The guanine nucleotide exchange factor Net1 facilitates the specification of dorsal cell fates in zebrafish embryos by promoting maternal β-catenin activation

USP10 strikes down β-catenin by dual-wielding deubiquitinase activity and phase separation potential

Wnt/β-catenin signaling is a conserved pathway crucially governing development, homeostasis, and oncogenesis. Discoveries of its regulators hold great values in both basic and translational research. Through screening, we identified a deubiquitinase, USP10, as a critical modulator of β-catenin. Mechanistically, USP10 binds to key scaffold Axin1 via conserved motifs and stabilizes Axin1 through K48-linked deubiquitination. Surprisingly, USP10 physically tethers Axin1 and β-catenin and promotes the phase separation for β-catenin suppression regardless of the enzymatic activity. Function-wise, USP10 enzymatic activity preferably regulates embryonic development and both the enzymatic activity and physical function jointly control intestinal homeostasis by antagonizing β-catenin. In colorectal cancer, USP10 substantially represses cancer growth mainly through physical promotion of phase separation and correlates with Wnt/β-catenin magnitude clinically. Collectively, we discovered USP10 functioning in multiple biological processes against β-catenin and unearthed the enzyme-dependent and -independent "dual-regulating" mechanism. These two functions of USP10 work in parallel and are context dependent.

Neuroepithelial cell-transforming 1 promotes cardiac fibrosis via the Wnt/β-catenin signaling pathway

This study found that the level of neuroepithelial cell-transforming gene 1 protein (NET1) was significantly increased in a mouse cardiac fibrosis model. Moreover, the expression level of NET1 was increased in cardiac fibrosis induced by TGF-β1, suggesting that NET1 was involved in the pathological process of cardiac fibrosis. Overexpression of NET1 promoted β-catenin expression in the nucleus and significantly increased the proliferation and migration of cardiac fibroblasts. NET1 may form a complex with β-catenin through GSK3β. Knockdown of β-catenin alleviated the effects of NET1 overexpression on collagen production and cell migration. In the heart of NET1 knockout mice, NET1 knockout can reduce the expression of β-catenin, α-SMA, and collagen content induced by MI. In conclusion, NET1 may regulate the activation of Wnt/β-catenin and TGF/Smads signaling pathway, promote collagen synthesis in fibroblasts, and participate in cardiac fibrosis. Thus, NET1 may be a potential therapeutic target in cardiac fibrosis.

AAV-Net1 facilitates the trans-differentiation of supporting cells into hair cells in the murine cochlea

Mechanosensitive hair cells (HCs) in the cochlear sensory epithelium are critical for sound detection and transduction. Mammalian HCs in the cochlea undergo cytogenesis during embryonic development, and irreversible damage to hair cells postnatally is a major cause of deafness. During the development of the organ of Corti, HCs and supporting cells (SCs) originate from the same precursors. In the neonatal cochlea, damage to HCs activates adjacent SCs to act as HC precursors and to differentiate into new HCs. However, the plasticity of SCs to produce new HCs is gradually lost with cochlear development. Here, we delineate an essential role for the guanine nucleotide exchange factor Net1 in SC trans-differentiation into HCs. Net1 overexpression mediated by AAV-ie in SCs promoted cochlear organoid formation and HC differentiation under two and three-dimensional culture conditions. Also, AAV-Net1 enhanced SC proliferation in Lgr5-EGFPCreERT2 mice and HC generation as indicated by lineage tracing of HCs in the cochleae of Lgr5-EGFPCreERT2/Rosa26-tdTomatoloxp/loxp mice. We further found that the up-regulation of Wnt/β-catenin and Notch signaling in AAV-Net1-transduced cochleae might be responsible for the SC proliferation and HC differentiation. Also, Net1 overexpression in SCs enhanced SC proliferation and HC regeneration and survival after HC damage by neomycin. Taken together, our study suggests that Net1 might serve as a potential target for HC regeneration and that AAV-mediated gene regulation may be a promising approach in stem cell-based therapy in hearing restoration.

Tmem88 confines ectodermal Wnt2bb signaling in pharyngeal arch artery progenitors for balancing cell cycle progression and cell fate decision

Pharyngeal arch artery (PAA) progenitors undergo proliferative expansion and angioblast differentiation to build vessels connecting the heart with the dorsal aortae. However, it remains unclear whether and how these two processes are orchestrated. Here we demonstrate that Tmem88 is required to fine-tune PAA progenitor proliferation and differentiation. Loss of zebrafish tmem88a/b leads to an excessive expansion and a failure of differentiation of PAA progenitors. Moreover, tmem88a/b deficiency enhances cyclin D1 expression in PAA progenitors via aberrant Wnt signal activation. Mechanistically, cyclin D1-CDK4/6 promotes progenitor proliferation through accelerating the G1/S transition while suppressing angioblast differentiation by phosphorylating Nkx2.5/Smad3. Ectodermal Wnt2bb signaling is confined by Tmem88 in PAA progenitors to ensure a balance between proliferation and differentiation. Therefore, the proliferation and angioblast differentiation of PAA progenitors manifest an inverse relationship and are delicately regulated by cell cycle machinery downstream of the Tmem88-Wnt pathway.

Chemokine signaling synchronizes angioblast proliferation and differentiation during pharyngeal arch artery vasculogenesis

Developmentally, the great vessels of the heart originate from the pharyngeal arch arteries (PAAs). During PAA vasculogenesis, PAA precursors undergo sequential cell fate decisions that are accompanied by proliferative expansion. However, how these two processes are synchronized remains poorly understood. Here, we find that the zebrafish chemokine receptor Cxcr4a is expressed in PAA precursors, and genetic ablation of either cxcr4a or the ligand gene cxcl12b causes PAA stenosis. Cxcr4a is required for the activation of the downstream PI3K/AKT cascade, which promotes not only PAA angioblast proliferation, but also differentiation. AKT has a well-known role in accelerating cell-cycle progression through the activation of cyclin-dependent kinases. Despite this, we demonstrate that AKT phosphorylates Etv2 and Scl, the key regulators of angioblast commitment, on conserved serine residues, thereby protecting them from ubiquitin-mediated proteasomal degradation. Altogether, our study reveals a central role for chemokine signaling in PAA vasculogenesis through orchestrating angioblast proliferation and differentiation.

Myoneurin regulates BMP signaling by competing with Ppm1a for Smad binding

A delicate balance of BMP activity is critical for tissue formation and organogenesis. However, the mechanical molecular details in ensuring the proper duration and intensity of BMP signaling have yet to be fully elucidated. Here, we identified a zebrafish mutant with a disrupted gene encoding for the BTB/POZ and zinc finger protein myoneurin (Mynn). mynn^−/− mutants exhibited severe loss of pharyngeal cartilage elements, owing to poor proliferation, blocked differentiation, and low viability of cranial neural crest cells. Depletion of mynn in both zebrafish embryos and mammalian cells led to a reduction of the BMP signal activity. Mechanistically, Mynn interacts with Smad proteins in the nucleus, thereby disrupting the association between Smad protein and the phosphatase Ppm1a. Ultimately, this interaction prevents Smad dephosphorylation. More broadly, our findings may provide a new strategy to balance BMP signal activity via competitive binding of Mynn and Ppm1a to Smad proteins during pharyngeal cartilage formation.

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mynn gene is essential for pharyngeal cartilage development

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mynn is required for the proliferation, differentiation, and survival of the CNCCs

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Mynn has an evolutionarily conserved function in supporting BMP signal

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Mynn maintains BMP signal activity by competing with Ppm1a for Smad binding

DGKA interacts with SRC/FAK to promote the metastasis of non-small cell lung cancer

Metastasis is responsible for the high mortality rate of lung cancer, but its underlying molecular mechanisms are poorly understood. Here, we demonstrated that the expression of diacylglycerol kinase alpha (DGKA) was elevated in the metastatic lesions of non-small cell lung cancer (NSCLC) and correlated with poor survival. Mechanistic studies revealed a direct physical interaction as well as a mutual regulation among DGKA, proto-oncogene tyrosine-protein kinase Src (SRC), and focal adhesion kinase 1 (FAK) proteins. The C-terminal domain of DGKA was responsible for the SRC SH3 domain binding, while the catalytic domain of DGKA interacted with the FREM domain of FAK. DGKA phosphorylated the SRC protein at Tyr416 and the FAK protein at Tyr397 to form and activate the DGKA/SRC/FAK complex, thus initiating the downstream WNT/β-catenin and VEGF signaling pathways, promoting epithelial-mesenchymal transition (EMT) and angiogenesis, and resulting in the metastasis of NSCLC. DGKA knockdown inhibited the invasive phenotype of NSCLC cells in vitro. Pharmacologic ablation of DGKA inhibited the metastasis of NSCLC cells in vivo, and this was reversed by the overexpression of DGKA. These results suggested that DGKA was a potential prognostic biomarker as well as a promising therapeutic target for NSCLC, especially when there was lymphatic or distant metastasis.

BMP Signaling: Lighting up the Way for Embryonic Dorsoventral Patterning

One of the most significant events during early embryonic development is the establishment of a basic embryonic body plan, which is defined by anteroposterior, dorsoventral (DV), and left-right axes. It is well-known that the morphogen gradient created by BMP signaling activity is crucial for DV axis patterning across a diverse set of vertebrates. The regulation of BMP signaling during DV patterning has been strongly conserved across evolution. This is a remarkable regulatory and evolutionary feat, as the BMP gradient has been maintained despite the tremendous variation in embryonic size and shape across species. Interestingly, the embryonic DV axis exhibits robust stability, even in face of variations in BMP signaling. Multiple lines of genetic, molecular, and embryological evidence have suggested that numerous BMP signaling components and their attendant regulators act in concert to shape the developing DV axis. In this review, we summarize the current knowledge of the function and regulation of BMP signaling in DV patterning. Throughout, we focus specifically on popular model animals, such as Xenopus and zebrafish, highlighting the similarities and differences of the regulatory networks between species. We also review recent advances regarding the molecular nature of DV patterning, including the initiation of the DV axis, the formation of the BMP gradient, and the regulatory molecular mechanisms behind BMP signaling during the establishment of the DV axis. Collectively, this review will help clarify our current understanding of the molecular nature of DV axis formation.

Nucleoporin 93 mediates β-catenin nuclear import to promote hepatocellular carcinoma progression and metastasis

Nuclear pore complex (NPC) embedded in the nuclear envelope, is the only channel for macromolecule nucleocytoplasmic transportation and has important biological functions. However, the deregulation of specific nucleoporins (Nups) and NPC-Nup-based mechanisms and their function in tumour progression remain poorly understood. Here, we aimed to identify the Nups that contribute to HCC progression and metastasis in 729 primary hepatocellular carcinoma (HCC) cases using molecular, cytological, and biochemical techniques. Our results revealed elevated Nup93 expression in HCC tissues, especially in cases with metastasis, and was linked to worse prognosis. Furthermore, Nup93 knockdown suppressed HCC cell metastasis and proliferation, while Nup93 overexpression promoted these activities. We observed that Nup93 promotes HCC metastasis and proliferation by regulating β-catenin translocation. In addition, we found that Nup93 interacted with β-catenin directly, independent of importin. Furthermore, LEF1 and β-catenin facilitated the Nup93-mediated metastasis and proliferation in HCC via a positive feedback loop. Thus, our findings provide novel insights into the mechanisms underlying the Nup93-induced promotion of HCC metastasis and suggest potential therapeutic targets in the LEF1-Nup93-β-catenin pathway for HCC therapeutics.

Epidermal growth factor-like domain 7 regulates breast cancer cell proliferation and vascular endothelial growth factor expression via the p38MAPK signaling pathway

OBJECTIVE

We aimed to investigate the effects of epidermal growth factor-like domain 7 (EGFL7) on breast cancer cell proliferation and angiogenesis and its association with the p38 mitogen-activated protein kinase (p38MAPK) signaling pathway.

METHODS

The vectors for stable overexpression of EGFL7 and the vectors for EGFL7 knockout were constructed. The breast cancer cell line MDA-MB-231 was selected for this study and the cells were divided into four groups: the control group, the empty vector group (transfected with an empty vector), the EGFL7 overexpression group (transfected with the EGFL7 overexpression vector), and the EGFL7 knockout group (transfected with the EGFL7 knockout vector). After 72 h of transfection, the mRNA and protein levels of EGFL7 in the cells were detected by RT-PCR and Western blot, respectively. The cell proliferation rates at 12 h, 24 h, 48 h and 72 h of culture in each group were detected using the MTT method. An in vitro tumor angiogenesis model of tumor-endothelial cells co-culture system was established and the angiogenesis ability at 12 h, 24 h, 48 h and 72 h of culture were compared among the groups using an in vitro angiogenesis assay. The cells in the EGFL7 overexpression group were further divided into three groups and were treated with p38MAPK inhibitor SB203580 at a dose of 0 μmol/L, 5 μmol/L, and 10 μmol/L, respectively. Afterward, the cells were co-cultured with endothelial cells for 48 h. Western blot was performed to detect the protein levels of vascular endothelial growth factor (VEGF), p38MAPK, and p-p38MAPK.

RESULTS

Compared with the control group, the EGFL7 mRNA level was higher in the EGFL7 overexpression group and lower in the EGFL7 knockout group (both P<0.05). Compared with the control group at 12 h, 24 h, 48 h, and 72 h of culture, the cell proliferation rates were lower in the EGFL knockout group and higher in the EGFL overexpression group, respectively (all P<0.05). Moreover, compared with the control group at these time points, the number of vascular sprouts and the protein levels of VEGF, p38MAPK, and p-p38MAPK were lower in the EGFL7 knockout group and higher in the EGFL7 overexpression group, respectively (all P<0.05). After the cells overexpressing EGFL7 were treated with SB203580, the level of p-p38MAPK was deceased, and the protein expression level of VEGF was inversely related with the SB203580 concentration (F=44.24, P<0.01).

CONCLUSION

EGFL7 can promote the proliferation of breast cancer cells and angiogenesis, and the mechanism may be associated with the activation of p38MAPK signaling pathway and promotion of VEGF expression.

Pharyngeal pouches provide a niche microenvironment for arch artery progenitor specification

The paired pharyngeal arch arteries (PAAs) are transient blood vessels connecting the heart with the dorsal aorta during embryogenesis. Although PAA malformations often occur along with pharyngeal pouch defects, the functional interaction between these adjacent tissues remains largely unclear. Here, we report that pharyngeal pouches are essential for PAA progenitor specification in zebrafish embryos. We reveal that the segmentation of pharyngeal pouches coincides spatiotemporally with the emergence of PAA progenitor clusters. These pouches physically associate with pharyngeal mesoderm in discrete regions and provide a niche microenvironment for PAA progenitor commitment by expressing BMP proteins. Specifically, pouch-derived BMP2a and BMP5 are the primary niche cues responsible for activating the BMP/Smad pathway in pharyngeal mesoderm, thereby promoting progenitor specification. In addition, BMP2a and BMP5 play an inductive function in the expression of the cloche gene npas4l in PAA progenitors. cloche mutants exhibit a striking failure to specify PAA progenitors and display ectopic expression of head muscle markers in the pharyngeal mesoderm. Therefore, our results support a crucial role for pharyngeal pouches in establishing a progenitor niche for PAA morphogenesis via BMP2a/5 expression.

Transcriptional adaptation: a mechanism underlying genetic robustness

Mutations play a crucial role in evolution as they provide the genetic variation that allows evolutionary change. Although some mutations in regulatory elements or coding regions can be beneficial, a large number of them disrupt gene function and reduce fitness. Organisms utilize several mechanisms to compensate for the damaging consequences of genetic perturbations. One such mechanism is the recently identified process of transcriptional adaptation (TA): during this event, mutations that cause mutant mRNA degradation trigger the transcriptional modulation of so-called adapting genes. In some cases, for example when one (or more) of the upregulated genes is functionally redundant with the mutated gene, this process compensates for the loss of the mutated gene's product. Notably, unlike other mechanisms underlying genetic robustness, TA is not triggered by the loss of protein function, an observation that has prompted studies into the machinery of TA and the contexts in which it functions. Here, we review the discovery and current understanding of TA, and discuss how its main features appear to be conserved across species. In light of these findings, we also speculate on the importance of TA in the context of human disease, and provide some recommendations for genome-editing strategies that should be more effective.

P21-Activated Kinase 1: Emerging biological functions and potential therapeutic targets in Cancer

The p21-Activated kinase 1 (PAK1), a member of serine-threonine kinases family, was initially identified as an interactor of the Rho GTPases RAC1 and CDC42, which affect a wide range of processes associated with cell motility, survival, metabolism, cell cycle, proliferation, transformation, stress, inflammation, and gene expression. Recently, the PAK1 has emerged as a potential therapeutic target in cancer due to its role in many oncogenic signaling pathways. Many PAK1 inhibitors have been developed as potential preclinical agents for cancer therapy. Here, we provide an overview of essential roles that PAK1 plays in cancer, including its structure and autoactivation mechanism, its crucial function from onset to progression to metastasis, metabolism, immune escape and even drug resistance in cancer; endogenous regulators; and cancer-related pathways. We also summarize the reported PAK1 small-molecule inhibitors based on their structure types and their potential application in cancer. In addition, we provide overviews on current progress and future challenges of PAK1 in cancer, hoping to provide new ideas for the diagnosis and treatment of cancer.

Premature Termination Codon-Bearing mRNA Mediates Genetic Compensation Response

The genetic compensation response (GCR), triggered by deleterious mutations but not by gene knockdown, has been proposed to explain many phenotypic discrepancies between gene-knockout and gene-knockdown models. GCRs have been observed in many model organisms from mice to Arabidopsis. Although the GCR is beneficial for organism survival, it impedes the exploration of gene function as many knockout mutants do not display discernible phenotypes due to the GCR. Uncovering how the mechanism of GCR operates is not only a fundamental goal in biology but also may provide a key solution in the unmasking of phenotypes in mutants displaying GCRs. Using zebrafish as the model, two recent studies have provided a molecular basis to explain this genetic paradox by demonstrating that the nonsense-mediated mRNA decay pathway is essential for nonsense mRNA to upregulate the expression of its homologous genes through an enhancement of histone H3 Lys4 trimethylation (H3K4me3) at the transcription start site regions of the compensatory genes. Here, we summarize the progress on the molecular mechanism of the GCR and make suggestions on how to overcome GCRs in the generation of genetic mutants.

The BMP ligand Pinhead together with Admp supports the robustness of embryonic patterning

Vertebrate embryonic dorsoventral axis is robustly stable in the face of variations in bone morphogenetic protein (BMP) signaling. However, the molecular mechanism behind this robustness remains uncharacterized. In this study, we show that zebrafish Pinhead, together with Admp, plays an important compensatory role in ensuring the robustness of axial patterning through fine-tuning of BMP signaling. pinhead encodes a BMP-like ligand expressed in the ventrolateral margin of the early gastrula. Transcription of pinhead and admp is under opposing regulation, where pinhead depletion results in a compensatory increase in admp transcription and vice versa, leading to normal axis formation in pinhead or admp mutants. Expression of pinhead and admp is directly repressed by the BMP/Smad pathway. When BMP signals were inhibited or excessively activated, pinhead/admp expression changed accordingly, allowing for self-regulation. Thus, this study reveals a negative feedback loop between BMP signaling and pinhead/admp that effectively stabilizes embryonic patterning by buffering against fluctuations in BMP signaling.

KIFC1 is activated by TCF-4 and promotes hepatocellular carcinoma pathogenesis by regulating HMGA1 transcriptional activity

Background

Kinesins play important roles in the development and progression of many human cancers. The functions and underlying mechanisms of kinesin family member C1 (KIFC1), a member of the kinesin-14 family, in the pathogenesis of hepatocellular carcinoma (HCC) have not been fully elucidated.

Methods

In this study, 168 HCC samples were first analyzed to examine the association between KIFC1 expression and patient clinicopathological features and prognosis. The role of KIFC1 in HCC cell proliferation and metastasis was investigated both in vivo and in vitro. The upstream regulation and downstream targets of KIFC1 were studied by qRT-PCR, western blotting, coimmunoprecipitation, chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays.

Results

KIFC1 was highly expressed in HCC tissues and positively associated with advanced stages and poor prognosis. KIFC1 knockdown suppressed HCC cell proliferation and invasion both in vitro and in vivo. Furthermore, KIFC1 knockdown decreased invadopodia formation and reduced epithelial-mesenchymal transition (EMT). HMGA1, an architectural transcriptional factor, was identified to interact with KIFC1. HMGA1 could bind to the promoters of Stat3, MMP2 and EMT-related genes and promote gene transcription. KIFC1 enhanced HMGA1 transcriptional activity and facilitated HCC proliferation and invasion. Moreover, KIFC1 was activated by TCF-4, and KIFC1 inhibition enhanced HCC cell sensitivity to paclitaxel.

Conclusions

Our findings suggest that KIFC1, activated by TCF-4, functions as an oncogene and promotes HCC pathogenesis through regulating HMGA1 transcriptional activity and that KIFC1 is a potential therapeutic target to enhance the paclitaxel sensitivity of HCC.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1331-8) contains supplementary material, which is available to authorized users.

Endodermal pouch-expressed dmrt2b is important for pharyngeal cartilage formation

Pharyngeal pouches, a series of outpocketings derived from the foregut endoderm, are essential for craniofacial skeleton formation. However, the molecular mechanisms underlying endodermal pouch-regulated head cartilage development are not fully understood. In this study, we find that zebrafish dmrt2b, a gene encoding Doublesex- and Mab-3-related transcription factor, is specifically expressed in endodermal pouches and required for normal pharyngeal cartilage development. Loss of dmrt2b doesn't affect cranial neural crest (CNC) specification and migration, but leads to prechondrogenic condensation defects by reducing cxcl12b expression after CNC cell movement into the pharyngeal arches. Moreover, dmrt2b inactivation results in reduced proliferation and impaired differentiation of CNC cells. We also show that dmrt2b suppresses crossveinless 2 expression in endodermal pouches to maintain BMP/Smad signaling in the arches, thereby facilitating CNC cell proliferation and chondrogenic differentiation. This work provides insight into how transcription factors expressed in endodermal pouches regulate pharyngeal skeleton development through tissue-tissue interactions.

Mutational analysis of dishevelled genes in zebrafish reveals distinct functions in embryonic patterning and gastrulation cell movements

Wnt signaling plays critical roles in dorsoventral fate specification and anteroposterior patterning, as well as in morphogenetic cell movements. Dishevelled proteins, or Dvls, mediate the activation of Wnt/ß-catenin and Wnt/planar cell polarity pathways. There are at least three highly conserved Dvl proteins in vertebrates, but the implication of each Dvl in key early developmental processes remains poorly understood. In this study, we use genome-editing approach to generate different combinations of maternal and zygotic dvl mutants in zebrafish, and examine their functions during early development. Maternal transcripts for dvl2 and dvl3a are most abundantly expressed, whereas the transcript levels of other dvl genes are negligible. Phenotypic and molecular analyses show that early dorsal fate specification is not affected in maternal and zygotic dvl2 and dvl3a double mutants, suggesting that the two proteins may be dispensable for the activation of maternal Wnt/ß-catenin signaling. Interestingly, convergence and extension movements and anteroposterior patterning require both maternal and the zygotic functions of Dvl2 and Dvl3a, but these processes are more sensitive to Dvl2 dosage. Zygotic dvl2 and dvl3a double mutants display mild axis extension defect with correct anteroposterior patterning. However, maternal and zygotic double mutants exhibit most strongly impaired convergence and extension movements, severe trunk and posterior deficiencies, and frequent occurrence of cyclopia and craniofacial defects. Our results suggest that Dvl2 and Dvl3a products are required for the activation of zygotic Wnt/ß-catenin signaling and Wnt/planar cell polarity pathway, and regulate zygotic developmental processes in a dosage-dependent manner. This work provides insight into the mechanisms of Dvl-mediated Wnt signaling pathways during early vertebrate development.

The embryogenesis of most animals is first supported by maternal gene products accumulated in the oocyte, and then by the expression of genes from the zygote. In all vertebrates, there are at least three Dishevelled (Dvl) proteins, which play critical roles in normal development and human diseases. They are both maternally and zygotically expressed, and can activate the ß-catenin-dependent Wnt pathway that regulates gene expression and cell fate, and the ß-catenin-independent Wnt pathway that orchestrates cell movements. In zebrafish embryo, Dvl2 and Dvl3a are most abundant, but their functions are not fully understood. We find that maternally and zygotically expressed Dvl2 plays a predominant role in the elongation of the anteroposterior axis, and the expression of genes involved in the development of the posterior region. Dvl3a cooperates with Dvl2 in these processes. Analyses after loss-of-function of these genes indicate that deficiency of maternal and zygotic Dvl2 and Dvl3a results in embryos with cyclopia, craniofacial defects, and severe abnormality in the trunk and posterior regions. Many human birth defects and other diseases, like cancer, are attributed to the dysfunction of the Wnt pathways. Our results help to understand the mechanisms of Dvl-mediated Wnt pathway activation, and the causes of developmental disorders.

Resistance-promoting effects of ependymoma treatment revealed through genomic analysis of multiple recurrences in a single patient

As in other brain tumors, multiple recurrences after complete resection and irradiation of supratentorial ependymoma are common and frequently result in patient death. This standard-of-care treatment was established in the pregenomic era without the ability to evaluate the effect that mutagenic therapies may exert on tumor evolution and in promoting resistance, recurrence, and death. We seized a rare opportunity to characterize treatment effects and the evolution of a single patient's ependymoma across four recurrences after different therapies. A combination of high-depth whole-genome and exome-based DNA sequencing of germline and tumor specimens, RNA sequencing of tumor specimens, and advanced computational analyses were used. Treatment with radiation and chemotherapies resulted in a substantial increase in mutational burden and diversification of the tumor subclonal architecture without eradication of the founding clone. Notable somatic alterations included a MEN1 driver, several epigenetic modifiers, and therapy-induced mutations that impacted multiple other cancer-relevant pathways and altered the neoantigen landscape. These genomic data provided new mechanistic insights into the genesis of ependymoma and pathways of resistance. They also revealed that radiation and chemotherapy were significant forces in shaping the increased subclonal complexity of each tumor recurrence while also failing to eradicate the founding clone. This raises the question of whether standard-of-care treatments have similar consequences in other patients with ependymoma and other types of brain tumors. If so, the perspective obtained by real-time genomic characterization of a tumor may be essential for making effective patient-specific and adaptive clinical decisions.

Mechanisms of RhoA inactivation and CDC42 and Rac1 activation during zebrafish optic nerve regeneration

When axons of the mammalian central nervous system (CNS) are injured, they fail to regenerate, while those of lower vertebrates undergo regeneration after injury. Wingless-type MMTV integration site family (Wnt) proteins play important roles in the CNS, and are reported to be activated after mammalian spinal cord or brain injury. Moreover, for axon growth to proceed, it is thought that small G-proteins, such as CDC42 and Rac1, need to be activated, whereas RhoA must be inactivated. However, the cell and molecular mechanisms involved in optic nerve regeneration remain unclear. In this study, we investigated axonal regeneration after injury using the zebrafish optic nerve as a model system. We sought to clarify the role of Wnt proteins and the mechanisms involved in the activation and inactivation of small G-proteins in nerve regeneration. After optic nerve injury, mRNA levels of Wnt5b, TAX1BP3 and ICAT increased in the retina, while those of Wnt10a decreased. These changes were associated with a reduction in β-catenin in nuclei. We found that Wnt5b activated CDC42 and Rac1, leading to the inactivation of RhoA, which appeared to be dependent on increased TAX1BP3 mRNA levels. Furthermore, we found that mRNA levels of Daam1a and ARHGEF16 decreased. We speculate that the decrease in β-catenin levels, which also further reduces levels of active RhoA, might contribute to regeneration in the zebrafish. Collectively, our novel results suggest that Wnt5b, Wnt10a, ICAT and TAX1BP3 participate in the activation and inactivation of small G-proteins, such as CDC42, Rac1 and RhoA, during the early stage of optic nerve regeneration in the zebrafish.

Toddler signaling regulates mesodermal cell migration downstream of Nodal signaling

Toddler/Apela/Elabela is a conserved secreted peptide that regulates mesendoderm development during zebrafish gastrulation. Two non-exclusive models have been proposed to explain Toddler function. The ‘specification model’ postulates that Toddler signaling enhances Nodal signaling to properly specify endoderm, whereas the ‘migration model’ posits that Toddler signaling regulates mesendodermal cell migration downstream of Nodal signaling. Here, we test key predictions of both models. We find that in toddler mutants Nodal signaling is initially normal and increasing endoderm specification does not rescue mesendodermal cell migration. Mesodermal cell migration defects in toddler mutants result from a decrease in animal pole-directed migration and are independent of endoderm. Conversely, endodermal cell migration defects are dependent on a Cxcr4a-regulated tether of the endoderm to mesoderm. These results suggest that Toddler signaling regulates mesodermal cell migration downstream of Nodal signaling and indirectly affects endodermal cell migration via Cxcr4a-signaling.

A GEF activity-independent function for nuclear Net1 in Nodal/Smad2 signal transduction and mesendoderm formation

Net1 is a well-characterized oncoprotein with RhoA-specific GEF activity. Oncogenic Net1 lacking the first 145 amino acids is present in the cytosol and contributes to the efficient activation of RhoA and the formation of actin stress fibers in a number of tumor cell types. Meanwhile, wild-type Net1 is predominantly localized in the nucleus at steady state due to its N-terminal nuclear localization sequences, where the function of nuclear Net1 has not been fully determined. Here, we find that zebrafish net1 is expressed specifically in mesendoderm precursors during gastrulation. Endogenous Net1 is located in the nucleus during early embryonic development. Gain- and loss-of-function experiments in zebrafish embryos and mammalian cells demonstrate that, regardless of its GEF activity, nuclear Net1 is critical for zebrafish mesendoderm formation and Nodal/Smad2 signal transduction. Detailed analyses of protein interactions reveal that Net1 associates with Smad2 in the nucleus in a GEF-independent manner, and then promotes Smad2 activation by enhancing recruitment of p300 to the transcriptional complex. These findings describe a novel genetic mechanism by which nuclear Net1 facilitates Smad2 transcriptional activity to guide mesendoderm development.