Identification of FAM181A and FAM181B as new interactors with the TEAD transcription factors

The Hippo pathway is a key signaling pathway in the control of organ size and development. The most distal elements of this pathway, the TEAD transcription factors, are regulated by several proteins, such as YAP (Yes-associated protein), TAZ (transcriptional co-activator with PDZ-binding motif) and VGLL1-4 (Vestigial-like members 1-4). In this article, combining structural data and motif searches in protein databases, we identify two new TEAD interactors: FAM181A and FAM181B. Our structural data show that they bind to TEAD via an Ω-loop as YAP/TAZ do, but only FAM181B possesses the LxxLF motif (x any amino acid) found in YAP/TAZ. The affinity of different FAM181A/B fragments for TEAD is in the low micromolar range and full-length FAM181A/B proteins interact with TEAD in cells. These findings, together with a recent report showing that FAM181A/B proteins have a role in nervous system development, suggest a potential new involvement of the TEAD transcription factors in the development of this tissue.

Upstream regulation of the Hippo-Yap pathway in cardiomyocyte regeneration

The response of the adult mammalian heart to injury such as myocardial infarction has long been described as primarily fibrotic scarring and adverse remodeling with little to no regeneration of cardiomyocytes. Emerging studies have challenged this paradigm by demonstrating that, indeed, adult mammalian cardiomyocytes are capable of completing cytokinesis albeit at levels vastly insufficient to compensate for the loss of functional cardiomyocytes following ischemic injury. Thus, there is great interest in identifying mechanisms to guide adult cardiomyocyte cell cycle re-entry and facilitate endogenous heart regeneration. The Hippo signaling pathway is a core kinase cascade that functions to suppress the transcriptional co-activators Yap and Taz by phosphorylation and therefore cytoplasmic retention or phospho-degradation. This pathway has recently sparked interest in the field of cardiac regeneration as inhibition of Hippo kinase signaling or overdriving the transcriptional co-activator, Yap, significantly promotes proliferation of terminally differentiated adult mammalian cardiomyocytes and can restore function in failing mouse hearts. Thus, the Hippo pathway is an attractive therapeutic target for promoting cardiomyocyte renewal and cardiac regeneration. Although the core kinases and transcriptional activators of the Hippo pathway have been studied extensively over the last twenty years, the regulatory inputs of this pathway, particularly in vertebrates, are poorly understood. Recent studies have elucidated several upstream regulatory inputs to the Hippo pathway in adult mammalian cardiomyocytes that influence cell proliferation and heart regeneration. Considering upstream inputs to the Hippo pathway are thought to be context and cell type specific, targeting these various components could serve as a therapeutic approach for refining Hippo-Yap signaling in the heart. Here, we provide an overview of the emerging regulatory inputs to the Hippo pathway as they relate to mammalian cardiomyocytes and heart regeneration.

Activating Hippo Pathway via Rassf1 by Ursolic Acid Suppresses the Tumorigenesis of Gastric Cancer

The Hippo pathway is often dysregulated in many carcinomas, which results in various stages of tumor progression. Ursolic acid (UA), a natural compound that exists in many herbal plants, is known to obstruct cancer progression and exerts anti-carcinogenic effect on a number of human cancers. In this study, we aimed to examine the biological mechanisms of action of UA through the Hippo pathway in gastric cancer cells. MTT assay showed a decreased viability of gastric cancer cells after treatment with UA. Following treatment with UA, colony numbers and the sizes of gastric cancer cells were significantly diminished and apoptosis was observed in SNU484 and SNU638 cells. The invasion and migration rates of gastric cancer cells were suppressed by UA in a dose-dependent manner. To further determine the gene expression patterns that are related to the effects of UA, a microarray analysis was performed. Gene ontology analysis revealed that several genes, such as the Hippo pathway upstream target gene, ras association domain family (RASSF1), and its downstream target genes (MST1, MST2, and LATS1) were significantly upregulated by UA, while the expression of YAP1 gene, together with oncogenes (FOXM1, KRAS, and BATF), were significantly decreased. Similar to the gene expression profiling results, the protein levels of RASSF1, MST1, MST2, LATS1, and p-YAP were increased, whereas those of CTGF were decreased by UA in gastric cancer cells. The p-YAP expression induced in gastric cancer cells by UA was reversed with RASSF1 silencing. In addition, the protein levels in the Hippo pathway were increased in the UA-treated xenograft tumor tissues as compared with that in the control tumor tissues; thus, UA significantly inhibited the tumorigenesis of gastric cancer in vivo in xenograft animals. Collectively, UA diminishes the proliferation and metastasis of gastric cancer via the regulation of Hippo pathway through Rassf1, which suggests that UA can be used as a potential chemopreventive and therapeutic agent for gastric cancer.

yap1b, a divergent Yap/Taz family member, cooperates with yap1 in survival and morphogenesis via common transcriptional targets

Yap1/Taz are well-known Hippo effectors triggering complex transcriptional programs controlling growth, survival and cancer progression. Here, we describe yap1b, a new Yap1/Taz family member with a unique transcriptional activation domain that cannot be phosphorylated by Src/Yes kinases. We show that yap1b evolved specifically in euteleosts (i.e. including medaka but not zebrafish) by duplication and adaptation of yap1. Using DamID-seq, we generated maps of chromatin occupancy for Yap1, Taz (Wwtr1) and Yap1b in gastrulating zebrafish and medaka embryos. Our comparative analyses uncover the genetic programs controlled by Yap family proteins during early embryogenesis, and show largely overlapping targets for Yap1 and Yap1b. CRISPR/Cas9-induced mutation of yap1b in medaka does not result in an overt phenotype during embryogenesis or adulthood. However, yap1b mutation strongly enhances the embryonic malformations observed in yap1 mutants. Thus yap1 ^-/-; yap1b ^-/- double mutants display more severe body flattening, eye misshaping and increased apoptosis than yap1 ^-/- single mutants, thus revealing overlapping gene functions. Our results indicate that, despite its divergent transactivation domain, Yap1b cooperates with Yap1 to regulate cell survival and tissue morphogenesis during early development.

MicroRNA-373 promotes the development of esophageal squamous cell carcinoma by targeting LATS2 and OXR1

INTRODUCTION

MicroRNA373 was highly expressed in many tumors including esophageal cancer. However, its molecular mechanism is still unclear, especially epigenetic modification, in esophageal squamous cell carcinoma (ESCC).

METHODS

In this study, we investigated serum levels of the miR-371-373 cluster in ESCC patients before and after surgical removal, and further focused on the expression level of miR-373-3p in tumor tissues of ESCC patients and its target genes. In addition, the epigenetic alterations of miR-373-3p promoter was analyzed.

RESULTS

The expression levels of miR-371-5p and miR-373-3p were significantly increased in preoperative serum of ESCC patients compared with that of healthy volunteers (P<0.01); however, they dropped significantly after surgical removal (P<0.01). Compared with adjacent normal tissues, miR-373-3p also showed significant up-regulation in cancer tissues (P<0.05). The methylation levels of miR-373-3p promoter were 42.86% in ESCC cancer tissue and 66.67% in adjacent normal tissues. The low methylation of the miR-373-3p promoter may promote the expression of miR-373-3p. Large tumor suppressor 2 (LATS2) and oxidation resistance 1(OXR1) are predicted to be targets of miR-373-3p by the bioinformatics method. They are the genes in the Hippo and the p53 signaling pathway, respectively. Their respective upstream genes, neurofibromatosis type 2 (NF2) and Jun Kinase, and the downstream genes, transcriptional co-activator with PDZ-binding motif (TAZ) and caspase 9, were also detected. The expression of all these genes were significantly decreased in ESCC cancer tissues compared with adjacent normal tissues.

CONCLUSIONS

This study shows that DNA epigenetic modification in the miR-373-3p promoter region and the Hippo and p53 signaling pathways play important roles during the miR-373-3p mediating ESCC development process.

YAP1-LATS2 feedback loop dictates senescent or malignant cell fate to maintain tissue homeostasis

Dysfunction of the homeostasis-maintaining systems in specific cell types or tissues renders the organism susceptible to a range of diseases, including cancers. One of the emerging mechanisms for maintaining tissue homeostasis is cellular senescence. Here, we report that the Hippo pathway plays a critical role in controlling the fate of ovarian cells. Hyperactivation of Yes-associated protein 1 (YAP1), the major effector of the Hippo pathway, induces senescence in cultured primary human ovarian surface epithelial cells (hOSEs). Large tumor suppressor 2 (LATS2), the primary upstream negative regulator of YAP1, is elevated in both YAP1-induced and natural replicative-triggered senescence. Deletion of LATS2 in hOSEs prevents these cells from natural replicative and YAP1-induced senescence. Most importantly, loss of LATS2 switches ovarian cells from YAP-induced senescence to malignant transformation. Our results demonstrate that LATS2 and YAP1, two major components of the Hippo/YAP signaling pathway, form a negative feedback loop to control YAP1 activity and prevent ovarian cells from malignant transformation. Human cancer genomic data extracted from TCGA datasets further confirm the clinical relevance of our finding.

YAPping about and not forgetting TAZ

The Hippo pathway has emerged as a major eukaryotic signalling pathway and is increasingly the subject of intense interest, as are the key effectors of canonical Hippo signalling, YES-associated protein (YAP) and TAZ. The Hippo pathway has key roles in diverse biological processes, including network signalling regulation, development, organ growth, tissue repair and regeneration, cancer, stem cell regulation and mechanotransduction. YAP and TAZ are multidomain proteins and function as transcriptional coactivators of key genes to evoke their biological effects. YAP and TAZ interact with numerous partners and their activities are controlled by a complex set of processes. This review provides an overview of Hippo signalling and its role in growth. In particular, the functional domains of YAP and TAZ and the complex mechanisms that regulate their protein stability and activity are discussed. Notably, the similarities and key differences are highlighted between the two paralogues including which partner proteins interact with which functional domains to regulate their activity.

Emerging roles of YAP/TAZ in lung physiology and diseases

The YAP and TAZ, as the downstream effectors of Hippo pathway, have emerged as important translational co-activators of a wide variety of biological processes. YAP/TAZ plays a crucial role in the lung development and physiology. Dysregulation of YAP/TAZ signaling pathway contributes to the development and progression of chronic lung diseases, including lung cancer, pulmonary fibrosis, pulmonary hypertension, COPD, asthma, and lung infection. Therefore, owing to its critical functions, delineation of the signaling mechanisms of YAP/TAZ in pathological conditions will shed light on developing strategies for its therapeutic targeting. Currently, the complex regulation of this pathway is under extensive investigation. In this review, we summarize and present recent findings of molecular mechanisms of YAP/TAZ in the lung physiological and pathological conditions, as well as the implications of YAP/TAZ for lung diseases treatment and regeneration.

The Ambivalent Function of YAP in Apoptosis and Cancer

Yes-associated protein, a core regulator of the Hippo-YAP signaling pathway, plays a vital role in inhibiting apoptosis. Thus, several studies and reviews suggest that yes-associated protein is a good target for treating cancer. Unfortunately, more and more evidence demonstrates that this protein is also an essential contributor of p73-mediated apoptosis. This questions the concept that yes-associated protein is always a good target for developing novel anti-cancer drugs. Thus, the aim of this review was to evaluate the clinical relevance of yes-associated protein for cancer pathophysiology. This review also summarized the molecules, processes and drugs, which regulate Hippo-YAP signaling and discusses their effect on apoptosis. In addition, issues are defined, which should be addressed in the future in order to provide a solid basis for targeting the Hippo-YAP signaling pathway in clinical trials.

The history and regulatory mechanism of the Hippo pathway

How the organ size is adjusted to the proper size during development and how organs know that they reach the original size during regeneration remain long-standing questions. Based on studies using multiple model organisms and approaches for over 20 years, a consensus has been established that the Hippo pathway plays crucial roles in controlling organ size and maintaining tissue homeostasis. Given the significance of these processes, the dysregulation of the Hippo pathway has also implicated various diseases, such as tissue degeneration and cancer. By regulating the downstream transcriptional coactivators YAP and TAZ, the Hippo pathway coordinates cell proliferation and apoptosis in response to a variety of signals including cell contact inhibition, polarity, mechanical sensation and soluble factors. Since the core components and their functions of the Hippo pathway are evolutionarily conserved, this pathway serves as a global regulator of organ size control. Therefore, further investigation of the regulatory mechanisms will provide physiological insights to better understand tissue homeostasis. In this review, the historical developments and current understandings of the regulatory mechanism of Hippo signaling pathway are discussed.

PTEN lipid phosphatase inactivation links the hippo and PI3K/Akt pathways to induce gastric tumorigenesis

Background

Phosphatase and tensin homolog (PTEN) is an important tumor suppressor gene, and its encoded protein has activities of both a protein phosphatase and a lipid phosphatase. However, the substitution effect of protein phosphatase activity remains unclear. PI3K/Akt is the most common pathway negatively regulated by PTEN. The Hippo and PI3K/Akt pathways have a joint effect in regulating cell proliferation and apoptosis. Therefore, how PTEN lipid phosphatase inactivation contributes to the occurrence and development of gastric cancer and the potential role of the Hippo and PI3K/Akt pathways in PTEN lipid phosphatase inactivation mediated gastric tumorigenesis remain to be explored.

Methods

Immunohistochemical staining was performed to detect the expression of p-PTEN and YAP in a gastric cancer tissue microarray. Stable cell lines expressing a wild-type or dominant-negative mutant PTEN were established. The proliferation and migration of stable cells were detected by MTT, BrdU, and colony-formation, transwell assay and high content analysis in vitro, and tumor growth differences were observed in xenograft nude mice. Changes in the expression of key molecules in the Hippo and Akt signaling pathways were detected by western blot. Nuclear-cytoplasm separation, immunofluorescence and coimmunoprecipitation analyses were conducted to explore the dysregulation of Hippo in the stable cell lines.

Results

PTEN lipid phosphatase inactivation strongly promoted the proliferation and migration of gastric cancer cells in vitro and tumor growth in vivo. A immunohistochemical analysis of gastric cancer tissues revealed a significant correlation between phosphorylated PTEN and nuclear YAP expression, and both were determined to be independent prognostic factors for gastric cancer. Mechanistically, PTEN lipid phosphatase inactivation abolished the MOB1-LATS1/2 interaction, decreased YAP phosphorylation and finally promoted YAP nuclear translocation, which enhanced the synergistic effect of YAP-TEAD, thus inducing cell proliferation and migration. Moreover, PTEN lipid phosphatase inactivation promoted the PI3K/Akt pathway, and disruption of YAP-TEAD-driven transcription decreased the activation of Akt in a dose-dependent manner.

Conclusions

Taken together, our findings indicate that PTEN lipid phosphatase inactivation links the Hippo and PI3K/Akt pathways to promote gastric tumorigenesis and cancer development.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0795-2) contains supplementary material, which is available to authorized users.

Understanding Animal Evolution: The Added Value of Sponge Transcriptomics and Genomics: The disconnect between gene content and body plan evolution

Sponges are important but often-neglected organisms. The absence of classical animal traits (nerves, digestive tract, and muscles) makes sponges challenging for non-specialists to work with and has delayed getting high quality genomic data compared to other invertebrates. Yet analyses of sponge genomes and transcriptomes currently available have radically changed our understanding of animal evolution. Sponges are of prime evolutionary importance as one of the best candidates to form the sister group of all other animals, and genomic data are essential to understand the mechanisms that control animal evolution and diversity. Here we review the most significant outcomes of current genomic and transcriptomic analyses of sponges, and discuss limitations and future directions of sponge transcriptomic and genomic studies.

Hippo-yap signaling in ocular development and disease

The Hippo-Yes associated protein (Yap) pathway plays an important role in organ size control by regulating cell proliferation, apoptosis, and stem cell renewal. Hippo-Yap signaling also functions at the level of cellular development in a variety of organs through its effects on cell cycle control, cell survival, cell polarity, and cell fate. Because of its important roles in normal development and homeostasis, abnormal regulation of this pathway has been shown to lead to pathological outcomes such as tissue overgrowth, tumor formation, and abnormal organogenesis, including ocular-specific disorders. In this review, we summarize how normal and perturbed control of Yap signaling is implicated in ocular development and disease Developmental Dynamics 247:794-806, 2018. © 2018 Wiley Periodicals, Inc.

The Hippo pathway effector Wwtr1 regulates cardiac wall maturation in zebrafish

Cardiac trabeculation is a highly regulated process that starts with the delamination of compact layer cardiomyocytes. The Hippo signaling pathway has been implicated in cardiac development but many questions remain. We have investigated the role of Wwtr1, a nuclear effector of the Hippo pathway, in zebrafish and find that its loss leads to reduced cardiac trabeculation. However, in mosaic animals, wwtr1^-/- cardiomyocytes contribute more frequently than wwtr1^+/- cardiomyocytes to the trabecular layer of wild-type hearts. To investigate this paradox, we examined the myocardial wall at early stages and found that compact layer cardiomyocytes in wwtr1^-/- hearts exhibit disorganized cortical actin structure and abnormal cell-cell junctions. Accordingly, wild-type cardiomyocytes in mosaic mutant hearts contribute less frequently to the trabecular layer than when present in mosaic wild-type hearts, indicating that wwtr1^-/- hearts are not able to support trabeculation. We also found that Nrg/Erbb2 signaling, which is required for trabeculation, could promote Wwtr1 nuclear export in cardiomyocytes. Altogether, these data suggest that Wwtr1 establishes the compact wall architecture necessary for trabeculation, and that Nrg/Erbb2 signaling negatively regulates its nuclear localization and therefore its activity.

NF2 signaling pathway plays a pro-apoptotic role in β-adrenergic receptor stimulated cardiac myocyte apoptosis

β-adrenergic receptor (β-AR) stimulation induces cardiac myocyte apoptosis in vitro and in vivo. Neurofibromin 2 (NF2) is a member of the ezrin/radixin/moesin (ERM) family of proteins. Post-translational modifications such as phosphorylation and sumoylation affect NF2 activity, subcellular localization and function. Here, we tested the hypothesis that β-AR stimulation induces post-translational modifications of NF2, and NF2 plays a pro-apoptotic role in β-AR-stimulated myocyte apoptosis.

p53 shades of Hippo

The three p53 family members, p53, p63 and p73, are structurally similar and share many biochemical activities. Yet, along with their common fundamental role in protecting genomic fidelity, each has acquired distinct functions related to diverse cell autonomous and non-autonomous processes. Similar to the p53 family, the Hippo signaling pathway impacts a multitude of cellular processes, spanning from cell cycle and metabolism to development and tumor suppression. The core Hippo module consists of the tumor-suppressive MST-LATS kinases and oncogenic transcriptional co-effectors YAP and TAZ. A wealth of accumulated data suggests a complex and delicate regulatory network connecting the p53 and Hippo pathways, in a highly context-specific manner. This generates multiple layers of interaction, ranging from interdependent and collaborative signaling to apparent antagonistic activity. Furthermore, genetic and epigenetic alterations can disrupt this homeostatic network, paving the way to genomic instability and cancer. This strengthens the need to better understand the nuances that control the molecular function of each component and the cross-talk between the different components. Here, we review interactions between the p53 and Hippo pathways within a subset of physiological contexts, focusing on normal stem cells and development, as well as regulation of apoptosis, senescence and metabolism in transformed cells.

Mutual regulation of the Hippo/Wnt/LPA/TGF‑β signaling pathways and their roles in glaucoma (Review)

Glaucoma is the leading cause of irreversible blindness worldwide and there is no effective treatment thus far. The trabecular meshwork has been identified as the major pathological area involved. Certain signaling pathways in the trabecular meshwork, including the Wnt, lysophosphatidic acid and transforming growth factor-β pathways, have been identified as novel therapeutic targets in glaucoma treatment. Meanwhile, it has been reported that key proteins in these pathways, particularly the primary transcription regulator Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), exhibit interactions with the Hippo pathway. The Hippo pathway, which was first identified in Drosophila, has drawn great focus with regard to various aspects of studies in recent years. One role of the Hippo pathway in the regulation of organ size was indicated by more recent evidence. Defining the relevant physiological function of the Hippo pathway has proven to be extremely complicated. Studies have ascribed a role for the Hippo pathway in an overwhelming number of processes, including cell proliferation, cell death and cell differentiation. Therefore, the present review aimed to unravel the roles of YAP and TAZ in the Hippo pathway and the pathogenesis of glaucoma. Furthermore, a new and creative study for the treatment of glaucoma is provided.

Regulation of posterior body and epidermal morphogenesis in zebrafish by localized Yap1 and Wwtr1

The vertebrate embryo undergoes a series of dramatic morphological changes as the body extends to form the complete anterior-posterior axis during the somite-forming stages. The molecular mechanisms regulating these complex processes are still largely unknown. We show that the Hippo pathway transcriptional coactivators Yap1 and Wwtr1 are specifically localized to the presumptive epidermis and notochord, and play a critical and unexpected role in posterior body extension by regulating Fibronectin assembly underneath the presumptive epidermis and surrounding the notochord. We further find that Yap1 and Wwtr1, also via Fibronectin, have an essential role in the epidermal morphogenesis necessary to form the initial dorsal and ventral fins, a process previously thought to involve bending of an epithelial sheet, but which we now show involves concerted active cell movement. Our results reveal how the Hippo pathway transcriptional program, localized to two specific tissues, acts to control essential morphological events in the vertebrate embryo.

Regulation of Tissue Growth by the Mammalian Hippo Signaling Pathway

The integrative control of diverse biological processes such as proliferation, differentiation, apoptosis and metabolism is essential to maintain cellular and tissue homeostasis. Disruption of these underlie the development of many disease states including cancer and diabetes, as well as many of the complications that arise as a consequence of aging. These biological outputs are governed by many cellular signaling networks that function independently, and in concert, to convert changes in hormonal, mechanical and metabolic stimuli into alterations in gene expression. First identified in Drosophila melanogaster as a powerful mediator of cell division and apoptosis, the Hippo signaling pathway is a highly conserved regulator of mammalian organ size and functional capacity in both healthy and diseased tissues. Recent studies have implicated the pathway as an effector of diverse physiological cues demonstrating an essential role for the Hippo pathway as an integrative component of cellular homeostasis. In this review, we will: (a) outline the critical signaling elements that constitute the mammalian Hippo pathway, and how they function to regulate Hippo pathway-dependent gene expression and tissue growth, (b) discuss evidence that shows this pathway functions as an effector of diverse physiological stimuli and (c) highlight key questions in this developing field.

Regulation of the Hippo-YAP Pathway by Glucose Sensor O-GlcNAcylation

The Hippo pathway is crucial in organ size control and tissue homeostasis, with deregulation leading to cancer. An extracellular nutrition signal, such as glucose, regulates the Hippo pathway activation. However, the mechanisms are still not clear. Here, we found that the Hippo pathway is directly regulated by the hexosamine biosynthesis pathway (HBP) in response to metabolic nutrients. Mechanistically, the core component of Hippo pathway (YAP) is O-GlcNAcylated by O-GlcNAc transferase (OGT) at serine 109. YAP O-GlcNAcylation disrupts its interaction with upstream kinase LATS1, prevents its phosphorylation, and activates its transcriptional activity. And this activation is not dependent on AMPK. We also identified OGT as a YAP-regulated gene that forms a feedback loop. Finally, we confirmed that glucose-induced YAP O-GlcNAcylation and activation promoted tumorigenesis. Together, our data establish a molecular mechanism and functional significance of the HBP in directly linking extracellular glucose signal to the Hippo-YAP pathway and tumorigenesis.

Yes-associated protein: A novel molecular target for the diagnosis, treatment and prognosis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common type of malignant tumor. The early-diagnosis and treatment options for HCC are limited, which is primarily due to an incomplete understanding of the underlying molecular mechanisms of the disease. Yes-associated protein (YAP) overexpression promotes proliferation and phenotypic transformation of HCC cells. Recently, elucidating the molecular mechanisms of the Hippo/YAP signaling pathway and investigating the interactions between the signaling molecules, as a potential strategy for the treatment of HCC, has become an area of interest. The present review will discuss the role of YAP in HCC pathogenesis, and the significance of YAP in diagnosis, treatment and determining the prognosis.

The LATS1 and LATS2 tumor suppressors: beyond the Hippo pathway

Proper cellular functionality and homeostasis are maintained by the convergent integration of various signaling cascades, which enable cells to respond to internal and external changes. The Dbf2-related kinases LATS1 and LATS2 (LATS) have emerged as central regulators of cell fate, by modulating the functions of numerous oncogenic or tumor suppressive effectors, including the canonical Hippo effectors YAP/TAZ, the Aurora mitotic kinase family, estrogen signaling and the tumor suppressive transcription factor p53. While the basic functions of the LATS kinase module are strongly conserved over evolution, the genomic duplication event leading to the emergence of two closely related kinases in higher organisms has increased the complexity of this signaling network. Here, we review the LATS1 and LATS2 intrinsic features as well as their reported cellular activities, emphasizing unique characteristics of each kinase. While differential activities between the two paralogous kinases have been reported, many converge to similar pathways and outcomes. Interestingly, the regulatory networks controlling the mRNA expression pattern of LATS1 and LATS2 differ strongly, and may contribute to the differences in protein binding partners of each kinase and in the subcellular locations in which each kinase exerts its functions.

The Hippo Pathway Maintains the Equatorial Division Plane in the Ciliate Tetrahymena

The mechanisms that govern pattern formation within the cell are poorly understood. Ciliates carry on their surface an elaborate pattern of cortical organelles that are arranged along the anteroposterior and circumferential axes by largely unknown mechanisms. Ciliates divide by tandem duplication: the cortex of the predivision cell is remodeled into two similarly sized and complete daughters. In the conditional cdaI-1 mutant of Tetrahymena thermophila, the division plane migrates from its initially correct equatorial position toward the cell's anterior, resulting in unequal cell division, and defects in nuclear divisions and cytokinesis. We used comparative whole genome sequencing to identify the cause of cdaI-1 as a mutation in a Hippo/Mst kinase. CdaI is a cortical protein with a cell cycle-dependent, highly polarized localization. Early in cell division, CdaI marks the anterior half of the cell, and later concentrates at the posterior end of the emerging anterior daughter. Despite the strong association of CdaI with the new posterior cell end, the cdaI-1 mutation does not affect the patterning of the new posterior cortical organelles. We conclude that, in Tetrahymena, the Hippo pathway maintains an equatorial position of the fission zone, and, by this activity, specifies the relative dimensions of the anterior and posterior daughter cell.

The Caenorhabditis elegans NF2/Merlin Molecule NFM-1 Nonautonomously Regulates Neuroblast Migration and Interacts Genetically with the Guidance Cue SLT-1/Slit

During nervous system development, neurons and their progenitors migrate to their final destinations. In Caenorhabditis elegans, the bilateral Q neuroblasts and their descendants migrate long distances in opposite directions, despite being born in the same posterior region. QR on the right migrates anteriorly and generates the AQR neuron positioned near the head, and QL on the left migrates posteriorly, giving rise to the PQR neuron positioned near the tail. In a screen for genes required for AQR and PQR migration, we identified an allele of nfm-1, which encodes a molecule similar to vertebrate NF2/Merlin, an important tumor suppressor in humans. Mutations in NF2 lead to neurofibromatosis type II, characterized by benign tumors of glial tissues. Here we demonstrate that in C. elegans, nfm-1 is required for the ability of Q cells and their descendants to extend protrusions and to migrate, but is not required for direction of migration. Using a combination of mosaic analysis and cell-specific expression, we show that NFM-1 is required nonautonomously, possibly in muscles, to promote Q lineage migrations. We also show a genetic interaction between nfm-1 and the C. elegans Slit homolog slt-1, which encodes a conserved secreted guidance cue. Our results suggest that NFM-1 might be involved in the generation of an extracellular cue that promotes Q neuroblast protrusion and migration that acts with or in parallel to SLT-1 In vertebrates, NF2 and Slit2 interact in axon pathfinding, suggesting a conserved interaction of NF2 and Slit2 in regulating migratory events.

Epidermal YAP2-5SA-ΔC Drives β-Catenin Activation to Promote Keratinocyte Proliferation in Mouse Skin In Vivo

The epidermis is a highly regenerative tissue. YAP is a pivotal regulator of stem/progenitor cells in tissue regeneration, including in the epidermis. The molecular mechanisms downstream of YAP that activate epidermal cell proliferation remain largely unknown. We found that YAP and β-catenin co-localize in the nuclei of keratinocytes in the regenerating epidermis in vivo and in proliferating HaCaT keratinocytes in vitro. Inactivation of YAP in HaCaT keratinocytes resulted in reduced activated β-catenin and reduced keratinocyte numbers in vitro. In addition, we found that in the hyperplastic epidermis of YAP2-5SA-ΔC mice, the mutant YAP2-5SA-ΔC protein was predominantly localized in the keratinocyte nuclei and caused increased expression of activated nuclear β-catenin. Accordingly, β-catenin transcriptional activity was elevated in the skin of live YAP2-5SA-ΔC/TOPFLASH mice. Lastly, loss of β-catenin in basal keratinocytes of YAP2-5SA-ΔC/K14-creERT/CtnnB1^-/- mice resulted in reduced proliferation of basal keratinocytes and a striking rescue of the hyperplastic abnormalities. Taken together, our work shows that YAP2-5SA-ΔC drives β-catenin activity to promote basal keratinocyte proliferation in the mouse skin in vivo. Our data shine new light on the etiology of regenerative dermatological disorders and other human diseases that display increased YAP and β-catenin activity.

A transcriptional time-course analysis of oral vs. aboral whole-body regeneration in the Sea anemone Nematostella vectensis

Background

The ability of regeneration is essential for the homeostasis of all animals as it allows the repair and renewal of tissues and body parts upon normal turnover or injury. The extent of this ability varies greatly in different animals with the sea anemone Nematostella vectensis, a basal cnidarian model animal, displaying remarkable whole-body regeneration competence.

Results

In order to study this process in Nematostella we performed an RNA-Seq screen wherein we analyzed and compared the transcriptional response to bisection in the wound-proximal body parts undergoing oral (head) or aboral (tail) regeneration at several time points up to the initial restoration of the basic body shape. The transcriptional profiles of regeneration responsive genes were analyzed so as to define the temporal pattern of differential gene expression associated with the tissue-specific oral and aboral regeneration. The identified genes were characterized according to their GO (gene ontology) assignations revealing groups that were enriched in the regeneration process with particular attention to their affiliation to the major developmental signaling pathways. While some of the genes and gene groups thus analyzed were previously known to be active in regeneration, we have also revealed novel and surprising candidate genes such as cilia-associated genes that likely participate in this important developmental program.

Conclusions

This work highlighted the main groups of genes which showed polarization upon regeneration, notably the proteinases, multiple transcription factors and the Wnt pathway genes that were highly represented, all displaying an intricate temporal balance between the two sides. In addition, the evolutionary comparison performed between regeneration in different animal model systems may reveal the basic mechanisms playing a role in this fascinating process.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3027-1) contains supplementary material, which is available to authorized users.

Yorkie Facilitates Organ Growth and Metamorphosis in Bombyx

The Hippo pathway, which was identified from genetic screens in the fruit fly, Drosophila melanogaster, has a major size-control function in animals. All key components of the Hippo pathway, including the transcriptional coactivator Yorkie that is the most critical substrate and downstream effector of the Hippo kinase cassette, are found in the silkworm, Bombyx mori. As revealed by microarray and quantitative real-time PCR, expression of Hippo pathway genes is particularly enriched in several mitotic tissues, including the ovary, testis, and wing disc. Developmental profiles of Hippo pathway genes are generally similar (with the exception of Yorkie) within each organ, but vary greatly in different tissues showing nearly opposing expression patterns in the wing disc and the posterior silk gland (PSG) on day 2 of the prepupal stage. Importantly, the reduction of Yorkie expression by RNAi downregulated Yorkie target genes in the ovary, decreased egg number, and delayed larval-pupal-adult metamorphosis. In contrast, baculovirus-mediated Yorkie(CA) overexpression upregulated Yorkie target genes in the PSG, increased PSG size, and accelerated larval-pupal metamorphosis. Together the results show that Yorkie potentially facilitates organ growth and metamorphosis, and suggest that the evolutionarily conserved Hippo pathway is critical for size control, particularly for PSG growth, in the silkworm.

The Hippo signal transduction network for exercise physiologists

The ubiquitous transcriptional coactivators Yap (gene symbol Yap1) and Taz (gene symbol Wwtr1) regulate gene expression mainly by coactivating the Tead transcription factors. Being at the center of the Hippo signaling network, Yap and Taz are regulated by the Hippo kinase cassette and additionally by a plethora of exercise-associated signals and signaling modules. These include mechanotransduction, the AKT-mTORC1 network, the SMAD transcription factors, hypoxia, glucose homeostasis, AMPK, adrenaline/epinephrine and angiotensin II through G protein-coupled receptors, and IL-6. Consequently, exercise should alter Hippo signaling in several organs to mediate at least some aspects of the organ-specific adaptations to exercise. Indeed, Tead1 overexpression in muscle fibers has been shown to promote a fast-to-slow fiber type switch, whereas Yap in muscle fibers and cardiomyocytes promotes skeletal muscle hypertrophy and cardiomyocyte adaptations, respectively. Finally, genome-wide association studies in humans have linked the Hippo pathway members LATS2, TEAD1, YAP1, VGLL2, VGLL3, and VGLL4 to body height, which is a key factor in sports.

Comparative study of Hippo pathway genes in cellular conveyor belts of a ctenophore and a cnidarian

Background

The Hippo pathway regulates growth rate and organ size in fly and mouse, notably through control of cell proliferation. Molecular interactions at the heart of this pathway are known to have originated in the unicellular ancestry of metazoans. They notably involve a cascade of phosphorylations triggered by the kinase Hippo, with subsequent nuclear to cytoplasmic shift of Yorkie localisation, preventing its binding to the transcription factor Scalloped, thereby silencing proliferation genes. There are few comparative expression data of Hippo pathway genes in non-model animal species and notably none in non-bilaterian phyla.

Results

All core Hippo pathway genes could be retrieved from the ctenophore Pleurobrachia pileus and the hydrozoan cnidarian Clytia hemisphaerica, with the important exception of Yorkie in ctenophore. Expression study of the Hippo, Salvador and Scalloped genes in tentacle “cellular conveyor belts” of these two organisms revealed striking differences. In P. pileus, their transcripts were detected in areas where undifferentiated progenitors intensely proliferate and where expression of cyclins B and D was also seen. In C. hemisphaerica, these three genes and Yorkie are expressed not only in the proliferating but also in the differentiation zone of the tentacle bulb and in mature tentacle cells. However, using an antibody designed against the C. hemiphaerica Yorkie protein, we show in two distinct cell lineages of the medusa that Yorkie localisation is predominantly nuclear in areas of active cell proliferation and mainly cytoplasmic elsewhere.

Conclusions

This is the first evidence of nucleocytoplasmic Yorkie shift in association with the arrest of cell proliferation in a cnidarian, strongly evoking the cell division-promoting role of this protein and its inhibition by the activated Hippo pathway in bilaterian models. Our results furthermore highlight important differences in terms of deployment and regulation of Hippo pathway genes between cnidarians and ctenophores.

Electronic supplementary material

The online version of this article (doi:10.1186/s13227-016-0041-y) contains supplementary material, which is available to authorized users.

Activation of Yap-Directed Transcription by Knockdown of Conserved Cellular Functions

The Yap-Hippo pathway has a significant role in regulating cell proliferation and growth, thus controlling organ size and regeneration. The Hippo pathway regulates two highly conserved, transcription coactivators, YAP and TAZ. The upstream regulators of the Yap-Hippo pathway have not been fully characterized. The aim of this study was to use a siRNA screen, in a liver biliary cell line, to identify regulators of the Yap-Hippo pathway that allow activation of the YAP transcription coactivator at high cell density. Activation of the YAP transcription coactivator was monitored using a high-content, image-based assay that measured the intracellular localization of native YAP protein. Active siRNAs were identified and further validated by quantification of CYR61 mRNA levels (a known YAP target gene). The effect of compounds targeting the putative gene targets identified as hits was also used for further validation. A number of validated hits reveal basic aspects of Yap-Hippo biology, such as components of the nuclear pore, by which YAP cytoplasmic-nuclear shuttling occurs, or how proteasomal degradation regulates intracellular YAP concentrations, which then alter YAP localization and transcription. Such results highlight how targeting conserved cellular functions can lead to validated activity in phenotypic assays.

Thyroid development in zebrafish lacking Taz

Taz is a signal-responsive transcriptional coregulator implicated in several biological functions, from chondrogenesis to regulation of organ size. Less well studied, however, is its role in thyroid formation. Here, we explored the in vivo effects on thyroid development of morpholino (MO)-mediated knockdown of wwtr1, the gene encoding zebrafish Taz. The wwtr1 gene is expressed in the thyroid primordium and pharyngeal tissue of developing zebrafish. Compared to mammalian cells, in which Taz promotes expression of thyroid transcription factors and thyroid differentiation genes, wwtr1 MO injection in zebrafish had little or no effect on the expression of thyroid transcription factors, and differentially altered the expression of thyroid differentiation genes. Analysis of wwtr1 morphants at later stages of development revealed that the number and the lumen of thyroid follicles, and the number of thyroid follicle cells, were significantly smaller. In addition, Taz-depleted larvae displayed patterning defects in ventral cranial vessels that correlate with lateral displacement of thyroid follicles. These findings indicate that the zebrafish Taz protein is needed for the normal differentiation of the thyroid and are the first to suggest that Taz confers growth advantage to the endocrine gland.

YAP and TAZ: a nexus for Hippo signaling and beyond

The Hippo pathway is a potent regulator of cellular proliferation, differentiation, and tissue homeostasis. Here we review the regulatory mechanisms of the Hippo pathway and discuss the function of Yes-associated protein (YAP)/transcriptional coactivator with a PDZ-binding domain (TAZ), the prime mediators of the Hippo pathway, in stem cell biology and tissue regeneration. We highlight their activities in both the nucleus and the cytoplasm and discuss their role as a signaling nexus and integrator of several other prominent signaling pathways such as the Wnt, G protein-coupled receptor (GPCR), epidermal growth factor (EGF), bone morphogenetic protein (BMP)/transforming growth factor beta (TGFβ), and Notch pathways.

YAP is essential for tissue tension to ensure vertebrate 3D body shape

Vertebrates have a unique 3D body shape in which correct tissue and organ shape and alignment are essential for function. For example, vision requires the lens to be centred in the eye cup which must in turn be correctly positioned in the head. Tissue morphogenesis depends on force generation, force transmission through the tissue, and response of tissues and extracellular matrix to force. Although a century ago D'Arcy Thompson postulated that terrestrial animal body shapes are conditioned by gravity, there has been no animal model directly demonstrating how the aforementioned mechano-morphogenetic processes are coordinated to generate a body shape that withstands gravity. Here we report a unique medaka fish (Oryzias latipes) mutant, hirame (hir), which is sensitive to deformation by gravity. hir embryos display a markedly flattened body caused by mutation of YAP, a nuclear executor of Hippo signalling that regulates organ size. We show that actomyosin-mediated tissue tension is reduced in hir embryos, leading to tissue flattening and tissue misalignment, both of which contribute to body flattening. By analysing YAP function in 3D spheroids of human cells, we identify the Rho GTPase activating protein ARHGAP18 as an effector of YAP in controlling tissue tension. Together, these findings reveal a previously unrecognised function of YAP in regulating tissue shape and alignment required for proper 3D body shape. Understanding this morphogenetic function of YAP could facilitate the use of embryonic stem cells to generate complex organs requiring correct alignment of multiple tissues.

Roles of Hippo signaling pathway in size control of organ regeneration

Animals have an intrinsic regeneration ability for injured tissues and organs. Species that have high regeneration ability such as newts can regenerate an organ with exactly the same size and shape as those of the original one. It has been unclear how a regenerating organ grows and ceases growth at an appropriate size. Organ size control in regeneration is seen in various organs of various species that have high regeneration ability. In animal species that do not have sufficient regeneration ability, a wound heals (the injury is closed, but lost parts are not regenerated), but an organ cannot be restored to its original size. On the other hand, perturbation of regeneration sometimes results in oversized or extra structures. In this sense, organ size control plays essential roles in proper regeneration. In this article, we introduce the concept of size control in organ regeneration regulated by the Hippo signaling pathway. We focused on the transcriptional regulator Yap, which shuttles between the nuclei and cytoplasm to exert a regulatory function in a context-dependent manner. The Yap-mediated Hippo pathway is thought to sense cell density, extracellular matrix (ECM) contact and cell position and to regulate gene expression for control of organ size. This mechanism can reasonably explain size control of organ regeneration.

Genome-wide analysis of the WW domain-containing protein genes in silkworm and their expansion in eukaryotes

WW domains are protein modules that mediate protein-protein interactions through recognition of proline-rich peptide motifs and phosphorylated serine/threonine-proline sites. WW domains are found in many different structural and signaling proteins that are involved in a variety of cellular processes. WW domain-containing proteins (WWCPs) and complexes have been implicated in major human diseases including cancer as well as in major signaling cascades such as the Hippo tumor suppressor pathway, making them targets for new diagnostics and therapeutics. There are a number of reports about the WWCPs in different species, but systematic analysis of the WWCP genes and its ligands is still lacking in silkworm and the other organisms. In this study, WWCP genes and PY motif-containing proteins have been identified and analyzed in 56 species including silkworm. Whole-genome screening of B. mori identified thirty-three proteins with thirty-nine WW domains located on thirteen chromosomes. In the 39 silkworm WW domains, 15 domains belong to the Group I WW domain; 14 domains were in Group II/III, 9 domains derived from 8 silkworm WWCPs could not be classified into any group, and Group IV contains only one WW domain. Based on gene annotation, silkworm WWCP genes have functions in multi-biology processes. A detailed list of WWCPs from the other 55 species was sorted in this work. In 14,623 silkworm predicted proteins, nearly 18 % contained PY motif, nearly 30 % contained various motifs totally that could be recognized by WW domains. Gene Ontology and KEGG analysis revealed that dozens of WW domain-binding proteins are involved in Wnt, Hedgehog, Notch, mTOR, EGF and Jak-STAT signaling pathway. Tissue expression patterns of WWCP genes and potential WWCP-binding protein genes on the third day of the fifth instar (L5D3) were examined by microarray analysis. Tissue expression profile analysis found that several WWCP genes and poly-proline or PY motif-containing protein genes took tissue- or gender-dependent expression manner in silkworms. We further analyzed WWCPs and PY motif-containing proteins in representative organisms of invertebrates and vertebrates. The results showed that there are no less than 16 and up to 29 WWCPs in insects, the average is 22. The number of WW domains in insects is no less than 19, and up to 47, the average is 36. In vertebrates, excluding the Hydrobiontes, the number of WWCPs is no less than 34 and up to 49, the average is 43. The number of WW domains in vertebrates is no less than 56 and up to 85, the average is 73. Phylogenetic analysis revealed that most homologous genes of the WWCP subfamily in vertebrates were duplicated during evolution and functions diverged. Nearly 1,000 PY motif-containing protein genes were found in insect genomes and nearly 2,000 genes in vertebrates. The different distributions of WWCP genes and PY motif-containing protein genes in different species revealed a possible positive correlation with organism complexity. In conclusion, this comprehensive bio-information analysis of WWCPs and its binding ligands would provide rich fundamental knowledge and useful information for further exploration of the function of the WW domain-containing proteins not only in silkworm, but also in other species.

The Hippo pathway is controlled by Angiotensin II signaling and its reactivation induces apoptosis in podocytes

The Hippo pathway fulfills a crucial function in controlling the balance between proliferation, differentiation and apoptosis in cells. Recent studies showed that G protein-coupled receptors (GPCRs) serve as upstream regulators of Hippo signaling, that either activate or inactivate the Hippo pathway via the large tumor suppressor kinase (LATS) and its substrate, the co-transcription factor Yes-associated protein (YAP). In this study, we focused on the Angiotensin II type 1 receptor (AT1R), which belongs to the GPCR family and has an essential role in the control of blood pressure and water homeostasis. We found that Angiotensin II (Ang II) inactivates the pathway by decreasing the activity of LATS kinase; therefore, leading to an enhanced nuclear shuttling of unphosphorylated YAP in HEK293T cells. This shuttling of YAP is actin-dependent as disruption of the actin cytoskeleton inhibited dephosphorylation of LATS and YAP. Interestingly, in contrast to HEK293T cells, podocytes, which are a crucial component of the glomerular filtration barrier, display a predominant nuclear YAP localization in vivo and in vitro. Moreover, stimulation with Ang II did not alter Hippo pathway activity in podocytes, which show a deactivated pathway. Reactivation of the LATS kinase activity in podocytes resulted in an increased cytoplasmic YAP localization accompanied by a strong induction of apoptosis. Thus, our work indicates that the control of LATS activation and subsequent YAP localization is important for podocyte homeostasis and survival.

Targeting Hippo pathway by specific interruption of YAP-TEAD interaction using cyclic YAP-like peptides

Hippo signaling pathway is emerging as a novel target for anticancer therapy because it plays key roles in organ size control and tumorigenesis. As the downstream effectors, Yes-associated protein (YAP)-transcriptional enhancer activation domain family member (TEAD) association is essential for YAP-driven oncogenic activity, while TEAD is largely dispensable for normal tissue growth. We present the design of YAP-like peptides (17mer) to occupy the interface 3 on TEAD. Introducing cysteines at YAP sites 87 and 96 can induce disulfide formation, as confirmed by crystallography. The engineered peptide significantly improves the potency in disrupting YAP-TEAD interaction in vitro. To confirm that blocking YAP-TEAD complex formation by directly targeting on TEAD is a valid approach, we report a significant reduction in tumor growth rate in a hepatocellular carcinoma xenograft model after introducing the dominant-negative mutation (Y406H) of TEAD1 to abolish YAP-TEAD interaction. Our results suggest that targeting TEAD is a promising strategy against YAP-induced oncogenesis.

Current directions and future perspectives from the third Nematostella research conference

The third Nematostella vectensis Research Conference took place in December 2013 in Eilat, Israel, as a satellite to the 8th International Conference on Coelenterate Biology. The starlet sea anemone, N. vectensis, has emerged as a powerful cnidarian model, in large part due to the extensive genomic and transcriptomic resources and molecular approaches that are becoming available for Nematostella, which were the focus of several presentations. In addition, research was presented highlighting the broader utility of this species for studies of development, circadian rhythms, signal transduction, and gene-environment interactions.

A one-dimensional model of PCP signaling: polarized cell behavior in the notochord of the ascidian Ciona

Despite its importance in development and physiology the planar cell polarity (PCP) pathway remains one of the most enigmatic signaling mechanisms. The notochord of the ascidian Ciona provides a unique model for investigating the PCP pathway. Interestingly, the notochord appears to be the only embryonic structure in Ciona activating the PCP pathway. Moreover, the Ciona notochord as a single-file array of forty polarized cells is a uniquely tractable system for the study of polarization dynamics and the transmission of the PCP pathway. Here, we test models for propagation of a polarizing signal, interrogating temporal, spatial and signaling requirements. A simple cell-cell relay cascading through the entire length of the notochord is not supported; instead a more complex mechanism is revealed, with interactions influencing polarity between neighboring cells, but not distant ones. Mechanisms coordinating notochord-wide polarity remain elusive, but appear to entrain general (i.e., global) polarity even while local interactions remain important. However, this global polarizer does not appear to act as a localized, spatially-restricted determinant. Coordination of polarity along the long axis of the notochord requires the PCP pathway, a role we demonstrate is temporally distinct from this pathway's earlier role in convergent extension and intercalation. We also reveal polarity in the notochord to be dynamic: a cell's polarity state can be changed and then restored, underscoring the Ciona notochord's amenability for in vivo studies of PCP.

Hippo-YAP signaling pathway: A new paradigm for cancer therapy

In the past decades, the Hippo signaling pathway has been delineated and shown to play multiple roles in the control of organ size in both Drosophila and mammals. In mammals, the Hippo pathway is a kinase cascade leading from Mst1/2 to YAP and its paralog TAZ. Several studies have demonstrated that YAP/TAZ is a candidate oncogene and that other members of the Hippo pathway are tumor suppressive genes. The dysregulation of the Hippo pathway has been observed in a variety of cancers. This review chronicles the recent progress in elucidating the function of Hippo signaling in tumorigenesis and provide a rich source of potential targets for cancer therapy.

The role of the Hippo pathway in human disease and tumorigenesis

Understanding the molecular nature of human cancer is essential to the development of effective and personalized therapies. Several different molecular signal transduction pathways drive tumorigenesis when deregulated and respond to different types of therapeutic interventions. The Hippo signaling pathway has been demonstrated to play a central role in the regulation of tissue and organ size during development. The deregulation of Hippo signaling leads to a concurrent combination of uncontrolled cellular proliferation and inhibition of apoptosis, two key hallmarks in cancer development. The molecular nature of this pathway was first uncovered in Drosophila melanogaster through genetic screens to identify regulators of cell growth and cell division. The pathway is strongly conserved in humans, rendering Drosophila a suitable and efficient model system to better understand the molecular nature of this pathway. In the present study, we review the current understanding of the molecular mechanism and clinical impact of the Hippo pathway. Current studies have demonstrated that a variety of deregulated molecules can alter Hippo signaling, leading to the constitutive activation of the transcriptional activator YAP or its paralog TAZ. Additionally, the Hippo pathway integrates inputs from a number of growth signaling pathways, positioning the Hippo pathway in a central role in the regulation of tissue size. Importantly, deregulated Hippo signaling is frequently observed in human cancers. YAP is commonly activated in a number of in vitro and in vivo models of tumorigenesis, as well as a number of human cancers. The common activation of YAP in many different tumor types provides an attractive target for potential therapeutic intervention.

A TEAD1/p65 complex regulates the eutherian-conserved MnSOD intronic enhancer, eRNA transcription and the innate immune response

Manganese superoxide dismutase (MnSOD), a critical anti-oxidant enzyme, detoxifies the mitochondrial-derived reactive oxygen species, superoxide, elicited through normal respiration or the inflammatory response. Proinflammatory stimuli induce MnSOD gene expression through a eutherian-conserved, intronic enhancer element. We identified two prototypic enhancer binding proteins, TEAD1 and p65, that when co-expressed induce MnSOD expression comparable to pro-inflammatory stimuli. TEAD1 causes the nuclear sequestration of p65 leading to a novel TEAD1/p65 complex that associates with the intronic enhancer and is necessary for cytokine induction of MnSOD. Unlike typical NF-κB-responsive genes, the induction of MnSOD does not involve p50. Beyond MnSOD, the TEAD1/p65 complex regulates a subset of genes controlling the innate immune response that were previously viewed as solely NF-κB-dependent. We also identified an enhancer-derived RNA (eRNA) that is induced by either proinflammatory stimuli or the TEAD1/p65 complex, potentially linking the intronic enhancer to intra- and interchromosomal gene regulation through the inducible eRNA.

The Hippo pathway effectors TAZ and YAP in development, homeostasis and disease

Studies over the past 20 years have defined the Hippo signaling pathway as a major regulator of tissue growth and organ size. Diverse roles for the Hippo pathway have emerged, the majority of which in vertebrates are determined by the transcriptional regulators TAZ and YAP (TAZ/YAP). Key processes regulated by TAZ/YAP include the control of cell proliferation, apoptosis, movement and fate. Accurate control of the levels and localization of these factors is thus essential for early developmental events, as well as for tissue homeostasis, repair and regeneration. Recent studies have revealed that TAZ/YAP activity is regulated by mechanical and cytoskeletal cues as well as by various extracellular factors. Here, I provide an overview of these and other regulatory mechanisms and outline important developmental processes controlled by TAZ and YAP.

The Hippo pathway controls a switch between retinal progenitor cell proliferation and photoreceptor cell differentiation in zebrafish

The precise regulation of numbers and types of neurons through control of cell cycle exit and terminal differentiation is an essential aspect of neurogenesis. The Hippo signaling pathway has recently been identified as playing a crucial role in promoting cell cycle exit and terminal differentiation in multiple types of stem cells, including in retinal progenitor cells. When Hippo signaling is activated, the core Mst1/2 kinases activate the Lats1/2 kinases, which in turn phosphorylate and inhibit the transcriptional cofactor Yap. During mouse retinogenesis, overexpression of Yap prolongs progenitor cell proliferation, whereas inhibition of Yap decreases this proliferation and promotes retinal cell differentiation. However, to date, it remains unknown how the Hippo pathway affects the differentiation of distinct neuronal cell types such as photoreceptor cells. In this study, we investigated whether Hippo signaling regulates retinogenesis during early zebrafish development. Knockdown of zebrafish mst2 induced early embryonic defects, including altered retinal pigmentation and morphogenesis. Similar abnormal retinal phenotypes were observed in zebrafish embryos injected with a constitutively active form of yap [(yap (5SA)]. Loss of Yap's TEAD-binding domain, two WW domains, or transcription activation domain attenuated the retinal abnormalities induced by yap (5SA), indicating that all of these domains contribute to normal retinal development. Remarkably, yap (5SA)-expressing zebrafish embryos displayed decreased expression of transcription factors such as otx5 and crx, which orchestrate photoreceptor cell differentiation by activating the expression of rhodopsin and other photoreceptor cell genes. Co-immunoprecipitation experiments revealed that Rx1 is a novel interacting partner of Yap that regulates photoreceptor cell differentiation. Our results suggest that Yap suppresses the differentiation of photoreceptor cells from retinal progenitor cells by repressing Rx1-mediated transactivation of photoreceptor cell genes during zebrafish retinogenesis.

The transcription factors Tec1 and Ste12 interact with coregulators Msa1 and Msa2 to activate adhesion and multicellular development

In Saccharomyces cerevisiae and related yeast species, the TEA transcription factor Tec1, together with a second transcription factor, Ste12, controls development, including cell adhesion and filament formation. Tec1-Ste12 complexes control target genes through Tec1 binding sites (TEA consensus sequences [TCSs]) that can be further combined with Ste12 binding sites (pheromone response elements [PREs]) for cooperative DNA binding. The activity of Tec1-Ste12 complexes is known to be under negative control of the Dig1 and Dig2 (Dig1/2) transcriptional corepressors that confer regulation by upstream signaling pathways. Here, we found that Tec1 and Ste12 can associate with the transcriptional coregulators Msa1 and Msa2 (Msa1/2), which were previously found to associate with the cell cycle transcription factor complexes SBF (Swi4/Swi6 cell cycle box binding factor) and MBF (Mbp1/Swi6 cell cycle box binding factor) to control G1-specific transcription. We further show that Tec1-Ste12-Msa1/2 complexes (i) do not contain Swi4 or Mbp1, (ii) assemble at single TCSs or combined TCS-PREs in vitro, and (iii) coregulate genes involved in adhesive and filamentous growth by direct promoter binding in vivo. Finally, we found that, in contrast to Dig proteins, Msa1/2 seem to act as coactivators that enhance the transcriptional activity of Tec1-Ste12. Taken together, our findings add an additional layer of complexity to our understanding of the control mechanisms exerted by the evolutionarily conserved TEA domain and Ste12-like transcription factors.