The Fes/Fer non-receptor tyrosine kinase cooperates with Src42A to regulate dorsal closure in Drosophila

Natural genetic variation in Drosophila melanogaster reveals genes associated with Coxiella burnetii infection

The gram-negative bacterium Coxiella burnetii is the causative agent of Query (Q) fever in humans and coxiellosis in livestock. Host genetics are associated with C. burnetii pathogenesis both in humans and animals; however, it remains unknown if specific genes are associated with severity of infection. We employed the Drosophila Genetics Reference Panel to perform a genome-wide association study to identify host genetic variants that affect host survival to C. burnetii infection. The genome-wide association study identified 64 unique variants (P < 10⁻⁵) associated with 25 candidate genes. We examined the role each candidate gene contributes to host survival during C. burnetii infection using flies carrying a null mutation or RNAi knockdown of each candidate. We validated 15 of the 25 candidate genes using at least one method. This is the first report establishing involvement of many of these genes or their homologs with C. burnetii susceptibility in any system. Among the validated genes, FER and tara play roles in the JAK/STAT, JNK, and decapentaplegic/TGF-β signaling pathways which are components of known innate immune responses to C. burnetii infection. CG42673 and DIP-ε play roles in bacterial infection and synaptic signaling but have no previous association with C. burnetii pathogenesis. Furthermore, since the mammalian ortholog of CG13404 (PLGRKT) is an important regulator of macrophage function, CG13404 could play a role in host susceptibility to C. burnetii through hemocyte regulation. These insights provide a foundation for further investigation regarding the genetics of C. burnetii susceptibility across a wide variety of hosts.

The Seminiferous Epithelial Cycle of Spermatogenesis: Role of Non-receptor Tyrosine Kinases

Non-receptor tyrosine kinases (NRTKs) are implicated in various biological processes including cell proliferation, differentiation, survival, and apoptosis, as well as cell adhesion and movement. NRTKs are expressed in all mammals and in different cell types, with extraordinarily high expression in the testis. Their association with the plasma membrane and dynamic subcellular localization are crucial parameters in their activation and function. Many NRTKs are found in endosomal protein trafficking pathways, which suggests a novel mechanism to regulate the timely junction restructuring in the mammalian testis to facilitate spermiation and germ cell transport across the seminiferous epithelium.

Mask, a component of the Hippo pathway, is required for Drosophila eye morphogenesis

Hippo signaling is an important regulator of tissue size, but it also has a lesser-known role in tissue morphogenesis. Here we use the Drosophila pupal eye to explore the role of the Hippo effector Yki and its cofactor Mask in morphogenesis. We found that Mask is required for the correct distribution and accumulation of adherens junctions and appropriate organization of the cytoskeleton. Accordingly, disrupting mask expression led to severe mis-patterning and similar defects were observed when yki was reduced or in response to ectopic wts. Further, the patterning defects generated by reducing mask expression were modified by Hippo pathway activity. RNA-sequencing revealed a requirement for Mask for appropriate expression of numerous genes during eye morphogenesis. These included genes implicated in cell adhesion and cytoskeletal organization, a comprehensive set of genes that promote cell survival, and numerous signal transduction genes. To validate our transcriptome analyses, we then considered two loci that were modified by Mask activity: FER and Vinc, which have established roles in regulating adhesion. Modulating the expression of either locus modified mask mis-patterning and adhesion phenotypes. Further, expression of FER and Vinc was modified by Yki. It is well-established that the Hippo pathway is responsive to changes in cell adhesion and the cytoskeleton, but our data indicate that Hippo signaling also regulates these structures.

A single-cell atlas of adult Drosophila ovary identifies transcriptional programs and somatic cell lineage regulating oogenesis

Oogenesis is a complex developmental process that involves spatiotemporally regulated coordination between the germline and supporting, somatic cell populations. This process has been modeled extensively using the Drosophila ovary. Although different ovarian cell types have been identified through traditional means, the large-scale expression profiles underlying each cell type remain unknown. Using single-cell RNA sequencing technology, we have built a transcriptomic data set for the adult Drosophila ovary and connected tissues. Using this data set, we identified the transcriptional trajectory of the entire follicle-cell population over the course of their development from stem cells to the oogenesis-to-ovulation transition. We further identify expression patterns during essential developmental events that take place in somatic and germline cell types such as differentiation, cell-cycle switching, migration, symmetry breaking, nurse-cell engulfment, egg-shell formation, and corpus luteum signaling. Extensive experimental validation of unique expression patterns in both ovarian and nearby, nonovarian cells also led to the identification of many new cell type-and stage-specific markers. The inclusion of several nearby tissue types in this data set also led to our identification of functional convergence in expression between distantly related cell types such as the immune-related genes that were similarly expressed in immune cells (hemocytes) and ovarian somatic cells (stretched cells) during their brief phagocytic role in nurse-cell engulfment. Taken together, these findings provide new insight into the temporal regulation of genes in a cell-type specific manner during oogenesis and begin to reveal the relatedness in expression between cell and tissues types.

FER promotes cell migration via regulating JNK activity

Objectives

Cell migration has a key role in cancer metastasis, which contributes to drug resistance and tumour recurrence. Better understanding of the mechanisms involved in this process will potentially reveal new drug targets for cancer therapy. Fer is a non‐receptor protein tyrosine kinase aberrantly expressed in various human cancers, whereas its role in tumour progression remains elusive.

Materials and Methods

Transgenic flies and epigenetic analysis were employed to investigate the role of Drosophila Fer (FER) in cell migration and underlying mechanisms. Co‐immunoprecipitation assay was used to monitor the interaction between FER and Drosophila JNK (Bsk). The conservation of Fer in regulating JNK signalling was explored in mammalian cancer and non‐cancer cells.

Results

Overexpression of FER triggered cell migration and activated JNK signalling in the Drosophila wing disc. Upregulation and downregulation in the basal activity of Bsk exacerbated and eliminated FER‐mediated migration, respectively. In addition, loss of FER blocked signal transduction of the JNK pathway. Specifically, FER interacted with and promoted the activity of Bsk, which required both the kinase domain and the C‐terminal of Bsk. Lastly, Fer regulated JNK activities in mammalian cells.

Conclusions

Our study reveals FER as a positive regulator of JNK‐mediated cell migration and suggests its potential role as a therapeutic target for cancer metastasis.

Identifying Genetic Players in Cell Sheet Morphogenesis Using a Drosophila Deficiency Screen for Genes on Chromosome 2R Involved in Dorsal Closure

Cell sheet morphogenesis characterizes key developmental transitions and homeostasis, in vertebrates and throughout phylogeny, including gastrulation, neural tube formation and wound healing. Dorsal closure, a process during Drosophila embryogenesis, has emerged as a model for cell sheet morphogenesis. ∼140 genes are currently known to affect dorsal closure and new genes are identified each year. Many of these genes were identified in screens that resulted in arrested development. Dorsal closure is remarkably robust and many questions regarding the molecular mechanisms involved in this complex biological process remain. Thus, it is important to identify all genes that contribute to the kinematics and dynamics of closure. Here, we used a set of large deletions (deficiencies), which collectively remove 98.5% of the genes on the right arm of Drosophila melanogaster’s 2^nd chromosome to identify “dorsal closure deficiencies”. Through two crosses, we unambiguously identified embryos homozygous for each deficiency and time-lapse imaged them for the duration of closure. Images were analyzed for defects in cell shapes and tissue movements. Embryos homozygous for 47 deficiencies have notable, diverse defects in closure, demonstrating that a number of discrete processes comprise closure and are susceptible to mutational disruption. Further analysis of these deficiencies will lead to the identification of at least 30 novel “dorsal closure genes”. We expect that many of these novel genes will identify links to pathways and structures already known to coordinate various aspects of closure. We also expect to identify new processes and pathways that contribute to closure.

The adherens junction-associated LIM domain protein Smallish regulates epithelial morphogenesis

Cell–cell adhesion and cell shape are regulated at adherens junctions during embryonic morphogenesis. Beati et al. show that the Drosophila LIM domain protein Smallish interacts with Bazooka, Canoe, and Src42A at adherens junctions. Loss-of-function and gain-of-function phenotypes reveal a function for Smallish in regulation of actomyosin contractility and cell shape.

In epithelia, cells adhere to each other in a dynamic fashion, allowing the cells to change their shape and move along each other during morphogenesis. The regulation of adhesion occurs at the belt-shaped adherens junction, the zonula adherens (ZA). Formation of the ZA depends on components of the Par–atypical PKC (Par-aPKC) complex of polarity regulators. We have identified the Lin11, Isl-1, Mec-3 (LIM) protein Smallish (Smash), the orthologue of vertebrate LMO7, as a binding partner of Bazooka/Par-3 (Baz), a core component of the Par-aPKC complex. Smash also binds to Canoe/Afadin and the tyrosine kinase Src42A and localizes to the ZA in a planar polarized fashion. Animals lacking Smash show loss of planar cell polarity (PCP) in the embryonic epidermis and reduced cell bond tension, leading to severe defects during embryonic morphogenesis of epithelial tissues and organs. Overexpression of Smash causes apical constriction of epithelial cells. We propose that Smash is a key regulator of morphogenesis coordinating PCP and actomyosin contractility at the ZA.

Dual Roles of Fer Kinase Are Required for Proper Hematopoiesis and Vascular Endothelium Organization during Zebrafish Development

Fer kinase, a protein involved in the regulation of cell-cell adhesion and proliferation, has been shown to be required during invertebrate development and has been implicated in leukemia, gastric cancer, and liver cancer. However, in vivo roles for Fer during vertebrate development have remained elusive. In this study, we bridge the gap between the invertebrate and vertebrate realms by showing that Fer kinase is required during zebrafish embryogenesis for normal hematopoiesis and vascular organization with distinct kinase dependent and independent functions. In situ hybridization, quantitative PCR and fluorescence activated cell sorting (FACS) analyses revealed an increase in both erythrocyte numbers and gene expression patterns as well as a decrease in the organization of vasculature endothelial cells. Furthermore, rescue experiments have shown that the regulation of hematopoietic proliferation is dependent on Fer kinase activity, while vascular organizing events only require Fer in a kinase-independent manner. Our data suggest a model in which separate kinase dependent and independent functions of Fer act in conjunction with Notch activity in a divergent manner for hematopoietic determination and vascular tissue organization.

Dynamic interplay between adhesion surfaces in carcinomas: Cell-cell and cell-matrix crosstalk

Cell-cell and cell-matrix signaling and communication between adhesion sites involve mechanisms which are required for cellular functions during normal development and homeostasis; however these cellular functions and mechanisms are often deregulated in cancer. Aberrant signaling at cell-cell and cell-matrix adhesion sites often involves downstream mediators including Rho GTPases and tyrosine kinases. This review discusses these molecules as putative mediators of cellular crosstalk between cell-cell and cell-matrix adhesion sites, in addition to their attractiveness as therapeutic targets in cancer. Interestingly, inter-junctional crosstalk mechanisms are frequently typified by the way in which bacterial and viral pathogens opportunistically infect or intoxicate mammalian cells. This review therefore also discusses the concept of learning from pathogen-host interaction studies to better understand coordinated communication between cell-cell and cell-matrix adhesion sites, in addition to highlighting the potential therapeutic usefulness of exploiting pathogens or their products to tap into inter-junctional crosstalk. Taken together, we feel that increased knowledge around mechanisms of cell-cell and cell-matrix adhesion site crosstalk and consequently a greater understanding of their therapeutic targeting offers a unique opportunity to contribute to the emerging molecular revolution in cancer biology.

Phosphoproteomics-mediated identification of Fer kinase as a target of mutant Shp2 in Noonan and LEOPARD syndrome

Noonan syndrome (NS) and LEOPARD syndrome (LS) cause congenital afflictions such as short stature, hypertelorism and heart defects. More than 50% of NS and almost all of LS cases are caused by activating and inactivating mutations of the phosphatase Shp2, respectively. How these biochemically opposing mutations lead to similar clinical outcomes is not clear. Using zebrafish models of NS and LS and mass spectrometry-based phosphotyrosine proteomics, we identified a down-regulated peptide of Fer kinase in both NS and LS. Further investigation showed a role for Fer during development, where morpholino-based knockdown caused craniofacial defects, heart edema and short stature. During gastrulation, loss of Fer caused convergence and extension defects without affecting cell fate. Moreover, Fer knockdown cooperated with NS and LS, but not wild type Shp2 to induce developmental defects, suggesting a role for Fer in the pathogenesis of both NS and LS.

The unfulfilled gene and nervous system development in Drosophila

The unfulfilled gene of Drosophila encodes a member of the NR2E subfamily of nuclear receptors. Like related members of the NR2E subfamily, UNFULFILLED is anticipated to function as a dimer, binding to DNA response elements and regulating the expression of target genes. The UNFULFILLED protein may be regulated by ligand-binding and may also be post-transcriptionally modified by sumoylation and phosphorylation. unfulfilled mutants display a range of aberrant phenotypes, problems with eclosion and post-eclosion behaviors, compromised fertility, arrhythmicity, and a lack of all adult mushroom body lobes. The locus of the fertility problem has not been determined. The behavioral arrhythmicity is due to the unfulfilled-dependent disruption of gene expression in a set of pacemaker neurons. The eclosion and the mushroom body lobe phenotypes of unfulfilled mutants are the result of developmental problems associated with failures in axon pathfinding or re-extension. Interest in genes that act downstream of unfulfilled has resulted in the identification of a growing number of unfulfilled interacting loci, providing the first glimpse into the composition of unfulfilled-dependent gene networks. This article is part of a Special Issue entitled: Nuclear receptors in animal development.

unfulfilled interacting genes display branch-specific roles in the development of mushroom body axons in Drosophila melanogaster

The mushroom body (MB) of Drosophila melanogaster is an organized collection of interneurons that is required for learning and memory. Each of the three subtypes of MB neurons, γ, α´/β´, and α/β, branch at some point during their development, providing an excellent model in which to study the genetic regulation of axon branching. Given the sequential birth order and the unique patterning of MB neurons, it is likely that specific gene cascades are required for the different guidance events that form the characteristic lobes of the MB. The nuclear receptor UNFULFILLED (UNF), a transcription factor, is required for the differentiation of all MB neurons. We have developed and used a classical genetic suppressor screen that takes advantage of the fact that ectopic expression of unf causes lethality to identify candidate genes that act downstream of UNF. We hypothesized that reducing the copy number of unf-interacting genes will suppress the unf-induced lethality. We have identified 19 candidate genes that when mutated suppress the unf-induced lethality. To test whether candidate genes impact MB development, we performed a secondary phenotypic screen in which the morphologies of the MBs in animals heterozygous for unf and a specific candidate gene were analyzed. Medial MB lobes were thin, missing, or misguided dorsally in five double heterozygote combinations (;unf/+;axin/+, unf/+;Fps85D/+, ;unf/+;Tsc1/+, ;unf/+;Rheb/+, ;unf/+;msn/+). Dorsal MB lobes were missing in ;unf/+;DopR2/+ or misprojecting beyond the termination point in ;unf/+;Sytβ double heterozygotes. These data suggest that unf and unf-interacting genes play specific roles in axon development in a branch-specific manner.

Innexin 3, a new gene required for dorsal closure in Drosophila embryo

BACKGROUND

Dorsal closure is a morphogenetic event that occurs during mid-embryogenesis in many insects including Drosophila, during which the ectoderm migrates on the extraembryonic amnioserosa to seal the embryo dorsally. The contribution of the ectoderm in this event has been known for a long time. However, amnioserosa tension and contractibility have recently been shown also to be instrumental to the closure. A critical pre-requisite for dorsal closure is integrity of these tissues that in part is mediated by cell-cell junctions and cell adhesion. In this regard, mutations impairing junction formation and/or adhesion lead to dorsal closure. However, no role for the gap junction proteins Innexins has so far been described.

RESULTS AND DISCUSSION

Here, we show that Innexin 1, 2 and 3, are present in the ectoderm but also in the amnioserosa in plaques consistent with gap junctions. However, only the loss of Inx3 leads to dorsal closure defects that are completely rescued by overexpression of inx3::GFP in the whole embryo. Loss of Inx3 leads to the destabilisation of Inx1, Inx2 and DE-cadherin at the plasma membrane, suggesting that these four proteins form a complex. Accordingly, in addition to the known interaction of Inx2 with DE-cadherin, we show that Inx3 can bind to DE-cadherin. Furthermore, Inx3-GFP overexpression recruits DE-cadherin from its wildtype plasma membrane domain to typical Innexin plaques, strengthening the notion that they form a complex. Finally, we show that Inx3 stability is directly dependent on tissue tension. Taken together, we propose that Inx3 is a critical factor for dorsal closure and that it mediates the stability of Inx1, 2 and DE-cadherin by forming a complex.

Adherens junctions and cadherins in Drosophila development

Drosophila represents a paradigm for the analysis of the cellular, molecular and genetic mechanisms of development and is an ideal model system to study the contribution of Adherens Junctions (AJs) and their major components, cadherins, to morphogenesis. The combination of different techniques and approaches has allowed researchers to identify the requirements of these epithelial junctions in vivo in the context of a whole organism. The functional analysis of mutants for AJ core components, particularly for Drosophila DE-cadherin, has shown that AJs play critical roles in virtually all stages of development. For instance, AJs maintain tissue integrity while allowing the remodelling and homeostasis of many tissues. They control cell shape, contribute to cell polarity, facilitate cell-cell recognition during cell sorting, orient cell divisions, or regulate cell rearrangements, among other activities. Remarkably, these activities require a very fine control of the organisation and turnover of AJs during development. In addition, AJs engage in diverse and complex interactions with the cytoskeleton, signalling networks, intracellular trafficking machinery or polarity cues to perform these functions. Here, by summarising the requirements of AJs and cadherins during Drosophila morphogenesis, we illustrate the capital contribution of this model system to our knowledge of the mechanisms and biology of AJs.

F-BAR domain proteins: Families and function

The F-BAR domain is emerging as an important player in membrane remodeling pathways. F-BAR domain proteins couple membrane remodeling with actin dynamics associated with endocytic pathways and filopodium formation. Here, we provide a comprehensive analysis of F-BAR domain proteins in terms of their evolutionary relationships and protein function. F-BAR domain containing proteins can be categorized into five subfamilies based on their phylogeny which is consistent with the additional protein domains they possess, for example, RhoGAP domains, Cdc42 binding sites, SH3 domains and tyrosine kinase domains. We derive a protein-protein interaction network suggesting that dynamin1/2, N-WASP, Huntingtin, intersectin and Cdc42 are central nodes influencing F-BAR domain protein function.

Endocytic and recycling endosomes modulate cell shape changes and tissue behaviour during morphogenesis in Drosophila

During development tissue deformations are essential for the generation of organs and to provide the final form of an organism. These deformations rely on the coordination of individual cell behaviours which have their origin in the modulation of subcellular activities. Here we explore the role endocytosis and recycling on tissue deformations that occur during dorsal closure of the Drosophila embryo. During this process the AS contracts and the epidermis elongates in a coordinated fashion, leading to the closure of a discontinuity in the dorsal epidermis of the Drosophila embryo. We used dominant negative forms of Rab5 and Rab11 to monitor the impact on tissue morphogenesis of altering endocytosis and recycling at the level of single cells. We found different requirements for endocytosis (Rab5) and recycling (Rab11) in dorsal closure, furthermore we found that the two processes are differentially used in the two tissues. Endocytosis is required in the AS to remove membrane during apical constriction, but is not essential in the epidermis. Recycling is required in the AS at early stages and in the epidermis for cell elongation, suggesting a role in membrane addition during these processes. We propose that the modulation of the balance between endocytosis and recycling can regulate cellular morphology and tissue deformations during morphogenesis.

Mechanical control of global cell behaviour during dorsal closure in Drosophila

Halfway through embryonic development, the epidermis of Drosophila exhibits a gap at the dorsal side covered by an extraembryonic epithelium, the amnioserosa (AS). Dorsal closure (DC) is the process whereby interactions between the two epithelia establish epidermal continuity. Although genetic and biomechanical analysis have identified the AS as a force-generating tissue, we do not know how individual cell behaviours are transformed into tissue movements. To approach this question we have applied a novel image-analysis method to measure strain rates in local domains of cells and performed a kinematic analysis of DC. Our study reveals spatial and temporal differences in the rate of apical constriction of AS cells. We find a slow phase of DC, during which apical contraction of cells at the posterior end predominates, and a subsequent fast phase, during which all the cells engage in the contraction, which correlates with the zippering process. There is a radial gradient of AS apical contraction, with marginal cells contracting earlier than more centrally located cells. We have applied this analysis to the study of mutant situations and associated a particular genotype with quantitative and reproducible changes in the rate of cell contraction and hence in the overall rate of the process. Our mutant analysis reveals the contribution of mechanical elements to the rate and pattern of DC.

Kinome signaling through regulated protein-protein interactions in normal and cancer cells

The flow of molecular information through normal and oncogenic signaling pathways frequently depends on protein phosphorylation, mediated by specific kinases, and the selective binding of the resulting phosphorylation sites to interaction domains present on downstream targets. This physical and functional interplay of catalytic and interaction domains can be clearly seen in cytoplasmic tyrosine kinases such as Src, Abl, Fes, and ZAP-70. Although the kinase and SH2 domains of these proteins possess similar intrinsic properties of phosphorylating tyrosine residues or binding phosphotyrosine sites, they also undergo intramolecular interactions when linked together, in a fashion that varies from protein to protein. These cooperative interactions can have diverse effects on substrate recognition and kinase activity, and provide a variety of mechanisms to link the stimulation of catalytic activity to substrate recognition. Taken together, these data have suggested how protein kinases, and the signaling pathways in which they are embedded, can evolve complex properties through the stepwise linkage of domains within single polypeptides or multi-protein assemblies.

Expression of Fer testis (FerT) tyrosine kinase transcript variants and distribution sites of FerT during the development of the acrosome-acroplaxome-manchette complex in rat spermatids

We report the association of testicular Fer, a non-receptor tyrosine kinase, with acrosome development and remodeling of the acrosome-associated acroplaxome plate during spermatid head shaping. A single gene expresses two forms of Fer tyrosine kinases in testis: a somatic form (FerS) and a truncated testis-type form (FerT). FerT transcript variants are seen in spermatocytes and spermatids. FerS transcripts are not detected in round spermatids but are moderately transcribed in spermatocytes. FerT protein is associated with the spermatid medial/trans-Golgi region, proacrosomal vesicles, the cytosolic side of the outer acrosome membrane and adjacent to the inner acrosome membrane facing the acroplaxome. FerT coexist in the acroplaxome with phosphorylated cortactin, a regulator of F-actin dynamics. We propose that FerT participates in acrosome development and that phosphorylated cortactin may contribute to structural changes in F-actin in the acroplaxome during spermatid head shaping.

Phosphorylation networks regulating JNK activity in diverse genetic backgrounds

Cellular signaling networks have evolved to enable swift and accurate responses, even in the face of genetic or environmental perturbation. Thus, genetic screens may not identify all the genes that regulate different biological processes. Moreover, although classical screening approaches have succeeded in providing parts lists of the essential components of signaling networks, they typically do not provide much insight into the hierarchical and functional relations that exist among these components. We describe a high-throughput screen in which we used RNA interference to systematically inhibit two genes simultaneously in 17,724 combinations to identify regulators of Drosophila JUN NH(2)-terminal kinase (JNK). Using both genetic and phosphoproteomics data, we then implemented an integrative network algorithm to construct a JNK phosphorylation network, which provides structural and mechanistic insights into the systems architecture of JNK signaling.

Structural coupling of SH2-kinase domains links Fes and Abl substrate recognition and kinase activation

The SH2 domain of cytoplasmic tyrosine kinases can enhance catalytic activity and substrate recognition, but the molecular mechanisms by which this is achieved are poorly understood. We have solved the structure of the prototypic SH2-kinase unit of the human Fes tyrosine kinase, which appears specialized for positive signaling. In its active conformation, the SH2 domain tightly interacts with the kinase N-terminal lobe and positions the kinase αC helix in an active configuration through essential packing and electrostatic interactions. This interaction is stabilized by ligand binding to the SH2 domain. Our data indicate that Fes kinase activation is closely coupled to substrate recognition through cooperative SH2-kinase-substrate interactions. Similarly, we find that the SH2 domain of the active Abl kinase stimulates catalytic activity and substrate phosphorylation through a distinct SH2-kinase interface. Thus, the SH2 and catalytic domains of active Fes and Abl pro-oncogenic kinases form integrated structures essential for effective tyrosine kinase signaling.

Requirements for adherens junction components in the interaction between epithelial tissues during dorsal closure in Drosophila

Dynamic interactions between epithelial sheets are a regular feature of morphogenetic processes. Dorsal closure in Drosophila relies on the coordinated movements of two epithelia, the epidermis and the amnioserosa, and provides an excellent model system for a genetic and cell biological approach. Here, we have analyzed the contribution of junctional organization of these epithelia to dorsal closure. We observe a stringent requirement for adherens junctions at the leading edge, the interface between the amnioserosa and the epidermis, for the transmission of the forces generated during the process. We also find that interactions between Armadillo and E-cadherin play an important role in maintaining the adhesion at the leading edge, revealing the particular dynamics of this interface. Our results show that regulated cell adhesion is a crucial element of the interactions that shape epithelial sheets in morphogenetic processes.

Fer-mediated cortactin phosphorylation is associated with efficient fibroblast migration and is dependent on reactive oxygen species generation during integrin-mediated cell adhesion

The molecular details linking integrin engagement to downstream cortactin (Ctn) tyrosine phosphorylation are largely unknown. In this report, we show for the first time that Fer and Ctn are potently tyrosine phosphorylated in response to hydrogen peroxide (H2O2) in a variety of cell types. Working with catalytically inactive fer and src/yes/fyn-deficient murine embryonic fibroblasts (ferDR/DR and syf MEF, respectively), we observed that H2O2-induced Ctn tyrosine phosphorylation is primarily dependent on Fer but not Src family kinase (SFK) activity. We also demonstrated for the first time that Fer is activated by fibronectin engagement and, in concert with SFKs, mediates Ctn tyrosine phosphorylation in integrin signaling pathways. Reactive oxygen species (ROS) scavengers or the NADPH oxidase inhibitor, diphenylene iodonium, attenuated integrin-induced Fer and Ctn tyrosine phosphorylation. Taken together, these findings provide novel genetic evidence that a ROS-Fer signaling arm contributes to SFK-mediated Ctn tyrosine phosphorylation in integrin signaling. Lastly, a migration defect in ferDR/DR MEF suggests that integrin signaling through the ROS-Fer-Ctn signaling arm may be linked to mechanisms governing cell motility. These data demonstrate for the first time an oxidative link between integrin adhesion and an actin-binding protein involved in actin polymerization.