Most mammary development is postnatal. Mammary growth that occurs before puberty is diminutive in amount but consequential for future milk production, especially in dairy heifers. With advanced knowledge on fundamental aspects that govern prepubertal mammary development, scientists and farmers alike can ensure that heifers perform their best once they become cows. The Hippo pathway has been identified as an evolutionarily conserved pathway that regulates organ size in many animal species; it might contribute to mammary growth in dairy heifers. This pathway is mediated by yes-associated protein (YAP) and through downstream gene transcription activation, results in cell proliferation. Because YAP has never been identified in bovine mammary tissue, questions examined in this body of work mainly focused on the abundance and localization of YAP in mammary tissue of prepubertal heifers. The first trial investigated effects of in vivo estradiol administration on YAP abundance and localization in prepubertal bovine mammary epithelial and myoepithelial cells. While YAP was present in nuclei and cytoplasm of both cell types, it was also discovered that estrogen did not influence YAP abundance or location. The second research trial focused on determining the effects of in vivo estradiol blockade on YAP abundance and localization in prepubertal bovine mammary epithelial and myoepithelial cells. Similar to the first experiment, results indicate that YAP abundance and localization was not influenced by estrogen blockade. Despite not being responsive to in vivo estradiol administration (experiment 1) or estradiol blockade (experiment 2) under the conditions of our experiments, YAP was present in nearly all mammary epithelial cells and myoepithelial cells of the 21 total prepubertal heifers examined. Its presence hints at an underlying biological function but that function was not ascertained here. It will be up to the next researcher to deduce what YAP contributes to mammary growth in prepubertal dairy heifers. / MSLFS

Lors d’une blessure, les cellules migrent et prolifèrent collectivement pour rétablir la continuité de l’épithélium. En migrant, les cellules exercent des forces entre elles ainsi que sur le substrat et de nombreuses études suggèrent un couplage mécanique entre la migration et la prolifération. Récemment découvert, le cofacteur de transcription Yap (Yes-associated protein) est régulé par des signaux mécaniques. L’activation de YAP se traduit par sa rétention nucléaire et augmente la prolifération cellulaire. D’un point de vue mécanique, l’engagement des intégrines dans les adhésions focales, l’aire d’étalement des cellules et la contractilité de l’actomyosine activent YAP. Au contraire, l’engagement des cadhérines dans les jonctions intercellulaires inhibent Yap. A ce jour, les contributions respectives des contacts cellulaires et de l’actomyosine pour la régulation de Yap de de la prolifération restent inexplorées.Au cours de cette thèse, nous nous sommes intéressés au rôle des adhésions au substrat, des jonctions cellule-cellule, du cytosquelette d’actomyosine et de la tension mécanique inter- et intracellulaire sur l’activation de YAP et sur la prolifération cellulaire pendant la cicatrisation épithéliale.D’abord, nous avons étudié le rôle de l’étalement cellulaire et des forces transmises par les contacts cellule-substrat sur la régulation de la localisation de Yap. En confinement sur des motifs adhésifs micro-fabriqués, les kératinocytes humains (HaCaT) adoptent un mouvement collectif oscillatoire. En combinant la vidéomicroscopie, la microscopie à force de traction (TFM) et l’analyse quantitative d’images, nous avons d’abord montré que la migration des cellules est alternativement divergente et convergente ce qui régule l’étalement des cellules. Nous avons ensuite montré que l’étalement d’une cellule est corrélé aux forces de traction sur le substrat et à la relocalisation nucléaire de Yap. Bien qu’ils soient encore préliminaires, ces résultats suggèrent que Yap est régulé par les forces transmises au contacts cellule-substrat pendant la migration épithéliale.Ensuite, nous nous sommes intéressés à la régulation de Yap et de la prolifération cellulaire pendant la migration épitheliale en absence de contacts cellule-substrat. Pour cela, nous avons forcé la migration de monocouches de cellules HaCaT sur des bandes adhérentes séparées de bandes cytorépulsives. Lorsqu’elles migrent sur les bandes adhérentes, les cellules HaCaT étendent une couche de cellules suspendues au-dessus des bandes cytorépulsives. Les cellules suspendues sont cohésives entre elles mais n’interagissent pas avec le substrat. Dans le feuillet de cellules suspendues, les fibres de stress d’actine se réorganisent à l’échelle du tissu grâce au renforcement des contacts cellule-cellule et la contractilité est augmentée. Ce modèle est le premier qui permet de découpler la contractilité de l’actomyosine et les adhésions cellule-substrat pendant la migration épithéliale. Malgré l’augmentation des contraintes d’étirement, l’absence de contacts cellule-substrat empêche la localisation nucléaire de YAP et inhibe la prolifération des cellules suspendues. En conclusion, l’engagement de contacts cellule-substrat sont nécessaires à la localisation nucléaire de Yap et à l’augmentation de la prolifération pendant la cicatrisation épithéliale in vitro.Ces travaux démontrent que les forces de traction sur le substrat sont associées à la localisation nucléaire de Yap et à l’augmentation de la prolifération pendant la migration épithéliale in vitro / After a wound, cells both migrate and proliferate collectively to restore epithelial continuity and to heal the wound. While migrating, cells exert forces on the substrate and pull on each other. Several previous studies suggest a mechanical coupling between collective cell migration and proliferation. Recently discovered, the transcription co-factor Yap (Yes-associated protein) is regulated by mechanical signal. Yap activation induces its nuclear retention and cell cycle progression. Integrin engagement on cell-substrate contacts, cell spreading and actin contractility are related to Yap activation. In turn, cadherin engagement and forces in cell-cell contacts induces Yap nuclear exclusion and reduce cell proliferation. Integrins and cadherins anchor actomyosin cytoskeleton and to date, and the respective contributions of cell-substrate adhesions, cell-cell junctions and actin cytoskeleton on regulation Yap and cell proliferation remain unexplored.In this thesis, we interested in the role of substrate adhesions, cell-cell junctions, actomyosin cytoskeleton and cell mechanical loading on Yap activation and cell proliferation during epithelial wound healing.First, we aim to understand the role of cell spreading and mechanical loading of cell-substrate contacts on the regulation of Yap localisation. Confined on microfabricated adhesive patterns, human keratinocytes HaCaT adopt an oscillatory collective motion. Combining videomicroscopy, traction force microscopy (TFM) and quantitative image analysis, we show that collective cell movements are alternatively divergent and convergent which regulate local cell spreading. Then, we show that cell spreading correlate with traction forces on the substrate and nuclear localisation of Yap. While it remains preliminary, our data show that forces at cell-substrate contacts and cell spreading induce nuclear localisation of Yap during collective cell movements.In the second part of the thesis, we interested on Yap localisation and proliferation during epithelial migration in absence of cell-substrate contacts. To do so, we forced migration of monolayer of HaCaT keratinocytes on micropattern comprising alternatively adherent and cytorepulsive stripes. While migrating on adherent line, cells extend a multicellular layer over the non-adherent areas. Suspended cells are cohesive with each other but do not engage cell-substrate adhesion. In the suspended cell layer, actin stress fibres reorganise at the tissue level thanks to reinforcement of cell-cell contacts and contractility is increased. This model is the first one that allow to decouple actomyosin contractility and cell-substrate contact during epithelial migration. Despite increased stretching stress, absence of cell-substrate contacts induces Yap cytoplasmic localisation and inhibits cell proliferation. To conclude, cell-substrate contact engagement is necessary to induce Yap nuclear localisation and increase cell proliferation during epithelial wound healing in vitro.This work demonstrates that traction forces through cell-substrate contacts are associated to nuclear localisation of Yap and to increased cell proliferation during epithelial wound healing in vitro

Indiana University-Purdue University Indianapolis (IUPUI) / The glial cells of the retina aid in function and maintenance of the retina. The macroglia, Muller cells and the retinal astrocytes, become reactive following injury or disease in the retina, a response that is characterized by hypertrophy, dedifferentiation, loss of functionality, proliferation, and remodeling of tissue and extracellular matrix (ECM). The microglia which are the resident macrophages, also respond to injury/disease becoming activated, undergoing characteristic molecular and morphological changes, which include regulation of secreted factors, changes in inflammatory response and increased phagocytosis. Reactivity in Muller glia is thought to be the result of secreted signals, such as epidermal growth factor, ciliary neurotrophic factor, and broblast growth factor, which are released at the injury site to interact with quiescent glial cells. Furthermore, microglia and macroglia have been shown by some studies to interact following activation. While BMPs are known to be upregulated following injury in the CNS, little information is available concerning their role in reactive gliosis in the retina. We hypothesize that BMP7 indirectly triggers Muller gliosis by activating microglia. Using RT-qPCR, immunofluorescence and western blot, we assessed changes in gliosis markers in the mouse retinal glia following treatment with BMP. Our results showed that BMP7 was able to trigger Muller cell gliosis in the retina in vitro and in vivo. Furthermore, ablation of microglia lead to a subdued gliosis response in the mouse retina following BMP7 exposure. Thus, BMP7 triggers activation of retinal microglia in addition to the Muller glia. IFN-gamma and IL6 could play a role in microglia mediated activation of Muller glia, following exposure to BMP7. We also assessed the role of the Hippo/YAP pathway in the regulation of gliosis in the retina. We demonstrated that YAP was localized to the nucleus of the Muller cells of the retina and was upregulated in IFN-gamma induced gliosis in the mouse retina.

The neural crest (NC) is a multipotent embryonic cell type derived from the ectoderm during neurulation giving rise to a variety of cell lineages such as neurons, glia and pigment cells. Most genes associated with the correct initiation, differentiation and migration of the neural crest have been found through reverse genetics. Similarities between neural crest development and some features of cancer progression are remarkable. For instance, it has been suggested that some cancer types recapitulate NC processes in an unregulated manner such as epithelial-mesenchymal transition or active cell migration throughout the body to form distant metastases. However, to date very little is known about initiators and drivers that direct neural crest cell migration to specific target sites. The Medaka mutant hirame represents an interesting melanocyte specific migration defect on the yolk sac caused by a loss of functional Yes-associated protein (YAP). Medaka hirame mutants were initially studied for their profound changes in body morphology. Genomic mapping identified the causal mutation as a nonsense point mutation within the first WW domain in the Yes-associated protein 1 (YAP1), causing translation of a dysfunctional YAP protein. YAP is a downstream transcriptional co-activator of the recently discovered and evolutionarily conserved Hippo pathway. Alterations within Hippo signalling are linked to cell survival, proliferation and abnormal tissue overgrowth. We demonstrate that hirame melanocyte precursors (melanoblasts) are initially present in normal abundance, but show an early migration defect with a lack of melanoblasts on the yolk sac, and corresponding accumulation in the lateral parts of the body. Subsequently, we observe an overall decline in differentiated melanocyte numbers during late stage embryogenesis. We designed an overexpression cassette linking enhanced GFP to either wild type or a mutated activated version of YAP and present evidence that it can efficiently rescue the melanocyte defect after injection of mRNA into one-cell stage embryos. Furthermore, analysis of the yolk sac anatomy via transmission electron microscopy indicates that a fraction of yolk membrane cells undergo apoptosis and we propose that this may contribute to the establishment of altered environmental cues leading to abnormal melanoblast migration onto the yolk sac. Injection of yap mRNA directly into the yolk sac however, failed to rescue melanoblast patterning. To advance our study, we isolated and characterised a 3.6 kb Medaka dopachrome tautomerase (Dct) promoter fragment, and used it to drive expression of enhanced green fluorescent protein (eGFP) in vivo. We generated germline transgenics with this construct that showed lineage-specific expression of eGFP within early migrating melanoblasts, a phenotype that is maintained in differentiated melanocytes throughout embryogenesis. In addition, using this promoter we overexpressed our egfp-yap fusion cassette and established transgenic lines to assess the cell autonomy of YAP within the melanocyte lineage. However, no fluorescent signal could be detected in the latter transgenics, necessitating future experimentation to properly characterise these lines. Finally, we analysed a range of neural crest markers to examine the extent of the neural crest defects in hirame mutants. In addition to the melanocyte phenotype, we identified a dramatic reduction in xanthophore numbers, although early leucophore development appears unaffected. We also observed a decreased number of dorsal root ganglia in the peripheral nervous system as well as smaller and partly ectopic cranial neural crest ganglia populations within the epibranchial arches. The characterisation of a novel Medaka melanocyte specific promoter as well as additional novel NC markers will be widely applicable and useful to the wider Medaka research community as a tool for the study of neural crest related mechanisms during development.

The mechanisms by which epithelial progenitor cells integrate local signals to balance proliferation with differentiation and regulate patterning during lung organogenesis are still poorly understood. The Hippo pathway and its transcription co-activator Yap have recently emerged as major regulators of progenitor cell expansion and differentiation in development and cancer. Here we investigated the role of Yap signaling in the cellular and molecular events associated with lung epithelial morphogenesis and differentiation. We provide evidence that when airway epithelial tubules are forming and branching, a nuclear to cytoplasmic shift of Yap marks the boundary between the progenitors of the distal lung and the airway compartment. At this transition zone, Yap specifies a transcriptional program that controls the expression of Sox2, restricting distal gene expression and initiating an airway progenitor cell program key to generate the airway epithelium and its branched tubular structures. In Yap deficient mice, epithelial progenitors are unable to properly respond to local Tgf beta-induced cues to control levels and distribution of Sox2, resulting in expansion of the distal epithelial compartment and inability to form airways. Moreover, we show that Yap levels and phosphorylation status play a major role in regulating differentiation of airway progenitors later in development and in adult life. Analysis of YAP-interacting partners in adult airway progenitors by Mass Spectroscopy suggests phosphorylated Yap interactions with ciliome proteins. Our study reveals a crucial role for Yap in specification and differentiation of airway progenitors likely to be also relevant in regeneration-repair of the adult airway epithelium.

Dysregulated Hippo pathway signaling promotes the onset of aggressive cancers through the induced nuclear activity of yes-associated protein (YAP) and transcriptional co-activator with PDZ binding motif (TAZ) (YAP/TAZ). Uncontrolled nuclear YAP/TAZ activity evokes tumor-initiating properties in a range of epithelial-derived cancers, including oral and breast cancers, but their downstream targets and mechanisms of action are unclear. Recent studies have suggested that the pro-tumorigenic roles for YAP/TAZ relate to their convergence with growth factor signaling pathways. Based on these previous studies, I hypothesized that YAP/TAZ driven transcription contributes to carcinoma progression, and that cooperation with transforming growth factor β (TGFβ)-induced signals promotes aggressive oncogenic traits. In this thesis I show that dysregulated YAP localization precedes oral squamous cell carcinoma (OSCC) development, and that nuclear YAP/TAZ activity drives cell proliferation, survival, and migration in vitro, and is required for tumor growth and metastasis in vivo. Global gene expression studies in OSCC cells revealed that YAP/TAZ-mediated gene expression correlates with expression changes that occur in human OSCCs identified by “The Cancer Genome Atlas” (TCGA), many of which encode cell cycle and survival regulators. By exploring the relationship with growth factor signaling, I found that YAP/TAZ induce pro-tumorigenic events by converging with TGFβ-induced signals, particularly in breast cancer cells where TGFβ is known to promote metastatic properties. My observations indicated that YAP/TAZ are necessary for maintaining and promoting TGFβ-induced tumorigenic phenotypes in breast cancer cells, and that these phenotypes result from the cooperative activity of YAP/TAZ, the TEA domain family of transcription factors (TEADs), and TGFβ-activated SMAD2/3 in the nucleus. Genome-wide expression analyses indicated that YAP/TAZ, TEADs, and TGFβ-induced signals coordinate a specific pro-tumorigenic transcriptional program. Importantly, genes cooperatively regulated by these complexes, such as the novel targets neuronal growth regulator 1 (NEGR1) and urothelial cancer associated 1 (UCA1), are necessary to maintain tumorigenic activity in metastatic breast cancer cells. Nuclear YAP/TAZ also cooperate with TGFβ signaling to promote phenotypic and transcriptional changes in non-tumorigenic cells to overcome TGFβ-mediated growth inhibition. This work thus defines novel roles for YAP/TAZ in cancer, offering molecular mechanisms that may be useful for identifying and targeting YAP/TAZ-driven cancers.

Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 347-375). Also available for download via the World Wide Web; free to University of Oregon users.

Hemangioma is a type of tumor commonly found in infants that is characterized by heavy vascularization and a disfiguring appearance. Hemangioma, though benign, can sometimes proliferate and be threatening to infants. Current treatments for infantile hemangioma include surgical removal as well as the use of topical and oral medication. However, current therapies are often ineffective at treating lesions and are commonly accompanied by dangerous side effects, creating the need for a new, safer treatment. This study targets the Yes-Associated Protein-1 (YAP-1), which has been described as an oncogene, by use of an interfering RNA technique in attempts to mediate tumor growth and progression. Western blotting of treatment and control BEND3 murine cells reveals that YAP-1 is knocked-down in treatment groups which have been infected with shYAP-1 siRNA genes. By successfully knocking down the YAP-1 protein, the potential for developing a novel targeted therapy for infantile hemangioma has been established.

Typescript. / Thesis (D.P.H.)--University of Hawaii at Manoa, 1987. / Bibliography: leaves 149-151. / vii, 151 leaves, bound 29 cm

The Hippo signaling pathway has been implicated in both mammalian organ size regulation, as well as tumor suppression. Specifically, the Hippo pathway plays a critical role regulating the activity of transcriptional co-activator, and downstream effector, Yes-associated protein (YAP), which modulates pro-proliferative transcriptional elements. Recent investigations have demonstrated that this pathway is activated in non-regenerating livers and its inhibition leads to liver overgrowth and tumorigenesis. The majority of the existing evidence regarding the role of the Hippo pathway in hepatocyte proliferation is based on in vitro studies and knock-out animal models. However, the role of the Hippo pathway during the natural process of liver regeneration, remains unknown. Here alterations in the Hippo signaling pathway were investigated, namely its interaction with angiomotin-like 2 (AmotL2) and Set7, during liver regeneration using a 70% rat partial hepatectomy (PH) model. Overall, results indicated no significant difference between AmotL2 levels in control and regenerating tissue at various time points during liver regeneration. No significant alterations in YAP methylation during liver regeneration were found compared to control tissue. In the end, results regarding the role of both AmotL2 and Set7 provided inconclusive evidence about their roles during the regenerative process. Given the role of the Hippo pathway in hepatocyte proliferation, a hypothesis was made that this pathway may play a role in pediatric liver tumors. YAP localization was evaluated using immunohistochemical analysis in tumor sections from patients with hepatoblastoma or hepatocellular carcinoma. Once again, the results were inconclusive at the time of the preparation of this manuscript due to technical difficulties in achieving satisfactory staining of the specimens. Further studies will be directed at elucidating the role of the Hippo pathway during liver regeneration as well as developing better conditions for the immunohistochemical staining of human liver specimens.