Smt3 is required for Drosophila melanogaster metamorphosis

Research progress of ubiquitin and ubiquitin-like signaling in Toxoplasma gondii

Toxoplasmosis, a zoonotic parasitic disease caused by Toxoplasma gondii (T. gondii), is prevalent worldwide. The fact should be emphasized that a considerable proportion of individuals infected with T. gondii may remain asymptomatic; nevertheless, the condition can have severe implications for pregnant women or immunocompromised individuals. The current treatment of toxoplasmosis primarily relies on medication; however, traditional anti-toxoplasmosis drugs exhibit significant limitations in terms of efficacy, side effects, and drug resistance. The life cycles of T. gondii are characterized by distinct stages and its body morphology goes through dynamic alterations during the growth cycle that are intricately governed by a wide array of post-translational modifications (PTMs). Ubiquitin (Ub) signaling and ubiquitin-like (Ubl) signaling are two crucial post-translational modification pathways within cells, regulating protein function, localization, stability, or interactions by attaching Ub or ubiquitin-like proteins (Ubls) to target proteins. While these signaling mechanisms share some functional similarities, they have distinct regulatory mechanisms and effects. T. gondii possesses both Ub and Ubls and plays a significant role in regulating the parasite's life cycle and maintaining its morphology through PTMs of substrate proteins. Investigating the role and mechanism of protein ubiquitination in T. gondii will provide valuable insights for preventing and treating toxoplasmosis. This review explores the distinctive characteristics of Ub and Ubl signaling in T. gondii, with the aim of inspiring research ideas for the identification of safer and more effective drug targets against toxoplasmosis.

Developmental analysis of Spalt function in the Drosophila prothoracic gland

The Spalt transcriptional regulators participate in a variety of cell fate specification processes during development, regulating transcription through interactions with DNA AT-rich regions. Spalt proteins also bind to heterochromatic regions, and some of their effects require interactions with the NuRD chromatin remodeling and deacetylase complex. Most of the biological roles of Spalt proteins have been characterized in diploid cells engaged in cell proliferation. Here, we address the function of Drosophila Spalt genes in the development of a larval tissue formed by polyploid cells, the prothoracic gland, the cells of which undergo several rounds of DNA replication without mitosis during larval development. We show that prothoracic glands depleted of Spalt expression display severe changes in the size of the nucleolus, the morphology of the nuclear envelope and the disposition of the chromatin within the nucleus, leading to a failure in the synthesis of ecdysone. We propose that loss of ecdysone production in the prothoracic gland of Spalt mutants is primarily caused by defects in nuclear pore complex function that occur as a consequence of faulty interactions between heterochromatic regions and the nuclear envelope.

The steroid hormone ecdysone regulates growth rate in response to oxygen availability

In almost all animals, physiologically low oxygen (hypoxia) during development slows growth and reduces adult body size. The developmental mechanisms that determine growth under hypoxic conditions are, however, poorly understood. Here we show that the growth and body size response to moderate hypoxia (10% O₂) in Drosophila melanogaster is systemically regulated via the steroid hormone ecdysone. Hypoxia increases level of circulating ecdysone and inhibition of ecdysone synthesis ameliorates the negative effect of low oxygen on growth. We also show that the effect of ecdysone on growth under hypoxia is through suppression of the insulin/IGF-signaling pathway, via increased expression of the insulin-binding protein Imp-L2. These data indicate that growth suppression in hypoxic Drosophila larvae is accomplished by a systemic endocrine mechanism that overlaps with the mechanism that slows growth at low nutrition. This suggests the existence of growth-regulatory mechanisms that respond to general environmental perturbation rather than individual environmental factors.

Transcriptional Regulators of Ecdysteroid Biosynthetic Enzymes and Their Roles in Insect Development

Steroid hormones are responsible for coordinating many aspects of biological processes in most multicellular organisms, including insects. Ecdysteroid, the principal insect steroid hormone, is biosynthesized from dietary cholesterol or plant sterols. In the last 20 years, a number of ecdysteroidogenic enzymes, including Noppera-bo, Neverland, Shroud, Spook/Spookier, Cyp6t3, Phantom, Disembodied, Shadow, and Shade, have been identified and characterized in molecular genetic studies using the fruit fly Drosophila melanogaster. These enzymes are encoded by genes collectively called the Halloween genes. The transcriptional regulatory network, governed by multiple regulators of transcription, chromatin remodeling, and endoreplication, has been shown to be essential for the spatiotemporal expression control of Halloween genes in D. melanogaster. In this review, we summarize the latest information on transcriptional regulators that are crucial for controlling the expression of ecdysteroid biosynthetic enzymes and their roles in insect development.

Intrinsic and damage-induced JAK/STAT signaling regulate developmental timing by the Drosophila prothoracic gland

Development involves tightly paced, reproducible sequences of events, yet it must adjust to conditions external to it, such as resource availability and organismal damage. A major mediator of damage-induced immune responses in vertebrates and insects is JAK/STAT signaling. At the same time, JAK/STAT activation by the Drosophila Upd cytokines is pleiotropically involved in normal development of multiple organs. Whether inflammatory and developmental JAK/STAT roles intersect is unknown. Here, we show that JAK/STAT is active during development of the prothoracic gland (PG), which controls metamorphosis onset through ecdysone production. Reducing JAK/STAT signaling decreased PG size and advanced metamorphosis. Conversely, JAK/STAT hyperactivation by overexpression of pathway components or SUMOylation loss caused PG hypertrophy and metamorphosis delay. Tissue damage and tumors, known to secrete Upd cytokines, also activated JAK/STAT in the PG and delayed metamorphosis, at least in part by inducing expression of the JAK/STAT target Apontic. JAK/STAT damage signaling, therefore, regulates metamorphosis onset by co-opting its developmental role in the PG. Our findings in Drosophila provide insights on how systemic effects of damage and cancer can interfere with hormonally controlled development and developmental transitions.

Summary: Damage signaling from tumors mediated by JAK/STAT-activating Upd cytokines delays the Drosophila larva–pupa transition through co-option of a JAK/STAT developmental role in the prothoracic gland.

The role of SUMOylation during development

During the development of multicellular organisms, transcriptional regulation plays an important role in the control of cell growth, differentiation and morphogenesis. SUMOylation is a reversible post-translational process involved in transcriptional regulation through the modification of transcription factors and through chromatin remodelling (either modifying chromatin remodelers or acting as a ‘molecular glue’ by promoting recruitment of chromatin regulators). SUMO modification results in changes in the activity, stability, interactions or localization of its substrates, which affects cellular processes such as cell cycle progression, DNA maintenance and repair or nucleocytoplasmic transport. This review focuses on the role of SUMO machinery and the modification of target proteins during embryonic development and organogenesis of animals, from invertebrates to mammals.

Control of Drosophila wing size by morphogen range and hormonal gating

The stereotyped dimensions of animal bodies and their component parts result from tight constraints on growth. Yet, the mechanisms that stop growth when organs reach the right size are unknown. Growth of the Drosophila wing-a classic paradigm-is governed by two morphogens, Decapentaplegic (Dpp, a BMP) and Wingless (Wg, a Wnt). Wing growth during larval life ceases when the primordium attains full size, concomitant with the larval-to-pupal molt orchestrated by the steroid hormone ecdysone. Here, we block the molt by genetically dampening ecdysone production, creating an experimental paradigm in which the wing stops growing at the correct size while the larva continues to feed and gain body mass. Under these conditions, we show that wing growth is limited by the ranges of Dpp and Wg, and by ecdysone, which regulates the cellular response to their signaling activities. Further, we present evidence that growth terminates because of the loss of two distinct modes of morphogen action: 1) maintenance of growth within the wing proper and 2) induced growth of surrounding "pre-wing" cells and their recruitment into the wing. Our results provide a precedent for the control of organ size by morphogen range and the hormonal gating of morphogen action.

Regulation of Body Size and Growth Control

The control of body and organ growth is essential for the development of adults with proper size and proportions, which is important for survival and reproduction. In animals, adult body size is determined by the rate and duration of juvenile growth, which are influenced by the environment. In nutrient-scarce environments in which more time is needed for growth, the juvenile growth period can be extended by delaying maturation, whereas juvenile development is rapidly completed in nutrient-rich conditions. This flexibility requires the integration of environmental cues with developmental signals that govern internal checkpoints to ensure that maturation does not begin until sufficient tissue growth has occurred to reach a proper adult size. The Target of Rapamycin (TOR) pathway is the primary cell-autonomous nutrient sensor, while circulating hormones such as steroids and insulin-like growth factors are the main systemic regulators of growth and maturation in animals. We discuss recent findings in Drosophila melanogaster showing that cell-autonomous environment and growth-sensing mechanisms, involving TOR and other growth-regulatory pathways, that converge on insulin and steroid relay centers are responsible for adjusting systemic growth, and development, in response to external and internal conditions. In addition to this, proper organ growth is also monitored and coordinated with whole-body growth and the timing of maturation through modulation of steroid signaling. This coordination involves interorgan communication mediated by Drosophila insulin-like peptide 8 in response to tissue growth status. Together, these multiple nutritional and developmental cues feed into neuroendocrine hubs controlling insulin and steroid signaling, serving as checkpoints at which developmental progression toward maturation can be delayed. This review focuses on these mechanisms by which external and internal conditions can modulate developmental growth and ensure proper adult body size, and highlights the conserved architecture of this system, which has made Drosophila a prime model for understanding the coordination of growth and maturation in animals.

Compartment and cell-type specific hypoxia responses in the developing Drosophila brain

Environmental factors such as the availability of oxygen are instructive cues that regulate stem cell maintenance and differentiation. We used a genetically encoded biosensor to monitor the hypoxic state of neural cells in the larval brain of Drosophila. The biosensor reveals brain compartment and cell-type specific levels of hypoxia. The values correlate with differential tracheolation that is observed throughout development between the central brain and the optic lobe. Neural stem cells in both compartments show the strongest hypoxia response while intermediate progenitors, neurons and glial cells reveal weaker responses. We demonstrate that the distance between a cell and the next closest tracheole is a good predictor of the hypoxic state of that cell. Our study indicates that oxygen availability appears to be the major factor controlling the hypoxia response in the developing Drosophila brain and that cell intrinsic and cell-type specific factors contribute to modulate the response in an unexpected manner.

This article has an associated First Person interview with the first author of the paper.

Summary: A fluorescent biosensor reveals cell type specific hypoxia levels in the Drosophila brain in unprecedented detail. It paves the way for further functional studies addressing the role of oxygen in neural stem cell maintenance and differentiation.

Engineering Nanogels for Drug Delivery to Pathogenic Fungi Aspergillus fumigatus by Tuning Polymer Amphiphilicity

Invasive aspergillosis is a serious threat to immunodeficient and critically ill patients caused mainly by the fungus Aspergillus fumigatus. Here, poly(glycidol)-based nanogels (NGs) are proposed as delivery vehicles for antifungal agents for sustained drug release. NGs are formed by simple self-assembly of random copolymers, followed by oxidative cross-linking of thiol functionalities. We investigate the impact of copolymer amphiphilicity on NG interaction with mature fungal hyphae in order to select the optimal drug delivery system for model antifungal drug amphotericin B. The results show that drug-loaded NGs decrease minimal inhibitory concentration (MIC) for around four times and slow down the fungal biofilm synthesis at concentrations lower than MIC. Our results suggest that amphiphilicity of nanoparticle's polymer matrix is an important factor in understanding the action of nanocarriers toward fungal cells and should be considered in the development of nanoparticle-based antifungal therapy.

Not So Slim Anymore-Evidence for the Role of SUMO in the Regulation of Lipid Metabolism

One of the basic building blocks of all life forms are lipids-biomolecules that dissolve in nonpolar organic solvents but not in water. Lipids have numerous structural, metabolic, and regulative functions in health and disease; thus, complex networks of enzymes coordinate the different compositions and functions of lipids with the physiology of the organism. One type of control on the activity of those enzymes is the conjugation of the Small Ubiquitin-like Modifier (SUMO) that in recent years has been identified as a critical regulator of many biological processes. In this review, I summarize the current knowledge about the role of SUMO in the regulation of lipid metabolism. In particular, I discuss (i) the role of SUMO in lipid metabolism of fungi and invertebrates; (ii) the function of SUMO as a regulator of lipid metabolism in mammals with emphasis on the two most well-characterized cases of SUMO regulation of lipid homeostasis. These include the effect of SUMO on the activity of two groups of master regulators of lipid metabolism-the Sterol Regulatory Element Binding Protein (SERBP) proteins and the family of nuclear receptors-and (iii) the role of SUMO as a regulator of lipid metabolism in arteriosclerosis, nonalcoholic fatty liver, cholestasis, and other lipid-related human diseases.

SUMOylation in the control of cholesterol homeostasis

SUMOylation—protein modification by the small ubiquitin-related modifier (SUMO)—affects several cellular processes by modulating the activity, stability, interactions or subcellular localization of a variety of substrates. SUMO modification is involved in most cellular processes required for the maintenance of metabolic homeostasis. Cholesterol is one of the main lipids required to preserve the correct cellular function, contributing to the composition of the plasma membrane and participating in transmembrane receptor signalling. Besides these functions, cholesterol is required for the synthesis of steroid hormones, bile acids, oxysterols and vitamin D. Cholesterol levels need to be tightly regulated: in excess, it is toxic to the cell, and the disruption of its homeostasis is associated with various disorders like atherosclerosis and cardiovascular diseases. This review focuses on the role of SUMO in the regulation of proteins involved in the metabolism of cholesterol.

NMR characterization of conformational fluctuations and noncovalent interactions of SUMO protein from Drosophila melanogaster (dSmt3)

Structural heterogeneity in the native-state ensemble of dSmt3, the only small ubiquitin-like modifier (SUMO) in Drosophila melanogaster, was investigated and compared with its human homologue SUMO1. Temperature dependence of amide proton's chemical shift was studied to identify amino acids possessing alternative structural conformations in the native state. Effect of small concentration of denaturant (1M urea) on this population was also monitored to assess the ruggedness of near-native energy landscape. Owing to presence of many such amino acids, especially in the β₂ -loop-α region, the native state of dSmt3 seems more flexible in comparison to SUMO1. Information about backbone dynamics in ns-ps timescale was quantified from the measurement of ¹⁵ N-relaxation experiments. Furthermore, the noncovalent interaction of dSmt3 and SUMO1 with Daxx12 (Daxx⁷²⁹ DPEEIIVLSDSD⁷⁴⁰ ), a [V/I]-X-[V/I]-[V/I]-based SUMO interaction motif, was characterized using Bio-layer Interferometery and NMR spectroscopy. Daxx12 fits itself in the groove formed by β₂ -loop-α structural region in both dSmt3 and SUMO1, but the binding is stronger with the former. Flexibility of β₂ -loop-α region in dSmt3 is suspected to assist its interaction with Daxx12. Our results highlight the role of native-state flexibility in assisting noncovalent interactions of SUMO proteins especially in organisms where a single SUMO isoform has to tackle multiple substrates single handedly.

A comprehensive platform for the analysis of ubiquitin-like protein modifications using in vivo biotinylation

Post-translational modification by ubiquitin and ubiquitin-like proteins (UbLs) is fundamental for maintaining protein homeostasis. Efficient isolation of UbL conjugates is hampered by multiple factors, including cost and specificity of reagents, removal of UbLs by proteases, distinguishing UbL conjugates from interactors, and low quantities of modified substrates. Here we describe bioUbLs, a comprehensive set of tools for studying modifications in Drosophila and mammals, based on multicistronic expression and in vivo biotinylation using the E. coli biotin protein ligase BirA. While the bioUbLs allow rapid validation of UbL conjugation for exogenous or endogenous proteins, the single vector approach can facilitate biotinylation of most proteins of interest. Purification under denaturing conditions inactivates deconjugating enzymes and stringent washes remove UbL interactors and non-specific background. We demonstrate the utility of the method in Drosophila cells and transgenic flies, identifying an extensive set of putative SUMOylated proteins in both cases. For mammalian cells, we show conjugation and localization for many different UbLs, with the identification of novel potential substrates for UFM1. Ease of use and the flexibility to modify existing vectors will make the bioUbL system a powerful complement to existing strategies for studying this important mode of protein regulation.

Vesicle-Mediated Steroid Hormone Secretion in Drosophila melanogaster

Steroid hormones are a large family of cholesterol derivatives regulating development and physiology in both the animal and plant kingdoms, but little is known concerning mechanisms of their secretion from steroidogenic tissues. Here, we present evidence that in Drosophila, endocrine release of the steroid hormone ecdysone is mediated through a regulated vesicular trafficking mechanism. Inhibition of calcium signaling in the steroidogenic prothoracic gland results in the accumulation of unreleased ecdysone, and the knockdown of calcium-mediated vesicle exocytosis components in the gland caused developmental defects due to deficiency of ecdysone. Accumulation of synaptotagmin-labeled vesicles in the gland is observed when calcium signaling is disrupted, and these vesicles contain an ABC transporter that functions as an ecdysone pump to fill vesicles. We propose that trafficking of steroid hormones out of endocrine cells is not always through a simple diffusion mechanism as presently thought, but instead can involve a regulated vesicle-mediated release process.

Drosophila 4EHP is essential for the larval-pupal transition and required in the prothoracic gland for ecdysone biosynthesis

Maternal expression of the translational regulator 4EHP (eIF4E-Homologous Protein) has an established role in generating protein gradients essential for specifying the Drosophila embryonic pattern. We generated a null mutation of 4EHP, which revealed for the first time that it is essential for viability and for completion of development. In fact, 4EHP null larvae, and larvae ubiquitously expressing RNAi targeting 4EHP, are developmentally delayed, fail to grow and eventually die. In addition, we found that expressing RNAi that targets 4EHP specifically in the prothoracic gland disrupted ecdysone biosynthesis, causing a block of the transition from the larval to pupal stages. This phenotype can be rescued by dietary administration of ecdysone. Consistent with this, 4EHP is highly expressed in the prothoracic gland and it is required for wild type expression levels of steroidogenic enzymes. Taken together, these results uncover a novel essential function for 4EHP in regulating ecdysone biosynthesis.

Transcriptional regulation of insect steroid hormone biosynthesis and its role in controlling timing of molting and metamorphosis

The developmental transition from juvenile to adult is often accompanied by many systemic changes in morphology, metabolism, and reproduction. Curiously, both mammalian puberty and insect metamorphosis are triggered by a pulse of steroid hormones, which can harmonize gene expression profiles in the body and thus orchestrate drastic biological changes. However, understanding of how the timing of steroid hormone biosynthesis is regulated at the molecular level is poor. The principal insect steroid hormone, ecdysteroid, is biosynthesized from dietary cholesterol in the specialized endocrine organ called the prothoracic gland. The periodic pulses of ecdysteroid titers determine the timing of molting and metamorphosis. To date, at least nine families of ecdysteroidogenic enzyme genes have been identified. Expression levels of these genes correlate well with ecdysteroid titers, indicating that the transcriptional regulatory network plays a critical role in regulating the ecdysteroid biosynthesis pathway. In this article, we summarize the transcriptional regulation of ecdysteroid biosynthesis. We first describe the development of prothoracic gland cells during Drosophila embryogenesis, and then provide an overview of the transcription factors that act in ecdysteroid biosynthesis and signaling. We also discuss the external signaling pathways that target these transcriptional regulators. Furthermore, we describe conserved and/or diverse aspects of steroid hormone biosynthesis in insect species as well as vertebrates.

Evolution of SUMO Function and Chain Formation in Insects

SUMOylation, the covalent binding of Small Ubiquitin-like Modifier (SUMO) to target proteins, is a posttranslational modification that regulates critical cellular processes in eukaryotes. In insects, SUMOylation has been studied in holometabolous species, particularly in the dipteran Drosophila melanogaster, which contains a single SUMO gene (smt3). This has led to the assumption that insects contain a single SUMO gene. However, the analysis of insect genomes shows that basal insects contain two SUMO genes, orthologous to vertebrate SUMO1 and SUMO2/3. Our phylogenetical analysis reveals that the SUMO gene has been duplicated giving rise to SUMO1 and SUMO2/3 families early in Metazoan evolution, and that later in insect evolution the SUMO1 gene has been lost after the Hymenoptera divergence. To explore the consequences of this loss, we have examined the characteristics and different biological functions of the two SUMO genes (SUMO1 and SUMO3) in the hemimetabolous cockroach Blattella germanica and compared them with those of Drosophila Smt3. Here, we show that the metamorphic role of the SUMO genes is evolutionary conserved in insects, although there has been a regulatory switch from SUMO1 in basal insects to SUMO3 in more derived ones. We also show that, unlike vertebrates, insect SUMO3 proteins cannot form polySUMO chains due to the loss of critical lysine residues within the N-terminal part of the protein. Furthermore, the formation of polySUMO chains by expression of ectopic human SUMO3 has a deleterious effect in Drosophila. These findings contribute to the understanding of the functional consequences of the evolution of SUMO genes.

The Systemic Control of Growth

Growth is a complex process that is intimately linked to the developmental program to form adults with proper size and proportions. Genetics is an important determinant of growth, as exemplified by the role of local diffusible molecules setting up organ proportions. In addition, organisms use adaptive responses allowing modulating the size of individuals according to environmental cues, for example, nutrition. Here, we describe some of the physiological principles participating in the determination of final individual size.

CDK8-Cyclin C Mediates Nutritional Regulation of Developmental Transitions through the Ecdysone Receptor in Drosophila

The steroid hormone ecdysone and its receptor (EcR) play critical roles in orchestrating developmental transitions in arthropods. However, the mechanism by which EcR integrates nutritional and developmental cues to correctly activate transcription remains poorly understood. Here, we show that EcR-dependent transcription, and thus, developmental timing in Drosophila, is regulated by CDK8 and its regulatory partner Cyclin C (CycC), and the level of CDK8 is affected by nutrient availability. We observed that cdk8 and cycC mutants resemble EcR mutants and EcR-target genes are systematically down-regulated in both mutants. Indeed, the ability of the EcR-Ultraspiracle (USP) heterodimer to bind to polytene chromosomes and the promoters of EcR target genes is also diminished. Mass spectrometry analysis of proteins that co-immunoprecipitate with EcR and USP identified multiple Mediator subunits, including CDK8 and CycC. Consistently, CDK8-CycC interacts with EcR-USP in vivo; in particular, CDK8 and Med14 can directly interact with the AF1 domain of EcR. These results suggest that CDK8-CycC may serve as transcriptional cofactors for EcR-dependent transcription. During the larval–pupal transition, the levels of CDK8 protein positively correlate with EcR and USP levels, but inversely correlate with the activity of sterol regulatory element binding protein (SREBP), the master regulator of intracellular lipid homeostasis. Likewise, starvation of early third instar larvae precociously increases the levels of CDK8, EcR and USP, yet down-regulates SREBP activity. Conversely, refeeding the starved larvae strongly reduces CDK8 levels but increases SREBP activity. Importantly, these changes correlate with the timing for the larval–pupal transition. Taken together, these results suggest that CDK8-CycC links nutrient intake to developmental transitions (EcR activity) and fat metabolism (SREBP activity) during the larval–pupal transition.

During the larval-pupal transition in Drosophila, CDK8-CycC helps to link nutrient intake to development by activating ecdysone receptor-dependent transcription and to fat metabolism by inhibiting SREBP-activated gene expression.

Arthropods are estimated to account for over 80% of animal species on earth. Characterized by their rigid exoskeletons, juvenile arthropods must periodically shed their thick outer cuticles by molting in order to grow. The steroid hormone ecdysone plays an essential role in regulating the timing of developmental transitions, but exactly how ecdysone and its receptor EcR activates transcription correctly after integrating nutritional and developmental cues remains unknown. Our developmental genetic analyses of two Drosophila mutants, cdk8 and cycC, show that they are lethal during the prepupal stage, with aberrant accumulation of fat and a severely delayed larval–pupal transition. As we have reported previously, CDK8-CycC inhibits fat accumulation by directly inactivating SREBP, a master transcription factor that controls the expression of lipogenic genes, which explains the abnormal fat accumulation in the cdk8 and cycC mutants. We find that CDK8 and CycC are required for EcR to bind to its target genes, serving as transcriptional cofactors for EcR-dependent gene expression. The expression of EcR target genes is compromised in cdk8 and cycC mutants and underpins the retarded pupariation phenotype. Starvation of feeding larvae precociously up-regulates CDK8 and EcR, prematurely down-regulates SREBP activity, and leads to early pupariation, whereas re-feeding starved larvae has opposite effects. Taken together, these results suggest that CDK8 and CycC play important roles in coordinating nutrition intake with fat metabolism by directly inhibiting SREBP-dependent gene expression and regulating developmental timing by activating EcR-dependent transcription in Drosophila.

Ecdysone promotes growth of imaginal discs through the regulation of Thor in D. melanogaster

Animals have a determined species-specific body size that results from the combined action of hormones and signaling pathways regulating growth rate and duration. In Drosophila, the steroid hormone ecdysone controls developmental transitions, thereby regulating the duration of the growth period. Here we show that ecdysone promotes the growth of imaginal discs in mid-third instar larvae, since imaginal discs from larvae with reduced or no ecdysone synthesis are smaller than wild type due to smaller and fewer cells. We show that insulin-like peptides are produced and secreted normally in larvae with reduced ecdysone synthesis, and upstream components of insulin/insulin-like signaling are activated in their discs. Instead, ecdysone appears to regulate the growth of imaginal discs via Thor/4E-BP, a negative growth regulator downstream of the insulin/insulin-like growth factor/Tor pathways. Discs from larvae with reduced ecdysone synthesis have elevated levels of Thor, while mutations in Thor partially rescue their growth. The regulation of organ growth by ecdysone is evolutionarily conserved in hemimetabolous insects, as shown by our results obtained using Blattella germanica. In summary, our data provide new insights into the relationship between components of the insulin/insulin-like/Tor and ecdysone pathways in the control of organ growth.

Frataxin inactivation leads to steroid deficiency in flies and human ovarian cells

Friedreich ataxia (FA), the most common inherited autosomal-recessive ataxia in Caucasians, is characterized by progressive degeneration of the central and peripheral nervous system, hypertrophic cardiomyopathy and increased incidence of diabetes. FA is caused by a GAA repeat expansion in the first intron of the gene encoding frataxin, an evolutionarily conserved mitochondrial protein, which results in decreased gene expression. Ubiquitous inactivation of the fly frataxin ortholog dfh blocks the transition from larval to pupal stages. In this study, we show that this phenotype is due to ecdysteroid deficiency and that feeding larvae with the 20-hydroxyecdysone steroid hormone rescues this developmental blockage. In mammals, adrenodoxin, the ferredoxin FDX1, is an Fe-S-containing protein essential for the synthesis of various steroid hormones. We show here that the two fly ferredoxins, Fdxh and Fdxh2 (encoded by CG1319), are also involved in steroidogenesis. This provides a potent mechanism by which frataxin, known to be involved in Fe-S cluster biosynthesis, could affect steroidogenesis through reduced ferredoxin activity. Finally, we show that frataxin inactivation decreases progesterone synthesis in human KGN ovarian granulosa cells. Thus, the involvement of frataxin in steroid synthesis appears to be a conserved function of the protein from flies to human and our data suggest that steroidogenesis could be affected in FA patients.

Sumoylation modulates 20-hydroxyecdysone signaling by maintaining USP protein levels in Drosophila

The nuclear receptor complex for the insect steroid hormone, 20-hydroxyecdysone (20E), is a heterodimer of EcR and USP. It has been shown that Drosophila EcR and USP can be sumoylated in mammalian cells, but it is unknown whether EcR-USP sumoylation naturally occurs in Drosophila. In Drosophila cells, USP, but not EcR, was sumoylated by Smt3, the only Drosophila SUMO protein. The presence of EcR enhanced USP sumoylation, which is further enhanced by 20E treatment. In addition to the Lys20 sumoylation site, five potential acceptor lysine residues in USP were predicted and verified. Mutation of the USP sumoylation sites or reduction of smt3 expression by RNAi attenuated 20E-induced reporter activity. Moreover, in the salivary glands, reducing smt3 expression by RNAi decreased 20E-induced reporter activity, gene expression, and autolysosome formation. Importantly, at least partially, the smt3 RNAi-mediated reduction in 20E signaling resulted from decreased protein levels of USP. In conclusion, sumoylation modulates 20E signaling by maintaining USP protein levels in Drosophila.

Mitochondrial fusion but not fission regulates larval growth and synaptic development through steroid hormone production

Mitochondrial fusion and fission affect the distribution and quality control of mitochondria. We show that Marf (Mitochondrial associated regulatory factor), is required for mitochondrial fusion and transport in long axons. Moreover, loss of Marf leads to a severe depletion of mitochondria in neuromuscular junctions (NMJs). Marf mutants also fail to maintain proper synaptic transmission at NMJs upon repetitive stimulation, similar to Drp1 fission mutants. However, unlike Drp1, loss of Marf leads to NMJ morphology defects and extended larval lifespan. Marf is required to form contacts between the endoplasmic reticulum and/or lipid droplets (LDs) and for proper storage of cholesterol and ecdysone synthesis in ring glands. Interestingly, human Mitofusin-2 rescues the loss of LD but both Mitofusin-1 and Mitofusin-2 are required for steroid-hormone synthesis. Our data show that Marf and Mitofusins share an evolutionarily conserved role in mitochondrial transport, cholesterol ester storage and steroid-hormone synthesis.

DOI:http://dx.doi.org/10.7554/eLife.03558.001

Mitochondria are the main source of energy for cells. These vital and highly dynamic organelles continually change shape by fusing with each other and splitting apart to create new mitochondria, repairing and replacing those damaged by cell stress.

For nerve impulses to be transmitted across the gaps (called synapses) between nerve cells, mitochondria need to supply the very ends of the nerve fibers with energy. To do this, the mitochondria must be transported from the main body of the nerve cell to the tips of the nerve fibers. This may not happen if mitochondria are the wrong shape, size or damaged.

While searching for genetic mutations that disrupt nerve function in the fruit fly Drosophila, Sandoval et al. spotted mutations in a gene called Marf. Further investigations revealed that flies with mutant versions of Marf have small, round mitochondria, and their nerves cannot transmit signals to muscles when they are highly stimulated. This is because the mutant mitochondria are not easily transported along nerve fibers, and so not enough energy is supplied to the synapses. The synapses of the Marf mutants are also abnormally shaped. Sandoval et al. found that this is not because Marf is lost in the neurons themselves, but because it is lost from a hormone-producing tissue called the ring gland.

Another problem found in flies with mutated Marf genes is that they stop developing while in their larval stage. Sandoval et al. established that this could also be related to the loss of Marf from the ring gland. The Marf protein has two different functions in the ring gland: forming and storing droplets of fatty molecules used in hormone production, and synthesising a hormone that controls when a fly larva matures into the adult fly. This suggests that the lower levels of this hormone produced by Marf mutant flies underlies their prolonged larval stages and synapse defects.

Vertebrates (animals with backbones, such as humans) have two genes that are related to the fly's Marf gene. When the human forms of these genes were introduced into mutant flies that lack a working copy of Marf, hormone production was only restored if both genes were introduced together. This indicates that these genes have separate roles in vertebrates, but that these roles are both performed by the single fly gene.

The role of Marf in tethering mitochondria in the ring gland may allow us to better understand how this process affects hormone production and how the different parts of the cell communicate.

DOI:http://dx.doi.org/10.7554/eLife.03558.002

A conserved SUMOylation signaling for cell cycle control in a holocentric species Bombyx mori

SUMOylation is an essential post-translational modification that regulates a variety of cellular processes including cell cycle progression. Although the SUMOylation pathway has been identified and investigated in many eukaryotes, the mechanisms of SUMOylation in regulating the functions of various substrates are still poorly understood. Here, we utilized a model species, the silkworm Bombyx mori that possesses holocentric chromosomes, to exploit the role of the SUMOylation system in cell cycle regulation. We identified all the components that are involved in the SUMOylation pathway in the silkworm genome. Our data revealed a cell cycle-dependent transcription of the SUMOylation genes, localization of the SUMOylation proteins, and abundance of the SUMOylation substrates in cultured silkworm cells. Importantly, the proliferation of the silkworm cells was strikingly inhibited by interference with SUMOylation genes expression, possibly due to an arrest of the SUMOylation-deficient cells at the G2/M phase. Furthermore, disruption of the SUMOylation genes induced the defects of holocentric chromosome congression and segregation during mitosis, which was consistent with high expressions of the SUMOylation genes and high enrichments of global SUMOylation at this stage, suggesting that the SUMOylation system in silkworm is essential for cell cycle regulation, with one particular role in mitosis.

Regulation of Toll signaling and inflammation by β-arrestin and the SUMO protease Ulp1

The Toll signaling pathway has a highly conserved function in innate immunity and is regulated by multiple factors that fine tune its activity. One such factor is β-arrestin Kurtz (Krz), which we previously implicated in the inhibition of developmental Toll signaling in the Drosophila melanogaster embryo. Another level of controlling Toll activity and immune system homeostasis is by protein sumoylation. In this study, we have uncovered a link between these two modes of regulation and show that Krz affects sumoylation via a conserved protein interaction with a SUMO protease, Ulp1. Loss of function of krz or Ulp1 in Drosophila larvae results in a similar inflammatory phenotype, which is manifested as increased lamellocyte production; melanotic mass formation; nuclear accumulation of Toll pathway transcriptional effectors, Dorsal and Dif; and expression of immunity genes, such as Drosomycin. Moreover, mutations in krz and Ulp1 show dosage-sensitive synergistic genetic interactions, suggesting that these two proteins are involved in the same pathway. Using Dorsal sumoylation as a readout, we found that altering Krz levels can affect the efficiency of SUMO deconjugation mediated by Ulp1. Our results demonstrate that β-arrestin controls Toll signaling and systemic inflammation at the level of sumoylation.

TnaA, an SP-RING protein, interacts with Osa, a subunit of the chromatin remodeling complex BRAHMA and with the SUMOylation pathway in Drosophila melanogaster

Tonalli A (TnaA) is a Drosophila melanogaster protein with an XSPRING domain. The XSPRING domain harbors an SP-RING zinc-finger, which is characteristic of proteins with SUMO E3 ligase activity. TnaA is required for homeotic gene expression and is presumably involved in the SUMOylation pathway. Here we analyzed some aspects of the TnaA location in embryo and larval stages and its genetic and biochemical interaction with SUMOylation pathway proteins. We describe that there are at least two TnaA proteins (TnaA130 and TnaA123) differentially expressed throughout development. We show that TnaA is chromatin-associated at discrete sites on polytene salivary gland chromosomes of third instar larvae and that tna mutant individuals do not survive to adulthood, with most dying as third instar larvae or pupae. The tna mutants that ultimately die as third instar larvae have an extended life span of at least 4 to 15 days as other SUMOylation pathway mutants. We show that TnaA physically interacts with the SUMO E2 conjugating enzyme Ubc9, and with the BRM complex subunit Osa. Furthermore, we show that tna and osa interact genetically with SUMOylation pathway components and individuals carrying mutations for these genes show a phenotype that can be the consequence of misexpression of developmental-related genes.

Scavenger receptors mediate the role of SUMO and Ftz-f1 in Drosophila steroidogenesis

SUMOylation participates in ecdysteroid biosynthesis at the onset of metamorphosis in Drosophila melanogaster. Silencing the Drosophila SUMO homologue smt3 in the prothoracic gland leads to reduced lipid content, low ecdysone titers, and a block in the larval–pupal transition. Here we show that the SR-BI family of Scavenger Receptors mediates SUMO functions. Reduced levels of Snmp1 compromise lipid uptake in the prothoracic gland. In addition, overexpression of Snmp1 is able to recover lipid droplet levels in the smt3 knockdown prothoracic gland cells. Snmp1 expression depends on Ftz-f1 (an NR5A-type orphan nuclear receptor), the expression of which, in turn, depends on SUMO. Furthermore, we show by in vitro and in vivo experiments that Ftz-f1 is SUMOylated. RNAi–mediated knockdown of ftz-f1 phenocopies that of smt3 at the larval to pupal transition, thus Ftz-f1 is an interesting candidate to mediate some of the functions of SUMO at the onset of metamorphosis. Additionally, we demonstrate that the role of SUMOylation, Ftz-f1, and the Scavenger Receptors in lipid capture and mobilization is conserved in other steroidogenic tissues such as the follicle cells of the ovary. smt3 knockdown, as well as ftz-f1 or Scavenger knockdown, depleted the lipid content of the follicle cells, which could be rescued by Snmp1 overexpression. Therefore, our data provide new insights into the regulation of metamorphosis via lipid homeostasis, showing that Drosophila Smt3, Ftz-f1, and SR-BIs are part of a general mechanism for uptake of lipids such as cholesterol, required during development in steroidogenic tissues.

Steroid hormones are cholesterol derivates that control many aspects of animal physiology, including development of the adult organisms, growth, energy storage, and reproduction. In insects, pulses of the steroid hormone ecdysone precede molting and metamorphosis, the regulation of hormonal synthesis being a crucial step that determines animal viability and size. Reduced levels of the small ubiquitin-like modifier SUMO in the prothoracic gland block the synthesis of ecdysone, as SUMO is needed for cholesterol intake. Here we show that SUMO is required for the expression of Scavenger Receptors (Class B, type I). These membrane receptors are necessary for lipid uptake by the gland. Strikingly, their expression is sufficient to recover lipid content when SUMO is removed. The expression of the Scavenger Receptors depends on Ftz-f1, a nuclear transcription factor homologous to mammalian Steroidogenic factor 1 (SF-1). Interestingly, the expression of Ftz-f1 also depends on SUMO and, in addition, Ftz-f1 is SUMOylated. This modification modulates its capacity to activate the Scavenger Receptor Snmp1. The role of SUMO, Scavenger Receptors, and Ftz-f1 on lipid intake is conserved in other tissues that synthesize steroid hormones, such as the ovaries. These factors are conserved in vertebrates, with mutations underlying human disease, so this mechanism to regulate lipid uptake could have implications for human health.

Developmental checkpoints and feedback circuits time insect maturation

The transition from juvenile to adult is a fundamental process that allows animals to allocate resource toward reproduction after completing a certain amount of growth. In insects, growth to a species-specific target size induces pulses of the steroid hormone ecdysone that triggers metamorphosis and reproductive maturation. The past few years have seen significant progress in understanding the interplay of mechanisms that coordinate timing of ecdysone production and release. These studies show that the neuroendocrine system monitors complex size-related and nutritional signals, as well as external cues, to time production and release of ecdysone. Based on results discussed here, we suggest that developmental progression to adulthood is controlled by checkpoints that regulate the genetic timing program enabling it to adapt to different environmental conditions. These checkpoints utilize a number of signaling pathways to modulate ecdysone production in the prothoracic gland. Release of ecdysone activates an autonomous cascade of both feedforward and feedback signals that determine the duration of the ecdysone pulse at each developmental transitions. Conservation of the genetic mechanisms that coordinate the juvenile-adult transition suggests that insights from the fruit fly Drosophila will provide a framework for future investigation of developmental timing in metazoans.

Protein interactions on telomeric retrotransposons in Drosophila

Telomere length in Drosophila is maintained by targeted transposition of three non-LTR retrotransposons: HeT-A, TART and TAHRE (HTT), but understanding the regulation of this process is hindered by our poor knowledge of HTT associated proteins. We have identified new protein components of the HTT array: Chromator (Chro), the TRF2/DREF complex and the sumoylation machinery. Chro was localized on telomeric HTT arrays by immunostaining, where it may interact with Prod directly, as indicated by yeast two-hybrid interaction, co-IP, and colocalization on polytene chromosomes. The TRF2/DREF complex may promote the open structure of HTT chromatin. The protein interactions controlling HTT chromatin structure and telomere length may be modulated by sumoylation.

SUMOylation in Drosophila Development

Small ubiquitin-related modifier (SUMO), an ~90 amino acid ubiquitin-like protein, is highly conserved throughout the eukaryotic domain. Like ubiquitin, SUMO is covalently attached to lysine side chains in a large number of target proteins. In contrast to ubiquitin, SUMO does not have a direct role in targeting proteins for proteasomal degradation. However, like ubiquitin, SUMO does modulate protein function in a variety of other ways. This includes effects on protein conformation, subcellular localization, and protein–protein interactions. Significant insight into the in vivo role of SUMOylation has been provided by studies in Drosophila that combine genetic manipulation, proteomic, and biochemical analysis. Such studies have revealed that the SUMO conjugation pathway regulates a wide variety of critical cellular and developmental processes, including chromatin/chromosome function, eggshell patterning, embryonic pattern formation, metamorphosis, larval and pupal development, neurogenesis, development of the innate immune system, and apoptosis. This review discusses our current understanding of the diverse roles for SUMO in Drosophila development.

A differential requirement for SUMOylation in proliferating and non-proliferating cells during Drosophila development

SUMOylation is a highly conserved post-translational modification shown to modulate target protein activity in a wide variety of cellular processes. Although the requirement for SUMO modification of specific substrates has received significant attention in vivo and in vitro, the developmental requirements for SUMOylation at the cell and tissue level remain poorly understood. Here, we show that in Drosophila melanogaster, both heterodimeric components of the SUMO E1-activating enzyme are zygotically required for mitotic progression but are dispensable for cell viability, homeostasis and DNA synthesis in non-dividing cells. Explaining the lack of more pleiotropic effects following a global block of SUMO conjugation, we further demonstrate that low levels of global substrate SUMOylation are detected in mutants lacking either or both E1 subunits. These results not only suggest that minimal SUMOylation persists in the absence of Aos1/Uba2, but also show that the process of cell division is selectively sensitive to reductions in global SUMOylation. Supporting this view, knockdown of SUMO or its E1 and E2 enzymes robustly disrupts proliferating cells in the developing eye, without any detectable effects on the development or differentiation of neighboring post-mitotic cells.

Synergism between altered cortical polarity and the PI3K/TOR pathway in the suppression of tumour growth

Loss of function of pins (partner of inscuteable) partially disrupts neuroblast (NB) polarity and asymmetric division, results in fewer and smaller NBs and inhibits Drosophila larval brain growth. Food deprivation also inhibits growth. However, we find that the combination of loss of function of pins and dietary restriction results in loss of NB asymmetry, overproliferation of Miranda-expressing cells, brain overgrowth and increased frequency of tumour growth on allograft transplantation. The same effects are observed in well-fed pins larvae that are mutant for pi3k (phosphatidylinositol 3-kinase) or exposed to the TOR inhibitor rapamycin. Thus, pathways that are sensitive to food deprivation and dependent on PI3K and TOR are essential to suppress tumour growth in Drosophila larval brains with compromised pins function. These results highlight an unexpected crosstalk whereby the normally growth-promoting, nutrient-sensing PI3K/TOR pathway suppresses tumour formation in neural stem cells with compromised cell polarity.

Overexpression of SUMO perturbs the growth and development of Caenorhabditis elegans

Small ubiquitin-related modifiers (SUMOs) are important regulator proteins. Caenorhabditis elegans contains a single SUMO ortholog, SMO-1, necessary for the reproduction of C. elegans. In this study, we constructed transgenic C. elegans strains expressing human SUMO-1 under the control of pan-neuronal (aex-3) or pan-muscular (myo-4) promoter and SUMO-2 under the control of myo-4 promoter. Interestingly, muscular overexpression of SUMO-1 or -2 resulted in morphological changes of the posterior part of the nematode. Movement, reproduction and aging of C. elegans were perturbed by the overexpression of SUMO-1 or -2. Genome-wide expression analyses revealed that several genes encoding components of SUMOylation pathway and ubiquitin-proteasome system were upregulated in SUMO-overexpressing nematodes. Since muscular overexpression of SMO-1 also brought up reproductive and mobility perturbations, our results imply that the phenotypes were largely due to an excess of SUMO, suggesting that a tight control of SUMO levels is important for the normal development of multicellular organisms.

Transcription factor fork head regulates the promoter of diapause hormone gene in the cotton bollworm, Helicoverpa armigera, and the modification of SUMOylation

The transcription factor fork head (FoxA) plays important roles in development and metabolism. Here, we cloned a fork head gene in Helicoverpa armigera, and found that the fork head protein is mainly located in the nucleus. This fork head gene belongs to the FoxA subfamily of the Fox transcription factors. The diapause hormone and pheromone biosynthesis-activating neuropeptide (DH-PBAN), which are two well-documented insect neuropeptides that regulate insect development and pheromone biosynthesis, are encoded by a single mRNA. In the present study, fork head was shown to bind strongly to the promoter of H. armigera DH-PBAN gene, and regulate its promoter activity. Furthermore, the effect of SUMOylation of the FH protein on the regulation of Har-DH-PBAN gene was investigated, and we show that the SUMO can modify Har-FH protein and cause down-regulation of DH-PBAN gene expression. These results suggest that SUMOylated FH plays a key role in insect diapause in H. armigera.

Neuroendocrine regulation of Drosophila metamorphosis requires TGFbeta/Activin signaling

In insects, initiation of metamorphosis requires a surge in the production of the steroid hormone 20-hydroxyecdysone from the prothoracic gland, the primary endocrine organ of juvenile larvae. Here, we show that blocking TGFβ/Activin signaling, specifically in the Drosophila prothoracic gland, results in developmental arrest prior to metamorphosis. The terminal, giant third instar larval phenotype results from a failure to induce the large rise in ecdysteroid titer that triggers metamorphosis. We further demonstrate that activin signaling regulates competence of the prothoracic gland to receive PTTH and insulin signals, and that these two pathways act at the mRNA and post-transcriptional levels, respectively, to control ecdysone biosynthetic enzyme expression. This dual regulatory circuitry may provide a cross-check mechanism to ensure that both developmental and nutritional inputs are synchronized before initiating the final genetic program leading to reproductive adult development. As steroid hormone production in C. elegans and mammals is also influenced by TGFβ/Activin signaling, this family of secreted factors may play a general role in regulating developmental transitions across phyla.

Drosophila Smt3 negatively regulates JNK signaling through sequestering Hipk in the nucleus

Post-translational modification by the small ubiquitin-related modifier (SUMO) is important for a variety of cellular and developmental processes. However, the precise mechanism(s) that connects sumoylation to specific developmental signaling pathways remains relatively less clear. Here, we show that Smt3 knockdown in Drosophila wing discs causes phenotypes resembling JNK gain of function, including ectopic apoptosis and apoptosis-induced compensatory growth. Smt3 depletion leads to an increased expression of JNK target genes Mmp1 and puckered. We show that, although knockdown of the homeodomain-interacting protein kinase (Hipk) suppresses Smt3 depletion-induced activation of JNK, Hipk overexpression synergistically enhances this type of JNK activation. We further demonstrate that Hipk is sumolylated in vivo, and its nuclear localization is dependent on the sumoylation pathway. Our results thus establish a mechanistic connection between the sumoylation pathway and the JNK pathway through the action of Hipk. We propose that the sumoylation-controlled balance between cytoplasmic and nuclear Hipk plays a crucial role in regulating JNK signaling.

The Putzig-NURF nucleosome remodeling complex is required for ecdysone receptor signaling and innate immunity in Drosophila melanogaster

Putzig (Pzg) was originally identified as being an integral component of the TRF2/DREF complex in Drosophila melanogaster, thereby regulating the transcriptional activation of replication-related genes. In a DREF-independent manner, Pzg was shown to mediate Notch target gene activation. This function of Pzg entails an association with the nucleosome remodeling factor complex NURF, which directly binds the ecdysone receptor EcR and coregulates targets of the EcR via the NURF-specific subunit Nurf-301. In contrast, Nurf-301 acts as a negative regulator of JAK/STAT signaling. Here, we provide evidence to show that Pzg is fundamental for these functions of NURF, apart from the regulation of Notch signaling activity. A jump-out mutagenesis provided us with a pzg null mutant displaying early larval lethality, defects in growth, and molting accompanied by aberrant feeding behavior. We show that Pzg is associated with EcR in vivo and required for the transcriptional induction of EcR target genes, whereas reduced ecdysteroid levels imply a NURF-independent function of Pzg. Moreover, pzg interferes with JAK/STAT-signaling activity by acting as a corepressor of Ken. Lamellocyte differentiation was consistently affected in a JAK/STAT mutant background and the expression level of defense response genes was elevated in pzg mutants, leading to the formation of melanotic tumors. Our results suggest that Pzg acts as an important partner of NURF in the regulation of EcR and JAK/STAT signaling.

Honeybee (Apis mellifera ligustica) drone embryo proteomes

Little attention has been paid to the drone honeybee (Apis mellifera ligustica) which is a haploid individual carrying only the set of alleles that it inherits from its mother. Molecular mechanisms underlying drone embryogenesis are poorly understood. This study evaluated protein expression profiles of drone embryogenesis at embryonic ages of 24, 48 and 72h. More than 100 reproducible proteins were analyzed by mass spectrometry on 2D electrophoresis gels. Sixty-two proteins were significantly changed at the selected three experimental age points. Expression of the metabolic energy requirement-related protein peaked at the embryonic age of 48h, whereas development and metabolizing amino acid-related proteins expressed optimally at 72h. Cytoskeleton, protein folding and antioxidant-related proteins were highly expressed at 48 and 72h. Protein networks of the identified proteins were constructed and protein expressions were validated at the transcription level. This first proteomic study of drone embryogenesis in the honeybee may provide geneticists an exact timetable and candidate protein outline for further manipulations of drone stem cells.

Microarray analysis of a salamander hopeful monster reveals transcriptional signatures of paedomorphic brain development

Background

The Mexican axolotl (Ambystoma mexicanum) is considered a hopeful monster because it exhibits an adaptive and derived mode of development - paedomorphosis - that has evolved rapidly and independently among tiger salamanders. Unlike related tiger salamanders that undergo metamorphosis, axolotls retain larval morphological traits into adulthood and thus present an adult body plan that differs dramatically from the ancestral (metamorphic) form. The basis of paedomorphic development was investigated by comparing temporal patterns of gene transcription between axolotl and tiger salamander larvae (Ambystoma tigrinum tigrinum) that typically undergo a metamorphosis.

Results

Transcript abundances from whole brain and pituitary were estimated via microarray analysis on four different days post hatching (42, 56, 70, 84 dph) and regression modeling was used to independently identify genes that were differentially expressed as a function of time in both species. Collectively, more differentially expressed genes (DEGs) were identified as unique to the axolotl (n = 76) and tiger salamander (n = 292) than were identified as shared (n = 108). All but two of the shared DEGs exhibited the same temporal pattern of expression and the unique genes tended to show greater changes later in the larval period when tiger salamander larvae were undergoing anatomical metamorphosis. A second, complementary analysis that directly compared the expression of 1320 genes between the species identified 409 genes that differed as a function of species or the interaction between time and species. Of these 409 DEGs, 84% exhibited higher abundances in tiger salamander larvae at all sampling times.

Conclusions

Many of the unique tiger salamander transcriptional responses are probably associated with metamorphic biological processes. However, the axolotl also showed unique patterns of transcription early in development. In particular, the axolotl showed a genome-wide reduction in mRNA abundance across loci, including genes that regulate hypothalamic-pituitary activities. This suggests that an axolotls failure to undergo anatomical metamorphosis late in the larval period is indirectly associated with a mechanism(s) that acts earlier in development to broadly program transcription. The axolotl hopeful monster provides a model to identify mechanisms of early brain development that proximally and ultimately affect the expression of adult phenotypes.

Sumoylation modulates the activity of Spalt-like proteins during wing development in Drosophila

The Spalt-like family of zinc finger transcription factors is conserved throughout evolution and is involved in fundamental processes during development and during embryonic stem cell maintenance. Although human SALL1 is modified by SUMO-1 in vitro, it is not known whether this post-translational modification plays a role in regulating the activity of this family of transcription factors. Here, we show that the Drosophila Spalt transcription factors are modified by sumoylation. This modification influences their nuclear localization and capacity to induce vein formation through the regulation of target genes during wing development. Furthermore, spalt genes interact genetically with the sumoylation machinery to repress vein formation in intervein regions and to attain the wing final size. Our results suggest a new level of regulation of Sall activity in vivo during animal development through post-translational modification by sumoylation. The evolutionary conservation of this family of transcription factors suggests a functional role for sumoylation in vertebrate Sall members.