How size is controlled: from Hippos to Yorkies

Zika Virus Strains and Dengue Virus Induce Distinct Proteomic Changes in Neural Stem Cells and Neurospheres

Brain abnormalities and congenital malformations have been linked to the circulating strain of Zika virus (ZIKV) in Brazil since 2016 during the microcephaly outbreak; however, the molecular mechanisms behind several of these alterations and differential viral molecular targets have not been fully elucidated. Here we explore the proteomic alterations induced by ZIKV by comparing the Brazilian (Br ZIKV) and the African (MR766) viral strains, in addition to comparing them to the molecular responses to the Dengue virus type 2 (DENV). Neural stem cells (NSCs) derived from induced pluripotent stem (iPSCs) were cultured both as monolayers and in suspension (resulting in neurospheres), which were then infected with ZIKV (Br ZIKV or ZIKV MR766) or DENV to assess alterations within neural cells. Large-scale proteomic analyses allowed the comparison not only between viral strains but also regarding the two- and three-dimensional cellular models of neural cells derived from iPSCs, and the effects on their interaction. Altered pathways and biological processes were observed related to cell death, cell cycle dysregulation, and neurogenesis. These results reinforce already published data and provide further information regarding the biological alterations induced by ZIKV and DENV in neural cells.

Pitx2-Sox2-Lef1 interactions specify progenitor oral/dental epithelial cell signaling centers

Epithelial signaling centers control epithelial invagination and organ development, but how these centers are specified remains unclear. We report that Pitx2 (the first transcriptional marker for tooth development) controls the embryonic formation and patterning of epithelial signaling centers during incisor development. We demonstrate using Krt14Cre /Pitx2flox/flox (Pitx2cKO ) and Rosa26CreERT/Pitx2flox/flox mice that loss of Pitx2 delays epithelial invagination, and decreases progenitor cell proliferation and dental epithelium cell differentiation. Developmentally, Pitx2 regulates formation of the Sox2+ labial cervical loop (LaCL) stem cell niche in concert with two signaling centers: the initiation knot and enamel knot. The loss of Pitx2 disrupted the patterning of these two signaling centers, resulting in tooth arrest at E14.5. Mechanistically, Pitx2 transcriptional activity and DNA binding is inhibited by Sox2, and this interaction controls gene expression in specific Sox2 and Pitx2 co-expression progenitor cell domains. We demonstrate new transcriptional mechanisms regulating signaling centers by Pitx2, Sox2, Lef1 and Irx1.

FoxO6 regulates Hippo signaling and growth of the craniofacial complex

The mechanisms that regulate post-natal growth of the craniofacial complex and that ultimately determine the size and shape of our faces are not well understood. Hippo signaling is a general mechanism to control tissue growth and organ size, and although it is known that Hippo signaling functions in neural crest specification and patterning during embryogenesis and before birth, its specific role in postnatal craniofacial growth remains elusive. We have identified the transcription factor FoxO6 as an activator of Hippo signaling regulating neonatal growth of the face. During late stages of mouse development, FoxO6 is expressed specifically in craniofacial tissues and FoxO6-/- mice undergo expansion of the face, frontal cortex, olfactory component and skull. Enlargement of the mandible and maxilla and lengthening of the incisors in FoxO6-/- mice are associated with increases in cell proliferation. In vitro and in vivo studies demonstrated that FoxO6 activates Lats1 expression, thereby increasing Yap phosphorylation and activation of Hippo signaling. FoxO6-/- mice have significantly reduced Hippo Signaling caused by a decrease in Lats1 expression and decreases in Shh and Runx2 expression, suggesting that Shh and Runx2 are also linked to Hippo signaling. In vitro, FoxO6 activates Hippo reporter constructs and regulates cell proliferation. Furthermore PITX2, a regulator of Hippo signaling is associated with Axenfeld-Rieger Syndrome causing a flattened midface and we show that PITX2 activates FoxO6 expression. Craniofacial specific expression of FoxO6 postnatally regulates Hippo signaling and cell proliferation. Together, these results identify a FoxO6-Hippo regulatory pathway that controls skull growth, odontogenesis and face morphology.

The role of transcriptional coactivator TAZ in gliomas

The transcriptional coactivator with PDZ-binding motif (TAZ) is one of the important downstream effectors of Hippo pathway. In this study, the potential implication of TAZ in gliomagenesis was explored. TAZ expression was identified to be upregulated in glioma specimens and positively correlated with tumor grade. Meanwhile, its expression in nucleus was increased more significantly with the ascending order of tumor grade. Knocking down TAZ inhibited glioma cell proliferation, invasion and promoted apoptosis. Conversely, enforced upregulation of TAZ promoted proliferation, invasion of glioma cells, and suppressed apoptosis in vitro. When orthotopic glioblastoma mouse model implanted with TAZ knocked down cells, glioma growth was inhibited and survival period was prolonged. Expression of Ki67, MMP-9, Cyclin D1, Bcl-2 and C-myc was varied in accordance with the level of TAZ in glioma cell. The biomarkers of EMT (epithelial-mesenchymal transition), vimentin and N-cadherin, were downregulated when TAZ was suppressed. Using Co-immunoprecipitation TAZ was identified to bind to TEAD4. Therefore, our findings indicate that TAZ is overexpressed in glioma and translocated more into nucleus in high grade glioma. TAZ is involved in gliomagenesis by promoting glioma growth and may benefit to EMT progression. This result suggests that TAZ serves as a potential target for the treatment of glioma.

WWC3 inhibits intimal proliferation following vascular injury via the Hippo signaling pathway

The Hippo signaling pathway is involved in the formation and development of the cardiovascular system. In the present study, the effects of WWC family member 3 (WWC3) on vascular smooth muscle cells (VSMCs) following injury were investigated, in addition to the associated mechanisms underlying this process. Platelet-derived growth factor BB (PDGF-BB) was used as a cell injury factor, and rats with balloon injuries were used as a model of carotid intimal injury. Furthermore, the expression levels of WWC3 in VSMCs and arteries post-injury were investigated, in addition to the effect of WWC3 on the proliferation and migration of VSMCs. The results demonstrated that following injury, WWC3 expression was suppressed in VSMCs and the rat carotid artery, and the activity of the Hippo signaling pathway was significantly downregulated. In addition, the expression of YY1-associated protein-1 (YAP) and a number of its downstream target genes, including connective tissue growth factor (CTGF), were enhanced, thus enhancing the proliferation and migration of VSMCs. Knockdown of WWC3 suppressed the levels of large tumor suppressor kinase 1 (LATS1) expression and YAP phosphorylation, and the expression of YAP, CTGF and cyclin E was subsequently enhanced, thus promoting cell proliferation and migration. Similar results were obtained following overexpression of WWC3. Treatment with PDGF-BB was revealed to suppress the proliferation and migration of VSMCs transfected with the WWC3 plasmid, compared with VSMCs transfected with an empty vector. The present study demonstrated that WWC3 may interact with LATS1 in order to upregulate the Hippo signaling pathway via co-immunoprecipitation and enhancement of the phosphorylation of LATS1, in addition to the corresponding suppression of the nuclear import of YAP. However, VSMCs transfected with WWC3 plasmid with a deletion of the WW domain fail to exhibit this effect. These results suggested that WWC3 expression is downregulated in VSMCs during neointimal hyperplasia following injury (PDGF-BB stimulation or balloon injury). WWC3 upregulates the activity of the Hippo signaling pathway, and weakens the proliferation and migration of VSMCs. Furthermore, the results of the present study suggested that WWC3 may interact with LATS1 to promote the phosphorylation of YAP and reduce its nuclear translocation, upregulate the activity of the Hippo pathway, and suppress the proliferation and migration of VSMCs following injury.

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.

YAP and TAZ mediate steroid-induced alterations in the trabecular meshwork cytoskeleton in human trabecular meshwork cells

Primary open angle glaucoma is an important type of glaucoma as it is one of the most common causes of blindness. Previous studies have demonstrated that in glaucomatous patients, the human trabecular meshwork (HTM) is markedly stiffened. The purpose of the present study was to determine the regulatory role of Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) in HTM cells. Primary HTM cells were cultured with different concentrations of dexamethasone (DEX), and the expression levels of YAP and TAZ were evaluated using reverse transcription-quantitative polymerase chain reaction and western blotting. The results revealed that DEX increased the expression of YAP and TAZ in a dose-dependent manner. In addition, the western blot analysis of cytoskeleton-associated proteins revealed that the inhibition of YAP and/or TAZ using small interfering RNA resulted in the increased expression of collagen I, and decreased expression of fibronectin, laminin and collagen IV. The expression of β-catenin, a key protein in the Wnt pathway, was also observed to be regulated by YAP and TAZ. A 5-ethynyl-2′-deoxyuridine staining assay indicated that YAP and TAZ induced the proliferation of HTM cells. The investigation of cross-linked actin network formation by the HTM cells demonstrated that the knockdown of YAP and TAZ genes rescued HTM cells from cytoskeletal reorganization. Furthermore, functional evaluation of a HTM cell monolayer using a permeability assay demonstrated that the inhibition of YAP and TAZ attenuated the DEX-induced impairment of permeability. These findings suggest that YAP and TAZ play pivotal roles in the DEX-induced cytoskeletal changes of HTM cells, and reveal novel potential mechanisms for the development and progression of glaucoma.

Molecular mechanism of size control in development and human diseases

How multicellular organisms control their size is a fundamental question that fascinated generations of biologists. In the past 10 years, tremendous progress has been made toward our understanding of the molecular mechanism underlying size control. Original studies from Drosophila showed that in addition to extrinsic nutritional and hormonal cues, intrinsic mechanisms also play important roles in the control of organ size during development. Several novel signaling pathways such as insulin and Hippo-LATS signaling pathways have been identified that control organ size by regulating cell size and/or cell number through modulation of cell growth, cell division, and cell death. Later studies using mammalian cell and mouse models also demonstrated that the signaling pathways identified in flies are also conserved in mammals. Significantly, recent studies showed that dysregulation of size control plays important roles in the development of many human diseases such as cancer, diabetes, and hypertrophy.

Pattern, growth, and control

Systems biology seeks not only to discover the machinery of life but to understand how such machinery is used for control, i.e., for regulation that achieves or maintains a desired, useful end. This sort of goal-directed, engineering-centered approach also has deep historical roots in developmental biology. Not surprisingly, developmental biology is currently enjoying an influx of ideas and methods from systems biology. This Review highlights current efforts to elucidate design principles underlying the engineering objectives of robustness, precision, and scaling as they relate to the developmental control of growth and pattern formation. Examples from vertebrate and invertebrate development are used to illustrate general lessons, including the value of integral feedback in achieving set-point control; the usefulness of self-organizing behavior; the importance of recognizing and appropriately handling noise; and the absence of "free lunch." By illuminating such principles, systems biology is helping to create a functional framework within which to make sense of the mechanistic complexity of organismal development.

AXL receptor kinase is a mediator of YAP-dependent oncogenic functions in hepatocellular carcinoma

Yes-associated protein (YAP) is a downstream effector of the Hippo signaling pathway, which controls organ expansion and tissue development. We have recently defined the tumorigenic potential and clinical significance of the YAP1 oncogene in human hepatocellular carcinoma (HCC). The present study aims to define the tumorigenic properties of YAP in HCC and elucidate the related downstream signaling mechanism. In a gain-of-function study, we demonstrated that ectopic increased expression of YAP in the immortalized non-tumorigenic hepatocyte cell line MIHA confers tumorigenic and metastatic potentials, as evidenced by (1) enhanced aptitudes in cell viability, anchorage-independent growth, migration and invasion; (2) tumor formation in a xenograft mouse model; and (3) induction of HCC biomarker α-fetoprotein and activation of mitogen-activated protein kinase. Furthermore, we have identified AXL, a receptor tyrosine kinase, as a key downstream target that drives YAP-dependent oncogenic functions. RNAi-mediated knockdown of AXL expression decreased the ability of YAP-expressing MIHA cells and of the primary HCC cell line to proliferate and invade. These results indicate that AXL is a mediator of YAP-dependent oncogenic activities and implicates it as a potential therapeutic target for HCC.

YAP1 is amplified and up-regulated in hedgehog-associated medulloblastomas and mediates Sonic hedgehog-driven neural precursor proliferation

Medulloblastoma is the most common solid malignancy of childhood, with treatment side effects reducing survivors' quality of life and lethality being associated with tumor recurrence. Activation of the Sonic hedgehog (Shh) signaling pathway is implicated in human medulloblastomas. Cerebellar granule neuron precursors (CGNPs) depend on signaling by the morphogen Shh for expansion during development, and have been suggested as a cell of origin for certain medulloblastomas. Mechanisms contributing to Shh pathway-mediated proliferation and transformation remain poorly understood. We investigated interactions between Shh signaling and the recently described tumor-suppressive Hippo pathway in the developing brain and medulloblastomas. We report up-regulation of the oncogenic transcriptional coactivator yes-associated protein 1 (YAP1), which is negatively regulated by the Hippo pathway, in human medulloblastomas with aberrant Shh signaling. Consistent with conserved mechanisms between brain tumorigenesis and development, Shh induces YAP1 expression in CGNPs. Shh also promotes YAP1 nuclear localization in CGNPs, and YAP1 can drive CGNP proliferation. Furthermore, YAP1 is found in cells of the perivascular niche, where proposed tumor-repopulating cells reside. Post-irradiation, YAP1 was found in newly growing tumor cells. These findings implicate YAP1 as a new Shh effector that may be targeted by medulloblastoma therapies aimed at eliminating medulloblastoma recurrence.

Yes-associated protein is an independent prognostic marker in hepatocellular carcinoma

BACKGROUND

Yes-associated protein (YAP), a downstream target of the Hippo signaling pathway, was recently linked to hepatocarcinogenesis in a mouse hepatocellular carcinoma (HCC) model. The objective of the current study was to investigate the clinical significance of YAP in HCC and its prognostic values in predicting survival and tumor recurrence.

METHODS

The authors collected 177 pairs of tumor and adjacent nontumor tissue from HCC patients with definitive clinicopathologic and follow-up data. YAP expression was determined by immunohistochemistry, Western blot analysis, and quantitative polymerase chain reaction. Association of YAP with each clinicopathologic feature was analyzed by Pearson chi-square test, and HCC-specific disease-free survival and overall survival by Kaplan-Meier curves and log-rank test. Multivariate Cox regression analyses of YAP in HCC were also performed.

RESULTS

YAP was expressed in the majority of HCC cases (approximately 62%) and mainly accumulated in the tumor nucleus. Overexpression of YAP in HCC was significantly associated with poorer tumor differentiation (Edmonson grade; P = .021) and high serum alpha-fetoprotein (AFP) level (P < .001). Kaplan-Meier and Cox regression data indicated that YAP was an independent predictor for HCC-specific disease-free survival (hazards ratio [HR], 1.653; 95% confidence interval [95% CI], 1.081-2.528 [P = .02]) and overall survival (HR, 2.148; 95% CI, 1.255-3.677 [P = .005]).

CONCLUSIONS

YAP is an independent prognostic marker for overall survival and disease-free survival times of HCC patients and clinicopathologically associated with tumor differentiation and serum AFP level. It is a potential therapeutic target for this aggressive malignancy.

Yes-associated protein is an independent prognostic marker in hepatocellular carcinoma

BACKGROUND

Yes-associated protein (YAP), a downstream target of the Hippo signaling pathway, was recently linked to hepatocarcinogenesis in a mouse hepatocellular carcinoma (HCC) model. The objective of the current study was to investigate the clinical significance of YAP in HCC and its prognostic values in predicting survival and tumor recurrence.

METHODS

The authors collected 177 pairs of tumor and adjacent nontumor tissue from HCC patients with definitive clinicopathologic and follow-up data. YAP expression was determined by immunohistochemistry, Western blot analysis, and quantitative polymerase chain reaction. Association of YAP with each clinicopathologic feature was analyzed by Pearson chi-square test, and HCC-specific disease-free survival and overall survival by Kaplan-Meier curves and log-rank test. Multivariate Cox regression analyses of YAP in HCC were also performed.

RESULTS

YAP was expressed in the majority of HCC cases (approximately 62%) and mainly accumulated in the tumor nucleus. Overexpression of YAP in HCC was significantly associated with poorer tumor differentiation (Edmonson grade; P = .021) and high serum alpha-fetoprotein (AFP) level (P < .001). Kaplan-Meier and Cox regression data indicated that YAP was an independent predictor for HCC-specific disease-free survival (hazards ratio [HR], 1.653; 95% confidence interval [95% CI], 1.081-2.528 [P = .02]) and overall survival (HR, 2.148; 95% CI, 1.255-3.677 [P = .005]).

CONCLUSIONS

YAP is an independent prognostic marker for overall survival and disease-free survival times of HCC patients and clinicopathologically associated with tumor differentiation and serum AFP level. It is a potential therapeutic target for this aggressive malignancy.

The Hippo-YAP pathway: new connections between regulation of organ size and cancer

The control of organ size is a basic biological question. In the past several years, the Hippo signaling pathway has been delineated and shown to be crucial in control of organ size in both Drosophila and mammals. Acting downstream of the Hippo pathway is the Yki/YAP/TAZ transcription co-activators. In mammalian cells, the Hippo pathway kinase cascade inhibits YAP and its paralog TAZ by phosphorylation and promotion of their cytoplasmic localization. The TEAD family transcription factors have recently been identified as evolutionarily conserved key mediators of YAP biological functions. yap is a candidate oncogene, and several other components of the Hippo pathway are tumor suppressors. Dysregulation of the Hippo pathway contributes to the loss of contact inhibition observed in cancer cells. Therefore, the Hippo-YAP pathway connects the regulation of organ size and tumorigenesis.

Development and morphogenesis of the Wolffian/epididymal duct, more twists and turns

The epididymis serves a critical function of preparing the male germ cells for fertilization. In order for the epididymis to carry out this role it must undergo a highly coordinated succession of molecular and morphogenic events during development. These events begin with the formation of the Wolffian or nephric duct, the embryonic precursor of the male reproductive system, and end with the three-dimensional coiled postnatal epididymis that is comprised of several distinctly functional segments. How the duct changes from a simple straight tube to a highly convoluted structure will be the focus of this article. In reviewing the literature's current understanding of epididymal morphogenesis, we will highlight some of the classic morphological studies and discuss some of the more recent genetic models that have all served to contribute to our understanding of this system. Where published information is scarce we will provide potential hypotheses that warrant further investigation and may open up new directions of exploration using the epididymis as a model for tubular morphogenesis.

Drosophila is an inclusive model for human diseases, growth and development

Cytogenetic studies over the last century have led to the complete mapping of the Drosophila polytene chromosomes. The resulting data and the analysis of puffing at specific gene sites, manifestations of enhanced transcriptional activity, have led to the use of the fruit fly as the most well-understood animal model for a plethora of cellular mechanisms and genetic defects. In recent years the fly data base has contributed greatly to the use of Drosophila as a remarkable model for the functional genomics of many human genes. Here I review briefly the diversity of "model genes" studied in this dipteran, ranging from mental acuity, sleep and development, to recent studies from our laboratory, and those of our collaborators, on steroid hormone biosynthesis and neurodegeneration.