Dpp signaling inhibits proliferation in the Drosophila wing by Omb-dependent regional control of bantam

Cell recruitment and the origins of Anterior-Posterior asymmetries in the Drosophila wing

The mechanisms underlying the establishment of asymmetric structures during development remain elusive. The wing of Drosophila is asymmetric along the Anterior-Posterior (AP) axis, but the developmental origins of this asymmetry is unknown. Here, we investigate the contribution of cell recruitment, a process that drives cell fate differentiation in the Drosophila wing disc, to the asymmetric shape and pattern of the adult wing. Genetic impairment of cell recruitment in the wing disc results in a significant gain of AP symmetry, which results from a reduction of the region between longitudinal vein 5 and the wing margin (L5-M) in the adult wing. Morphometric analysis confirms that blocking of cell recruitment results in a more symmetric wing with respect to controls, suggesting a contribution of cell recruitment to the establishment of asymmetry in the adult wing. In order to verify if this phenotype is originated during the time in which cell recruitment occurs during larval development, we examined the expression of a reporter for the selector gene vestigial (vg) in the corresponding pro-vein regions of the wing disc, but our findings could not explain our findings in adult wings. However, the circularity of the Vg pattern significantly increases in recruitment-impaired wing discs, suggesting that cell recruitment may contribute to AP asymmetries in the adult wing shape by altering the roundness of the Vg pattern. We conclude that cell recruitment, a widespread mechanism that participates in growth and patterning of several developing systems, may contribute, at least partially, to the asymmetric shape of the Drosophila wing.

Bursicon regulates wing expansion via PKA in the oriental fruit fly, Bactrocera dorsalis

BACKGROUND

Bursicon is a heterodimeric neuropeptide that is involved in many physiological activities such as cuticle tanning, wing expansion, reproduction and immunity in insects. In this study, the role of bursicon in the wing expansion was investigated in Bactrocera dorsalis, an important invasive insect pest in agriculture.

RESULTS

The cDNA sequences and deduced amino acids of bursicon genes (named BdBurs-α and BdBurs-β) were determined, and two proteins typically contained 11 cysteine residues in conserved positions that were highly conserved in other insect species. The spatiotemporal expressions of bursicon genes showed that higher expression occurred at the pupal, early adult stage and ovaries, and lower expression at the late larval stage and in wing tissue (8-day-old pupae). Dysfunction of bursicon genes by dsRNA microinjection into 5-day-old pupae reduced PKA (a downstream component of the bursicon pathway) activity and resulted in malformed adult wings. PKA inhibitor injection into 5-day-old pupae also resulted in similar phenotypes. Hematoxylin & eosin staining of the adult wing showed that RNAi and PKA inhibitor treatment reduced the thickness of the wing cuticle, which wing cuticle thickness were ≈50% thinner than in the control. Furthermore, the expression of hedgehog (Bdhh) (one of 10 tested genes related to wing development) was significantly upregulated after RNAi and PKA inhibitor application.

CONCLUSION

The results indicate that bursicon plays a crucial role in the wing expansion of B. dorsalis, suggesting bursicon genes have potential to be the targets for B. dorsalis control. © 2023 Society of Chemical Industry.

The transcription factor optomotor-blind restricts apterous expression through TrxG and PcG genes

The establishment of body pattern is a fundamental process in developmental biology. In Drosophila, the wing disc is subdivided into dorsal (D) and ventral (V) compartments by the D/V boundary. The dorsal fate is adopted by expressing the selector gene apterous (ap). ap expression is regulated by three combinational cis-regulatory modules which are activated by EGFR pathway, Ap-Vg auto-regulatory and epigenetic mechanisms. Here, we found that the Tbx family transcription factor Optomotor-blind (Omb) restricted ap expression in the ventral compartment. Loss of omb induced autonomous initiation of ap expression in the middle third instar larvae in the ventral compartment. Oppositely, over-activation of omb inhibited ap in the medial pouch. All three enhancers apE, apDV and apP were upregulated in omb null mutants, indicating a combinational regulation of ap modulators. However, Omb affected ap expression neither by directly regulating EGFR signaling, nor via Vg regulation. Therefore, a genetic screen of epigenetic regulators, including the Trithorax group (TrxG) and Polycomb group (PcG) genes was performed. We found that knocking down the TrxG gene kohtalo (kto), domino (dom) or expressing the PcG gene grainy head (grh), the ectopic ap in omb mutants was repressed. The inhibition of apDV by kto knockdown and grh activation could contribute to ap repression. Moreover, Omb and the EGFR pathway are genetically parallel in ap regulation in the ventral compartment. Collectively, Omb is a repressive signal for ap expression in the ventral compartment, which requires TrxG and PcG genes.

Transgenerational inheritance of wing development defects in Drosophila melanogaster induced by cadmium

The transgenerational inheritance of phenotype induced by environmental factors is a new focus in epigenetic research. In this study, Drosophila melanogaster (F₀) was cultured in the medium containing cadmium (Cd, 4.5 mg/kg) from eggs to adults, and offspring (F₁-F₄) were continuously kept in standard medium (without cadmium). The phenotype analysis showed that cadmium induced developmental defects on wings and apoptosis in the wing disc cells of Drosophila (F₀). The wing defects were transmitted for at least four generations even without Cd afterwards. And the effect on the mRNA expression of wing development related genes (shg, omb, F-actin, Mekk1) can be maintained for at least two or three generations. More importantly, under cadmium stress, the post-translational modification (PTM) on the histones H3K4me3 in the third instar larvae and ovaries or testes of adult flies increased significantly, while the levels of H3K9me3 and H3K27me3 decreased significantly. The expression of histone methylation related genes (dSet-1, ash1, Lsd1) increased significantly and these changes can be transmitted to offspring from one or two generations in ovaries or testes. These results suggest that the phenotypic defects of wings caused by cadmium can be inherited to the offspring, and this transgenerational inheritance effect may be related to the epigenetic regulation of histone methylation. Therefore, the adaptability of offspring should be considered when evaluating the toxicity and environmental risk of cadmium.

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.

T-box transcription factors Dorsocross and optomotor-blind control Drosophila leg patterning in a functionally redundant manner

The T-box genes are essential transcription factors during limb development. In Drosophila, Dorsocross (Doc) and optomotor-blind (omb), members of the Tbx2 and Tbx6 families, are best studied in the Drosophila wing development. Despite prominently expressed in leg discs, the specific function of these genes in leg growth is still not revealed. Here we demonstrated that Doc and omb regulated the morphogenesis of leg intermediate regions in a functionally redundant manner. Loss of Doc or omb individually did not result in any developmental defects of the legs, but loss of both genes induced significant defects in femur and proximal tibia of the adult legs. These genes located in the dorsal domain, where the Doc region expanded and cross-overlapped with the omb region corresponding to the presumptive leg intermediate region. We detected that the normal epithelial folds in the leg discs were disrupted along with dorsal repression of cell proliferation and activation of cell apoptosis when Doc and omb were both reduced. Furthermore, the dorsal expression of dachshund (dac), a canonical leg developmental gene specifying the leg intermediate region, was maintained by Doc and omb. Meanwhile, the Notch pathway was compromised in the dorsal domain when these genes were reduced, which might contribute to the joint defect of the adult leg intermediate regions. Our study provides cytological and genetic evidence for understanding the redundant function of Doc and omb in leg morphogenesis.

Overexpressed Gliotactin activates BMP signaling through interfering with the Tkv-Dad association

Epithelial junctions ensure cell-cell adhesion and establish permeability barriers between cells. At the corners of epithelia, the tricellular junction (TCJ) is formed by three adjacent epithelial cells and generates a functional barrier. In Drosophila, a key TCJ protein is Gliotactin (Gli) where loss of Gli disrupts barrier formation and function. Conversely, overexpressed Gli spreads away from the TCJ and triggers apoptosis, delamination, and cell migration. Thus, Gli protein levels are tightly regulated and by two mechanisms, at the protein levels by tyrosine phosphorylation and endocytosis and at the mRNA level through microRNA-184. Regulation of Gli mRNA is mediated through a Gli-BMP-miR184 feedback loop. Excessive Gli triggers BMP signaling pathway through the activation of Tkv type-I BMP receptor and Mad. Elevated level of pMad induces micrRNA-184 expression which in turn targets the Gli 3'UTR and mRNA degradation. Gli activation of Tkv is not through its ligand Dpp but rather through the inhibition of Dad, an inhibitory-Smad. Here, we show that ectopic expression of Gli interferes with Tkv-Dad association by sequestering Dad away from Tkv. The reduced inhibitory effect of Dad on Tkv results in the increased Tkv-pMad signaling activity, and this effect is continuous through larval and pupal wing formation.

The Drosophila MLR COMPASS-like complex regulates bantam miRNA expression differentially in the context of cell fate

The conserved MLR COMPASS-like complexes are histone modifiers that are recruited by a variety of transcription factors to enhancer regions where they act as necessary epigenetic tools for enhancer establishment and function. A critical in vivo target of the Drosophila MLR complex is the bantam miRNA that regulates cell survival and functions in feedback regulation of cellular signaling pathways during development. We determine that loss of Drosophila MLR complex function in developing wing and eye imaginal discs results in growth and patterning defects that are sensitive to bantam levels. Consistent with an essential regulatory role in modulating bantam transcription, the MLR complex binds to tissue-specific bantam enhancers and contributes to fine-tuning expression levels during larval tissue development. In wing imaginal discs, the MLR complex attenuates bantam enhancer activity by negatively regulating expression; whereas, in differentiating eye discs, the complex exerts either positive or negative regulatory activity on bantam transcription depending on cell fate. Furthermore, while the MLR complex is not required to control bantam levels in undifferentiated eye cells anterior to the morphogenetic furrow, it serves to prepare critical enhancer control of bantam transcription for later regulation upon differentiation. Our investigation into the transcriptional regulation of a single target in a developmental context has provided novel insights as to how the MLR complex contributes to the precise timing of gene expression, and how the complex functions to help orchestrate the regulatory output of conserved signaling pathways during animal development.

Network-regulated organ allometry: The developmental regulation of morphological scaling

Morphological scaling relationships, or allometries, describe how traits grow coordinately and covary among individuals in a population. The developmental regulation of scaling is essential to generate correctly proportioned adults across a range of body sizes, while the mis-regulation of scaling may result in congenital birth defects. Research over several decades has identified the developmental mechanisms that regulate the size of individual traits. Nevertheless, we still have poor understanding of how these mechanisms work together to generate correlated size variation among traits in response to environmental and genetic variation. Conceptually, morphological scaling can be generated by size-regulatory factors that act directly on multiple growing traits (trait-autonomous scaling), or indirectly via hormones produced by central endocrine organs (systemically regulated scaling), and there are a number of well-established examples of such mechanisms. There is much less evidence, however, that genetic and environmental variation actually acts on these mechanisms to generate morphological scaling in natural populations. More recent studies indicate that growing organs can themselves regulate the growth of other organs in the body. This suggests that covariation in trait size can be generated by network-regulated scaling mechanisms that respond to changes in the growth of individual traits. Testing this hypothesis, and one of the main challenges of understanding morphological scaling, requires connecting mechanisms elucidated in the laboratory with patterns of scaling observed in the natural world. This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Comparative Development and Evolution > Organ System Comparisons Between Species.

Flexible manipulation of Omb levels in the endogenous expression region of Drosophila wing by combinational overexpression and suppression strategy

Manipulating an exogenous or endogenous gene of interest at a defined level is critical for a wide variety of experiments. The Gal4/UAS system has been widely used to direct gene expression for studying complex genetic and biological problems in Drosophila melanogaster and other model organisms. Driven by a given tissue-specific Gal4, expressing UAS-transgene or UAS-RNAi (RNA interference) could be used to up- or down-regulate target gene expression, respectively. However, the efficiency of the Gal4/UAS system is roughly predefined by properties of transposon vector constructs and the insertion site in the transgenic stock. Here, we describe a simple way to modulate optomotor blind (omb) expression levels in its endogenous expression region of the wing disc. We co-expressed UAS-omb and UAS-omb-RNAi together under the control of dpp-Gal4 driver which is expressed in the omb expression region of the wing pouch. The repression effect is more sensitive to temperature than that of overexpression. At low temperature, overexpression plays a dominant role but the efficiency is attenuated by UAS-omb-RNAi. In contrast, at high temperature RNAi predominates in gene expression regulation. By this strategy, we could manipulate omb expression levels at a moderate level. It allows us to manipulate omb expression levels in the same tissue between overexpression and repression at different stages by temperature control.

CYP303A1 has a conserved function in adult eclosion in Locusta migratoria and Drosophila melanogaster

Insect cytochrome P450 monooxygenases (CYPs) play essential roles in both xenobiotic metabolism and developmental processes. However, the exact physiological function of many CYP genes remains largely unknown. Screening the expression of the CYP genes from the CYP2 and mitochondrial CYP clans of Drosophila melanogaster revealed that Cyp303a1 is highly expressed in the pupal stage. Knockdown of CYP303A1 transcripts by RNAi using the Gal4/UAS system with a ubiquitous driver (tubulin-Gal4) in Drosophila or by dsRNA injection in the last nymph stage of Locusta migratoria resulted in severe defects in eclosion and lethality during and after adult emergence. In Drosophila, tissue-specific RNAi of Cyp303a1 with a wing-specific driver (MS1096-Gal4) revealed that Cyp303a1 was essential for wing extension. Stage-specific RNAi of Cyp303a1 using Gal80^ts for thermal-dependent-suppression found that the expression of Cyp303a1 at the middle pupal stage was absolutely required. Meanwhile, Cyp303a1 mutants exhibited more than 80% lethality at the late embryonic development stages. Embryonic lethality of the Cyp303a1 mutants was fully rescued by the ubiquitous overexpression of exogenous Cyp303a1. Taken together, we conclude that Cyp303a1 is indispensable for embryonic development and adult eclosion in D. melanogaster, the latter role being conserved over 400 million years of insect evolution.

Comparative Identification of MicroRNAs in Apis cerana cerana Workers' Midguts in Responseto Nosema ceranae Invasion

Here, the expression profiles and differentially expressed miRNAs (DEmiRNAs) in the midguts of Apis cerana cerana workers at 7 d and 10 d post-inoculation (dpi) with N. ceranae were investigated via small RNA sequencing and bioinformatics. Five hundred and twenty nine (529) known miRNAs and 25 novel miRNAs were identified in this study, and the expression of 16 predicted miRNAs was confirmed by Stem-loop RT-PCR. A total of 14 DEmiRNAs were detected in the midgut at 7 dpi, including eight up-regulated and six down-regulated miRNAs, while 12 DEmiRNAs were observed in the midgut at 10 dpi, including nine up-regulated and three down-regulated ones. Additionally, five DEmiRNAs were shared, while nine and seven DEmiRNAs were specifically expressed in midguts at 7 dpi and 10 dpi. Gene ontology analysis suggested some DEmiRNAs and corresponding target mRNAs were involved in various functions including immune system processes and response to stimulus. KEGG pathway analysis shed light on the potential functions of some DEmiRNAs in regulating target mRNAs engaged in material and energy metabolisms, cellular immunity and the humoral immune system. Further investigation demonstrated a complex regulation network between DEmiRNAs and their target mRNAs, with miR-598-y, miR-252-y, miR-92-x and miR-3654-y at the center. Our results can facilitate future exploration of the regulatory roles of miRNAs in host responses to N. ceranae, and provide potential candidates for further investigation of the molecular mechanisms underlying eastern honeybee-microsporidian interactions.

Fruit fly research in China

Served as a model organism over a century, fruit fly has significantly pushed forward the development of global scientific research, including in China. The high similarity in genomic features between fruit fly and human enables this tiny insect to benefit the biomedical studies of human diseases. In the past decades, Chinese biologists have used fruit fly to make numerous achievements on understanding the fundamental questions in many diverse areas of biology. Here, we review some of the recent fruit fly studies in China, and mainly focus on those studies in the fields of stem cell biology, cancer therapy and regeneration medicine, neurological disorders and epigenetics.

spalt is functionally conserved in Locusta and Drosophila to promote wing growth

Locusta has strong fly wings to ensure its long distance migration, but the molecular mechanism that regulates the Locusta wing development is poorly understood. To address the developmental mechanism of the Locusta flying wing, we cloned the Dpp target gene spalt (sal) and analyzed its function in wing growth in the Locusta. The Locusta wing size is apparently reduced with vein defects when sal is interfered by injection of dsRNA, indicating that sal is required for locust wing growth and vein formation. This function is conserved during the Drosophila wing development. To better understand sal’s function in wing growth, we then used Drosophila wing disc as a model for further study. We found that sal promotes cell proliferation in the whole wing disc via positive regulation of a microRNA bantam. Our results firstly unravel sal’s function in the Locusta wing growth and confirm a highly conserved function of sal in Locusta and Drosophila.

Fold formation at the compartment boundary of Drosophila wing requires Yki signaling to suppress JNK dependent apoptosis

Compartment boundaries prevent cell populations of different lineage from intermingling. In many cases, compartment boundaries are associated with morphological folds. However, in the Drosophila wing imaginal disc, fold formation at the anterior/posterior (A/P) compartment boundary is suppressed, probably as a prerequisite for the formation of a flat wing surface. Fold suppression depends on optomotor-blind (omb). Omb mutant animals develop a deep apical fold at the A/P boundary of the larval wing disc and an A/P cleft in the adult wing. A/P fold formation is controlled by different signaling pathways. Jun N-terminal kinase (JNK) and Yorkie (Yki) signaling are activated in cells along the fold and are necessary for the A/P fold to develop. While JNK promotes cell shape changes and cell death, Yki target genes are required to antagonize apoptosis, explaining why both pathways need to be active for the formation of a stable fold.

The Effect of MicroRNA bantam on Baculovirus AcMNPV Infection in Vitro and in Vivo

The role of microRNA bantam, one of the most abundant microRNAs in Sf9 cells, was studied for its role in baculovirus infection in vitro and in vivo. The expression level of bantam was increased after AcMNPV infection in Sf9 cells and in Spodoptera litura larvae. In Sf9 cells, application of bantam inhibitor or mimic altered the expression of many virus genes, the most affected gene being lef8, gp41 and p10, the expression level of which was increased by 8, 10 and 40 times, respectively, in the presence of bantam inhibitor. Virus DNA replication was decreased in the presence of bantam mimic and increased in the presence of bantam inhibitor in a dose dependent manner. However, the production of budded virus did not change significantly. Feeding the larvae of S. litura and Spodoptera exigua with bantam antagomiR, a more stable form of the inhibitor, resulted in an abnormal larval growth and a decreased pupation rate. In S. litura, larvae died 3.5 days sooner than the control when bantam antagomiR was applied, together with AcMNPV. In infected S. exigua, larval mortality increased from 47% without antagomiR to 80% with it. The results suggest that microRNA bantam plays an important role in insect growth, as well as in baculovirus-insect interaction.

MicroRNA function in Drosophila melanogaster

Over the last decade, microRNAs have emerged as critical regulators in the expression and function of animal genomes. This review article discusses the relationship between microRNA-mediated regulation and the biology of the fruit fly Drosophila melanogaster. We focus on the roles that microRNAs play in tissue growth, germ cell development, hormone action, and the development and activity of the central nervous system. We also discuss the ways in which microRNAs affect robustness. Many gene regulatory networks are robust; they are relatively insensitive to the precise values of reaction constants and concentrations of molecules acting within the networks. MicroRNAs involved in robustness appear to be nonessential under uniform conditions used in conventional laboratory experiments. However, the robust functions of microRNAs can be revealed when environmental or genetic variation otherwise has an impact on developmental outcomes.

The Drosophila tricellular junction protein Gliotactin regulates its own mRNA levels through BMP-mediated induction of miR-184

Epithelial bicellular and tricellular junctions are essential for establishing and maintaining permeability barriers. Tricellular junctions are formed by the convergence of three bicellular junctions at the corners of neighbouring epithelia. Gliotactin, a member of the Neuroligin family, is located at theDrosophilatricellular junction, and is crucial for the formation of tricellular and septate junctions, as well as permeability barrier function. Gliotactin protein levels are tightly controlled by phosphorylation at tyrosine residues and endocytosis. Blocking endocytosis or overexpressing Gliotactin results in the spread of Gliotactin from the tricellular junction, resulting in apoptosis, delamination and migration of epithelial cells. We show that Gliotactin levels are also regulated at the mRNA level by micro (mi)RNA-mediated degradation and that miRNAs are targeted to a short region in the 3'UTR that includes a conserved miR-184 target site. miR-184 also targets a suite of septate junction proteins, including NrxIV, coracle and Mcr. miR-184 expression is triggered when Gliotactin is overexpressed, leading to activation of the BMP signalling pathway. Gliotactin specifically interferes with Dad, an inhibitory SMAD, leading to activation of the Tkv type-I receptor and activation of Mad to elevate the biogenesis and expression of miR-184.

miR-58 family and TGF-β pathways regulate each other in Caenorhabditis elegans

Despite the fact that microRNAs (miRNAs) modulate the expression of around 60% of protein-coding genes, it is often hard to elucidate their precise role and target genes. Studying miRNA families as opposed to single miRNAs alone increases our chances of observing not only mutant phenotypes but also changes in the expression of target genes. Here we ask whether the TGF-β signalling pathways, which control many animal processes, might be modulated by miRNAs in Caenorhabditis elegans. Using a mutant for four members of the mir-58 family, we show that both TGF-β Sma/Mab (controlling body size) and TGF-β Dauer (regulating dauer, a stress-resistant larval stage) are upregulated. Thus, mir-58 family directly inhibits the expression of dbl-1 (ligand), daf-1, daf-4 and sma-6 (receptors) of TGF-β pathways. Epistasis experiments reveal that whereas the small body phenotype of the mir-58 family mutant must invoke unknown targets independent from TGF-β Sma/Mab, its dauer defectiveness can be rescued by DAF-1 depletion. Additionally, we found a negative feedback loop between TGF-β Sma/Mab and mir-58 and the related mir-80. Our results suggest that the interaction between mir-58 family and TGF-β genes is key on decisions about animal growth and stress resistance in C. elegans and perhaps other organisms.

Putative Breast Cancer Driver Mutations in TBX3 Cause Impaired Transcriptional Repression

The closely related T-box transcription factors TBX2 and TBX3 are frequently overexpressed in melanoma and various types of human cancers, in particular, breast cancer. The overexpression of TBX2 and TBX3 can have several cellular effects, among them suppression of senescence, promotion of epithelial-mesenchymal transition, and invasive cell motility. In contrast, loss of function of TBX3 and most other human T-box genes causes developmental haploinsufficiency syndromes. Stephens and colleagues (1), by exome sequencing of breast tumor samples, identified five different mutations in TBX3, all affecting the DNA-binding T-domain. One in-frame deletion of a single amino acid, p.N212delN, was observed twice. Due to the clustering of these mutations to the T-domain and for statistical reasons, TBX3 was inferred to be a driver gene in breast cancer. Since mutations in the T-domain generally cause loss of function and because the tumorigenic action of TBX3 has generally been attributed to overexpression, we determined whether the putative driver mutations had loss- or gain-of-function properties. We tested two in-frame deletions, one missense, and one frameshift mutant protein for DNA-binding in vitro, and for target gene repression in cell culture. In addition, we performed an in silico analysis of somatic TBX mutations in breast cancer, collected in The Cancer Genome Atlas (TCGA). Both the experimental and the in silico analysis indicate that the observed mutations predominantly cause loss of TBX3 function.

The orthologous Tbx transcription factors Omb and TBX2 induce epithelial cell migration and extrusion in vivo without involvement of matrix metalloproteinases

The transcription factors TBX2 and TBX3 are overexpressed in various human cancers. Here, we investigated the effect of overexpressing the orthologous Tbx genes Drosophila optomotor-blind (omb) and human TBX2 in the epithelium of the Drosophila wing imaginal disc and observed two types of cell motility. Omb/TBX2 overexpressing cells could move within the plane of the epithelium. Invasive cells migrated long-distance as single cells retaining or regaining normal cell shape and apico-basal polarity in spite of attenuated apical DE-cadherin concentration. Inappropriate levels of DE-cadherin were sufficient to drive cell migration in the wing disc epithelium. Omb/TBX2 overexpression and reduced DE-cadherin-dependent adhesion caused the formation of actin-rich lateral cell protrusions. Omb/TBX2 overexpressing cells could also delaminate basally, penetratingthe basal lamina, however, without degradation of extracellular matrix. Expression of Timp, an inhibitor of matrix metalloproteases, blocked neither intraepithelial motility nor basal extrusion. Our results reveal an MMP-independent mechanism of cell invasion and suggest a conserved role of Tbx2-related proteins in cell invasion and metastasis-related processes.

The transcription factor optomotor-blind antagonizes Drosophila haltere growth by repressing decapentaplegic and hedgehog targets

In Drosophila, decapentaplegic, which codes for a secreted signaling molecule, is activated by the Hedgehog signaling pathway at the anteroposterior compartment border of the two dorsal primordia; the wing and the haltere imaginal discs. In the wing disc, Decapentaplegic and Hedgehog signaling targets are implicated in cell proliferation and cell survival. However, most of their known targets in the wing disc are not expressed in the haltere disc due to their repression by the Hox gene Ultrabithorax. The T-box gene optomotor-blind escapes this repression in the haltere disc, and therefore is expressed in both the haltere and wing discs. Optomotor-blind is a major player during wing development and its function has been intensely investigated in this tissue, however, its role in haltere development has not been reported so far. Here we show that Optomotor-blind function in the haltere disc differs from that in the wing disc. Unlike its role in the wing, Optomotor-blind does not prevent apoptosis in the haltere but rather limits growth by repressing several Decapentaplegic and Hedgehog targets involved both in wing proliferation and in modulating the spread of morphogens similar to Ultrabithorax function but without disturbing Ultrabithorax expression.

Optomotor-blind negatively regulates Drosophila eye development by blocking Jak/STAT signaling

Organ formation requires a delicate balance of positive and negative regulators. In Drosophila eye development, wingless (wg) is expressed at the lateral margins of the eye disc and serves to block retinal development. The T-box gene optomotor-blind (omb) is expressed in a similar pattern and is regulated by Wg. Omb mediates part of Wg activity in blocking eye development. Omb exerts its function primarily by blocking cell proliferation. These effects occur predominantly in the ventral margin. Our results suggest that the primary effect of Omb is the blocking of Jak/STAT signaling by repressing transcription of upd which encodes the Jak receptor ligand Unpaired.

Muscle cell fate choice requires the T-box transcription factor midline in Drosophila

Drosophila Midline (Mid) is an ortholog of vertebrate Tbx20, which plays roles in the developing heart, migrating cranial motor neurons, and endothelial cells. Mid functions in cell-fate specification and differentiation of tissues that include the ectoderm, cardioblasts, neuroblasts, and egg chambers; however, a role in the somatic musculature has not been described. We identified mid in genetic and molecular screens for factors contributing to somatic muscle morphogenesis. Mid is expressed in founder cells (FCs) for several muscle fibers, and functions cooperatively with the T-box protein H15 in lateral oblique muscle 1 and the segment border muscle. Mid is particularly important for the specification and development of the lateral transverse (LT) muscles LT3 and LT4, which arise by asymmetric division of a single muscle progenitor. Mid is expressed in this progenitor and its two sibling FCs, but is maintained only in the LT4 FC. Both muscles were frequently missing in mid mutant embryos, and LT4-associated expression of the transcription factor Krüppel (Kr) was lost. When present, LT4 adopted an LT3-like morphology. Coordinately, mid misexpression caused LT3 to adopt an LT4-like morphology and was associated with ectopic Kr expression. From these data, we concluded that mid functions first in the progenitor to direct development of LT3 and LT4, and later in the FCs to influence whichever of these differentiation profiles is selected. Mid is the first T-box factor shown to influence LT3 and LT4 muscle identity and, along with the T-box protein Optomotor-blind-related-gene 1 (Org-1), is representative of a new class of transcription factors in muscle specification.

BMP2-SMAD signaling represses the proliferation of embryonic neural stem cells through YAP

Previous studies have shown that the Hippo pathway effector yes-associated protein (YAP) plays an important role in maintaining stem cell proliferation. However, the precise molecular mechanism of YAP in regulating murine embryonic neural stem cells (NSCs) remains largely unknown. Here, we show that bone morphogenetic protein-2 (BMP2) treatment inhibited the proliferation of mouse embryonic NSCs, that YAP was critical for mouse NSC proliferation, and that BMP2 treatment-induced inhibition of mouse NSC proliferation was abrogated by YAP knockdown, indicating that the YAP protein mediates the inhibitory effect of BMP2 signaling. Additionally, we found that BMP2 treatment reduced YAP nuclear translocation, YAP-TEAD interaction, and YAP-mediated transactivation. BMP2 treatment inhibited YAP/TEAD-mediated Cyclin D1 (ccnd1) expression, and knockdown of ccnd1 abrogated the BMP2-mediated inhibition of mouse NSC proliferation. Mechanistically, we found that Smad1/4, effectors of BMP2 signaling, competed with YAP for the interaction with TAED1 and inhibited YAP's cotranscriptional activity. Our data reveal mechanistic cross talk between BMP2 signaling and the Hippo-YAP pathway in murine NSC proliferation, which may be exploited as a therapeutic target in neurodegenerative diseases and aging.

bantam miRNA is important for Drosophila blood cell homeostasis and a regulator of proliferation in the hematopoietic progenitor niche

The Drosophila hematopoietic system is utilized in this study to gain novel insights into the process of growth control of the hematopoietic progenitor niche in blood development. The niche microenvironment is an essential component controlling the balance between progenitor populations and differentiated, mature blood cells and has been shown to lead to hematopoietic malignancies in humans when misregulated. MicroRNAs are one class of regulators associated with blood malignancies; however, there remains a relative paucity of information about the role of miRNAs in the niche. Here we demonstrate that bantam miRNA is endogenously active in the Drosophila hematopoietic progenitor niche, the posterior signaling center (PSC), and functions in the primary hematopoietic organ, the lymph gland, as a positive regulator of growth. Loss of bantam leads to a significant reduction in the PSC and overall lymph gland size, as well as a loss of the progenitor population and correlative premature differentiation of mature hemocytes. Interestingly, in addition to being essential for proper lymph gland development, we have determined bantam to be a novel upstream component of the insulin signaling cascade in the PSC and have unveiled dMyc as one factor central to bantam activity. These important findings identify bantam as a new hematopoietic regulator, place it in an evolutionarily conserved signaling pathway, present one way in which it is regulated, and provide a mechanism through which it facilitates cellular proliferation in the hematopoietic niche.

De novo transcriptome analysis of wing development-related signaling pathways in Locusta migratoria manilensis and Ostrinia furnacalis (Guenée)

Background

Orthopteran migratory locust, Locusta migratoria, and lepidopteran Asian corn borer, Ostrinia furnacalis, are two types of insects undergoing incomplete and complete metamorphosis, respectively. Identification of candidate genes regulating wing development in these two insects would provide insights into the further study about the molecular mechanisms controlling metamorphosis development. We have sequenced the transcriptome of O. furnacalis larvae previously. Here we sequenced and characterized the transcriptome of L. migratoria wing discs with special emphasis on wing development-related signaling pathways.

Methodology/Principal Findings

Illumina Hiseq2000 was used to sequence 8.38 Gb of the transcriptome from dissected nymphal wing discs. De novo assembly generated 91,907 unigenes with mean length of 610 nt. All unigenes were searched against five databases including Nt, Nr, Swiss-Prot, COG, and KEGG for annotations using blastn or blastx algorithm with an cut-off E-value of 10⁻⁵. A total of 23,359 (25.4%) unigenes have homologs within at least one database. Based on sequence similarity to homologs known to regulate Drosophila melanogaster wing development, we identified 50 and 46 potential wing development-related unigenes from L. migratoria and O. furnacalis transcriptome, respectively. The identified unigenes encode putative orthologs for nearly all components of the Hedgehog (Hh), Decapentaplegic (Dpp), Notch (N), and Wingless (Wg) signaling pathways, which are essential for growth and pattern formation during wing development. We investigated the expression profiles of the component genes involved in these signaling pathways in forewings and hind wings of L. migratoria and O. furnacalis. The results revealed the tested genes had different expression patterns in two insects.

Conclusions/Significance

This study provides the comprehensive sequence resource of the wing development-related signaling pathways of L. migratoria. The obtained data gives an insight into better understanding the molecular mechanisms involved in the wing development in L. migratoria and O. furnacalis, two insect species with different metamorphosis types.

Dpp/BMP signaling in flies: from molecules to biology

Decapentaplegic (Dpp), the fly homolog of the secreted mammalian BMP2/4 signaling molecules, is involved in almost all aspects of fly development. Dpp has critical functions at all developmental stages, from patterning of the eggshell to the determination of adult intestinal stem cell identity. Here, we focus on recent findings regarding the transcriptional regulatory logic of the pathway, on a new feedback regulator, Pentagone, and on Dpp's roles in scaling and growth of the Drosophila wing.

Systemically interfering with immune response by a fluorescent cationic dendrimer delivered gene suppression

A water-soluble, fluorescent, cationic dendrimer systemically delivers dsRNA into insect cells and tissues, resulting in the suppression of the immune gene.

Highly water-soluble perylenediimide-cored poly(amido amine) vector for efficient gene transfection

A highly water-soluble perylenediimide-core poly(amido amine) (PDI-PAmAm) with peripheral amine groups has been synthesized. PDI-PAmAm can be rapidly internalized into live cells with high efficacy of gene delivery and low cytotoxicity.