Organization of wing formation and induction of a wing-patterning gene at the dorsal/ventral compartment boundary

Wg/Wnt-signaling-induced nuclear translocation of β-catenin is attenuated by a β-catenin peptide through its interference with the IFT-A complex

Wnt/Wingless (Wg) signaling is critical in development and disease, including cancer. Canonical Wnt signaling is mediated by β-catenin/Armadillo (Arm in Drosophila) transducing signals to the nucleus, with IFT-A/Kinesin 2 complexes promoting nuclear translocation of β-catenin/Arm. Here, we demonstrate that a conserved small N-terminal Arm34-87/β-catenin peptide binds to IFT140, acting as a dominant interference tool to attenuate Wg/Wnt signaling in vivo. Arm34-87 expression antagonizes endogenous Wnt/Wg signaling, resulting in the reduction of its target expression. Arm34-87 inhibits Wg/Wnt signaling by interfering with nuclear translocation of endogenous Arm/β-catenin, and this can be modulated by levels of wild-type β-catenin or IFT140, with the Arm34-87 effect being enhanced or suppressed. Importantly, this mechanism is conserved in mammals with the equivalent β-catenin24-79 peptide blocking nuclear translocation and pathway activation, including in cancer cells. Our work indicates that Wnt signaling can be regulated by a defined N-terminal β-catenin peptide and thus might serve as an entry point for therapeutic applications to attenuate Wnt/β-catenin signaling.

Transcriptome analysis reveals the role of Zelda in the regulation of embryonic and wing development of Tribolium castaneum

Zinc finger protein (Zelda) of Tribolium castaneum (TcZelda) has been showed to play pivotal roles in embryonic development and metamorphosis. However, the regulatory mechanism of TcZelda associated with these physiology processes is unclear. Herein, the developmental expression profile showed that Zelda of T. castaneum was highly expressed in early eggs. Tissue expression profiling revealed that TcZelda was mainly expressed in the larval head and adult ovary of late adults and late larvae. TcZelda knockdown led to a 95% mortality rate in adults. These results suggested that TcZelda is related to the activation of the zygote genome in early embryonic development. Furthermore, 592 differentially expressed genes were identified from the dsZelda treated group. Compared with the control group, altered disjunction (ALD) and AGAP005368-PA (GAP) in the dsZelda group were significantly down-regulated, while TGF-beta, propeptide (TGF) was significantly up-regulated, suggesting that TcZelda may be involved in insect embryonic development. In addition, the expression of Ubx ultrabithorax (UBX), Cx cephalothorax (CX), En engrailed (EN), and two Endocuticle structural glycoprotein sgabd (ABD) genes were significantly down-regulated, suggesting that they may cooperate with TcZelda to regulate the development of insect wings. Additionally, Elongation (ELO), fatty acid synthase (FAS), and fatty acyl-CoA desaturase (FAD) expression was inhibited in dsZelda insects, which could disturb the lipase signaling pathways, thus, disrupting the insect reproductive system and pheromone synthesis. These results may help reveal the function of TcZelda in insects and the role of certain genes in the gene regulatory network and provide new ideas for the prevention and control of T. castaneum.

Vestigial-dependent induction contributes to robust patterning but is not essential for wing-fate recruitment in Drosophila

Cell recruitment is a process by which a differentiated cell induces neighboring cells to adopt its same cell fate. In Drosophila, cells expressing the protein encoded by the wing selector gene, vestigial (vg), drive a feed-forward recruitment signal that expands the Vg pattern as a wave front. However, previous studies on Vg pattern formation do not reveal these dynamics. Here, we use live imaging to show that multiple cells at the periphery of the wing disc simultaneously activate a fluorescent reporter of the recruitment signal, suggesting that cells may be recruited without the need for their contact neighbors be recruited in advance. In support of this observation, when Vg expression is inhibited either at the dorsal-ventral boundary or away from it, the activation of the recruitment signal still occurs at a distance, suggesting that Vg expression is not absolutely required to send or propagate the recruitment signal. However, the strength and extent of the recruitment signal is clearly compromised. We conclude that a feed-forward, contact-dependent cell recruitment process is not essential for Vg patterning, but it is necessary for robustness. Overall, our findings reveal a previously unidentified role of cell recruitment as a robustness-conferring cell differentiation mechanism.

The vestigial Quadrant Enhancer is dispensable for pattern formation and development of the Drosophila wing

In Drosophila , the pattern of the wing selector gene, vestigial ( vg ), is established by at least two enhancers: the Boundary Enhancer, which drives expression along the disc's Dorsal-Ventral boundary; and the Quadrant Enhancer (QE) that patterns the rest of the wing pouch. Using CRISPR/Cas9 editing, we deleted DNA fragments around the reported QE sequence and found that the full Vg pattern is formed. Furthermore, adult wings arising from these gene-edited animals are normal in shape and pattern, but slightly smaller in size, although this reduction is not wing-specific in males. We suggest that other enhancers act redundantly to establish the vg pattern and rescue wing development.

The roles of growth regulation and appendage patterning genes in the morphogenesis of treehopper pronota

Treehoppers of the insect family Membracidae have evolved enlarged and elaborate pronotal structures, which is hypothesized to involve co-opted expression of genes that are shared with the wings. Here, we investigate the similarity between the pronotum and wings in relation to growth. Our study reveals that the ontogenetic allometry of the pronotum is similar to that of wings in Membracidae, but not the outgroup. Using transcriptomics, we identify genes related to translation and protein synthesis, which are mutually upregulated. These genes are implicated in the eIF2, eIF4/p70S6K and mTOR pathways, and have known roles in regulating cell growth and proliferation. We find that species-specific differential growth patterning of the pronotum begins as early as the third instar, which suggests that expression of appendage patterning genes occurs long before the metamorphic molt. We propose that a network related to growth and size determination is the more likely mechanism shared with wings. However, regulators upstream of the shared genes in pronotum and wings need to be elucidated to substantiate whether co-option has occurred. Finally, we believe it will be helpful to distinguish the mechanisms leading to pronotal size from those regulating pronotal shape as we make sense of this spectacular evolutionary innovation.

A hemimetabolous wing development suggests the wing origin from lateral tergum of a wingless ancestor

The origin and evolution of the novel insect wing remain enigmatic after a century-long discussion. The mechanism of wing development in hemimetabolous insects, in which the first functional wings evolved, is key to understand where and how insect wings evolutionarily originate. This study explored the developmental origin and the postembryonic dramatic growth of wings in the cricket Gryllus bimaculatus. We find that the lateral tergal margin, which is homologous between apterygote and pterygote insects, comprises a growth organizer to expand the body wall to form adult wing blades in Gryllus. We also find that Wnt, Fat-Dachsous, and Hippo pathways are involved in the disproportional growth of Gryllus wings. These data provide insights into where and how insect wings originate. Wings evolved from the pre-existing lateral terga of a wingless insect ancestor, and the reactivation or redeployment of Wnt/Fat-Dachsous/Hippo-mediated feed-forward circuit might have expanded the lateral terga.

Here, the authors investigate wing development in cricket and find support for evolution of the novel insect wing from the pre-existing dorsal body wall of a wingless ancestor by activation of an evolutionarily conserved growth mechanism.

Out from under the wing: reconceptualizing the insect wing gene regulatory network as a versatile, general module for body-wall lobes in arthropods

Body plan evolution often occurs through the differentiation of serially homologous body parts, particularly in the evolution of arthropod body plans. Recently, homeotic transformations resulting from experimental manipulation of gene expression, along with comparative data on the expression and function of genes in the wing regulatory network, have provided a new perspective on an old question in insect evolution: how did the insect wing evolve? We investigated the metamorphic roles of a suite of 10 wing- and body-wall-related genes in a hemimetabolous insect, Oncopeltus fasciatus. Our results indicate that genes involved in wing development in O. fasciatus play similar roles in the development of adult body-wall flattened cuticular evaginations. We found extensive functional similarity between the development of wings and other bilayered evaginations of the body wall. Overall, our results support the existence of a versatile development module for building bilayered cuticular epithelial structures that pre-dates the evolutionary origin of wings. We explore the consequences of reconceptualizing the canonical wing-patterning network as a bilayered body-wall patterning network, including consequences for long-standing debates about wing homology, the origin of wings and the origin of novel bilayered body-wall structures. We conclude by presenting three testable predictions that result from this reconceptualization.

What crustaceans can tell us about the evolution of insect wings and other morphologically novel structures

Acquisition of novel structures often has a profound impact on the adaptation of organisms. The wing of insects is one such example, facilitating their massive success and enabling them to become the dominant clade on this planet. However, its evolutionary origin as well as the mechanisms underpinning its evolution remain elusive. Studies in crustaceans, a wingless sister group of insects, have played a pivotal role in the wing origin debate. Three recent investigations into the genes related to insect wings and legs in crustaceans provided intriguing insights into how and where insect wings evolved. Interestingly, each study proposes a distinct mechanism as a key process underlying insect wing evolution. Here, I discuss what we can learn about the evolution of insect wings and morphological novelty in general by synthesizing the outcomes of these studies.

A unified mechanism for the control of Drosophila wing growth by the morphogens Decapentaplegic and Wingless

Development of the Drosophila wing-a paradigm of organ development-is governed by 2 morphogens, Decapentaplegic (Dpp, a BMP) and Wingless (Wg, a Wnt). Both proteins are produced by defined subpopulations of cells and spread outwards, forming gradients that control gene expression and cell pattern as a function of concentration. They also control growth, but how is unknown. Most studies have focused on Dpp and yielded disparate models in which cells throughout the wing grow at similar rates in response to the grade or temporal change in Dpp concentration or to the different amounts of Dpp "equalized" by molecular or mechanical feedbacks. In contrast, a model for Wg posits that growth is governed by a progressive expansion in morphogen range, via a mechanism in which a minimum threshold of Wg sustains the growth of cells within the wing and recruits surrounding "pre-wing" cells to grow and enter the wing. This mechanism depends on the capacity of Wg to fuel the autoregulation of vestigial (vg)-the selector gene that specifies the wing state-both to sustain vg expression in wing cells and by a feed-forward (FF) circuit of Fat (Ft)/Dachsous (Ds) protocadherin signaling to induce vg expression in neighboring pre-wing cells. Here, we have subjected Dpp to the same experimental tests used to elucidate the Wg model and find that it behaves indistinguishably. Hence, we posit that both morphogens act together, via a common mechanism, to control wing growth as a function of morphogen range.

Vestigial mediates the effect of insulin signaling pathway on wing-morph switching in planthoppers

Wing polymorphism is an evolutionary feature found in a wide variety of insects, which offers a model system for studying the evolutionary significance of dispersal. In the wing-dimorphic planthopper Nilaparvata lugens, the insulin/insulin-like growth factor signaling (IIS) pathway acts as a ‘master signal’ that directs the development of either long-winged (LW) or short-winged (SW) morphs via regulation of the activity of Forkhead transcription factor subgroup O (NlFoxO). However, downstream effectors of the IIS–FoxO signaling cascade that mediate alternative wing morphs are unclear. Here we found that vestigial (Nlvg), a key wing-patterning gene, is selectively and temporally regulated by the IIS–FoxO signaling cascade during the wing-morph decision stage (fifth-instar stage). RNA interference (RNAi)-mediated silencing of Nlfoxo increase Nlvg expression in the fifth-instar stage (the last nymphal stage), thereby inducing LW development. Conversely, silencing of Nlvg can antagonize the effects of IIS activity on LW development, redirecting wing commitment from LW to the morph with intermediate wing size. In vitro and in vivo binding assays indicated that NlFoxO protein may suppress Nlvg expression by directly binding to the first intron region of the Nlvg locus. Our findings provide a first glimpse of the link connecting the IIS pathway to the wing-patterning network on the developmental plasticity of wings in insects, and help us understanding how phenotypic diversity is generated by the modification of a common set of pattern elements.

Many insects are capable of developing into either long-winged or short-winged adults, but the underlying molecular basis remains largely unknown. Pioneer studies showed that the insulin/insulin-like growth factor signaling pathway acts as a ‘master signal’ that directs wing buds to develop into long or short wings in the wing-dimorphic planthopper, Nilaparvata lugens. However, downstream effectors mediating the IIS pathway effects are unknown. Our findings highlight that vestigial, a key wing-patterning gene, is a main downstream effector that mediates the IIS activity on the development of alternative wing morphs during the wing-morph decision stage. The molecular mechanism of wing formation, including the function of vestigial, has been studied in great depth in the model insect Drosophila melanogaster. Our data provide a first glimpse of the link connecting the IIS pathway to the wing-patterning network in regulating developmental plasticity of wings in insects.

Vestigial suppresses apoptosis and cell migration in a manner dependent on the level of JNK-Caspase signaling in the Drosophila wing disc

The Decapentaplegic (Dpp) and Wingless (Wg) signal pathways play important roles in numerous biological processes in Drosophila. The Drosophila vestigial (vg) gene is selectively required for wing imaginal disc cell proliferation, which is essential for the formation of the adult wing and halter structures, and is regulated by Dpp and Wg signaling. Using a Drosophila invasion model of wing epithelium, we showed herein that inhibition of Dpp or Wg signaling promoted cells to migrate across the cell lineage restrictive anterior/posterior (A/P) compartment boundary. Being downstream of both Dpp and Wg signaling, vg can block cell migration induced by loss of either pathway. In addition, suppression of vg is sufficient to induce cell migration across the A/P boundary. Transcriptomic analysis revealed potential downstream genes involved in the cell migration after suppressing vg in the wing disc. We further demonstrated that the c-Jun N-terminal kinase (JNK) signaling promoted cell migration induced by vg suppression by upregulating Caspase activity. Taken together, our results revealed the requirement of Vg for suppressing cell migration and clarified how developmental signals collaborate to stabilize cells along the compartment boundary.

Wing serial homologues and the diversification of insect outgrowths: insights from the pupae of scarab beetles

Modification of serially homologous structures is a common avenue towards functional innovation in developmental evolution, yet ancestral affinities among serial homologues may be obscured as structure-specific modifications accumulate over time. We sought to assess the degree of homology to wings of three types of body wall projections commonly observed in scarab beetles: (i) the dorsomedial support structures found on the second and third thoracic segments of pupae, (ii) the abdominal support structures found bilaterally in most abdominal segments of pupae, and (iii) the prothoracic horns which depending on species and sex may be restricted to pupae or also found in adults. We functionally investigated 14 genes within, as well as two genes outside, the canonical wing gene regulatory network to compare and contrast their role in the formation of each of the three presumed wing serial homologues. We found 11 of 14 wing genes to be functionally required for the proper formation of lateral and dorsal support structures, respectively, and nine for the formation of prothoracic horns. At the same time, we document multiple instances of divergence in gene function across our focal structures. Collectively, our results support the hypothesis that dorsal and lateral support structures as well as prothoracic horns share a developmental origin with insect wings. Our findings suggest that the morphological and underlying gene regulatory diversification of wing serial homologues across species, life stages and segments has contributed significantly to the extraordinary diversity of arthropod appendages and outgrowths.

Plant homeodomain proteins provide a mechanism for how leaves grow wide

The mechanisms whereby leaf anlagen undergo proliferative growth and expansion to form wide, flat leaves are unclear. The maize gene NARROWSHEATH1 (NS1) is a WUSCHEL-related homeobox3 (WOX3) homolog expressed at the margins of leaf primordia, and is required for mediolateral outgrowth. To investigate the mechanisms of NS1 function, we used chromatin immunoprecipitation and laser-microdissection RNA-seq of leaf primordial margins to identify gene targets bound and modulated by NS1. Microscopic analyses of cell division and gene expression in expanding leaves, and reverse genetic analyses of homologous NS1 target genes in Arabidopsis, reveal that NS1 controls mediolateral outgrowth by repression of a growth inhibitor and promotion of cell division at primordial leaf margins. Intriguingly, homologous WOX gene products are expressed in stem cell-organizing centers and traffic to adjoining cells to activate stem-cell identity non-autonomously. In contrast, WOX3/NS1 does not traffic, and stimulates cell divisions in the same cells in which it is transcribed.

Highlighted Article: The NS1 homeodomain transcription factor regulates lateral organ outgrowth from shoot meristems and leaf primordial margins by repressing the expression of negative growth regulators.

A dynamic cell recruitment process drives growth of the Drosophila wing by overscaling the vestigial expression pattern

Organs mainly attain their size by cell growth and proliferation, but sometimes also grow through recruitment of undifferentiated cells. Here we investigate the participation of cell recruitment in establishing the pattern of Vestigial (Vg), the product of the wing selector gene in Drosophila. We find that the Vg pattern overscales along the dorsal-ventral (DV) axis of the wing imaginal disc, i.e., it expands faster than the DV length of the pouch. The overscaling of the Vg pattern cannot be explained by differential proliferation, apoptosis, or oriented-cell divisions, but can be recapitulated by a mathematical model that explicitly considers cell recruitment. When impairing cell recruitment genetically, we find that the Vg pattern almost perfectly scales and adult wings are approximately 20% smaller. Conversely, impairing cell proliferation results in very small wings, suggesting that cell recruitment and cell proliferation additively contribute to organ growth in this system. Furthermore, using fluorescent reporter tools, we provide direct evidence that cell recruitment is initiated between early and mid third-instar larval development. Altogether, our work quantitatively shows when, how, and by how much cell recruitment shapes the Vg pattern and drives growth of the Drosophila wing.

Genes regulating wing patterning in Drosophila melanogaster show reduced expression under exposure of Daminozide, the fruit ripening retardant

In our previous study we demonstrated that the fruit ripening retardant Daminozide or Alar causes change in life history traits, distortion of adult wing structure, DNA damage in brain cells and mutagenic effects in fruit fly Drosophila melanogaster. As a continuation of the previous study the present work is designed to explore the metabolic modification of Daminozide following ingestion, the effects of Daminozide on the expression of genes which are pivotal for wing development and molecular interactions of Daminozide with those proteins involved in wing patterning. We demonstrated through reporter gene construct assay using X-gal staining method and transgenic Drosophila melanogaster stocks that the vestigial, wingless and decapentaplegic genes in wing imaginal disc from 3^rd instar larvae exhibited reduced expression when exposed to Daminozide in compare to control larvae. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) of those genes confirmed that exposure to Daminozide reduces the transcription level of those genes. In silico approach with molecular docking study revealed Daminozide may bind and interfere with the optimal functioning of expressed wing signaling proteins.

miR-147b-modulated expression of vestigial regulates wing development in the bird cherry-oat aphid Rhopalosiphum padi

BACKGROUND

Most aphids exhibit wing polyphenism in which wingless and winged morphs produce depending on the population density and host plant quality. Although the influence of environmental factors on wing polyphenism of aphids have been extensively investigated, molecular mechanisms underlining morph differentiation (i.e. wing development /degeneration), one downstream aspect of the wing polyphenism, has been poorly understood.

RESULTS

We examined the expression levels of the twenty genes involved in wing development network, and only vestigial (vg) showed significantly different expression levels in both whole-body and wall-body of third instar nymphs, with 5.4- and 16.14- fold higher expression in winged lines compared to wingless lines, respectively in Rhopalosiphum padi. vg expression was higher in winged lines compared to wingless lines in third, fourth instar nymphs and adults. Larger difference expression was observed in third (21.38-fold) and fourth (20.91-fold) instar nymphs relative to adults (3.12-fold). Suppression of vg using RNAi repressed the wing development of third winged morphs. Furthermore, dual luciferase reporter assay revealed that the miR-147 can target the vg mRNA. Modulation of miR-147b levels by microinjection of its agomir (mimic) decreased vg expression levels and repressed wing development.

CONCLUSIONS

Our findings suggest that vg is essential for wing development in R. padi and that miR-147b modulates its expression.

L1 Cell Adhesion Molecule Overexpression Down Regulates Phosphacan and Up Regulates Structural Plasticity-Related Genes Rostral and Caudal to the Complete Spinal Cord Transection

L1 cell adhesion molecule (L1CAM) supports spinal cord cellular milieu after contusion and compression lesions, contributing to neuroprotection, promoting axonal outgrowth, and reducing outgrowth-inhibitory molecules in lesion proximity. We extended investigations into L1CAM molecular targets and explored long-distance effects of L1CAM rostral and caudal to complete spinal cord transection (SCT) in adult rats. L1CAM overexpression in neurons and glia after Th10/Th11 SCT was achieved using adeno-associated viral vector serotype 5 (AAV5) injected into an L1-lumbar segment immediately after transection. At 5 weeks, a L1CAM mRNA profound decrease detected rostral and caudal to the transection site was alleviated by AAV5-L1CAM treatment, with increased endogenous L1CAM rostral to the SCT. Transected corticospinal tract fibers showed attenuated retraction after treatment, accompanied by a multi-segmental increase of lesion-reduced expression of adenylate cyclase 1 (Adcy1), synaptophysin, growth-associated protein 43, and myelin basic protein genes caudal to transection, and Adcy1 rostral to transection. In parallel, chondroitin sulfate proteoglycan phosphacan elevated after SCT was downregulated after treatment. Low-molecular L1CAM isoforms generated after spinalization indicated the involvement of sheddases in L1CAM processing and long-distance effects. A disintegrin and metalloproteinase (ADAM)10 sheddase immunoreactivity, stronger in AAV5-L1CAM than AAV5- enhanced green fluorescent protein (EGFP)-transduced motoneurons indicated local ADAM10 upregulation by L1CAM. The results suggest that increased L1CAM availability and penetration of diffusible L1CAM fragments post-lesion induce both local and long-distance neuronal and glial responses toward better neuronal maintenance, neurite growth, and myelination. Despite the fact that intervention promoted beneficial molecular changes, kinematic analysis of hindlimb movements showed minor improvement, indicating that spinalized rats require longer L1CAM treatment to regain locomotor functions.

A refutation to 'A new A-P compartment boundary and organizer in holometabolous insect wings'

We respond to a recent report by Abbasi and Marcus who present two main findings: first they argue that there is an organiser and a compartment boundary within the posterior compartment of the butterfly wing. Second, they present evidence for a previously undiscovered lineage boundary near wing vein 5 in Drosophila, a boundary that delineates a "far posterior" compartment. Clones of cells were marked with the yellow mutation and they reported that these clones always fail to cross a line close to vein 5 on the Drosophila wing. In our hands yellow proved an unusable marker for clones in the wing blade and therefore we reexamined the matter. We marked clones of cells with multiple wing hairs or forked and found a substantial proportion of these clones cross the proposed lineage boundary near vein 5, in conflict with their findings and conclusion. As internal controls we showed that these same clones respect the other two well established compartment boundaries: the anteroposterior compartment boundary is always respected. The dorsoventral boundary is mostly respected, and is crossed only by clones that are induced early in development, consistent with many reports. We question the validity of Abbasi and Marcus' conclusions regarding the butterfly wing but present no new data.Arising from: R. Abbasi and J. M. Marcus Sci. Rep. 7, 16337 (2017); https://doi.org/10.1038/s41598-017-16553-5 .

On the mechanisms of development in monocot and eudicot leaves

Contents Summary 706 I. Introduction 707 II. Leaf zones in monocot and eudicot leaves 707 III. Monocot and eudicot leaf initiation: differences in degree and timing, but not kind 710 IV. Reticulate and parallel venation: extending the model? 711 V. Flat laminar growth: patterning and coordination of adaxial-abaxial and mediolateral axes 713 VI. Stipules and ligules: ontogeny of primordial elaborations 715 VII. Leaf architecture 716 VIII. Stomatal development: shared and diverged mechanisms for making epidermal pores 717 IX. Conclusion 719 Acknowledgements 720 References 720 SUMMARY: Comparisons of concepts in monocot and eudicot leaf development are presented, with attention to the morphologies and mechanisms separating these angiosperm lineages. Monocot and eudicot leaves are distinguished by the differential elaborations of upper and lower leaf zones, the formation of sheathing/nonsheathing leaf bases and vasculature patterning. We propose that monocot and eudicot leaves undergo expansion of mediolateral domains at different times in ontogeny, directly impacting features such as venation and leaf bases. Furthermore, lineage-specific mechanisms in compound leaf development are discussed. Although models for the homologies of enigmatic tissues, such as ligules and stipules, are proposed, tests of these hypotheses are rare. Likewise, comparisons of stomatal development are limited to Arabidopsis and a few grasses. Future studies may investigate correlations in the ontogenies of parallel venation and linear stomatal files in monocots, and the reticulate patterning of veins and dispersed stoma in eudicots. Although many fundamental mechanisms of leaf development are shared in eudicots and monocots, variations in the timing, degree and duration of these ontogenetic events may contribute to key differences in morphology. We anticipate that the incorporation of an ever-expanding number of sequenced genomes will enrich our understanding of the developmental mechanisms generating eudicot and monocot leaves.

Ubiquitylation-independent activation of Notch signalling by Delta

Ubiquitylation (ubi) by the E3-ligases Mindbomb1 (Mib1) and Neuralized (Neur) is required for activation of the DSL ligands Delta (Dl) and Serrate (Ser) to activate Notch signalling. These ligases transfer ubiquitin to lysines of the ligands' intracellular domains (ICDs), which sends them into an Epsin-dependent endocytic pathway. Here, we have tested the requirement of ubi of Dl for signalling. We found that Dl requires ubi for its full function, but can also signal in two ubi-independent modes, one dependent and one independent of Neur. We identified two neural lateral specification processes where Dl signals in an ubi-independent manner. Neur, which is needed for these processes, was shown to be able to activate Dl in an ubi-independent manner. Our analysis suggests that one important role of DSL protein ubi by Mib1 is their release from cis-inhibitory interactions with Notch, enabling them to trans-activate Notch on adjacent cells.

The activity of the Drosophila Vestigial protein is modified by Scalloped-dependent phosphorylation

The Drosophila vestigial gene is required for proliferation and differentiation of the adult wing and for differentiation of larval and adult muscle identity. Vestigial is part of a multi-protein transcription factor complex, which includes Scalloped, a TEAD-class DNA binding protein. Binding Scalloped is necessary for translocation of Vestigial into the nucleus. We show that Vestigial is extensively post-translationally modified and at least one of these modifications is required for proper function during development. We have shown that there is p38-dependent phosphorylation of Serine 215 in the carboxyl-terminal region of Vestigial. Phosphorylation of Serine 215 occurs in the nucleus and requires the presence of Scalloped. Comparison of a phosphomimetic and non-phosphorylatable mutant forms of Vestigial shows differences in the ability to rescue the wing and muscle phenotypes associated with a null vestigial allele.

A comparative genomic analysis of targets of Hox protein Ultrabithorax amongst distant insect species

In the fruitfly Drosophila melanogaster, the differential development of wing and haltere is dependent on the function of the Hox protein Ultrabithorax (Ubx). Here we compare Ubx-mediated regulation of wing patterning genes between the honeybee, Apis mellifera, the silkmoth, Bombyx mori and Drosophila. Orthologues of Ubx are expressed in the third thoracic segment of Apis and Bombyx, although they make functional hindwings. When over-expressed in transgenic Drosophila, Ubx derived from Apis or Bombyx could suppress wing development, suggesting evolutionary changes at the level of co-factors and/or targets of Ubx. To gain further insights into such events, we identified direct targets of Ubx from Apis and Bombyx by ChIP-seq and compared them with those of Drosophila. While majority of the putative targets of Ubx are species-specific, a considerable number of wing-patterning genes are retained, over the past 300 millions years, as targets in all the three species. Interestingly, many of these are differentially expressed only between wing and haltere in Drosophila but not between forewing and hindwing in Apis or Bombyx. Detailed bioinformatics and experimental validation of enhancer sequences suggest that, perhaps along with other factors, changes in the cis-regulatory sequences of earlier targets contribute to diversity in Ubx function.

A Hox Transcription Factor Collective Binds a Highly Conserved Distal-less cis-Regulatory Module to Generate Robust Transcriptional Outcomes

cis-regulatory modules (CRMs) generate precise expression patterns by integrating numerous transcription factors (TFs). Surprisingly, CRMs that control essential gene patterns can differ greatly in conservation, suggesting distinct constraints on TF binding sites. Here, we show that a highly conserved Distal-less regulatory element (DCRE) that controls gene expression in leg precursor cells recruits multiple Hox, Extradenticle (Exd) and Homothorax (Hth) complexes to mediate dual outputs: thoracic activation and abdominal repression. Using reporter assays, we found that abdominal repression is particularly robust, as neither individual binding site mutations nor a DNA binding deficient Hth protein abolished cooperative DNA binding and in vivo repression. Moreover, a re-engineered DCRE containing a distinct configuration of Hox, Exd, and Hth sites also mediated abdominal Hox repression. However, the re-engineered DCRE failed to perform additional segment-specific functions such as thoracic activation. These findings are consistent with two emerging concepts in gene regulation: First, the abdominal Hox/Exd/Hth factors utilize protein-protein and protein-DNA interactions to form repression complexes on flexible combinations of sites, consistent with the TF collective model of CRM organization. Second, the conserved DCRE mediates multiple cell-type specific outputs, consistent with recent findings that pleiotropic CRMs are associated with conserved TF binding and added evolutionary constraints.

Enhancers are regulatory elements that interact with transcription factor proteins to control cell-specific gene expression during development. Surprisingly, only a subset of enhancers are highly conserved at the sequence level, even though the expression patterns they control are often conserved and essential for proper development. Why some enhancer sequences are highly conserved whereas others are not is not well understood. In this study, we characterize a highly conserved enhancer that regulates gene expression in leg precursor cells. We find that this enhancer has dual regulatory activities that include gene activation in thoracic segments and gene repression in abdominal segments. Surprisingly, we show that the conserved enhancer can tolerate numerous sequence changes yet mediate robust transcription factor binding and abdominal repression. These findings are consistent with abdominal transcription factors binding numerous different configurations of binding sites. So, why is this enhancer highly conserved? We found that overlapping sequences within the enhancer also contribute to thoracic activation, suggesting the enhancer sequences are under added functional constraints. Altogether, our results provide new insights into why some enhancers are highly conserved at the sequence level while others can tolerate sequence changes.

Combgap contributes to recruitment of Polycomb group proteins in Drosophila

Polycomb group (PcG) proteins are responsible for maintaining the silenced transcriptional state of many developmentally regulated genes. PcG proteins are organized into multiprotein complexes that are recruited to DNA via cis-acting elements known as "Polycomb response elements" (PREs). In Drosophila, PREs consist of binding sites for many different DNA-binding proteins, some known and others unknown. Identification of these DNA-binding proteins is crucial to understanding the mechanism of PcG recruitment to PREs. We report here the identification of Combgap (Cg), a sequence-specific DNA-binding protein that is involved in recruitment of PcG proteins. Cg can bind directly to PREs via GTGT motifs and colocalizes with the PcG proteins Pleiohomeotic (Pho) and Polyhomeotic (Ph) at the majority of PREs in the genome. In addition, Cg colocalizes with Ph at a number of targets independent of Pho. Loss of Cg leads to decreased recruitment of Ph at only a subset of sites; some of these sites are binding sites for other Polycomb repressive complex 1 (PRC1) components, others are not. Our data suggest that Cg can recruit Ph in the absence of PRC1 and illustrate the diversity and redundancy of PcG protein recruitment mechanisms.

Integration of Orthogonal Signaling by the Notch and Dpp Pathways in Drosophila

The transcription factor Suppressor of Hairless and its coactivator, the Notch intracellular domain, are polyglutamine (pQ)-rich factors that target enhancer elements and interact with other locally bound pQ-rich factors. To understand the functional repertoire of such enhancers, we identify conserved regulatory belts with binding sites for the pQ-rich effectors of both Notch and BMP/Dpp signaling, and the pQ-deficient tissue selectors Apterous (Ap), Scalloped (Sd), and Vestigial (Vg). We find that the densest such binding site cluster in the genome is located in the BMP-inducible nab locus, a homolog of the vertebrate transcriptional cofactors NAB1/NAB2 We report three major findings. First, we find that this nab regulatory belt is a novel enhancer driving dorsal wing margin expression in regions of peak phosphorylated Mad in wing imaginal discs. Second, we show that Ap is developmentally required to license the nab dorsal wing margin enhancer (DWME) to read out Notch and Dpp signaling in the dorsal compartment. Third, we find that the nab DWME is embedded in a complex of intronic enhancers, including a wing quadrant enhancer, a proximal wing disc enhancer, and a larval brain enhancer. This enhancer complex coordinates global nab expression via both tissue-specific activation and interenhancer silencing. We suggest that DWME integration of BMP signaling maintains nab expression in proliferating margin descendants that have divided away from Notch-Delta boundary signaling. As such, uniform expression of genes like nab and vestigial in proliferating compartments would typically require both boundary and nonboundary lineage-specific enhancers.

A Flippase-Mediated GAL80/GAL4 Intersectional Resource for Dissecting Appendage Development in Drosophila

Drosophila imaginal discs provide an ideal model to study processes important for cell signaling and cell specification, tissue differentiation, and cell competition during development. One challenge to understanding genetic control of cellular processes and cell interactions is the difficulty in effectively targeting a defined subset of cells in developing tissues in gene manipulation experiments. A recently developed Flippase-induced intersectional GAL80/GAL4 repression method incorporates several gene manipulation technologies in Drosophila to enable such fine-scale dissection in neural tissues. In particular, this approach brings together existing GAL4 transgenes, newly developed enhancer-trap flippase transgenes, and GAL80 transgenes flanked by Flippase recognition target sites. The combination of these tools enables gene activation/repression in particular subsets of cells within a GAL4 expression pattern. Here, we expand the utility of a large collection of these enhancer-trap flippase transgenic insertion lines by characterizing their expression patterns in third larval instar imaginal discs. We screened 521 different enhancer-trap flippase lines and identified 28 that are expressed in imaginal tissues, including two transgenes that show sex-specific expression patterns. Using a line that expresses Flippase in the wing imaginal disc, we demonstrate the utility of this intersectional approach for studying development by knocking down gene expression of a key member of the planar cell polarity pathway. The results of our experiments show that these enhancer-trap flippase lines enable fine-scale manipulation in imaginal discs.

The Drosophila melanogaster Mutants apblot and apXasta Affect an Essential apterous Wing Enhancer

The selector gene apterous (ap) plays a key role during the development of the Drosophila melanogaster wing because it governs the establishment of the dorsal-ventral (D-V) compartment boundary. The D-V compartment boundary is known to serve as an important signaling center that is essential for the growth of the wing. The role of Ap and its downstream effectors have been studied extensively. However, very little is known about the transcriptional regulation of ap during wing disc development. In this study, we present a first characterization of an essential wing-specific ap enhancer. First, we defined an 874-bp fragment about 10 kb upstream of the ap transcription start that faithfully recapitulates the expression pattern of ap in the wing imaginal disc. Analysis of deletions in the ap locus covering this element demonstrated that it is essential for proper regulation of ap and formation of the wing. Moreover, we showed that the mutations ap^blot and ap^Xasta directly affect the integrity of this enhancer, leading to characteristic wing phenotypes. Furthermore, we engineered an in situ rescue system at the endogenous ap gene locus, allowing us to investigate the role of enhancer fragments in their native environment. Using this system, we were able to demonstrate that the essential wing enhancer alone is not sufficient for normal wing development. The in situ rescue system will allow us to characterize the ap regulatory sequences in great detail at the endogenous locus.

Visualizing Notch signaling in vivo in Drosophila tissues

The ability to visualize Notch pathway activity in vivo is invaluable for studying the functions and mechanisms of Notch signaling. A variety of tools have been developed to enable monitoring of pathway activity in Drosophila, including endogenous Notch-responsive genes and synthetic transcriptional reporter constructs. Here we summarize some of the different Notch signaling reporters that are available, discuss their relative merits, and describe two methods for visualizing their expression (immunostaining and X-gal staining). These approaches are widely applicable to a range of tissues and stages in Drosophila development.

Notch inhibits Yorkie activity in Drosophila wing discs

During development, tissues and organs must coordinate growth and patterning so they reach the right size and shape. During larval stages, a dramatic increase in size and cell number of Drosophila wing imaginal discs is controlled by the action of several signaling pathways. Complex cross-talk between these pathways also pattern these discs to specify different regions with different fates and growth potentials. We show that the Notch signaling pathway is both required and sufficient to inhibit the activity of Yorkie (Yki), the Salvador/Warts/Hippo (SWH) pathway terminal transcription activator, but only in the central regions of the wing disc, where the TEAD factor and Yki partner Scalloped (Sd) is expressed. We show that this cross-talk between the Notch and SWH pathways is mediated, at least in part, by the Notch target and Sd partner Vestigial (Vg). We propose that, by altering the ratios between Yki, Sd and Vg, Notch pathway activation restricts the effects of Yki mediated transcription, therefore contributing to define a zone of low proliferation in the central wing discs.

A strand-specific switch in noncoding transcription switches the function of a Polycomb/Trithorax response element

Polycomb/Trithorax response elements (PRE/TREs) can switch their function reversibly between silencing and activation by mechanisms that are poorly understood. Here we show that a switch in forward and reverse noncoding transcription from the Drosophila melanogaster vestigial (vg) PRE/TRE switches the status of the element between silencing (induced by the forward strand) and activation (induced by the reverse strand). In vitro, both noncoding RNAs inhibit PRC2 histone methyltransferase activity, but, in vivo, only the reverse strand binds PRC2. Overexpression of the reverse strand evicts PRC2 from chromatin and inhibits its enzymatic activity. We propose that the interaction of RNAs with PRC2 is differentially regulated in vivo, allowing regulated inhibition of local PRC2 activity. Genome-wide analysis shows that strand switching of noncoding RNAs occurs at several hundred Polycomb-binding sites in fly and vertebrate genomes. This work identifies a previously unreported and potentially widespread class of PRE/TREs that switch function by switching the direction of noncoding RNA transcription.

Tools and methods for studying Notch signaling in Drosophila melanogaster

Notch signaling involves a highly conserved pathway that mediates communication between neighboring cells. Activation of Notch by its ligands, results in the release of the Notch intracellular domain (NICD), which enters the nucleus and regulates transcription. This pathway has been implicated in many developmental decisions and diseases (including cancers) over the past decades. The simplicity of the Notch pathway in Drosophila melanogaster, in combination with the availability of powerful genetics, make this an attractive model for studying fundamental principles of Notch regulation and function. In this article we present some of the established and emerging tools that are available to monitor and manipulate the Notch pathway in Drosophila and discuss their strengths and weaknesses.

A common set of DNA regulatory elements shapes Drosophila appendages

Animals have body parts made of similar cell types located at different axial positions, such as limbs. The identity and distinct morphology of each structure is often specified by the activity of different "master regulator" transcription factors. Although similarities in gene expression have been observed between body parts made of similar cell types, how regulatory information in the genome is differentially utilized to create morphologically diverse structures in development is not known. Here, we use genome-wide open chromatin profiling to show that among the Drosophila appendages, the same DNA regulatory modules are accessible throughout the genome at a given stage of development, except at the loci encoding the master regulators themselves. In addition, open chromatin profiles change over developmental time, and these changes are coordinated between different appendages. We propose that master regulators create morphologically distinct structures by differentially influencing the function of the same set of DNA regulatory modules.

The Drosophila gypsy insulator supports transvection in the presence of the vestigial enhancer

Though operationally defined as cis-regulatory elements, enhancers can also communicate with promoters on a separate homolog in trans, a mechanism that has been suggested to account for the ability of certain alleles of the same gene to complement one another in a process otherwise known as transvection. This homolog-pairing dependent process is facilitated in Drosophila by chromatin-associated pairing proteins, many of which remain unknown and their mechanism of action uncharacterized. Here we have tested the role of the gypsy chromatin insulator in facilitating pairing and communication between enhancers and promoters in trans using a transgenic eGFP reporter system engineered to allow for targeted deletions in the vestigial Boundary Enhancer (vgBE) and the hsp70 minimal promoter, along with one or two flanking gypsy elements. We found a modest 2.5-3x increase in eGFP reporter levels from homozygotes carrying an intact copy of the reporter on each homolog compared to unpaired hemizygotes, although this behavior was independent of gypsy. However, detectable levels of GFP protein along the DV wing boundary in trans-heterozygotes lacking a single enhancer and promoter was only observed in the presence of two flanking gypsy elements. Our results demonstrate that gypsy can stimulate enhancer-promoter communication in trans throughout the genome in a context-dependent manner, likely through modulation of local chromatin dynamics once pairing has been established by other elements and highlights chromatin structure as the master regulator of this phenomenon.

Dual phosphorylation of cdk1 coordinates cell proliferation with key developmental processes in Drosophila

Eukaryotic organisms use conserved checkpoint mechanisms that regulate Cdk1 by inhibitory phosphorylation to prevent mitosis from interfering with DNA replication or repair. In metazoans, this checkpoint mechanism is also used for coordinating mitosis with dynamic developmental processes. Inhibitory phosphorylation of Cdk1 is catalyzed by Wee1 kinases that phosphorylate tyrosine 15 (Y15) and dual-specificity Myt1 kinases found only in metazoans that phosphorylate Y15 and the adjacent threonine (T14) residue. Despite partially redundant roles in Cdk1 inhibitory phosphorylation, Wee1 and Myt1 serve specialized developmental functions that are not well understood. Here, we expressed wild-type and phospho-acceptor mutant Cdk1 proteins to investigate how biochemical differences in Cdk1 inhibitory phosphorylation influence Drosophila imaginal development. Phosphorylation of Cdk1 on Y15 appeared to be crucial for developmental and DNA damage-induced G2-phase checkpoint arrest, consistent with other evidence that Myt1 is the major Y15-directed Cdk1 inhibitory kinase at this stage of development. Expression of non-inhibitable Cdk1 also caused chromosome defects in larval neuroblasts that were not observed with Cdk1(Y15F) mutant proteins that were phosphorylated on T14, implicating Myt1 in a novel mechanism promoting genome stability. Collectively, these results suggest that dual inhibitory phosphorylation of Cdk1 by Myt1 serves at least two functions during development. Phosphorylation of Y15 is essential for the premitotic checkpoint mechanism, whereas T14 phosphorylation facilitates accumulation of dually inhibited Cdk1-Cyclin B complexes that can be rapidly activated once checkpoint-arrested G2-phase cells are ready for mitosis.

Microarray comparison of anterior and posterior Drosophila wing imaginal disc cells identifies novel wing genes

Signaling between cells in the anterior (A) and posterior (P) compartments directs Drosophila wing disc development and is dependent on expression of the homeodomain transcription factor Engrailed (En) in P cells. Downstream of en, posteriorly expressed Hedgehog (Hh) protein signals across the A/P border to establish a developmental organizer that directs pattern formation and growth throughout the wing primordium. Here we extend investigations of the processes downstream of en by using expression array analysis to compare A and P cells. A total of 102 candidate genes were identified that express differentially in the A and P compartments; four were characterized: Stubble (Sb) expression is restricted to A cells due to repression by en. CG15905, CG16884; CG10200/hase und igel (hui) are expressed in A cells downstream of Hh signaling; and RNA interference for hui, Stubble, and CG16884 revealed that each is essential to wing development.

Essential roles for stat92E in expanding and patterning the proximodistal axis of the Drosophila wing imaginal disc

The Drosophila wing imaginal disc is subdivided along the proximodistal axis into the distal pouch, the hinge, the surrounding pleura, and the notum. While the genetic pathways that specify the identity of each of these domains have been well studied, the mechanisms that coordinate the relative expansion of these domains are not well understood. Here we investigated the role of the stat92E signal transducer and activator of transcription in wing proximodistal development. We find that stat92E is active ubiquitously in early wing imaginal discs, where it acts to inhibit the induction of ectopic wing fields. Subsequently, stat92E activity is down regulated in the notum and distal pouch. These dynamics coincide with and contribute to the proportional subdivision and expansion of these primordia. As development proceeds, stat92E activity becomes restricted to the hinge, where it promotes normal expansion of the hinge, and restricts expansion of the notum. We also find that stat92E is required autonomously to specify dorsal pleura identity and inhibit notum identity to properly subdivide the body wall. Our data suggest that stat92E activity is regulated along the proximodistal axis to pattern this axis and control the relative expansion of the pouch, hinge, and notum.

Sequential Notch signalling at the boundary of fringe expressing and non-expressing cells

Wing development in Drosophila requires the activation of Wingless (Wg) in a small stripe along the boundary of Fringe (Fng) expressing and non-expressing cells (FB), which coincides with the dorso-ventral (D/V) boundary of the wing imaginal disc. The expression of Wg is induced by interactions between dorsal and ventral cells mediated by the Notch signalling pathway. It appears that mutual signalling from dorsal to ventral and ventral to dorsal cells by the Notch ligands Serrate (Ser) and Delta (Dl) respectively establishes a symmetric domain of Wg that straddles the D/V boundary. The directional signalling of these ligands requires the modification of Notch in dorsal cells by the glycosyltransferase Fng and is based on the restricted expression of the ligands with Ser expression to the dorsal and that of Dl to the ventral side of the wing anlage. In order to further investigate the mechanism of Notch signalling at the FB, we analysed the function of Fng, Ser and Dl during wing development at an ectopic FB and at the D/V boundary. We find that Notch signalling is initiated in an asymmetric fashion on only one side of the FB. During this initial asymmetric phase, only one ligand is required, with Ser initiating Notch-signalling at the D/V and Dl at the ectopic FB. Furthermore, our analysis suggests that Fng has also a positive effect on Ser signalling. Because of these additional properties, differential expression of the ligands, which has been a prerequisite to restrict Notch activation to the FB in the current model, is not required to restrict Notch signalling to the FB.

Integrating force-sensing and signaling pathways in a model for the regulation of wing imaginal disc size

The regulation of organ size constitutes a major unsolved question in developmental biology. The wing imaginal disc of Drosophila serves as a widely used model system to study this question. Several mechanisms have been proposed to have an impact on final size, but they are either contradicted by experimental data or they cannot explain a number of key experimental observations and may thus be missing crucial elements. We have modeled a regulatory network that integrates the experimentally confirmed molecular interactions underlying other available models. Furthermore, the network includes hypothetical interactions between mechanical forces and specific growth regulators, leading to a size regulation mechanism that conceptually combines elements of existing models, and can be understood in terms of a compression gradient model. According to this model, compression increases in the center of the disc during growth. Growth stops once compression levels in the disc center reach a certain threshold and the compression gradient drops below a certain level in the rest of the disc. Our model can account for growth termination as well as for the paradoxical observation that growth occurs uniformly in the presence of a growth factor gradient and non-uniformly in the presence of a uniform growth factor distribution. Furthermore, it can account for other experimental observations that argue either in favor or against other models. The model also makes specific predictions about the distribution of cell shape and size in the developing disc, which we were able to confirm experimentally.

Wnt/Wingless signaling in Drosophila

The Wingless (Wg) pathway represents one of the best-characterized intercellular signaling networks. Studies performed in Drosophila over the last 30 years have contributed to our understanding of the role of Wg signaling in the regulation of tissue growth, polarity, and patterning. These studies have revealed mechanisms conserved in the vertebrate Wnt pathways and illustrate the elegance of using the Drosophila model to understand evolutionarily conserved modes of gene regulation. In this article, we describe the function of Wg signaling in patterning the Drosophila embryonic epidermis and wing imaginal disc. As well, we present an overview of the establishment of the Wg morphogen gradient and discuss the differential modes of Wg-regulated gene expression.

Requirements for mediator complex subunits distinguish three classes of notch target genes at the Drosophila wing margin

Spatial and temporal gene regulation relies on a combinatorial code of sequence-specific transcription factors that must be integrated by the general transcriptional machinery. A key link between the two is the mediator complex, which consists of a core complex that reversibly associates with the accessory kinase module. We show here that genes activated by Notch signaling at the dorsal-ventral boundary of the Drosophila wing disc fall into three classes that are affected differently by the loss of kinase module subunits. One class requires all four kinase module subunits for activation, while the others require only Med12 and Med13, either for activation or for repression. These distinctions do not result from different requirements for the Notch coactivator Mastermind or the corepressors Hairless and Groucho. We propose that interactions with the kinase module through distinct cofactors allow the DNA-binding protein Suppressor of Hairless to carry out both its activator and repressor functions.

Enhancer-PRE communication contributes to the expansion of gene expression domains in proliferating primordia

Trithorax-group and Polycomb-group proteins interact with chromosomal elements, termed PRE/TREs, to ensure stable heritable maintenance of the transcriptional state of nearby genes. Regulatory elements that bind both groups of proteins are termed maintenance elements (MEs). Some of these MEs maintain the initial activated transcriptional state of a nearby reporter gene through several rounds of mitosis during development. Here, we show that expression of hedgehog in the posterior compartment of the Drosophila wing results from the communication between a previously defined ME and a nearby cis-regulatory element termed the C enhancer. The C enhancer integrates the activities of the Notch and Hedgehog signalling pathways and, from the early wing primordium stage, drives expression to a thin stripe in the posterior compartment that corresponds to the dorsal-ventral compartment boundary. The ME maintains the initial activated transcriptional state conferred by the C enhancer and contributes to the expansion, by growth, of its expression domain throughout the posterior compartment. Communication between the ME and the C enhancer also contributes to repression of gene expression in anterior cells. Most interestingly, we present evidence that enhancers and MEs of different genes are interchangeable modules whose communication is involved in restricting and expanding the domains of gene expression. Our results emphasize the modular role of MEs in regulation of gene expression within growing tissues.

Identification of a classical bipartite nuclear localization signal in the Drosophila TEA/ATTS protein scalloped

Drosophila melanogaster wing development has been shown to rely on the activity of a complex of two proteins, Scalloped (Sd) and Vestigial (Vg). Within this complex, Sd is known to provide DNA binding though its TEA/ATTS domain, while Vg modulates this binding and provides transcriptional activation through N- and C-terminal activation domains. There is also evidence that Sd is required for the nuclear translocation of Vg. Indeed, a candidate sequence which shows consensus to the bipartite family of nuclear localization signals (NLSs) has been identified within Sd previously, though it is not known if it is functional, or if additional unpredicted signals that mediate nuclear transport exist within the protein. By expressing various enhanced green fluorescent protein (eGFP) tagged constructs within Drosophila S2 cells, we demonstrate that this NLS is indeed functional and necessary for the proper nuclear localization of Sd. Additionally, the region containing the NLS is critical for the wildtype function of ectopically expressed Sd, in the context of wing development. Using site-directed mutagenesis, we have identified a group of five amino acids within this NLS which is critical for its function, as well as another group of two which is of lesser importance. Together with data that suggests that this sequence mediates interactions with Importin-α3, we conclude that the identified NLS is likely a classical bipartite signal. Further dissection of Sd has also revealed that a large portion of the C-terminal domain of the protein is required its proper nuclear localization. Finally, a Leptomycin B (LB) sensitive signal which appears to facilitate nuclear export is identified, raising the possibility that Sd also contains a nuclear export signal (NES).

Quantitative analysis of polycomb response elements (PREs) at identical genomic locations distinguishes contributions of PRE sequence and genomic environment

Background

Polycomb/Trithorax response elements (PREs) are cis-regulatory elements essential for the regulation of several hundred developmentally important genes. However, the precise sequence requirements for PRE function are not fully understood, and it is also unclear whether these elements all function in a similar manner. Drosophila PRE reporter assays typically rely on random integration by P-element insertion, but PREs are extremely sensitive to genomic position.

Results

We adapted the ΦC31 site-specific integration tool to enable systematic quantitative comparison of PREs and sequence variants at identical genomic locations. In this adaptation, a miniwhite (mw) reporter in combination with eye-pigment analysis gives a quantitative readout of PRE function. We compared the Hox PRE Frontabdominal-7 (Fab-7) with a PRE from the vestigial (vg) gene at four landing sites. The analysis revealed that the Fab-7 and vg PREs have fundamentally different properties, both in terms of their interaction with the genomic environment at each site and their inherent silencing abilities. Furthermore, we used the ΦC31 tool to examine the effect of deletions and mutations in the vg PRE, identifying a 106 bp region containing a previously predicted motif (GTGT) that is essential for silencing.

Conclusions

This analysis showed that different PREs have quantifiably different properties, and that changes in as few as four base pairs have profound effects on PRE function, thus illustrating the power and sensitivity of ΦC31 site-specific integration as a tool for the rapid and quantitative dissection of elements of PRE design.

IRF2BP2 is a skeletal and cardiac muscle-enriched ischemia-inducible activator of VEGFA expression

We sought to identify an essential component of the TEAD4/VGLL4 transcription factor complex that controls vascular endothelial growth factor A (VEGFA) expression in muscle. A yeast 2-hybrid screen was used to clone a novel component of the TEAD4 complex from a human heart cDNA library. We identified interferon response factor 2 binding protein 2 (IRF2BP2) and confirmed its presence in the TEAD4/VGLL4 complex in vivo by coimmunoprecipitation and mammalian 2-hybrid assays. Coexpression of IRF2BP2 with TEAD4/VGLL4 or TEAD1 alone potently activated, whereas knockdown of IRF2BP2 reduced, VEGFA expression in C(2)C(12) muscle cells. Thus, IRF2BP2 is required to activate VEGFA expression. In mouse embryos, IRF2BP2 was ubiquitously expressed but became progressively enriched in the fetal heart, skeletal muscles, and lung. Northern blot analysis revealed high levels of IRF2BP2 mRNA in adult human heart and skeletal muscles, but immunoblot analysis showed low levels of IRF2BP2 protein in skeletal muscle, indicating post-transcriptional regulation of IRF2BP2 expression. IRF2BP2 protein levels are markedly increased by ischemia in skeletal and cardiac muscle compared to normoxic controls. IRF2BP2 is a novel ischemia-induced coactivator of VEGFA expression that may contribute to revascularization of ischemic cardiac and skeletal muscles.

A feed-forward circuit linking wingless, fat-dachsous signaling, and the warts-hippo pathway to Drosophila wing growth

The secreted morphogen Wingless promotes Drosophila wing growth by fueling a wave front of Fat-Dachsous signaling that recruits new cells into the wing primordium.

During development, the Drosophila wing primordium undergoes a dramatic increase in cell number and mass under the control of the long-range morphogens Wingless (Wg, a Wnt) and Decapentaplegic (Dpp, a BMP). This process depends in part on the capacity of wing cells to recruit neighboring, non-wing cells into the wing primordium. Wing cells are defined by activity of the selector gene vestigial (vg) and recruitment entails the production of a vg-dependent “feed-forward signal” that acts together with morphogen to induce vg expression in neighboring non-wing cells. Here, we identify the protocadherins Fat (Ft) and Dachsous (Ds), the Warts-Hippo tumor suppressor pathway, and the transcriptional co-activator Yorkie (Yki, a YES associated protein, or YAP) as components of the feed-forward signaling mechanism, and we show how this mechanism promotes wing growth in response to Wg. We find that vg generates the feed-forward signal by creating a steep differential in Ft-Ds signaling between wing and non-wing cells. This differential down-regulates Warts-Hippo pathway activity in non-wing cells, leading to a burst of Yki activity and the induction of vg in response to Wg. We posit that Wg propels wing growth at least in part by fueling a wave front of Ft-Ds signaling that propagates vg expression from one cell to the next.

Under normal conditions, animals and their various body parts grow until they achieve a genetically predetermined size and shape—a process governed by secreted organizer proteins called morphogens. How morphogens control growth remains unknown. In Drosophila, wings develop at the larval stage from wing primordia. Recently, we discovered that the morphogen Wingless promotes growth of the Drosophila wing by inducing the recruitment of neighboring cells into the wing primordium. Wing cells are defined by the expression of the “selector” gene vestigial. Recruitment depends on the capacity of wing cells to send a short-range, feed-forward signal that allows Wingless to activate vestigial in adjacent non-wing cells. Here, we identify the molecular components and circuitry of the recruitment process. We define the protocadherins Fat and Dachsous as a bidirectional ligand-receptor system that is controlled by vestigial to generate the feed-forward signal. Further, we show that the signal is transduced by the conserved Warts-Hippo tumor suppressor pathway via activation of its transcriptional effector Yorkie. Finally, we propose that Wingless propels wing growth by fueling a wave front of Fat-Dachsous signaling and Yorkie activity that propagates vestigial expression from one cell to the next.

Mechanisms of growth and homeostasis in the Drosophila wing

Animal shape and size is controlled with amazing precision during development. External factors such as nutrient availability and crowding can alter overall animal size, but individual body parts scale reproducibly to match the body even with challenges from a changing environment. How is such precision achieved? Here, we review selected research from the last few years in Drosophila--arguably the premier genetic model for the study of animal growth--that sheds light on how body and tissue size are regulated by forces intrinsic to individual organs. We focus on two topics currently under intense study: the influence of pattern regulators on organ and tissue growth and the role of local competitive interactions between cells in tissue homeostasis and final size.