity and spindle orientation.

The Frizzled/Dishevelled planar cell polarity pathway is involved in mitotic spindle orientation, but how this is coordinated with the cell cycle is unclear. Here, the authors show with Drosophila sensory organ precursor cells that Cyclin A is recruited in prophase by Frizzled/Dishevelled, regulating division orientation.

Map7D2 and Map7D1 facilitate microtubule stabilization through distinct mechanisms in neuronal cells

The microtubule-associated proteins Map7D2 and Map7D1, which belong to the MAP7 family, stabilize microtubules through distinct mechanisms for the control of cell motility and neurite outgrowth.

Microtubule (MT) dynamics are modulated through the coordinated action of various MT-associated proteins (MAPs). However, the regulatory mechanisms underlying MT dynamics remain unclear. We show that the MAP7 family protein Map7D2 stabilizes MTs to control cell motility and neurite outgrowth. Map7D2 directly bound to MTs through its N-terminal half and stabilized MTs in vitro. Map7D2 localized prominently to the centrosome and partially on MTs in mouse N1-E115 neuronal cells, which expresses two of the four MAP7 family members, Map7D2 and Map7D1. Map7D2 loss decreased the resistance to the MT-destabilizing agent nocodazole without affecting acetylated/detyrosinated stable MTs, suggesting that Map7D2 stabilizes MTs via direct binding. In addition, Map7D2 loss increased the rate of random cell migration and neurite outgrowth, presumably by disturbing the balance between MT stabilization and destabilization. Map7D1 exhibited similar subcellular localization and gene knockdown phenotypes to Map7D2. However, in contrast to Map7D2, Map7D1 was required for the maintenance of acetylated stable MTs. Taken together, our data suggest that Map7D2 and Map7D1 facilitate MT stabilization through distinct mechanisms in cell motility and neurite outgrowth.

Gene Expression over Time during Cell Transformation Due to Non-Genotoxic Carcinogen Treatment of Bhas 42 Cells

The Bhas 42 cell transformation assay (Bhas 42 CTA) is the first Organization for Economic Cooperation and Development (OECD)-certificated method used as a specific tool for the detection of the cell-transformation potential of tumor-promoting compounds, including non-genotoxic carcinogens (NGTxCs), as separate from genotoxic carcinogens. This assay offers the great advantage of enabling the phenotypic detection of oncotransformation. A key benefit of using the Bhas 42 CTA in the study of the cell-transformation mechanisms of tumor-promoting compounds, including non-genotoxic carcinogens, is that the cell-transformation potential of the chemical can be detected directly without treatment with a tumor-initiating compound since Bhas 42 cell line was established by transfecting the v-Ha-ras gene into a mouse fibroblast cloned cell line. Here, we analyzed the gene expression over time, using DNA microarrays, in Bhas 42 cells treated with the tumor-promoting compound 12-O-tetradecanoylphorbol-13-acetate (TPA), and NGTxC, with a total of three repeat experiments. This is the first paper to report on gene expression over time during the process of cell transformation with only a tumor-promoting compound. Pathways that were activated or inactivated during the process of cell transformation in the Bhas 42 cells treated with TPA were related not only directly to RAS but also to various pathways in the hallmarks of cancer.

Phosphorylation of β-catenin Ser60 by polo-like kinase 1 drives the completion of cytokinesis

β-Catenin is a multifunctional protein and participates in numerous processes required for embryonic development, cell proliferation, and homeostasis through various molecular interactions and signaling pathways. To date, however, there is no direct evidence that β-catenin contributes to cytokinesis. Here, we identify a novel p-S60 epitope on β-catenin generated by Plk1 kinase activity, which can be found at the actomyosin contractile ring of early telophase cells and at the midbody of late telophase cells. Depletion of β-catenin leads to cytokinesis-defective phenotypes, which eventually result in apoptotic cell death. In addition, phosphorylation of β-catenin Ser60 by Plk1 is essential for the recruitment of Ect2 to the midbody, activation of RhoA, and interaction between β-catenin, Plk1, and Ect2. Time-lapse image analysis confirmed the importance of β-catenin phospho-Ser60 in furrow ingression and the completion of cytokinesis. Taken together, we propose that phosphorylation of β-catenin Ser60 by Plk1 in cooperation with Ect2 is essential for the completion of cytokinesis. These findings may provide fundamental knowledge for the research of cytokinesis failure-derived human diseases.

Stem cells' centrosomes: How can organelles identified 130 years ago contribute to the future of regenerative medicine?

At the core of regenerative medicine lies the expectation of repair or replacement of damaged tissues or whole organs. Donor scarcity and transplant rejection are major obstacles, and exactly the obstacles that stem cell-based therapy promises to overcome. These therapies demand a comprehensive understanding of the asymmetric division of stem cells, i.e. their ability to produce cells with identical potency or differentiated cells. It is believed that with better understanding, researchers will be able to direct stem cell differentiation. Here, we describe extraordinary advances in manipulating stem cell fate that show that we need to focus on the centrosome and the centrosome-derived primary cilium. This belief comes from the fact that this organelle is the vehicle that coordinates the asymmetric division of stem cells. This is supported by studies that report the significant role of the centrosome/cilium in orchestrating signaling pathways that dictate stem cell fate. We anticipate that there is sufficient evidence to place this organelle at the center of efforts that will shape the future of regenerative medicine.

Parsing β-catenin's cell adhesion and Wnt signaling functions in malignant mammary tumor progression

During malignant progression, epithelial cancer cells dissolve their cell-cell adhesion and gain invasive features. By virtue of its dual function, β-catenin contributes to cadherin-mediated cell-cell adhesion, and it determines the transcriptional output of Wnt signaling: via its N terminus, it recruits the signaling coactivators Bcl9 and Pygopus, and via the C terminus, it interacts with the general transcriptional machinery. This duality confounds the simple loss-of-function analysis of Wnt signaling in cancer progression. In many cancer types including breast cancer, the functional contribution of β-catenin's transcriptional activities, as compared to its adhesion functions, to tumor progression has remained elusive. Employing the mouse mammary tumor virus (MMTV)-PyMT mouse model of metastatic breast cancer, we compared the complete elimination of β-catenin with the specific ablation of its signaling outputs in mammary tumor cells. Notably, the complete lack of β-catenin resulted in massive apoptosis of mammary tumor cells. In contrast, the loss of β-catenin's transcriptional activity resulted in a reduction of primary tumor growth, tumor invasion, and metastasis formation in vivo. These phenotypic changes were reflected by stalled cell cycle progression and diminished epithelial-mesenchymal transition (EMT) and cell migration of breast cancer cells in vitro. Transcriptome analysis revealed subsets of genes which were specifically regulated by β-catenin's transcriptional activities upon stimulation with Wnt3a or during TGF-β-induced EMT. Our results uncouple the signaling from the adhesion function of β-catenin and underline the importance of Wnt/β-catenin-dependent transcription in malignant tumor progression of breast cancer.

Wnt signaling recruits KIF2A to the spindle to ensure chromosome congression and alignment during mitosis

Canonical Wnt signaling plays critical roles in development and tissue renewal by regulating β-catenin target genes. Recent evidence showed that β-catenin-independent Wnt signaling is also required for faithful execution of mitosis. However, the targets and specific functions of mitotic Wnt signaling still remain uncharacterized. Using phosphoproteomics, we identified that Wnt signaling regulates the microtubule depolymerase KIF2A during mitosis. We found that Dishevelled recruits KIF2A via its N-terminal and motor domains, which is further promoted upon LRP6 signalosome formation during cell division. We show that Wnt signaling modulates KIF2A interaction with PLK1, which is critical for KIF2A localization at the spindle. Accordingly, inhibition of basal Wnt signaling leads to chromosome misalignment in somatic cells and pluripotent stem cells. We propose that Wnt signaling monitors KIF2A activity at the spindle poles during mitosis to ensure timely chromosome alignment. Our findings highlight a function of Wnt signaling during cell division, which could have important implications for genome maintenance, notably in stem cells.

Wnt10b-GSK3β-dependent Wnt/STOP signaling prevents aneuploidy in human somatic cells

Wnt signaling is crucial for proper development, tissue homeostasis and cell cycle regulation. A key role of Wnt signaling is the GSK3β-mediated stabilization of β-catenin, which mediates many of the critical roles of Wnt signaling. In addition, it was recently revealed that Wnt signaling can also act independently of β-catenin. In fact, Wnt mediated stabilization of proteins (Wnt/STOP) that involves an LRP6-DVL-dependent signaling cascade is required for proper regulation of mitosis and for faithful chromosome segregation in human somatic cells. We show that inhibition of Wnt/LRP6 signaling causes whole chromosome missegregation and aneuploidy by triggering abnormally increased microtubule growth rates in mitotic spindles, and this is mediated by increased GSK3β activity. We demonstrate that proper mitosis and maintenance of numerical chromosome stability requires continuous basal autocrine Wnt signaling that involves secretion of Wnts. Importantly, we identified Wnt10b as a Wnt ligand required for the maintenance of normal mitotic microtubule dynamics and for proper chromosome segregation. Thus, a self-maintaining Wnt10b-GSK3β-driven cellular machinery ensures the proper execution of mitosis and karyotype stability in human somatic cells.

Distinct Microtubule Organizing Center Mechanisms Combine to Generate Neuron Polarity and Arbor Complexity

Dendrite and axon arbor wiring patterns determine the connectivity and computational characteristics of a neuron. The identities of these dendrite and axon arbors are created by differential polarization of their microtubule arrays, and their complexity and pattern are generated by the extension and organization of these arrays. We describe how several molecularly distinct microtubule organizing center (MTOC) mechanisms function during neuron differentiation to generate and arrange dendrite and axon microtubules. The temporal and spatial organization of these MTOCs generates, patterns, and diversifies arbor wiring.

The crosstalk between microtubules, actin and membranes shapes cell division

Mitotic progression is orchestrated by morphological and mechanical changes promoted by the coordinated activities of the microtubule (MT) cytoskeleton, the actin cytoskeleton and the plasma membrane (PM). MTs assemble the mitotic spindle, which assists sister chromatid separation, and contact the rigid and tensile actomyosin cortex rounded-up underneath the PM. Here, we highlight the dynamic crosstalk between MTs, actin and cell membranes during mitosis, and discuss the molecular connections between them. We also summarize recent views on how MT traction forces, the actomyosin cortex and membrane trafficking contribute to spindle positioning in isolated cells in culture and in epithelial sheets. Finally, we describe the emerging role of membrane trafficking in synchronizing actomyosin tension and cell shape changes with cell-substrate adhesion, cell-cell contacts and extracellular signalling events regulating proliferation.

Comparative phosphorylation map of Dishevelled 3 links phospho-signatures to biological outputs

Background

Dishevelled (DVL) is an essential component of the Wnt signaling cascades. Function of DVL is controlled by phosphorylation but the molecular details are missing. DVL3 contains 131 serines and threonines whose phosphorylation generates complex barcodes underlying diverse DVL3 functions. In order to dissect the role of DVL phosphorylation we analyzed the phosphorylation of human DVL3 induced by previously reported (CK1ε, NEK2, PLK1, CK2α, RIPK4, PKCδ) and newly identified (TTBK2, Aurora A) DVL kinases.

Methods

Shotgun proteomics including TiO₂ enrichment of phosphorylated peptides followed by liquid chromatography tandem mass spectrometry on immunoprecipitates from HEK293T cells was used to identify and quantify phosphorylation of DVL3 protein induced by 8 kinases. Functional characterization was performed by in-cell analysis of phospho-mimicking/non-phosphorylatable DVL3 mutants and supported by FRET assays and NMR spectroscopy.

Results

We used quantitative mass spectrometry and calculated site occupancies and quantified phosphorylation of > 80 residues. Functional validation demonstrated the importance of CK1ε-induced phosphorylation of S268 and S311 for Wnt-3a-induced β-catenin activation. S630–643 cluster phosphorylation by CK1, NEK2 or TTBK2 is essential for even subcellular distribution of DVL3 when induced by CK1 and TTBK2 but not by NEK2. Further investigation showed that NEK2 utilizes a different mechanism to promote even localization of DVL3. NEK2 triggered phosphorylation of PDZ domain at S263 and S280 prevents binding of DVL C-terminus to PDZ and promotes an open conformation of DVL3 that is more prone to even subcellular localization.

Conclusions

We identify unique phosphorylation barcodes associated with DVL function. Our data provide an example of functional synergy between phosphorylation in structured domains and unstructured IDRs that together dictate the biological outcome.

CDK1-mediated BCL9 phosphorylation inhibits clathrin to promote mitotic Wnt signalling

Uncontrolled cell division is a hallmark of cancer. Deregulation of Wnt components has been linked to aberrant cell division by multiple mechanisms, including Wnt-mediated stabilisation of proteins signalling, which was notably observed in mitosis. Analysis of Wnt components revealed an unexpected role of B-cell CLL/lymphoma 9 (BCL9) in maintaining mitotic Wnt signalling to promote precise cell division and growth of cancer cell. Mitotic interactome analysis revealed a mechanistic role of BCL9 in inhibiting clathrin-mediated degradation of LRP6 signalosome components by interacting with clathrin and the components in Wnt destruction complex; this function was further controlled by CDK1-driven phosphorylation of BCL9 N-terminal, especially T172. Interestingly, T172 phosphorylation was correlated with cancer patient prognosis and enriched in tumours. Thus, our results revealed a novel role of BCL9 in controlling mitotic Wnt signalling to promote cell division and growth.

Cell-intrinsic and -extrinsic mechanisms promote cell-type-specific cytokinetic diversity

Cytokinesis, the physical division of one cell into two, is powered by constriction of an actomyosin contractile ring. It has long been assumed that all animal cells divide by a similar molecular mechanism, but growing evidence suggests that cytokinetic regulation in individual cell types has more variation than previously realized. In the four-cell Caenorhabditis elegans embryo, each blastomere has a distinct cell fate, specified by conserved pathways. Using fast-acting temperature-sensitive mutants and acute drug treatment, we identified cell-type-specific variation in the cytokinetic requirement for a robust formin^CYK-1-dependent filamentous-actin (F-actin) cytoskeleton. In one cell (P2), this cytokinetic variation is cell-intrinsically regulated, whereas in another cell (EMS) this variation is cell-extrinsically regulated, dependent on both Src^SRC-1 signaling and direct contact with its neighbor cell, P2. Thus, both cell-intrinsic and -extrinsic mechanisms control cytokinetic variation in individual cell types and can protect against division failure when the contractile ring is weakened.

The successful division of one cell into two is essential for all organisms to live, grow and reproduce. For an animal cell, the nucleus – the compartment containing the genetic material – must divide before the surrounding material. The rest of the cell, called the cytoplasm, physically separates later in a process known as cytokinesis.

Cytokinesis in animal cells is driven by the formation of a ring in the middle of the dividing cell. The ring is composed of myosin motor proteins and filaments made of a protein called actin. The movements of the motor proteins along the filaments cause the ring to contract and tighten. This pulls the cell membrane inward and physically pinches the cell into two. For a long time, the mechanism of cytokinesis was assumed to be same across different types of animal cell, but later evidence suggested otherwise. For example, in liver, heat and bone cells, cytokinesis naturally fails during development to create cells with two or more nuclei. If a similar ‘failure’ happened in other cell types, it could lead to diseases such as cancers or blood disorders. This raised the question: what are the molecular mechanisms that allow cytokinesis to happen differently in different cell types?

Davies et al. investigated this question using embryos of the worm Caenorhabditis elegans at a stage in their development when they consist of just four cells. The proteins forming the contractile ring in this worm are the same as those in humans. However, in the worm, the contractile ring can easily be damaged using chemical inhibitors or by mutating the genes that encode its proteins.

Davies et al. show that when the contractile ring was damaged, two of the four cells in the worm embryo still divided successfully. This result indicates the existence of new mechanisms to divide the cytoplasm that allow division even with a weak contractile ring. In a further experiment, the embryos were dissected to isolate each of the four cells. Davies et al. saw that one of the two dividing cells could still divide on its own, while the other cell could not. This shows that this new method of cytokinesis is regulated both by factors inherent to the dividing cell and by external signals from other cells. Moreover, one of these extrinsic signals was found to be a signaling protein that had previously been implicated in human cancers.

Future work will determine if these variations in cytokinesis between the different cell types found in the worm apply to humans too; and, more importantly from a therapeutic standpoint, if these new mechanisms exist in human cancers.

Map7/7D1 and Dvl form a feedback loop that facilitates microtubule remodeling and Wnt5a signaling

The Wnt signaling pathway can be grouped into two classes, the β-catenin-dependent and β-catenin-independent pathways. Wnt5a signaling through a β-catenin-independent pathway promotes microtubule (MT) remodeling during cell-substrate adhesion, cell migration, and planar cell polarity formation. Although Wnt5a signaling and MT remodeling are known to form an interdependent regulatory loop, the underlying mechanism remains unknown. Here we show that in HeLa cells, the paralogous MT-associated proteins Map7 and Map7D1 (Map7/7D1) form an interdependent regulatory loop with Disheveled, the critical signal transducer in Wnt signaling. Map7/7D1 bind to Disheveled, direct its cortical localization, and facilitate the cortical targeting of MT plus-ends in response to Wnt5a signaling. Wnt5a signaling also promotes Map7/7D1 movement toward MT plus-ends, and depletion of the Kinesin-1 member Kif5b abolishes the Map7/7D1 dynamics and Disheveled localization. Furthermore, Disheveled stabilizes Map7/7D1. Intriguingly, Map7/7D1 and its Drosophila ortholog, Ensconsin show planar-polarized distribution in both mouse and fly epithelia, and Ensconsin influences proper localization of Drosophila Disheveled in pupal wing cells. These results suggest that the role of Map7/7D1/Ensconsin in Disheveled localization is evolutionarily conserved.

A speculative outlook on embryonic aneuploidy: Can molecular pathways be involved?

The journey of embryonic development starts at oocyte fertilization, which triggers a complex cascade of events and cellular pathways that guide early embryogenesis. Recent technological advances have greatly expanded our knowledge of cleavage-stage embryo development, which is characterized by an increased rate of whole-chromosome losses and gains, mixoploidy, and atypical cleavage morphokinetics. Embryonic aneuploidy significantly contributes to implantation failure, spontaneous miscarriage, stillbirth or congenital birth defects in both natural and assisted human reproduction. Essentially, early embryo development is strongly determined by maternal factors. Owing to considerable limitations associated with human oocyte and embryo research, the use of animal models is inevitable. However, cellular and molecular mechanisms driving the error-prone early stages of development are still poorly described. In this review, we describe known events that lead to aneuploidy in mammalian oocytes and preimplantation embryos. As the processes of oocyte and embryo development are rigorously regulated by multiple signal-transduction pathways, we explore the putative role of signaling pathways in genomic integrity maintenance. Based on the existing evidence from human and animal data, we investigate whether critical early developmental pathways, like Wnt, Hippo and MAPK, together with distinct DNA damage response and DNA repair pathways can be associated with embryo genomic instability, a question that has, so far, remained largely unexplored.

Cftr Modulates Wnt/β-Catenin Signaling and Stem Cell Proliferation in Murine Intestine

BACKGROUND & AIMS

Cystic fibrosis (CF) patients and CF mouse models have increased risk for gastrointestinal tumors. CF mice show augmented intestinal proliferation of unknown etiology and an altered intestinal environment. We examined the role of the cystic fibrosis transmembrane conductance regulator (Cftr) in Wnt/β-catenin signaling, stem cell proliferation, and its functional expression in the active intestinal stem cell (ISC) population. Dysregulation of intracellular pH (pH_i) in CF ISCs was investigated for facilitation of Wnt/β-catenin signaling.

METHODS

Crypt epithelia from wild-type (WT) and CF mice were compared ex vivo and in intestinal organoids (enteroids) for proliferation and Wnt/β-catenin signaling by standard assays. Cftr in ISCs was assessed by immunoblot of sorted Sox9 ^{enhanced green fluorescent protein(EGFP)} intestinal epithelia and pH_i regulation by confocal microfluorimetry of leucine-rich G-protein-coupled receptor 5 ISCs. Plasma membrane association of the Wnt transducer Dishevelled 2 (Dvl2) was assessed by fluorescence imaging of live enteroids from WT and CF mice crossed with Dvl2-EGFP/ACTB-tdTomato,-EGFP)Luo/J (Rosa^mT/mG) mice.

RESULTS

Relative to WT, CF intestinal crypts showed an ∼30% increase in epithelial and Lgr5+ ISC proliferation and increased Wnt/β-catenin signaling. Cftr was expressed in Sox9^EGFPLo ISCs and loss of Cftr induced an alkaline pH_i in ISCs. CF crypt-base columnar cells showed a generalized increase in plasma membrane Dvl2-EGFP association as compared with WT. Dvl2-EGFP membrane association was charge- and pH-dependent and increased in WT crypt-base columnar cells by Cftr inhibition.

CONCLUSIONS

CF intestine shows increased ISC proliferation and Wnt/β-catenin signaling. Loss of Cftr increases pH_i in ISCs, which stabilizes the plasma membrane association of the Wnt transducer Dvl, likely facilitating Wnt/β-catenin signaling. Absence of Cftr-dependent suppression of ISC proliferation in the CF intestine may contribute to increased risk for intestinal tumors.

PLK1-mediated phosphorylation of WDR62/MCPH2 ensures proper mitotic spindle orientation

Primary microcephaly (MCPH) is an autosomal recessive disorder characterized by congenital reduction of head circumference. Here, we identified compound heterozygous mutations c.731 C > T (p.Ser 244 Leu) and c.2413 G > T (p.Glu 805 X) in the WDR62/MCPH2 gene, which encodes the mitotic centrosomal protein WDR62, in two siblings in a Japanese family with microcephaly using whole-exome sequencing. However, the molecular and cellular pathology of microcephaly caused by WDR62/MCPH2 mutation remains unclear. To clarify the physiological role of WDR62, we used the CRISPR/Cas9 system and single-stranded oligonucleotides as a point-mutation-targeting donor to generate human cell lines with knock-in of WDR62/MCPH2 c.731 C > T (p.Ser 244 Leu) missense mutation. In normal metaphase, the mitotic spindle forms parallel to the substratum to ensure symmetric cell division, while WDR62/MCPH2-mutated cells exhibited a randomized spindle orientation caused by the impaired astral microtubule assembly. It was shown that a mitotic kinase, Polo-like kinase 1 (PLK1), is required for the maintenance of spindle orientation through astral microtubule development. In this study, we demonstrated that WDR62 is a PLK1 substrate that is phosphorylated at Ser 897, and that this phosphorylation at the spindle poles promotes astral microtubule assembly to stabilize spindle orientation. Our findings provide insights into the role of the PLK1-WDR62 pathway in the maintenance of proper spindle orientation.

The connections of Wnt pathway components with cell cycle and centrosome: side effects or a hidden logic?

Wnt signaling cascade has developed together with multicellularity to orchestrate the development and homeostasis of complex structures. Wnt pathway components - such as β-catenin, Dishevelled (DVL), Lrp6, and Axin-- are often dedicated proteins that emerged in evolution together with the Wnt signaling cascade and are believed to function primarily in the Wnt cascade. It is interesting to see that in recent literature many of these proteins are connected with cellular functions that are more ancient and not limited to multicellular organisms - such as cell cycle regulation, centrosome biology, or cell division. In this review, we summarize the recent literature describing this crosstalk. Specifically, we attempt to find the answers to the following questions: Is the response to Wnt ligands regulated by the cell cycle? Is the centrosome and/or cilium required to activate the Wnt pathway? How do Wnt pathway components regulate the centrosomal cycle and cilia formation and function? We critically review the evidence that describes how these connections are regulated and how they help to integrate cell-to-cell communication with the cell and the centrosomal cycle in order to achieve a fine-tuned, physiological response.

WNT antagonists exhibit unique combinatorial antitumor activity with taxanes by potentiating mitotic cell death

The WNT pathway mediates intercellular signaling that regulates cell fate in both normal development and cancer. It is widely appreciated that the WNT pathway is frequently dysregulated in human cancers through a variety of genetic and epigenetic mechanisms. Targets in the WNT pathway are being extensively pursued for the development of new anticancer therapies, and we have advanced two WNT antagonists for clinical development: vantictumab (anti-FZD) and ipafricept (FZD8-Fc). We examined the antitumor efficacy of these WNT antagonists in combination with various chemotherapies in a large set of patient-derived xenograft models. In responsive models, WNT blockade led to profound synergy with taxanes such as paclitaxel, and the combination activity with taxanes was consistently more effective than with other classes of chemotherapy. Taxane monotherapy increased the frequency of cells with active WNT signaling. This selection of WNT-active chemotherapy-resistant tumorigenic cells was prevented by WNT-antagonizing biologics and required sequential dosing of the WNT antagonist followed by the taxane. The WNT antagonists potentiated paclitaxel-mediated mitotic blockade and promoted widespread mitotic cell death. By blocking WNT/β-catenin signaling before mitotic blockade by paclitaxel, we found that this treatment effectively sensitizes cancer stem cells to taxanes. This combination strategy and treatment regimen has been incorporated into ongoing clinical testing for vantictumab and ipafricept.

Wnt signaling in triple-negative breast cancer

Wnt signaling regulates a variety of cellular processes, including cell fate, differentiation, proliferation and stem cell pluripotency. Aberrant Wnt signaling is a hallmark of many cancers. An aggressive subtype of breast cancer, known as triple-negative breast cancer (TNBC), demonstrates dysregulation in canonical and non-canonical Wnt signaling. In this review, we summarize regulators of canonical and non-canonical Wnt signaling, as well as Wnt signaling dysfunction that mediates the progression of TNBC. We review the complex molecular nature of TNBC and the emerging therapies that are currently under investigation for the treatment of this disease.

A Comparative Perspective on Wnt/β-Catenin Signalling in Cell Fate Determination

The Wnt/β-catenin pathway is an ancient and highly conserved signalling pathway that plays fundamental roles in the regulation of embryonic development and adult homeostasis. This pathway has been implicated in numerous cellular processes, including cell proliferation, differentiation, migration, morphological changes and apoptosis. In this chapter, we aim to illustrate with specific examples the involvement of Wnt/β-catenin signalling in cell fate determination. We discuss the roles of the Wnt/β-catenin pathway in specifying cell fate throughout evolution, how its function in patterning during development is often reactivated during regeneration and how perturbation of this pathway has negative consequences for the control of cell fate.The origin of all life was a single cell that had the capacity to respond to cues from the environment. With evolution, multicellular organisms emerged, and as a result, subsets of cells arose to form tissues able to respond to specific instructive signals and perform specialised functions. This complexity and specialisation required two types of messages to direct cell fate: intra- and intercellular. A fundamental question in developmental biology is to understand the underlying mechanisms of cell fate choice. Amongst the numerous external cues involved in the generation of cellular diversity, a prominent pathway is the Wnt signalling pathway in all its forms.

Essential role of the Dishevelled DEP domain in a Wnt-dependent human-cell-based complementation assay

Dishevelled (DVL) assembles Wnt signalosomes through dynamic head-to-tail polymerisation by means of its DIX domain. It thus transduces Wnt signals to cytoplasmic effectors including β-catenin, to control cell fates during normal development, tissue homeostasis and also in cancer. To date, most functional studies of Dishevelled relied on its Wnt-independent signalling activity resulting from overexpression, which is sufficient to trigger polymerisation, bypassing the requirement for Wnt signals. Here, we generate a human cell line devoid of endogenous Dishevelled (DVL1- DVL3), which lacks Wnt signal transduction to β-catenin. However, Wnt responses can be restored by DVL2 stably re-expressed at near-endogenous levels. Using this assay to test mutant DVL2, we show that its DEP domain is essential, whereas its PDZ domain is dispensable, for signalling to β-catenin. Our results imply two mutually exclusive functions of the DEP domain in Wnt signal transduction - binding to Frizzled to recruit Dishevelled to the receptor complex, and dimerising to cross-link DIX domain polymers for signalosome assembly. Our assay avoids the caveats associated with overexpressing Dishevelled, and provides a powerful tool for rigorous functional tests of this pivotal human signalling protein.

Tumor suppressor protein DAB2IP participates in chromosomal stability maintenance through activating spindle assembly checkpoint and stabilizing kinetochore-microtubule attachments

Defects in kinetochore-microtubule (KT-MT) attachment and the spindle assembly checkpoint (SAC) during cell division are strongly associated with chromosomal instability (CIN). CIN has been linked to carcinogenesis, metastasis, poor prognosis and resistance to cancer therapy. We previously reported that the DAB2IP is a tumor suppressor, and that loss of DAB2IP is often detected in advanced prostate cancer (PCa) and is indicative of poor prognosis. Here, we report that the loss of DAB2IP results in impaired KT-MT attachment, compromised SAC and aberrant chromosomal segregation. We discovered that DAB2IP directly interacts with Plk1 and its loss inhibits Plk1 kinase activity, thereby impairing Plk1-mediated BubR1 phosphorylation. Loss of DAB2IP decreases the localization of BubR1 at the kinetochore during mitosis progression. In addition, the reconstitution of DAB2IP enhances the sensitivity of PCa cells to microtubule stabilizing drugs (paclitaxel, docetaxel) and Plk1 inhibitor (BI2536). Our findings demonstrate a novel function of DAB2IP in the maintenance of KT-MT structure and SAC regulation during mitosis which is essential for chromosomal stability.

β-Catenin-Independent Roles of Wnt/LRP6 Signaling

Wnt/LRP6 signaling is best known for the β-catenin-dependent regulation of target genes. However, pathway branches have recently emerged, including Wnt/STOP signaling, which act independently of β-catenin and transcription. We review here the molecular mechanisms underlying β-catenin-independent Wnt/LRP6 signaling cascades and their implications for cell biology, development, and physiology.

Dishevelled is a NEK2 kinase substrate controlling dynamics of centrosomal linker proteins

Dishevelled (DVL) is a key scaffolding protein and a branching point in Wnt signaling pathways. Here, we present conclusive evidence that DVL regulates the centrosomal cycle. We demonstrate that DVL dishevelled and axin (DIX) domain, but not DIX domain-mediated multimerization, is essential for DVL's centrosomal localization. DVL accumulates during the cell cycle and associates with NIMA-related kinase 2 (NEK2), which is able to phosphorylate DVL at a multitude of residues, as detected by a set of novel phospho-specific antibodies. This creates interfaces for efficient binding to CDK5 regulatory subunit-associated protein 2 (CDK5RAP2) and centrosomal Nek2-associated protein 1 (C-NAP1), two proteins of the centrosomal linker. Displacement of DVL from the centrosome and its release into the cytoplasm on NEK2 phosphorylation is coupled to the removal of linker proteins, an event necessary for centrosomal separation and proper formation of the mitotic spindle. Lack of DVL prevents NEK2-controlled dissolution of loose centrosomal linker and subsequent centrosomal separation. Increased DVL levels, in contrast, sequester centrosomal NEK2 and mimic monopolar spindle defects induced by a dominant negative version of this kinase. Our study thus uncovers molecular crosstalk between centrosome and Wnt signaling.

Proximity mapping of human separase by the BioID approach

Separase is a caspase-like cysteine protease that is best known for its essential role during the metaphase-to-anaphase transition when it cleaves the cohesin ring complex that keeps the sister chromatids together. Another important function of separase is to regulate the process of centriole separation, known as centriole disengagement, at the end of mitosis. We used proximity-dependent biotin identification (BioID) to expand our knowledge on the identity of separase's proximity interactors. We show that separase BioID labeled two domains at the mother centriole: an area underneath the centriolar appendages and another at the proximal end of the mother centriole. BioID analysis identified more than 200 proximity interactors of separase, one being the Alström Syndrome Protein 1 (ALMS1) at the base of centrioles. Other proximity interactors are the histone chaperons NAP1L1 and NAP1L4, which localize to the spindle poles during mitosis and the spindle assembly checkpoint proteins BUBR1, SKA1 and SKA3 that reside at kinetochores in early mitosis. Finally, we show that depletion of BUBR1 homolog from Caenorhabditis elegans delayed the recruitment of separase to mitotic chromosomes, and eventually anaphase onset.

Exercise for the heart: signaling pathways

Physical exercise, a potent functional intervention in protecting against cardiovascular diseases, is a hot topic in recent years. Exercise has been shown to reduce cardiac risk factors, protect against myocardial damage, and increase cardiac function. This improves quality of life and decreases mortality and morbidity in a variety of cardiovascular diseases, including myocardial infarction, cardiac ischemia/reperfusion injury, diabetic cardiomyopathy, cardiac aging, and pulmonary hypertension. The cellular adaptation to exercise can be associated with both endogenous and exogenous factors: (1) exercise induces cardiac growth via hypertrophy and renewal of cardiomyocytes, and (2) exercise induces endothelial progenitor cells to proliferate, migrate and differentiate into mature endothelial cells, giving rise to endothelial regeneration and angiogenesis. The cellular adaptations associated with exercise are due to the activation of several signaling pathways, in particular, the growth factor neuregulin1 (NRG1)-ErbB4-C/EBPβ and insulin-like growth factor (IGF)-1-PI3k-Akt signaling pathways. Of interest, microRNAs (miRNAs, miRs) such as miR-222 also play a major role in the beneficial effects of exercise. Thus, exploring the mechanisms mediating exercise-induced benefits will be instrumental for devising new effective therapies against cardiovascular diseases.

Phosphorylation-dependent Akt-Inversin interaction at the basal body of primary cilia

A primary cilium is a microtubule‐based sensory organelle that plays an important role in human development and disease. However, regulation of Akt in cilia and its role in ciliary development has not been demonstrated. Using yeast two‐hybrid screening, we demonstrate that Inversin (INVS) interacts with Akt. Mutation in the INVS gene causes nephronophthisis type II (NPHP2), an autosomal recessive chronic tubulointerstitial nephropathy. Co‐immunoprecipitation assays show that Akt interacts with INVS via the C‐terminus. In vitro kinase assays demonstrate that Akt phosphorylates INVS at amino acids 864–866 that are required not only for Akt interaction, but also for INVS dimerization. Co‐localization of INVS and phosphorylated form of Akt at the basal body is augmented by PDGF‐AA. Akt‐null MEF cells as well as siRNA‐mediated inhibition of Akt attenuated ciliary growth, which was reversed by Akt reintroduction. Mutant phosphodead‐ or NPHP2‐related truncated INVS, which lack Akt phosphorylation sites, suppress cell growth and exhibit distorted lumen formation and misalignment of spindle axis during cell division. Further studies will be required for elucidating functional interactions of Akt–INVS at the primary cilia for identifying the molecular mechanisms underlying NPHP2.

Wnt/β-catenin signaling in kidney injury and repair: a double-edged sword

The Wnt/β-catenin signaling cascade is an evolutionarily conserved, highly complex pathway that is known to be involved in kidney injury and repair after a wide variety of insults. Although the kidney displays an impressive ability to repair and recover after injury, these repair mechanisms can be overwhelmed, leading to maladaptive responses and eventual development of chronic kidney disease (CKD). Emerging evidence demonstrates that Wnt/β-catenin signaling possesses dual roles in promoting repair/regeneration or facilitating progression to CKD after acute kidney injury (AKI), depending on the magnitude and duration of its activation. In this review, we summarize the expression, intracellular modification, and secretion of Wnt family proteins and their regulation in a variety of kidney diseases. We also explore our current understanding of the potential mechanisms by which transient Wnt/β-catenin activation positively regulates adaptive responses of the kidney after AKI, and discuss how sustained activation of this signaling triggers maladaptive responses and causes destructive outcomes. A better understanding of these mechanisms may offer important opportunities for designing targeted therapy to promote adaptive kidney repair/recovery and prevent progression to CKD in patients.

PLK1-dependent activation of LRRK1 regulates spindle orientation by phosphorylating CDK5RAP2

Correct formation of the cell division axis requires the initial precise orientation of the mitotic spindle. Proper spindle orientation depends on centrosome maturation, and Polo-like kinase 1 (PLK1) is known to play a crucial role in this process. However, the molecular mechanisms that function downstream of PLK1 are not well understood. Here we show that LRRK1 is a PLK1 substrate that is phosphorylated on Ser 1790. PLK1 phosphorylation is required for CDK1-mediated activation of LRRK1 at the centrosomes, and this in turn regulates mitotic spindle orientation by nucleating the growth of astral microtubules from the centrosomes. Interestingly, LRRK1 in turn phosphorylates CDK5RAP2(Cep215), a human homologue of Drosophila Centrosomin (Cnn), in its γ-tubulin-binding motif, thus promoting the interaction of CDK5RAP2 with γ-tubulin. LRRK1 phosphorylation of CDK5RAP2 Ser 140 is necessary for CDK5RAP2-dependent microtubule nucleation. Thus, our findings provide evidence that LRRK1 regulates mitotic spindle orientation downstream of PLK1 through CDK5RAP2-dependent centrosome maturation.

Fresh WNT into the regulation of mitosis

Canonical Wnt signaling triggering β-catenin-dependent gene expression contributes to cell cycle progression, in particular at the G1/S transition. Recently, however, it became clear that the cell cycle can also feed back on Wnt signaling at the G2/M transition. This is illustrated by the fact that mitosis-specific cyclin-dependent kinases can phosphorylate the Wnt co-receptor LRP6 to prime the pathway for incoming Wnt signals when cells enter mitosis. In addition, there is accumulating evidence that various Wnt pathway components might exert additional, Wnt-independent functions that are important for proper regulation of mitosis. The importance of Wnt pathways during mitosis was most recently enforced by the discovery of Wnt signaling contributing to the stabilization of proteins other than β-catenin, specifically at G2/M and during mitosis. This Wnt-mediated stabilization of proteins, now referred to as Wnt/STOP, might on one hand contribute to maintaining a critical cell size required for cell division and, on the other hand, for the faithful execution of mitosis itself. In fact, most recently we have shown that Wnt/STOP is required for ensuring proper microtubule dynamics within mitotic spindles, which is pivotal for accurate chromosome segregation and for the maintenance of euploidy.

Maternal Wnt/STOP signaling promotes cell division during early Xenopus embryogenesis

During Xenopus development, Wnt signaling is thought to function first after midblastula transition to regulate axial patterning via β-catenin-mediated transcription. Here, we report that Wnt/glycogen synthase kinase 3 (GSK3) signaling functions posttranscriptionally already in mature oocytes via Wnt/stabilization of proteins (STOP) signaling. Wnt signaling is induced in oocytes after their entry into meiotic metaphase II and declines again upon exit into interphase. Wnt signaling inhibits Gsk3 and thereby protects proteins from polyubiquitination and degradation in mature oocytes. In a protein array screen, we identify a cluster of mitotic effector proteins that are polyubiquitinated in a Gsk3-dependent manner in Xenopus. Consequently inhibition of maternal Wnt/STOP signaling, but not β-catenin signaling, leads to early cleavage arrest after fertilization. The results support a novel role for Wnt signaling in cell cycle progression independent of β-catenin.

Wnt-mediated protein stabilization ensures proper mitotic microtubule assembly and chromosome segregation

Wnt signaling stimulates cell proliferation by promoting the G1/S transition of the cell cycle through β-catenin/TCF4-mediated gene transcription. However, Wnt signaling peaks in mitosis and contributes to the stabilization of proteins other than β-catenin, a pathway recently introduced as Wnt-dependent stabilization of proteins (Wnt/STOP). Here, we show that Wnt/STOP regulated by basal Wnt signaling during a normal cell cycle is required for proper spindle microtubule assembly and for faithful chromosome segregation during mitosis. Consequently, inhibition of basal Wnt signaling results in increased microtubule assembly rates, abnormal mitotic spindle formation and the induction of aneuploidy in human somatic cells.

Dosage changes of a segment at 17p13.1 lead to intellectual disability and microcephaly as a result of complex genetic interaction of multiple genes

The 17p13.1 microdeletion syndrome is a recently described genomic disorder with a core clinical phenotype of intellectual disability, poor to absent speech, dysmorphic features, and a constellation of more variable clinical features, most prominently microcephaly. We identified five subjects with copy-number variants (CNVs) on 17p13.1 for whom we performed detailed clinical and molecular studies. Breakpoint mapping and retrospective analysis of published cases refined the smallest region of overlap (SRO) for microcephaly to a genomic interval containing nine genes. Dissection of this phenotype in zebrafish embryos revealed a complex genetic architecture: dosage perturbation of four genes (ASGR1, ACADVL, DVL2, and GABARAP) impeded neurodevelopment and decreased dosage of the same loci caused a reduced mitotic index in vitro. Moreover, epistatic analyses in vivo showed that dosage perturbations of discrete gene pairings induce microcephaly. Taken together, these studies support a model in which concomitant dosage perturbation of multiple genes within the CNV drive the microcephaly and possibly other neurodevelopmental phenotypes associated with rearrangements in the 17p13.1 SRO.

Functional analysis of dishevelled-3 phosphorylation identifies distinct mechanisms driven by casein kinase 1ϵ and frizzled5

Dishevelled-3 (Dvl3), a key component of the Wnt signaling pathways, acts downstream of Frizzled (Fzd) receptors and gets heavily phosphorylated in response to pathway activation by Wnt ligands. Casein kinase 1ϵ (CK1ϵ) was identified as the major kinase responsible for Wnt-induced Dvl3 phosphorylation. Currently it is not clear which Dvl residues are phosphorylated and what is the consequence of individual phosphorylation events. In the present study we employed mass spectrometry to analyze in a comprehensive way the phosphorylation of human Dvl3 induced by CK1ϵ. Our analysis revealed >50 phosphorylation sites on Dvl3; only a minority of these sites was found dynamically induced after co-expression of CK1ϵ, and surprisingly, phosphorylation of one cluster of modified residues was down-regulated. Dynamically phosphorylated sites were analyzed functionally. Mutations within PDZ domain (S280A and S311A) reduced the ability of Dvl3 to activate TCF/LEF (T-cell factor/lymphoid enhancer factor)-driven transcription and induce secondary axis in Xenopus embryos. In contrast, mutations of clustered Ser/Thr in the Dvl3 C terminus prevented ability of CK1ϵ to induce electrophoretic mobility shift of Dvl3 and its even subcellular localization. Surprisingly, mobility shift and subcellular localization changes induced by Fzd5, a Wnt receptor, were in all these mutants indistinguishable from wild type Dvl3. In summary, our data on the molecular level (i) support previous the assumption that CK1ϵ acts via phosphorylation of distinct residues as the activator as well as the shut-off signal of Wnt/β-catenin signaling and (ii) suggest that CK1ϵ acts on Dvl via different mechanism than Fzd5.