Tissue-specific developmental requirements of Drosophila tyrosine hydroxylase isoforms

The matricellular protein Drosophila Cellular Communication Network Factor is required for synaptic transmission and female fertility

Within the extracellular matrix, matricellular proteins are dynamically expressed nonstructural proteins that interact with cell surface receptors, growth factors, and proteases, as well as with structural matrix proteins. The cellular communication network factors family of matricellular proteins serve regulatory roles to regulate cell function and are defined by their conserved multimodular organization. Here, we characterize the expression and neuronal requirement for the Drosophila cellular communication network factor family member. Drosophila cellular communication network factor is expressed in the nervous system throughout development including in subsets of monoamine-expressing neurons. Drosophila cellular communication network factor-expressing abdominal ganglion neurons innervate the ovaries and uterus and the loss of Drosophila cellular communication network factor results in reduced female fertility. In addition, Drosophila cellular communication network factor accumulates at the synaptic cleft and is required for neurotransmission at the larval neuromuscular junction. Analyzing the function of the single Drosophila cellular communication network factor family member will enhance our potential to understand how the microenvironment impacts neurotransmitter release in distinct cellular contexts and in response to activity.

Independent Contributions of Discrete Dopaminergic Circuits to Cellular Plasticity, Memory Strength, and Valence in Drosophila

Dopaminergic neurons play a key role in encoding associative memories, but little is known about how these circuits modulate memory strength. Here we report that different sets of dopaminergic neurons projecting to the Drosophila mushroom body (MB) differentially regulate valence and memory strength. PPL2 neurons increase odor-evoked calcium re- sponses to a paired odor in the MB and enhance behavioral memory strength when activated during olfactory classical conditioning. When paired with odor alone, they increase MB responses to the paired odor but do not drive behavioral approach or avoidance, suggesting that they increase the salience of the odor without encoding strong valence. This contrasts with the role of dopaminergic PPL1 neurons, which drive behavioral reinforcement but do not alter odor-evoked calcium responses in the MB when stimulated. These data suggest that different sets of dopaminergic neurons modulate olfactory valence and memory strength via independent actions on a memory-encoding brain region.

Boto et al. investigated the roles of two sets of dopaminergic neurons that converge on a memory-encoding brain region in flies. While one set, PPL1, drives aversive reinforcement (valence), PPL2 neurons enhance memory strength via modulation of Ca²⁺ response plasticity in memory-encoding mushroom body neurons.

Modulation of social space by dopamine in Drosophila melanogaster, but no effect on the avoidance of the Drosophila stress odorant

Appropriate response to others is necessary for social interactions. Yet little is known about how neurotransmitters regulate attractive and repulsive social cues. Using genetic and pharmacological manipulations in Drosophila melanogaster, we show that dopamine is contributing the response to others in a social group, specifically, social spacing, but not the avoidance of odours released by stressed flies (dSO). Interestingly, this dopamine-mediated behaviour is prominent only in the day-time, and its effect varies depending on tissue, sex and type of manipulation. Furthermore, alteration of dopamine levels has no effect on dSO avoidance regardless of sex, which suggests that a different neurotransmitter regulates this response.

A new brain dopamine-deficient Drosophila and its pharmacological and genetic rescue

Dopamine (DA) is a neurotransmitter with conserved behavioral roles between invertebrate and vertebrate animals. In addition to its neural functions, in insects DA is a critical substrate for cuticle pigmentation and hardening. Drosophila tyrosine hydroxylase (DTH) is the rate limiting enzyme for DA biosynthesis. Viable brain DA-deficient flies were previously generated using tissue-selective GAL4-UAS binary expression rescue of a DTH null mutation and these flies show specific behavioral impairments. To circumvent the limitations of rescue via binary expression, here we achieve rescue utilizing genomically integrated mutant DTH. As expected, our DA-deficient flies have no detectable DTH or DA in the brain, and show reduced locomotor activity. This deficit can be rescued by l-DOPA/carbidopa feeding, similar to human Parkinson's disease treatment. Genetic rescue via GAL4/UAS-DTH was also successful, although this required the generation of a new UAS-DTH1 transgene devoid of most untranslated regions, as existing UAS-DTH transgenes express in the brain without a Gal4 driver via endogenous regulatory elements. A surprising finding of our newly constructed UAS-DTH1m is that it expresses DTH at an undetectable level when regulated by dopaminergic GAL4 drivers even when fully rescuing DA, indicating that DTH immunostaining is not necessarily a valid marker for DA expression. This finding necessitated optimizing DA immunohistochemistry, showing details of DA innervation to the mushroom body and the central complex. When DA rescue is limited to specific DA neurons, DA does not diffuse beyond the DTH-expressing terminals, such that DA signaling can be limited to very specific brain regions.

Critical Analysis of the Melanogenic Pathway in Insects and Higher Animals

Animals synthesize melanin pigments for the coloration of their skin and use it for their protection from harmful solar radiation. Insects use melanins even more ingeniously than mammals and employ them for exoskeletal pigmentation, cuticular hardening, wound healing and innate immune responses. In this review, we discuss the biochemistry of melanogenesis process occurring in higher animals and insects. A special attention is given to number of aspects that are not previously brought to light: (1) the molecular mechanism of dopachrome conversion that leads to the production of two different dihydroxyindoles; (2) the role of catecholamine derivatives other than dopa in melanin production in animals; (3) the critical parts played by various biosynthetic enzymes associated with insect melanogenesis; and (4) the presence of a number of important gaps in both melanogenic and sclerotinogenic pathways. Additionally, importance of the melanogenic process in insect physiology especially in the sclerotization of their exoskeleton, wound healing reactions and innate immune responses is highlighted. The comparative biochemistry of melanization with sclerotization is also discussed.

Functional conservation of MBD proteins: MeCP2 and Drosophila MBD proteins alter sleep

Proteins containing a methyl-CpG-binding domain (MBD) bind 5mC and convert the methylation pattern information into appropriate functional cellular states. The correct readout of epigenetic marks is of particular importance in the nervous system where abnormal expression or compromised MBD protein function, can lead to disease and developmental disorders. Recent evidence indicates that the genome of Drosophila melanogaster is methylated and two MBD proteins, dMBD2/3 and dMBD-R2, are present. Are Drosophila MBD proteins required for neuronal function, and as MBD-containing proteins have diverged and evolved, does the MBD domain retain the molecular properties required for conserved cellular function across species? To address these questions, we expressed the human MBD-containing protein, hMeCP2, in distinct amine neurons and quantified functional changes in sleep circuitry output using a high throughput assay in Drosophila. hMeCP2 expression resulted in phase-specific sleep loss and sleep fragmentation with the hMeCP2-mediated sleep deficits requiring an intact MBD domain. Reducing endogenous dMBD2/3 and dMBD-R2 levels also generated sleep fragmentation, with an increase in sleep occurring upon dMBD-R2 reduction. To examine if hMeCP2 and dMBD-R2 are targeting common neuronal functions, we reduced dMBD-R2 levels in combination with hMeCP2 expression and observed a complete rescue of sleep deficits. Furthermore, chromosomal binding experiments indicate MBD-R2 and MeCP2 associate on shared genomic loci. Our results provide the first demonstration that Drosophila MBD-containing family members are required for neuronal function and suggest that the MBD domain retains considerable functional conservation at the whole organism level across species.

Tyrosine Hydroxylase is crucial for maintaining pupal tanning and immunity in Anopheles sinensis

Tyrosine hydroxylase (TH), the initial enzyme in the melanin pathway, catalyzes tyrosine conversion into Dopa. Although expression and regulation of TH have been shown to affect cuticle pigmentation in insects, no direct functional studies to date have focused on the specific physiological processes involving the enzyme during mosquito development. In the current study, silencing of AsTH during the time period of continuous high expression in Anopheles sinensis pupae led to significant impairment of cuticle tanning and thickness, imposing a severe obstacle to eclosion in adults. Meanwhile, deficiency of melanin in interference individuals led to suppression of melanization, compared to control individuals. Consequently, the ability to defend exogenous microorganisms declined sharply. Accompanying down-regulation of the basal expression of five antimicrobial peptide genes resulted in further significant weakening of immunity. TH homologs as well as the composition of upstream transcription factor binding sites at the pupal stage are highly conserved in the Anopheles genus, implying that the TH-mediated functions are crucial in Anopheles. The collective evidence strongly suggests that TH is essential for Anopheles pupae tanning and immunity and provides a reference for further studies to validate the utility of the key genes involved in the melanization pathway in controlling mosquito development.

A critical role for the Drosophila dopamine D1-like receptor Dop1R2 at the onset of metamorphosis

BACKGROUND

Insect metamorphosis relies on temporal and spatial cues that are precisely controlled. Previous studies in Drosophila have shown that untimely activation of genes that are essential to metamorphosis results in growth defects, developmental delay and death. Multiple factors exist that safeguard these genes against dysregulated expression. The list of identified negative regulators that play such a role in Drosophila development continues to expand.

RESULTS

By using RNAi transgene-induced gene silencing coupled to spatio/temporal assessment, we have unraveled an important role for the Drosophila dopamine 1-like receptor, Dop1R2, in development. We show that Dop1R2 knockdown leads to pre-adult lethality. In adults that escape death, abnormal wing expansion and/or melanization defects occur. Furthermore we show that salivary gland expression of this GPCR during the late larval/prepupal stage is essential for the flies to survive through adulthood. In addition to RNAi-induced effects, treatment of larvae with the high affinity D1-like receptor antagonist flupenthixol, also results in developmental arrest, and in morphological defects comparable to those seen in Dop1R2 RNAi flies. To examine the basis for pupal lethality in Dop1R2 RNAi flies, we carried out transcriptome analysis. These studies revealed up-regulation of genes that respond to ecdysone, regulate morphogenesis and/or modulate defense/immunity.

CONCLUSION

Taken together our findings suggest a role for Dop1R2 in the repression of genes that coordinate metamorphosis. Premature release of this inhibition is not tolerated by the developing fly.

Caffeine promotes wakefulness via dopamine signaling in Drosophila

Caffeine is the most widely-consumed psychoactive drug in the world, but our understanding of how caffeine affects our brains is relatively incomplete. Most studies focus on effects of caffeine on adenosine receptors, but there is evidence for other, more complex mechanisms. In the fruit fly Drosophila melanogaster, which shows a robust diurnal pattern of sleep/wake activity, caffeine reduces nighttime sleep behavior independently of the one known adenosine receptor. Here, we show that dopamine is required for the wake-promoting effect of caffeine in the fly, and that caffeine likely acts presynaptically to increase dopamine signaling. We identify a cluster of neurons, the paired anterior medial (PAM) cluster of dopaminergic neurons, as the ones relevant for the caffeine response. PAM neurons show increased activity following caffeine administration, and promote wake when activated. Also, inhibition of these neurons abrogates sleep suppression by caffeine. While previous studies have focused on adenosine-receptor mediated mechanisms for caffeine action, we have identified a role for dopaminergic neurons in the arousal-promoting effect of caffeine.

Store-Operated Calcium Entry through Orai Is Required for Transcriptional Maturation of the Flight Circuit in Drosophila

Store operated calcium entry (SOCE) is thought to primarily regulate calcium homeostasis in neurons. Subsequent to identification of Orai as the SOCE channel in nonexcitable cells, investigation of Orai function in neurons demonstrated a requirement for SOCE in Drosophila flight. Here, by analysis of an Orai mutant and by controlled expression of a dominant-negative Drosophila Orai transgene, we show that Orai-mediated SOCE is required in dopaminergic interneurons of the flight circuit during pupal development. Expression of dominant-negative Orai in dopaminergic neurons of pupae abolished flight. The loss of Orai-mediated SOCE alters transcriptional regulation of dopaminergic neurons, leading to downregulation of the enzyme tyrosine hydroxylase, which is essential for dopamine synthesis, and the dopamine transporter, which is required for dopamine uptake after synaptic release. These studies suggest that modulation of SOCE could serve as a novel mechanism for restoring dopamine levels in dopaminergic neurons.

SIGNIFICANCE STATEMENT

The specificity of an animal's response to an environmental stimulus is determined in part by the release of neurotransmitters, which are sensed by responding neurons through cognate receptors on their surface. One way by which neurons respond is through release of calcium from intracellular stores followed by store refilling from extracellular calcium sources. This mechanism is called store-operated calcium entry (SOCE). The function of SOCE in neurons has been debated. Here we describe a new function for SOCE in the regulation of neurotransmitter levels in Drosophila flight neurons. This cell-signaling mechanism is required to maintain optimal levels of a key enzyme for dopamine synthesis and may serve as a mechanism for restoring dopamine levels in relevant pathological conditions.

Maturation of a central brain flight circuit in Drosophila requires Fz2/Ca²⁺ signaling

The final identity of a differentiated neuron is determined by multiple signaling events, including activity dependent calcium transients. Non-canonical Frizzled2 (Fz2) signaling generates calcium transients that determine neuronal polarity, neuronal migration, and synapse assembly in the developing vertebrate brain. Here, we demonstrate a requirement for Fz2/Ca²⁺ signaling in determining the final differentiated state of a set of central brain dopaminergic neurons in Drosophila, referred to as the protocerebral anterior medial (PAM) cluster. Knockdown or inhibition of Fz2/Ca²⁺ signaling during maturation of the flight circuit in pupae reduces Tyrosine Hydroxylase (TH) expression in the PAM neurons and affects maintenance of flight. Thus, we demonstrate that Fz2/Ca²⁺ transients during development serve as a pre-requisite for normal adult behavior. Our results support a neural mechanism where PAM neuron send projections to the α' and β' lobes of a higher brain centre, the mushroom body, and function in dopaminergic re-inforcement of flight.

DOI:http://dx.doi.org/10.7554/eLife.07046.001

The fruit fly Drosophila melanogaster is an aerial acrobat. These insects can suddenly change direction in less than one hundredth of a second, explaining why a moving fly can be so difficult to swat. To perform their aerial manoeuvres, the flies continually combine information from multiple senses, including vision, hearing and smell, and use these data to control the activity of the neural circuits that support flight.

These flight circuits are established during the pupal stage of fly development, during which the fly transforms from a larva into its adult form. In 2013, researchers showed that a protein called dFrizzled2 must be present in pupae for flight circuits to mature correctly. This protein forms part of a pathway that ultimately controls which specific chemicals—called neurotransmitters—are released by neurons to communicate with other cells. Agrawal and Hasan—who worked on the 2013 study—now extend their findings to investigate the role of dFrizzled2 in more detail.

The new experiments show that for the flight circuits to mature, dFrizzled2 must be active in a cluster of neurons known collectively as PAM. Specifically, dFrizzled2 is needed to make an enzyme that helps to produce a neurotransmitter called dopamine. This in turn enables the PAM neurons to communicate with a region of the fruit fly brain called the mushroom body, which it thought to play an important role in complex behaviors such as reward-based learning.

The absence of dFrizzled2 results in adult flies that rarely remain airborne for more than 20 s at a time, whereas normal flies can typically fly for over 700 s. Given that dopamine is known to signal reward, one possibility is that the dopamine signals from the PAM neurons to the mushroom body serve as a reward to encourage continuous flight. Mutant flies that lack dFrizzled2—and thus these dopamine signals—lose their motivation to fly after only a few seconds.

Overall, Agrawal and Hasan's findings suggest that the mushroom body has an important role in coordinating a fly's movements with information from it senses. Future research will be needed to determine exactly how the mushroom body performs this role.

DOI:http://dx.doi.org/10.7554/eLife.07046.002

Systematic analysis of fly models with multiple drivers reveals different effects of ataxin-1 and huntingtin in neuron subtype-specific expression

The fruit fly, Drosophila melanogaster, is a commonly used model organism for neurodegenerative diseases. Its major advantages include a short lifespan and its susceptibility to manipulation using sophisticated genetic techniques. Here, we report the systematic comparison of fly models of two polyglutamine (polyQ) diseases. We induced expression of the normal and mutant forms of full-length Ataxin-1 and Huntingtin exon 1 in cholinergic, dopaminergic, and motor neurons, and glial cells using cell type-specific drivers. We systematically analyzed their effects based on multiple phenotypes: eclosion rate, lifespan, motor performance, and circadian rhythms of spontaneous activity. This systematic assay system enabled us to quantitatively evaluate and compare the functional disabilities of different genotypes. The results suggest different effects of Ataxin-1 and Huntingtin on specific types of neural cells during development and in adulthood. In addition, we confirmed the therapeutic effects of LiCl and butyrate using representative models. These results support the usefulness of this assay system for screening candidate chemical compounds that modify the pathologies of polyQ diseases.

RNA-seq profiling of small numbers of Drosophila neurons

Drosophila melanogaster has a robust circadian clock, which drives a rhythmic behavior pattern: locomotor activity increases in the morning shortly before lights on (M peak) and in the evening shortly before lights off (E peak). This pattern is controlled by ~75 pairs of circadian neurons in the Drosophila brain. One key group of neurons is the M-cells (PDF(+) large and small LNvs), which control the M peak. A second key group is the E-cells, consisting of four LNds and the fifth small LNv, which control the E peak. Recent studies show that the M-cells have a second role in addition to controlling the M peak; they communicate with the E-cells (as well as DN1s) to affect their timing, probably as a function of environmental conditions (Guo, Cerullo, Chen, & Rosbash, 2014). To learn about molecules within the M-cells important for their functional roles, we have adapted methods to manually sort fluorescent protein-expressing neurons of interest from dissociated Drosophila brains. We isolated mRNA and miRNA from sorted M-cells and amplified the resulting DNAs to create deep-sequencing libraries. Visual inspection of the libraries illustrates that they are specific to a particular neuronal subgroup; M-cell libraries contain timeless and dopaminergic cell libraries contain ple/TH. Using these data, it is possible to identify cycling transcripts as well as many mRNAs and miRNAs specific to or enriched in particular groups of neurons.

Dopaminergic modulation of cAMP drives nonlinear plasticity across the Drosophila mushroom body lobes

BACKGROUND

Activity of dopaminergic neurons is necessary and sufficient to evoke learning-related plasticity in neuronal networks that modulate learning. During olfactory classical conditioning, large subsets of dopaminergic neurons are activated, releasing dopamine across broad sets of postsynaptic neurons. It is unclear how such diffuse dopamine release generates the highly localized patterns of plasticity required for memory formation.

RESULTS

Here we have mapped spatial patterns of dopaminergic modulation of intracellular signaling and plasticity in Drosophila mushroom body (MB) neurons, combining presynaptic thermogenetic stimulation of dopaminergic neurons with postsynaptic functional imaging in vivo. Stimulation of dopaminergic neurons generated increases in cyclic AMP (cAMP) across multiple spatial regions in the MB. However, odor presentation paired with stimulation of dopaminergic neurons evoked plasticity in Ca(2+) responses in discrete spatial patterns. These patterns of plasticity correlated with behavioral requirements for each set of MB neurons in aversive and appetitive conditioning. Finally, broad elevation of cAMP differentially facilitated responses in the gamma lobe, suggesting that it is more sensitive to elevations of cAMP and that it is recruited first into dopamine-dependent memory traces.

CONCLUSIONS

These data suggest that the spatial pattern of learning-related plasticity is dependent on the postsynaptic neurons' sensitivity to cAMP signaling. This may represent a mechanism through which single-cycle conditioning allocates short-term memory to a specific subset of eligible neurons (gamma neurons).

Sexually dimorphic body color is regulated by sex-specific expression of yellow gene in ponerine ant, Diacamma sp

Most hymenopteran species exhibit conspicuous sexual dimorphism due to ecological differences between the sexes. As hymenopteran genomes, under the haplodiploid genetic system, exhibit quantitative differences between sexes while remaining qualitatively identical, sexual phenotypes are assumed to be expressed through sex-specific gene usage. In the present study, the molecular basis for expression of sexual dimorphism in a queenless ant, Diacamma sp., which exhibits a distinct color dimorphism, was examined. Worker females of the species appear bluish-black, while winged males exhibit a yellowish-brown body color. Initially, observations of the pigmentation processes during pupal development revealed that black pigmentation was present in female pupae but not in males, suggesting that sex-specific melanin synthesis was responsible for the observed color dimorphism. Therefore, five orthologs of the genes involved in the insect melanin synthesis (yellow, ebony, tan, pale and dopa decarboxylase) were subcloned and their spatiotemporal expression patterns were examined using real-time quantitative RT-PCR. Of the genes examined, yellow, which plays a role in black melanin synthesis in insects, was expressed at higher levels in females than in males throughout the entire body during the pupal stage. RNA interference of yellow was then carried out in order to determine the gene function, and produced females with a more yellowish, brighter body color similar to that of males. It was concluded that transcriptional regulation of yellow was responsible for the sexual color dimorphism observed in this species.

Pharmacological analysis of dopamine modulation in the Drosophila melanogaster larval heart

Dopamine (DA) and other neurotransmitters affect nonneuronal tissues in insects by circulating in the hemolymph. In several organisms, DA has been shown to modulate distinct aspects of cardiac function but the signal transduction pathways that mediate dopaminergic effects on the heart are not well characterized. Here, we used a semiintact Drosophila melanogaster larva preparation and drugs targeting DA receptors and canonical second messenger pathways to identify signaling cascades that mediate the effect of DA on a myogenic heart. DA has a positive chronotropic effect that is mimicked by SKF38393 (type-1 DA receptor agonist) and quinpirole (type-2 DA receptor agonist). SCH23390 and spiperone (type-1 and type-2 DA receptor antagonists) are moderately effective at inhibiting DA's effect. An adenylate cyclase inhibitor (SQ,22536) is also effective at blocking the stimulatory effect of DA but the drug has its own dose-dependent effect. Activation of protein kinase C with a diacylglycerol analog has a stimulatory effect on heart rate (HR). These results suggest that (1) both DA receptor subtypes are expressed in third instar larva cardiac myocytes to increase HR in response to rising levels of DA in the hemolymph, and (2) canonical second messenger pathways modulate HR in D. melanogaster larvae. Having these disparate signaling cascades converge toward a common modulatory function appears redundant, but in the context of multiple cardioactive chemicals this redundancy is likely to increase the fidelity of signal transduction.

Dopaminergic neurons encode a distributed, asymmetric representation of temperature in Drosophila

Dopaminergic circuits modulate a wide variety of innate and learned behaviors in animals, including olfactory associative learning, arousal, and temperature-preference behavior. It is not known whether distinct or overlapping sets of dopaminergic neurons modulate these behaviors. Here, I have functionally characterized the dopaminergic circuits innervating the Drosophila mushroom body with in vivo calcium imaging and conditional silencing of genetically defined subsets of neurons. Distinct subsets of PPL1 dopaminergic neurons innervating the vertical lobes of the mushroom body responded to decreases in temperature, but not increases, with rapidly adapting bursts of activity. PAM neurons innervating the horizontal lobes did not respond to temperature shifts. Ablation of the antennae and maxillary palps reduced, but did not eliminate, the responses. Genetic silencing of dopaminergic neurons innervating the vertical mushroom body lobes substantially reduced behavioral cold avoidance, but silencing smaller subsets of these neurons had no effect. These data demonstrate that overlapping dopaminergic circuits encode a broadly distributed, asymmetric representation of temperature that overlays regions implicated previously in learning, memory, and forgetting. Thus, diverse behaviors engage overlapping sets of dopaminergic neurons that encode multimodal stimuli and innervate a single anatomical target, the mushroom body.

Immune response in the barrier epithelia: lessons from the fruit fly Drosophila melanogaster

The barrier epithelia of multicellular organisms frequently come into direct contact with microorganisms and thus need to fulfill the important task of preventing the penetration of pathogens that could cause systemic infections. A functional immune defence in the epithelial linings of the digestive, respiratory and reproductive organs as well as the epidermis/skin of animals is therefore of crucial importance for survival. Epithelial defence reactions are likely to be evolutionarily ancient, and the use of invertebrate animal models, such as insects and nematodes, has been crucial in unravelling the mechanisms underlying epithelial immunity. This review addresses basic questions of epithelial immunity in animals and humans. It focuses on recent developments in the understanding of the immune responses in the fruit fly Drosophila melanogaster and how the innate immune system acts locally in the epidermis and cuticle, tracheae, gut and genital organs. Both basal immune activities in epithelia that are constantly exposed to microbes as well as positive and negative regulation in response to pathogenic organisms are covered. Important immuno-physiological aspects of epithelial defence mechanisms are also discussed, such as wound healing, re-epithelialization and intestinal homeostasis.

Repression of tyrosine hydroxylase is responsible for the sex-linked chocolate mutation of the silkworm, Bombyx mori

Pigmentation patterning has long interested biologists, integrating topics in ecology, development, genetics, and physiology. Wild-type neonatal larvae of the silkworm, Bombyx mori, are completely black. By contrast, the epidermis and head of larvae of the homozygous recessive sex-linked chocolate (sch) mutant are reddish brown. When incubated at 30 degrees C, mutants with the sch allele fail to hatch; moreover, homozygous mutants carrying the allele sch lethal (sch(l)) do not hatch even at room temperature (25 degrees C). By positional cloning, we narrowed a region containing sch to 239,622 bp on chromosome 1 using 4,501 backcross (BC1) individuals. Based on expression analyses, the best sch candidate gene was shown to be tyrosine hydroxylase (BmTh). BmTh coding sequences were identical among sch, sch(l), and wild-type. However, in sch the approximately 70-kb sequence was replaced with approximately 4.6 kb of a Tc1-mariner type transposon located approximately 6 kb upstream of BmTh, and in sch(l), a large fragment of an L1Bm retrotransposon was inserted just in front of the transcription start site of BmTh. In both cases, we observed a drastic reduction of BmTh expression. Use of RNAi with BmTh prevented pigmentation and hatching, and feeding of a tyrosine hydroxylase inhibitor also suppressed larval pigmentation in the wild-type strain, pnd(+) and in a pS (black-striped) heterozygote. Feeding L-dopa to sch neonate larvae rescued the mutant phenotype from chocolate to black. Our results indicate the BmTh gene is responsible for the sch mutation, which plays an important role in melanin synthesis producing neonatal larval color.

Roles of dopamine in circadian rhythmicity and extreme light sensitivity of circadian entrainment

Light has profound behavioral effects on almost all animals, and nocturnal animals show sensitivity to extremely low light levels [1-4]. Crepuscular, i.e., dawn/dusk-active animals such as Drosophila melanogaster are thought to show far less sensitivity to light [5-8]. Here we report that Drosophila respond to extremely low levels of monochromatic blue light. Light levels three to four orders of magnitude lower than previously believed impact circadian entrainment and the light-induced stimulation of locomotion known as positive behavioral masking. We use GAL4;UAS-mediated rescue of tyrosine hydroxylase (DTH) mutant (ple) flies to study the roles of dopamine in these processes. We present evidence for two roles of dopamine in circadian behaviors. First, rescue with either a wild-type DTH or a DTH mutant lacking neural expression leads to weak circadian rhythmicity, indicating a role for strictly regulated DTH and dopamine in robust circadian rhythmicity. Second, the DTH rescue strain deficient in neural dopamine selectively shows a defect in circadian entrainment to low light, whereas another response to light, positive masking, has normal light sensitivity. These findings imply separable pathways from light input to the behavioral outputs of masking versus circadian entrainment, with only the latter dependent on dopamine.

Neuroarchitecture of aminergic systems in the larval ventral ganglion of Drosophila melanogaster

Biogenic amines are important signaling molecules in the central nervous system of both vertebrates and invertebrates. In the fruit fly Drosophila melanogaster, biogenic amines take part in the regulation of various vital physiological processes such as feeding, learning/memory, locomotion, sexual behavior, and sleep/arousal. Consequently, several morphological studies have analyzed the distribution of aminergic neurons in the CNS. Previous descriptions, however, did not determine the exact spatial location of aminergic neurite arborizations within the neuropil. The release sites and pre-/postsynaptic compartments of aminergic neurons also remained largely unidentified. We here used gal4-driven marker gene expression and immunocytochemistry to map presumed serotonergic (5-HT), dopaminergic, and tyraminergic/octopaminergic neurons in the thoracic and abdominal neuromeres of the Drosophila larval ventral ganglion relying on Fasciclin2-immunoreactive tracts as three-dimensional landmarks. With tyrosine hydroxylase- (TH) or tyrosine decarboxylase 2 (TDC2)-specific gal4-drivers, we also analyzed the distribution of ectopically expressed neuronal compartment markers in presumptive dopaminergic TH and tyraminergic/octopaminergic TDC2 neurons, respectively. Our results suggest that thoracic and abdominal 5-HT and TH neurons are exclusively interneurons whereas most TDC2 neurons are efferent. 5-HT and TH neurons are ideally positioned to integrate sensory information and to modulate neuronal transmission within the ventral ganglion, while most TDC2 neurons appear to act peripherally. In contrast to 5-HT neurons, TH and TDC2 neurons each comprise morphologically different neuron subsets with separated in- and output compartments in specific neuropil regions. The three-dimensional mapping of aminergic neurons now facilitates the identification of neuronal network contacts and co-localized signaling molecules, as exemplified for DOPA decarboxylase-synthesizing neurons that co-express crustacean cardioactive peptide and myoinhibiting peptides.

A neuropeptide hormone cascade controls the precise onset of post-eclosion cuticular tanning in Drosophila melanogaster

A neuropeptide hormone-signalling pathway controls events surrounding eclosion in Drosophila melanogaster. Ecdysis-triggering hormone, eclosion hormone and crustacean cardioactive peptide (CCAP) together control pre-eclosion and eclosion events, whereas bursicon, through its receptor rickets (RK), controls post-eclosion development. Cuticular tanning is a convenient visible marker of the temporally precise post-eclosion developmental progression, and we investigated how it is controlled by the ecdysis neuropeptide cascade. Together, two enzymes, tyrosine hydroxylase (TH, encoded by ple) and dopa decarboxylase (DDC, encoded by Ddc), produce the dopamine that is required for tanning. Levels of both the ple and Ddc transcripts begin to accumulate before eclosion, coincident with the onset of pigmentation of the pharate adult bristles and epidermis. Since DDC activity is high before the post-eclosion onset of tanning, a different factor must be regulated to switch on tanning. Transcriptional control of ple does not regulate the onset of tanning because ple transcript levels remain unchanged from 24 hours before to 12 hours after eclosion. TH protein present before eclosion is degraded, and no TH activity can be detected at eclosion. However, TH protein rapidly accumulates within an hour of eclosion and we provide evidence that CCAP controls this process. Furthermore, we show that TH is transiently activated during tanning by phosphorylation at Ser32, as a result of bursicon signalling. We conclude that the ecdysis hormone cascade acts as a regulatory switch to control the precise onset of tanning by both translational and activational control of TH.

Selective loss of dopaminergic neurons and formation of Lewy body-like aggregations in alpha-synuclein transgenic fly neuronal cultures

A key pathological feature of Parkinson's disease (PD) is the selective loss of dopaminergic neurons accompanied by the formation of Lewy bodies (LB). Given the complex nature of the disease, it is imperative to develop a model system suitable for molecular and cellular manipulation in order to study the mechanisms underlying the pathogenesis of PD. Here, we report that a new in vitro model of PD has been developed by using Drosophila melanogaster primary neuronal cultures expressing a human mutant alpha-synuclein (alpha-Syn; A30P). The selective loss of dopaminergic (DA) neurons was observed when alpha-Syn was pan-neuronally expressed while non-dopaminergic neurons (e.g. GABAergic) were not influenced. This degeneration was also observed even when alpha-Syn was specifically expressed in DA neurons, demonstrating alpha-Syn toxicity is DA cell-autonomous. In all experiments, cultures 5 days or older showed clear degeneration of DA neurons whereas this degeneration was not significant in 3-day-old cultures. In addition, there were intracellular aggregations in 5-day or older alpha-Syn neurons that were recognized by anti-alpha-Syn or ubiquitin antibodies, demonstrating the formation of LB-like inclusions. By contrast, no such aggregations were found in 3-day-old neurons. The results demonstrate that mutated human alpha-Syn expressed in Drosophila primary neuronal cultures causes the selective loss of DA neurons and the formation of cellular aggregations. Therefore, this is one of the first in vitro models recapitulating two important cellular features of PD and will be useful in examining mechanisms underlying selective neurodegeneration mediated by alpha-Syn.

Sex-specific expression of alternative transcripts in Drosophila

A genome-wide microarray analysis of sex-specific expression of alternative transcripts in Drosophila shows sexual dimorphism in transcript abundance for 53% of the genes.

Background

Many genes produce multiple transcripts due to alternative splicing or utilization of alternative transcription initiation/termination sites. This 'transcriptome expansion' is thought to increase phenotypic complexity by allowing a single locus to produce several functionally distinct proteins. However, sex, genetic and developmental variation in the representation of alternative transcripts has never been examined systematically. Here, we describe a genome-wide analysis of sex-specific expression of alternative transcripts in Drosophila melanogaster.

Results

We compared transcript profiles in males and females from eight Drosophila lines (OregonR and 2b, and 6 RIL) using a newly designed 60-mer oligonucleotide microarray that allows us to distinguish a large proportion of alternative transcripts. The new microarray incorporates 7,207 oligonucleotides, satisfying stringent binding and specificity criteria that target both the common and the unique regions of 2,768 multi-transcript genes, as well as 12,912 oligonucleotides that target genes with a single known transcript. We estimate that up to 22% of genes that produce multiple transcripts show a sex-specific bias in the representation of alternative transcripts. Sexual dimorphism in overall transcript abundance was evident for 53% of genes. The X chromosome contains a significantly higher proportion of genes with female-biased transcription than the autosomes. However, genes on the X chromosome are no more likely to have a sexual bias in alternative transcript representation than autosomal genes.

Conclusion

Widespread sex-specific expression of alternative transcripts in Drosophila suggests that a new level of sexual dimorphism at the molecular level exists.

Roles of Drosophila DJ-1 in survival of dopaminergic neurons and oxidative stress

The loss of dopaminergic neurons in the substantia nigra is the pathological hallmark of Parkinson's disease (PD). While the etiology of sporadic PD remains elusive, an inherited form of early-onset familial PD is linked to mutations of DJ-1. To understand the biological function of DJ-1 and its relevance to the pathogenesis of PD, we investigated the function of DJ-1 using Drosophila. Drosophila possesses two homologs of human DJ-1: DJ-1alpha and DJ-1beta. We found that DJ-1alpha is expressed predominantly in the testis, while DJ-1beta is ubiquitously present in most tissues, resembling the expression pattern of human DJ-1. Loss-of-function DJ-1beta mutants demonstrated an extended survival of dopaminergic neurons and resistance to paraquat stress, but showed acute sensitivity to hydrogen peroxide treatment. We showed a compensatory upregulation of DJ-1alpha expression in the brain of the DJ-1beta mutant and demonstrated that overexpression of DJ-1alpha in dopaminergic neurons is sufficient to confer protection against paraquat insult. These results suggest that Drosophila homologs of DJ-1 play critical roles in the survival of dopaminergic neurons and response to oxidative stress.