Instruct: Given a scientific claim, retrieve documents that support or refute the claim.
Query: The first MBT repeat of the four malignant brain tumor (4MBT) domain of Drosophila's Sfmbt and of the orthologous mammalian L3MBTL2 is required for the interaction with the spacer region of Drosophila's Pleiohomeotic (Pho) or its human ortholog YY1.
L3mbtl2 has been implicated in transcriptional repression and chromatin compaction but its biological function has not been defined. Here we show that disruption of L3mbtl2 results in embryonic lethality with failure of gastrulation. This correlates with compromised proliferation and abnormal differentiation of L3mbtl2(-/-) embryonic stem (ES) cells. L3mbtl2 regulates genes by recruiting a Polycomb Repressive Complex1 (PRC1)-related complex, resembling the previously described E2F6-complex, and including G9A, Hdac1, and Ring1b. The presence of L3mbtl2 at target genes is associated with H3K9 dimethylation, low histone acetylation, and H2AK119 ubiquitination, but the latter is neither dependent on L3mbtl2 nor sufficient for repression. Genome-wide studies revealed that the L3mbtl2-dependent complex predominantly regulates genes not bound by canonical PRC1 and PRC2. However, some developmental regulators are repressed by the combined activity of all three complexes. Together, we have uncovered a highly selective, essential role for an atypical PRC1-family complex in ES cells and early development.
The Drosophila gene eyeless (ey) encodes a transcription factor with both a paired domain and a homeodomain. It is homologous to the mouse Small eye (Pax-6) gene and to the Aniridia gene in humans. These genes share extensive sequence identity, the position of three intron splice sites is conserved, and these genes are expressed similarly in the developing nervous system and in the eye during morphogenesis. Loss-of-function mutations in both the insect and in the mammalian genes have been shown to lead to a reduction or absence of eye structures, which suggests that ey functions in eye morphogenesis. By targeted expression of the ey complementary DNA in various imaginal disc primordia of Drosophila, ectopic eye structures were induced on the wings, the legs, and on the antennae. The ectopic eyes appeared morphologically normal and consisted of groups of fully differentiated ommatidia with a complete set of photoreceptor cells. These results support the proposition that ey is the master control gene for eye morphogenesis. Because homologous genes are present in vertebrates, ascidians, insects, cephalopods, and nemerteans, ey may function as a master control gene throughout the metazoa.
Over 70% of diffuse intrinsic pediatric gliomas, an aggressive brainstem tumor, harbor heterozygous mutations that create a K27M amino acid substitution (methionine replaces lysine 27) in the tail of histone H3.3. The role of the H3.3K27M mutation in tumorigenesis is not fully understood. Here, we use a human embryonic stem cell system to model this tumor. We show that H3.3K27M expression synergizes with p53 loss and PDGFRA activation in neural progenitor cells derived from human embryonic stem cells, resulting in neoplastic transformation. Genome-wide analyses indicate a resetting of the transformed precursors to a developmentally more primitive stem cell state, with evidence of major modifications of histone marks at several master regulator genes. Drug screening assays identified a compound targeting the protein menin as an inhibitor of tumor cell growth in vitro and in mice.
The evolutionarily conserved miR-302 family of microRNAs is expressed during early mammalian embryonic development. Here, we report that deletion of miR-302a-d in mice results in a fully penetrant late embryonic lethal phenotype. Knockout embryos have an anterior neural tube closure defect associated with a thickened neuroepithelium. The neuroepithelium shows increased progenitor proliferation, decreased cell death, and precocious neuronal differentiation. mRNA profiling at multiple time points during neurulation uncovers a complex pattern of changing targets over time. Overexpression of one of these targets, Fgf15, in the neuroepithelium of the chick embryo induces precocious neuronal differentiation. Compound mutants between mir-302 and the related mir-290 locus have a synthetic lethal phenotype prior to neurulation. Our results show that mir-302 helps regulate neurulation by suppressing neural progenitor expansion and precocious differentiation. Furthermore, these results uncover redundant roles for mir-290 and mir-302 early in development.
Cadherins and the immunoglobulin (Ig) proteins give rise to a multitude of surface receptors, which function as diverse cell adhesion molecules (CAMs) or signal-transducing receptors. These functions are often interdependent, and rely on a high degree of specificity in homophilic binding as well as heterophilic interactions. The Drosophila receptor Dscam is an exceptional example of homophilic binding specificity involved in a number of important biological processes, such as neural wiring and innate immunity. Combinatorial use of alternatively spliced Ig-domains enables the generation of an estimated 18,000 isoform-specific homophilic receptor pairs. Although isoform diversity of Dscam is unique to arthropods, recent genetic analysis of vertebrate DSCAM (Down Syndrome Cell Adhesion Molecule) genes has revealed an intriguing conservation of molecular functions underlying neural wiring. This review covers the multiple functions of Dscam across different species highlighting its remarkable versatility as well as its conserved basic functions in neural development. We discuss how an unprecedented expansion of complex alternative splicing has been uniquely employed by arthropods to generate diverse surface receptors, important for cell-cell communication, molecular self-recognition in neurons, and innate immune defenses. We end with a speculative hypothesis reconciling the striking differences in Dscam and DSCAM gene structures with their conserved functions in molecular recognition underlying neural circuit formation.
Two human Golli (for gene expressed in the oligodendrocyte lineage)-MBP (for myelin basic protein) cDNAs have been isolated from a human oligodendroglioma cell line. Analysis of these cDNAs has enabled us to determine the entire structure of the human Golli-MBP gene. The Golli-MBP gene, which encompasses the MBP transcription unit, is approximately 179 kb in length and consists of 10 exons, seven of which constitute the MBP gene. The human Golli-MBP gene contains two transcription start sites, each of which gives rise to a family of alternatively spliced transcripts. At least two Golli-MBP transcripts, containing the first three exons of the gene and one or more MBP exons, are produced from the first transcription start site. The second family of transcripts contains only MBP exons and produces the well-known MBPs. In humans, RNA blot analysis revealed that Golli-MBP transcripts were expressed in fetal thymus, spleen, and human B-cell and macrophage cell lines, as well as in fetal spinal cord. These findings clearly link the expression of exons encoding the autoimmunogen/encephalitogen MBP in the central nervous system to cells and tissues of the immune system through normal expression of the Golli-MBP gene. They also establish that this genetic locus, which includes the MBP gene, is conserved among species, providing further evidence that the MBP transcription unit is an integral part of the Golli transcription unit and suggest that this structural arrangement is important for the genetic function and/or regulation of these genes.
The transcription factor Oct4 is key in embryonic stem cell identity and reprogramming. Insight into its partners should illuminate how the pluripotent state is established and regulated. Here, we identify a considerably expanded set of Oct4-binding proteins in mouse embryonic stem cells. We find that Oct4 associates with a varied set of proteins including regulators of gene expression and modulators of Oct4 function. Half of its partners are transcriptionally regulated by Oct4 itself or other stem cell transcription factors, whereas one-third display a significant change in expression upon cell differentiation. The majority of Oct4-associated proteins studied to date show an early lethal phenotype when mutated. A fraction of the human orthologs is associated with inherited developmental disorders or causative of cancer. The Oct4 interactome provides a resource for dissecting mechanisms of Oct4 function, enlightening the basis of pluripotency and development, and identifying potential additional reprogramming factors.
We describe the landscape of somatic genomic alterations based on multidimensional and comprehensive characterization of more than 500 glioblastoma tumors (GBMs). We identify several novel mutated genes as well as complex rearrangements of signature receptors, including EGFR and PDGFRA. TERT promoter mutations are shown to correlate with elevated mRNA expression, supporting a role in telomerase reactivation. Correlative analyses confirm that the survival advantage of the proneural subtype is conferred by the G-CIMP phenotype, and MGMT DNA methylation may be a predictive biomarker for treatment response only in classical subtype GBM. Integrative analysis of genomic and proteomic profiles challenges the notion of therapeutic inhibition of a pathway as an alternative to inhibition of the target itself. These data will facilitate the discovery of therapeutic and diagnostic target candidates, the validation of research and clinical observations and the generation of unanticipated hypotheses that can advance our molecular understanding of this lethal cancer.
We cloned a new member of the murine brain kinesin superfamily, KIF3B, and found that its amino acid sequence is highly homologous but not identical to KIF3A, which we previously cloned and named KIF3 (47% identical). KIF3B is localized in various organ tissues and developing neurons of mice and accumulates with anterogradely moving membranous organelles after ligation of nerve axons. Immunoprecipitation assay of the brain revealed that KIF3B forms a complex with KIF3A and three other high molecular weight (approximately 100 kD)-associated polypeptides, called the kinesin superfamily-associated protein 3 (KAP3). In vitro reconstruction using baculovirus expression systems showed that KIF3A and KIF3B directly bind with each other in the absence of KAP3. The recombinant KIF3A/B complex (approximately 50-nm rod with two globular heads and a single globular tail) demonstrated plus end-directed microtubule sliding activity in vitro. In addition, we showed that KIF3B itself has motor activity in vitro, by making a complex of wild-type KIF3B and a chimeric motor protein (KIF3B head and KIF3A rod tail). Subcellular fractionation of mouse brain homogenates showed a considerable amount of the native KIF3 complex to be associated with membrane fractions other than synaptic vesicles. Immunoprecipitation by anti-KIF3B antibody-conjugated beads and its electron microscopic study also revealed that KIF3 is associated with membranous organelles. Moreover, we found that the composition of KAP3 is different in the brain and testis. Our findings suggest that KIF3B forms a heterodimer with KIF3A and functions as a new microtubule-based anterograde translocator for membranous organelles, and that KAP3 may determine functional diversity of the KIF3 complex in various kinds of cells in vivo.
BACKGROUND Mammalian phosphoinositide 3-kinases (PI 3-kinases) are involved in receptor-mediated signal transduction and have been implicated in processes such as transformation and mitogenesis through their role in elevating cellular phosphatidylinositol (3,4,5)-trisphosphate. Additionally, a PI 3-kinase activity which generates phosphatidylinositol 3-phosphate has been shown to be required for protein trafficking in yeast. RESULTS We have identified a family of three distinct PI 3-kinases in Drosophila, using an approach based on the polymerase chain reaction to amplify a region corresponding to the conserved catalytic domain of PI 3-kinases. One of these family members, PI3K_92D, is closely related to the prototypical PI 3-kinase, p110 alpha; PI3K_59F is homologous to Vps34p, whereas the third, PI3K_68D, is a novel PI 3-kinase which is widely expressed throughout the Drosophila life cycle. The PI3K_68D cDNA encodes a protein of 210 kDa, which lacks sequences implicated in linking p110 PI 3-kinases to p85 adaptor proteins, but contains an amino-terminal proline-rich sequence, which could bind to SH3 domains, and a carboxy-terminal C2 domain. Biochemical analyses demonstrate that PI3K_68D has a novel substrate specificity in vitro, restricted to phosphatidylinositol and phosphatidylinositol 4-phosphate, and is unable to phosphorylate phosphatidylinositol (4,5)-bisphosphate, the implied in vivo substrate for p110. CONCLUSIONS A family of PI 3-kinases in Drosophila, including a novel class represented by PI3K_68D, is described. PI3K_68D has the potential to bind to signalling molecules containing SH3 domains, lacks p85-adaptor-binding sequences, has a Ca(2+)-independent phospholipid-binding domain and displays a restricted in vitro substrate specificity, so it could define a novel signal transduction pathway.
Aberrant alternative splicing has been highlighted as a potential hallmark of cancer. Here, we identify TDP43 (TAR DNA-binding protein 43) as an important splicing regulator responsible for the unique splicing profile in triple-negative breast cancer (TNBC). Clinical data demonstrate that TDP43 is highly expressed in TNBC with poor prognosis. Knockdown of TDP43 inhibits tumor progression, including proliferation and metastasis, and overexpression of TDP43 promotes proliferation and malignancy of mammary epithelial cells. Deep sequencing analysis and functional experiments indicate that TDP43 alters most splicing events with splicing factor SRSF3 (serine/arginine-rich splicing factor 3), in the regulation of TNBC progression. The TDP43/SRSF3 complex controls specific splicing events, including downstream genes PAR3 and NUMB The effect of reduced metastasis and proliferation upon the knockdown of TDP43 or SRSF3 is mediated by the splicing regulation of PAR3 and NUMB exon 12, respectively. The TDP43/SRSF3 complex and downstream PAR3 isoform are potential therapeutic targets for TNBC.
A putative spindle matrix has been hypothesized to mediate chromosome motion, but its existence and functionality remain controversial. In this report, we show that Megator (Mtor), the Drosophila melanogaster counterpart of the human nuclear pore complex protein translocated promoter region (Tpr), and the spindle assembly checkpoint (SAC) protein Mad2 form a conserved complex that localizes to a nuclear derived spindle matrix in living cells. Fluorescence recovery after photobleaching experiments supports that Mtor is retained around spindle microtubules, where it shows distinct dynamic properties. Mtor/Tpr promotes the recruitment of Mad2 and Mps1 but not Mad1 to unattached kinetochores (KTs), mediating normal mitotic duration and SAC response. At anaphase, Mtor plays a role in spindle elongation, thereby affecting normal chromosome movement. We propose that Mtor/Tpr functions as a spatial regulator of the SAC, which ensures the efficient recruitment of Mad2 to unattached KTs at the onset of mitosis and proper spindle maturation, whereas enrichment of Mad2 in a spindle matrix helps confine the action of a diffusible "wait anaphase" signal to the vicinity of the spindle.
Both signal transducer and activator of transcription 3 (STAT3) and SALL4 are important in maintaining the pluripotent and self-renewal state of embryonic stem cells. We hypothesized that STAT3, a latent transcriptional factor, may regulate the gene expression of SALL4. In support of this hypothesis, DNA sequence analysis of the SALL4 gene promoter revealed four putative STAT3-binding sites. Using a SALL4-luciferase reporter gene assay, we found that modulation of the STAT3 activity significantly up-regulated the luciferase activity. By chromatin immunoprecipitation, the segment of the SALL4 promoter showing the highest affinity to STAT3 was localized to -366 to -163, in which there was only one putative STAT3 binding site starting at -199. Site-directed mutagenesis of all four putative STAT3-binding sites in the SALL4 promoter significantly reduced its responsiveness to STAT3, although the most dramatic effect was seen at the binding site starting at -199. We further tested the functional relationship between STAT3 and SALL4 using MDA-MB-231, a breast cell line carrying constitutive SALL4 expression and STAT3 activity. Down-regulation of the STAT3 activity using a dominant-negative construct resulted in a significant decrease in the expression of SALL4. To conclude, our data suggest that STAT3 and SALL4 probably cooperate in both physiological and pathological states.
The identification of brain tumor stem-like cells (BTSCs) has implicated a role of biological self-renewal mechanisms in clinical brain tumor initiation and propagation. The molecular mechanisms underlying the tumor-forming capacity of BTSCs, however, remain unknown. Here, we have generated molecular signatures of glioblastoma multiforme (GBM) using gene expression profiles of BTSCs and have identified both Sonic Hedgehog (SHH) signaling-dependent and -independent BTSCs and their respective glioblastoma surgical specimens. BTSC proliferation could be abrogated in a pathway-dependent fashion in vitro and in an intracranial tumor model in athymic mice. Both SHH-dependent and -independent brain tumor growth required phosphoinositide 3-kinase-mammalian target of rapamycin signaling. In human GBMs, the levels of SHH and PTCH1 expression were significantly higher in PTEN-expressing tumors than in PTEN-deficient tumors. In addition, we show that hyperactive SHH-GLI signaling in PTEN-coexpressing human GBM is associated with reduced survival time. Thus, distinct proliferation signaling dependence may underpin glioblastoma propagation by BTSCs. Modeling these BTSC proliferation mechanisms may provide a rationale for individualized glioblastoma treatment.
Previous reports have suggested that the protooncogene c-myb participates in T cell development in the thymus and mature T cell proliferation. We have generated two T cell-specific c-myb knockout mouse models, myb/LckCre and myb/CD4Cre. We have demonstrated that c-myb is required for the development of thymocytes at the DN3 stage, for survival and proliferation of double-positive thymocytes, for differentiation of single-positive CD4 and CD8 T cells, and for the proliferative responses of mature T cells. In addition, our data show that c-myb is directly involved in the formation of double-positive CD4+CD8+CD25+, CD4+CD25+, and CD8+CD25+ T cells, developmental processes that may imply a role for c-myb in autoimmune dysfunction.
The overall size and structure of a synaptic terminal is an important determinant of its function. In a large-scale mutagenesis screen, designed to identify Drosophila mutants with abnormally structured neuromuscular junctions (NMJs), we discovered mutations in Drosophila mical, a conserved gene encoding a multi-domain protein with a N-terminal monooxygenase domain. In mical mutants, synaptic boutons do not sprout normally over the muscle surface and tend to form clusters along synaptic branches and at nerve entry sites. Consistent with high expression of MICAL in somatic muscles, immunohistochemical stainings reveal that the subcellular localization and architecture of contractile muscle filaments are dramatically disturbed in mical mutants. Instead of being integrated into a regular sarcomeric pattern, actin and myosin filaments are disorganized and accumulate beneath the plasmamembrane. Whereas contractile elements are strongly deranged, the proposed organizer of sarcomeric structure, D-Titin, is much less affected. Transgenic expression of interfering RNA molecules demonstrates that MICAL is required in muscles for the higher order arrangement of myofilaments. Ultrastructural analysis confirms that myosin-rich thick filaments enter submembranous regions and interfere with synaptic development, indicating that the disorganized myofilaments may cause the synaptic growth phenotype. As a model, we suggest that the filamentous network around synaptic boutons restrains the spreading of synaptic branches.
Although GBP1 (guanylate binding protein 1) was among the first interferon-inducible proteins identified, its function is still largely unknown. Epidermal growth factor receptor (EGFR) activation by amplification or mutation is one of the most frequent genetic lesions in a variety of human tumors. These include glioblastoma multiforme (GBM), which is characterized by independent but interrelated features of extensive invasion into normal brain parenchyma, rapid growth, necrosis, and angiogenesis. In this study, we show that EGFR activation promoted GBP1 expression in GBM cell lines through a signaling pathway involving Src and p38 mitogen-activated protein kinase. Moreover, we identified YY1 (Yin Yang 1) as the downstream transcriptional regulator regulating EGFR-driven GBP1 expression. GBP1 was required for EGFR-mediated MMP1 (matrix metalloproteinase 1) expression and glioma cell invasion in vitro. Although deregulation of GBP1 expression did not affect glioma cell proliferation, overexpression of GBP1 enhanced glioma cell invasion through MMP1 induction, which required its C-terminal helical domain and was independent of its GTPase activity. Reducing GBP1 levels by RNA interference in invasive GBM cells also markedly inhibited their ability to infiltrate the brain parenchyma of mice. GBP1 expression was high and positively correlated with EGFR expression in human GBM tumors and cell lines, particularly those of the neural subtype. Together, these findings establish GBP1 as a previously unknown link between EGFR activity and MMP1 expression and nominate it as a novel potential therapeutic target for inhibiting GBM invasion.
By analyzing gene expression data in glioblastoma in combination with matched microRNA profiles, we have uncovered a posttranscriptional regulation layer of surprising magnitude, comprising more than 248,000 microRNA (miR)-mediated interactions. These include ∼7,000 genes whose transcripts act as miR "sponges" and 148 genes that act through alternative, nonsponge interactions. Biochemical analyses in cell lines confirmed that this network regulates established drivers of tumor initiation and subtype implementation, including PTEN, PDGFRA, RB1, VEGFA, STAT3, and RUNX1, suggesting that these interactions mediate crosstalk between canonical oncogenic pathways. siRNA silencing of 13 miR-mediated PTEN regulators, whose locus deletions are predictive of PTEN expression variability, was sufficient to downregulate PTEN in a 3'UTR-dependent manner and to increase tumor cell growth rates. Thus, miR-mediated interactions provide a mechanistic, experimentally validated rationale for the loss of PTEN expression in a large number of glioma samples with an intact PTEN locus.
Mutations or duplications in MECP2 cause Rett and Rett-like syndromes, neurodevelopmental disorders characterized by mental retardation, motor dysfunction, and autistic behaviors. MeCP2 is expressed in many mammalian tissues and functions as a global repressor of transcription; however, the molecular mechanisms by which MeCP2 dysfunction leads to the neural-specific phenotypes of RTT remain poorly understood. Here, we show that neuronal activity and subsequent calcium influx trigger the de novo phosphorylation of MeCP2 at serine 421 (S421) by a CaMKII-dependent mechanism. MeCP2 S421 phosphorylation is induced selectively in the brain in response to physiological stimuli. Significantly, we find that S421 phosphorylation controls the ability of MeCP2 to regulate dendritic patterning, spine morphogenesis, and the activity-dependent induction of Bdnf transcription. These findings suggest that, by triggering MeCP2 phosphorylation, neuronal activity regulates a program of gene expression that mediates nervous system maturation and that disruption of this process in individuals with mutations in MeCP2 may underlie the neural-specific pathology of RTT.
We developed the Yeast Gene Order Browser (YGOB; http://wolfe.gen.tcd.ie/ygob) to facilitate visual comparisons and computational analysis of synteny relationships in yeasts. The data presented in YGOB, currently covering seven species, are based on sets of homologous genes that have been intensively manually curated based on both sequence similarity and genomic context (synteny). We reconciled different laboratories' lists of paralogous Saccharomyces cerevisiae gene pairs formed by genome duplication (ohnologs), and present near-exhaustive lists of the ohnolog pairs retained in S. cerevisiae (551, including 22 previously unidentified), Saccharomyces castellii (599), and Candida glabrata (404).
In wild-type budding yeast strains, the proteins encoded by SIR3, SIR4 and RAP1 co-localize with telomeric DNA in a limited number of foci in interphase nuclei. Immunostaining of Sir2p shows that in addition to a punctate staining that coincides with Rap1 foci, Sir2p localizes to a subdomain of the nucleolus. The presence of Sir2p at both the spacer of the rDNA repeat and at telomeres is confirmed by formaldehyde cross-linking and immunoprecipitation with anti-Sir2p antibodies. In strains lacking Sir4p, Sir3p becomes concentrated in the nucleolus, by a pathway requiring SIR2 and UTH4, a gene that regulates life span in yeast. The unexpected nucleolar localization of Sir2p and Sir3p correlates with observed effects of sir mutations on rDNA stability and yeast longevity, defining a new site of action for silent information regulatory factors.
Significant endeavor has been applied to identify functional therapeutic targets in glioblastoma (GBM) to halt the growth of this aggressive cancer. We show that the receptor tyrosine kinase EphA3 is frequently overexpressed in GBM and, in particular, in the most aggressive mesenchymal subtype. Importantly, EphA3 is highly expressed on the tumor-initiating cell population in glioma and appears critically involved in maintaining tumor cells in a less differentiated state by modulating mitogen-activated protein kinase signaling. EphA3 knockdown or depletion of EphA3-positive tumor cells reduced tumorigenic potential to a degree comparable to treatment with a therapeutic radiolabelled EphA3-specific monoclonal antibody. These results identify EphA3 as a functional, targetable receptor in GBM.
Mutations in the X-linked methyl-CpG-binding protein 2 (MECP2), encoding a transcriptional repressor, cause Rett syndrome and a variety of related neurodevelopmental disorders. The vast majority of mutations associated with human disease are loss-of-function mutations, but precisely what aspect of MeCP2 function is responsible for these phenotypes remains unknown. We overexpressed wild-type human protein in transgenic mice using a large genomic clone containing the entire human MECP2 locus. Detailed neurobehavioral and electrophysiological studies in transgenic line MeCP2(Tg1), which expresses MeCP2 at approximately 2-fold wild-type levels, demonstrated onset of phenotypes around 10 weeks of age. Surprisingly, these mice displayed enhanced motor and contextual learning and enhanced synaptic plasticity in the hippocampus. After 20 weeks of age, however, these mice developed seizures, became hypoactive and approximately 30% of them died by 1 year of age. These data demonstrate that MeCP2 levels must be tightly regulated in vivo, and that even mild overexpression of this protein is detrimental. Furthermore, these results support the possibility that duplications or gain-of-function mutations in MECP2 might underlie some cases of X-linked delayed-onset neurobehavioral disorders.
The Drosophila spaghetti squash ( sqh ) gene encodes the regulatory myosin light chain (RMLC) of nonmuscle myosin II. Biochemical analysis of vertebrate nonmuscle and smooth muscle myosin II has established that phosphorylation of certain amino acids of the RMLC greatly increases the actin-dependent myosin ATPase and motor activity of myosin in vitro. We have assessed the in vivo importance of these sites, which in Drosophila correspond to serine-21 and threonine-20, by creating a series of transgenes in which these specific amino acids were altered. The phenotypes of the transgenes were examined in an otherwise null mutant background during oocyte development in Drosophila females. Germ line cystoblasts entirely lacking a functional sqh gene show severe defects in proliferation and cytokinesis. The ring canals, cytoplasmic bridges linking the oocyte to the nurse cells in the egg chamber, are abnormal, suggesting a role of myosin II in their establishment or maintenance. In addition, numerous aggregates of myosin heavy chain accumulate in the sqh null cells. Mutant sqh transgene sqh -A20, A21 in which both serine-21 and threonine-20 have been replaced by alanines behaves in most respects identically to the null allele in this system, with the exception that no heavy chain aggregates are found. In contrast, expression of sqh -A21, in which only the primary phosphorylation target serine-21 site is altered, partially restores functionality to germ line myosin II, allowing cystoblast division and oocyte development, albeit with some cytokinesis failure, defects in the rapid cytoplasmic transport from nurse cells to cytoplasm characteristic of late stage oogenesis, and some damaged ring canals. Substituting a glutamate for the serine-21 (mutant sqh -E21) allows oogenesis to be completed with minimal defects, producing eggs that can develop normally to produce fertile adults. Flies expressing sqh -A20, in which only the secondary phosphorylation site is absent, appear to be entirely wild type. Taken together, this genetic evidence argues that phosphorylation at serine-21 is critical to RMLC function in activating myosin II in vivo, but that the function can be partially provided by phosphorylation at threonine-20.
The YAP transcription coactivator has been implicated as an oncogene and is amplified in human cancers. Recent studies have established that YAP is phosphorylated and inhibited by the Hippo tumor suppressor pathway. Here we demonstrate that the TEAD family transcription factors are essential in mediating YAP-dependent gene expression. TEAD is also required for YAP-induced cell growth, oncogenic transformation, and epithelial-mesenchymal transition. CTGF is identified as a direct YAP target gene important for cell growth. Moreover, the functional relationship between YAP and TEAD is conserved in Drosophila Yki (the YAP homolog) and Scalloped (the TEAD homolog). Our study reveals TEAD as a new component in the Hippo pathway playing essential roles in mediating biological functions of YAP.