Novel subcellular locations and functions for secretory pathway Ca2+/Mn2+-ATPases

Functional-metabolic coupling in distinct renal cell types coordinates organ-wide physiology and delays premature ageing

Precise coupling between cellular physiology and metabolism is emerging as a vital relationship underpinning tissue health and longevity. Nevertheless, functional-metabolic coupling within heterogenous microenvironments in vivo remains poorly understood due to tissue complexity and metabolic plasticity. Here, we establish the Drosophila renal system as a paradigm for linking mechanistic analysis of metabolism, at single-cell resolution, to organ-wide physiology. Kidneys are amongst the most energetically-demanding organs, yet exactly how individual cell types fine-tune metabolism to meet their diverse, unique physiologies over the life-course remains unclear. Integrating live-imaging of metabolite and organelle dynamics with spatio-temporal genetic perturbation within intact functional tissue, we uncover distinct cellular metabolic signatures essential to support renal physiology and healthy ageing. Cell type-specific programming of glucose handling, PPP-mediated glutathione regeneration and FA β-oxidation via dynamic lipid-peroxisomal networks, downstream of differential ERR receptor activity, precisely match cellular energetic demands whilst limiting damage and premature senescence; however, their dramatic dysregulation may underlie age-related renal dysfunction.

Dietary calcium (Ca2+) impacts Ca2+ content and molecular expression of Ca2+-transporters in Malpighian tubules of the yellow fever mosquito, Aedes aegypti

The renal (Malpighian) tubules of insects play important roles in hemolymph Ca2+ regulation. Here we investigated how dietary Ca2+ loads from sucrose or blood meals affect the Ca2+ content and mRNA expression of Ca2+ transporters in Malpighian tubules of adult female mosquitoes. Using the yellow fever mosquito Aedes aegypti we found that feeding females 10% sucrose with elevated Ca2+ concentration ad libitum for 6 days led to increased Ca2+ content in Malpighian tubules. The increases of Ca2+ content correlated with up-regulations of mRNAs encoding intracellular Ca2+-ATPases (SERCA and SPCA), a plasma membrane Ca2+-ATPase (PMCA), and a K+-dependent Na+/Ca2+ exchanger (NCKX1). We also found that when adult females were fed blood, tubule Ca2+ content changed dynamically over the next 72 h in a manner consistent with redistribution of tubule Ca2+ stores to other tissues (e.g., ovaries). The changes in tubule Ca2+ were correlated with dynamic changes in mRNA abundances of SERCA, SPCA, PMCA, and NCKX1. Our results are the first to demonstrate that Malpighian tubules of adult female mosquitoes have a remarkable capacity to handle high dietary Ca2+ loads, most likely through the combination of storing excess Ca2+ within intracellular compartments and secreting it into the tubule lumen for excretion. Our results also suggest that the Malpighian tubules play key roles in supplying Ca2+ to other tissues during the processing of blood meals.

Manganese-driven CoQ deficiency

Overexposure to manganese disrupts cellular energy metabolism across species, but the molecular mechanism underlying manganese toxicity remains enigmatic. Here, we report that excess cellular manganese selectively disrupts coenzyme Q (CoQ) biosynthesis, resulting in failure of mitochondrial bioenergetics. While respiratory chain complexes remain intact, the lack of CoQ as lipophilic electron carrier precludes oxidative phosphorylation and leads to premature cell and organismal death. At a molecular level, manganese overload causes mismetallation and proteolytic degradation of Coq7, a diiron hydroxylase that catalyzes the penultimate step in CoQ biosynthesis. Coq7 overexpression or supplementation with a CoQ headgroup analog that bypasses Coq7 function fully corrects electron transport, thus restoring respiration and viability. We uncover a unique sensitivity of a diiron enzyme to mismetallation and define the molecular mechanism for manganese-induced bioenergetic failure that is conserved across species.

Drosophila melanogaster: a simple genetic model of kidney structure, function and disease

Although the genetic basis of many kidney diseases is being rapidly elucidated, their experimental study remains problematic owing to the lack of suitable models. The fruitfly Drosophila melanogaster provides a rapid, ethical and cost-effective model system of the kidney. The unique advantages of D. melanogaster include ease and low cost of maintenance, comprehensive availability of genetic mutants and powerful transgenic technologies, and less onerous regulation, as compared with mammalian systems. Renal and excretory functions in D. melanogaster reside in three main tissues - the transporting renal (Malpighian) tubules, the reabsorptive hindgut and the endocytic nephrocytes. Tubules contain multiple cell types and regions and generate a primary urine by transcellular transport rather than filtration, which is then subjected to selective reabsorption in the hindgut. By contrast, the nephrocytes are specialized for uptake of macromolecules and equipped with a filtering slit diaphragm resembling that of podocytes. Many genes with key roles in the human kidney have D. melanogaster orthologues that are enriched and functionally relevant in fly renal tissues. This similarity has allowed investigations of epithelial transport, kidney stone formation and podocyte and proximal tubule function. Furthermore, a range of unique quantitative phenotypes are available to measure function in both wild type and disease-modelling flies.

Lighting Up Ca2+ Dynamics in Animal Models

Calcium (Ca2+) signaling coordinates are crucial processes in brain physiology. Particularly, fundamental aspects of neuronal function such as synaptic transmission and neuronal plasticity are regulated by Ca2+, and neuronal survival itself relies on Ca2+-dependent cascades. Indeed, impaired Ca2+ homeostasis has been reported in aging as well as in the onset and progression of neurodegeneration. Understanding the physiology of brain function and the key processes leading to its derangement is a core challenge for neuroscience. In this context, Ca2+ imaging represents a powerful tool, effectively fostered by the continuous amelioration of Ca2+ sensors in parallel with the improvement of imaging instrumentation. In this review, we explore the potentiality of the most used animal models employed for Ca2+ imaging, highlighting their application in brain research to explore the pathogenesis of neurodegenerative diseases.

Physiology, Development, and Disease Modeling in the Drosophila Excretory System

The insect excretory system contains two organ systems acting in concert: the Malpighian tubules and the hindgut perform essential roles in excretion and ionic and osmotic homeostasis. For over 350 years, these two organs have fascinated biologists as a model of organ structure and function. As part of a recent surge in interest, research on the Malpighian tubules and hindgut of Drosophila have uncovered important paradigms of organ physiology and development. Further, many human disease processes can be modeled in these organs. Here, focusing on discoveries in the past 10 years, we provide an overview of the anatomy and physiology of the Drosophila excretory system. We describe the major developmental events that build these organs during embryogenesis, remodel them during metamorphosis, and repair them following injury. Finally, we highlight the use of the Malpighian tubules and hindgut as accessible models of human disease biology. The Malpighian tubule is a particularly excellent model to study rapid fluid transport, neuroendocrine control of renal function, and modeling of numerous human renal conditions such as kidney stones, while the hindgut provides an outstanding model for processes such as the role of cell chirality in development, nonstem cell-based injury repair, cancer-promoting processes, and communication between the intestine and nervous system.

Axonal Endoplasmic Reticulum Dynamics and Its Roles in Neurodegeneration

The physical continuity of axons over long cellular distances poses challenges for their maintenance. One organelle that faces this challenge is endoplasmic reticulum (ER); unlike other intracellular organelles, this forms a physically continuous network throughout the cell, with a single membrane and a single lumen. In axons, ER is mainly smooth, forming a tubular network with occasional sheets or cisternae and low amounts of rough ER. It has many potential roles: lipid biosynthesis, glucose homeostasis, a Ca2+ store, protein export, and contacting and regulating other organelles. This tubular network structure is determined by ER-shaping proteins, mutations in some of which are causative for neurodegenerative disorders such as hereditary spastic paraplegia (HSP). While axonal ER shares many features with the tubular ER network in other contexts, these features must be adapted to the long and narrow dimensions of axons. ER appears to be physically continuous throughout axons, over distances that are enormous on a subcellular scale. It is therefore a potential channel for long-distance or regional communication within neurons, independent of action potentials or physical transport of cargos, but involving its physiological roles such as Ca2+ or organelle homeostasis. Despite its apparent stability, axonal ER is highly dynamic, showing features like anterograde and retrograde transport, potentially reflecting continuous fusion and breakage of the network. Here we discuss the transport processes that must contribute to this dynamic behavior of ER. We also discuss the model that these processes underpin a homeostatic process that ensures both enough ER to maintain continuity of the network and repair breaks in it, but not too much ER that might disrupt local cellular physiology. Finally, we discuss how failure of ER organization in axons could lead to axon degenerative diseases, and how a requirement for ER continuity could make distal axons most susceptible to degeneration in conditions that disrupt ER continuity.

Calcium Imaging in Drosophila melanogaster

Drosophila melanogaster, colloquially known as the fruit fly, is one of the most commonly used model organisms in scientific research. Although the final architecture of a fly and a human differs greatly, most of the fundamental biological mechanisms and pathways controlling development and survival are conserved through evolution between the two species. For this reason, Drosophila has been productively used as a model organism for over a century, to study a diverse range of biological processes, including development, learning, behavior and aging. Ca²⁺ signaling comprises complex pathways that impact on virtually every aspect of cellular physiology. Within such a complex field of study, Drosophila offers the advantages of consolidated molecular and genetic techniques, lack of genetic redundancy and a completely annotated genome since 2000. These and other characteristics provided the basis for the identification of many genes encoding Ca²⁺ signaling molecules and the disclosure of conserved Ca²⁺ signaling pathways. In this review, we will analyze the applications of Ca²⁺ imaging in the fruit fly model, highlighting in particular their impact on the study of normal brain function and pathogenesis of neurodegenerative diseases.

Genetic analyses uncover pleiotropic compensatory roles for Drosophila Nucleobindin-1 in inositol trisphosphate-mediated intracellular calcium homeostasis

Nucleobindin-1 is an EF-hand calcium-binding protein with a distinctive profile, predominantly localized to the Golgi in insect and wide-ranging vertebrate cell types, alike. Its putative involvements in intracellular calcium (Ca²⁺) homeostasis have never been phenotypically characterized in any model organism. We have analyzed an adult-viable mutant that completely disrupts the G protein α-subunit binding and activating (GBA) motif of Drosophila Nucleobindin-1 (dmNUCB1). Such disruption does not manifest any obvious fitness-related, morphological/developmental, or behavioral abnormalities. A single copy of this mutation or the knockdown of dmnucb1 in restricted sets of cells variously rescues pleiotropic mutant phenotypes arising from impaired inositol 1,4,5-trisphosphate receptor (IP3R) activity (in turn depleting cytoplasmic Ca²⁺ levels across diverse tissue types). Additionally, altered dmNUCB1 expression or function considerably reverses lifespan and mobility improvements effected by IP3R mutants, in a Drosophila model of amyotrophic lateral sclerosis. Homology modeling-based analyses further predict a high degree of conformational conservation in Drosophila, of biochemically validated structural determinants in the GBA motif that specify in vertebrates, the unconventional Ca²⁺-regulated interaction of NUCB1 with Gαi subunits. The broad implications of our findings are hypothetically discussed, regarding potential roles for NUCB1 in GBA-mediated, Golgi-associated Ca²⁺ signaling, in health and disease.

Peroxisome Protein Prediction in Drosophila melanogaster

As a laboratory animal, Drosophila melanogaster has made extensive contributions to understanding many areas of fundamental biology as well as being an effective model for human disease. Until recently, there was relatively little known about fly peroxisomes. There were early studies that examined the role of peroxisome enzymes during development of organs like the eye. However, with the advent of a well-annotated, sequenced genome, several groups have collectively determined, first by sequence homology and increasingly by functional studies, Drosophila Peroxins and related peroxisome proteins. Notably, it was shown that Drosophila peroxisome biogenesis is mediated via a well-conserved PTS1 import system. Although the fly genome encodes a Pex7 homologue, a canonical PTS2 import system does not seem to be conserved in Drosophila. Given the homology between Drosophila and Saccharomyces cerevisiae or Homo sapiens peroxisome biogenesis and function, Drosophila has emerged as an effective multicellular system to model human Peroxisome Biogenesis Disorders. Finally, Drosophila peroxisome research has recently come into its own, facilitating new discoveries into the role of peroxisomes within specific tissues, such as testes or immune cells.

Mechanisms of calcium sequestration by isolated Malpighian tubules of the house cricket Acheta domesticus

Hemolymph calcium homeostasis in insects is achieved by the Malpighian tubules, primarily by sequestering excess Ca²⁺ within internal calcium stores (Ca-rich granules) most often located within type I (principal) tubule cells. Using both the scanning ion-selective electrode technique and the Ramsay secretion assay this study provides the first measurements of basolateral and transepithelial Ca²⁺ fluxes across the Malpighian tubules of an Orthopteran insect, the house cricket Acheta domesticus. Ca²⁺ transport was specific to midtubule segments, where 97% of the Ca²⁺ entering the tubule is sequestered within intracellular calcium stores and the remaining 3% is secreted into the lumen. Antagonists of voltage-gated (L-type) calcium channels decreased Ca²⁺ influx ≥fivefold in adenosine 3',5'-cyclic monophosphate (cAMP)-stimulated tubules, suggesting basolateral Ca²⁺ influx is facilitated by voltage-gated Ca²⁺ channels. Increasing fluid secretion through manipulation of intracellular levels of cAMP or Ca²⁺ had opposite effects on tubule Ca²⁺ transport. The adenylyl cyclase-cAMP-PKA pathway promotes Ca²⁺ sequestration whereas both 5-hydroxytryptamine and thapsigargin inhibited sequestration. Our results suggest that the midtubules of Acheta domesticus are dynamic calcium stores, which maintain hemolymph calcium concentration by manipulating rates of Ca²⁺ sequestration through stimulatory (cAMP) and inhibitory (Ca²⁺ ) regulatory pathways.

Vg1-Nodal heterodimers are the endogenous inducers of mesendoderm

Nodal is considered the key inducer of mesendoderm in vertebrate embryos and embryonic stem cells. Other TGF-beta-related signals, such as Vg1/Dvr1/Gdf3, have also been implicated in this process but their roles have been unclear or controversial. Here we report that zebrafish embryos without maternally provided vg1 fail to form endoderm and head and trunk mesoderm, and closely resemble nodal loss-of-function mutants. Although Nodal is processed and secreted without Vg1, it requires Vg1 for its endogenous activity. Conversely, Vg1 is unprocessed and resides in the endoplasmic reticulum without Nodal, and is only secreted, processed and active in the presence of Nodal. Co-expression of Nodal and Vg1 results in heterodimer formation and mesendoderm induction. Thus, mesendoderm induction relies on the combination of two TGF-beta-related signals: maternal and ubiquitous Vg1, and zygotic and localized Nodal. Modeling reveals that the pool of maternal Vg1 enables rapid signaling at low concentrations of zygotic Nodal.

All animals begin life as just one cell – a fertilized egg. In order to make a recognizable adult, each embryo needs to make the three types of tissue that will eventually form all of the organs: endoderm, which will form the internal organs; mesoderm, which will form the muscle and bones; and ectoderm, which will generate the skin and nervous system.

All vertebrates – animals with backbones like fish and humans – use the so-called Nodal signaling pathway to make the endoderm and mesoderm. Nodal is a signaling molecule that binds to receptors on the surface of cells. If Nodal binds to a receptor on a cell, it instructs that cell to become endoderm or mesoderm. As such, Nodal is critical for vertebrate life. However, there has been a 30-year debate in the field of developmental biology about whether a protein called Vg1, which has a similar molecular structure as Nodal, plays a role in the early development of vertebrates.

Zebrafish are often used to study animal development, and Montague and Schier decided to test whether these fish need the gene for Vg1 (also known as Gdf3) by deleting it using a genome editing technique called CRISPR/Cas9. It turns out that female zebrafish can survive without this gene. Yet, when the offspring of these females do not inherit the instructions to make Vg1 from their mothers, they fail to form the endoderm and mesoderm. This means that the embryos do not have hearts, blood or other internal organs, and they die within three days. Two other groups of researchers have independently reported similar results.

The findings reveal that Vg1 is critical for the Nodal signaling pathway to work in zebrafish. Montague and Schier then showed that, in this pathway, Nodal does not activate its receptors on its own. Instead, Nodal must interact with Vg1, and it is this Nodal-Vg1 complex that activates receptors, and instructs cells to become endoderm and mesoderm.

Scientists currently use the Nodal signaling pathway to induce human embryonic stem cells growing in the laboratory to become mesoderm and endoderm. As such, these new findings could ultimately help researchers to grow tissues and organs for human patients.

The essential roles of metal ions in insect homeostasis and physiology

Metal ions play distinct roles in living organisms, including insects. Some, like sodium and potassium, are central players in osmoregulation and 'blood and guts' transport physiology, and have been implicated in cold adaptation. Calcium is a key player as a second messenger, and as a structural element. Other metals, particularly those with multiple redox states, can be cofactors in many metalloenzymes, but can contribute to toxic oxidative stress on the organism in excess. This short review selects some examples where classical knowledge has been supplemented with recent advances, in order to emphasize the importance of metals as essential nutrients for insect survival.

Segment-specific Ca(2+) transport by isolated Malpighian tubules of Drosophila melanogaster: A comparison of larval and adult stages

Haemolymph calcium homeostasis in insects is achieved through the regulation of calcium excretion by Malpighian tubules in two ways: (1) sequestration of calcium within biomineralized granules and (2) secretion of calcium in soluble form within the primary urine. Using the scanning ion-selective electrode technique (SIET), basolateral Ca(2+) transport was measured at the distal, transitional, main and proximal tubular segments of anterior tubules isolated from both 3rd instar larvae and adults of the fruit fly Drosophila melanogaster. Basolateral Ca(2+) transport exceeded transepithelial secretion by 800-fold and 11-fold in anterior tubules of larvae and adults, respectively. The magnitude of Ca(2+) fluxes across the distal tubule of larvae and adults were larger than fluxes across the downstream segments by 10 and 40 times, respectively, indicating a dominant role for the distal segment in whole animal Ca(2+) regulation. Basolateral Ca(2+) transport across distal tubules of Drosophila varied throughout the life cycle; Ca(2+) was released by distal tubules of larvae, taken up by distal tubules of young adults and was released once again by tubules of adults ⩾ 168 h post-eclosion. In adults and larvae, SIET measurements revealed sites of both Ca(2+) uptake and Ca(2+) release across the basolateral surface of the distal segment of the same tubule, indicating that Ca(2+) transport is bidirectional. Ca(2+) uptake across the distal segment of tubules of young adults and Ca(2+) release across the distal segment of tubules of older adults was also suggestive of reversible Ca(2+) storage. Our results suggest that the distal tubules of D. melanogaster are dynamic calcium stores which allow efficient haemolymph calcium regulation through active Ca(2+) sequestration during periods of high dietary calcium intake and passive Ca(2+) release during periods of calcium deficiency.

Secretory pathway Ca(2+)-ATPase isoform 1 knockdown promotes Golgi apparatus stress injury in a mouse model of focal cerebral ischemia-reperfusion: In vivo and in vitro study

The present study was designed to investigate the potential role of secretory pathway Ca(2+)-ATPase isoform 1(SPCA1) in experimental focal cerebral ischemia-reperfusion injury. Cerebral ischemia-reperfusion was induced by transient middle cerebral artery occlusion (MCAO) for 2h s in Sprague-Dawley rats, and then the expression levels of SPAC1 mRNA and protein were determined. Results showed that SPCA1 level was transiently increased 1 day after reperfusion in peri-infarction area, while markedly increased in infarction core on 3day and 7 day after reperfusion. Then a SPCA1 lentivirus was used to achieve knockdown of SPCA1 gene: Ca(2+) transporting type 2C, member 1 (ATP2C1) gene. It has been observed that SPCA1 knockdown by lentivirus markedly increased cerebral infarction volume in vivo. Meanwhile, SPCA1 knockdown also facilitated per-oxidative production, including nitric oxide (NO) and 3-nitrotyrosine (3-NT) and decreased the expression of total superoxide dismutase (SOD) and manganese superoxide dismutase (MnSOD). Moreover, in vitro study showed that SPCA1 knockdown increased hydrogen peroxide (H2O2)-induced lactate dehydrogenase (LDH) leakage dose-dependently, and elevated caspase3 level in neuro-2a (N2a) cells. In addition, SPCA1 knockdown increased H2O2-induced production of nitric oxide and 3-NT dose-dependently, and reversed the increased activity of total SOD and MnSOD in neuro-2a cells. In conclusion, the present study indicated that SPCA1 could suppress over active Golgi apparatus (GA) stress thus attenuate cerebral ischemia-reperfusion injury.

Elemental mapping of the entire intact Drosophila gastrointestinal tract

The main role of the animal gastrointestinal (GI) tract is the selective absorption of dietary nutrients from ingested food sources. One class of vital micronutrients are the essential biometals such as copper, zinc and iron, which participate in a plethora of biological process, acting as enzymatic or structural co-factors for numerous proteins and also as important cellular signalling molecules. To help elucidate the mechanisms by which biometals are absorbed from the diet, we mapped elemental distribution in entire, intact Drosophila larval GI tracts using synchrotron X-ray fluorescence microscopy. Our results revealed distinct regions of the GI tract enriched for specific metals. Copper was found to be concentrated in the copper cell region but also in the region directly anterior to the copper cells and unexpectedly, in the middle midgut/iron cell region as well. Iron was observed exclusively in the iron cell region, confirming previous work with iron-specific histological stains. Zinc was observed throughout the GI tract with an increased accumulation in the posterior midgut region, while manganese was seen to co-localize with calcium specifically in clusters in the distal Malpighian tubules. This work simultaneously reveals distribution of a number of biologically important elements in entire, intact GI tracts. These distributions revealed not only a previously undescribed Ca/Mn co-localization, but also the unexpected presence of additional Cu accumulations in the iron cell region.

Changes in secretory pathway Ca(2+)-ATPase 2 following focal cerebral ischemia/reperfusion injury

This study aimed to investigate changes in secretory pathway Ca²⁺-ATPase 2 expression following cerebral ischemia/reperfusion injury, and to define the role of Ca²⁺-ATPases in oxidative stress. A rat model of cerebral ischemia/reperfusion injury was established using the unilateral middle cerebral artery occlusion method. Immunohistochemistry and reverse transcription-PCR assay results showed that compared with the control group, the expression of secretory pathway Ca²⁺-ATPase 2 protein and mRNA in the cerebral cortex and hippocampus of male rats did not significantly change during the ischemic period. However, secretory pathway Ca²⁺-ATPase 2 protein and mRNA expression reduced gradually at 1, 3, and 24 hours during the reperfusion period. Our experimental findings indicate that levels of secretory pathway Ca²⁺-ATPase 2 protein and mRNA expression in brain tissue change in response to cerebral ischemia/reperfusion injury.

Cell signalling mechanisms for insect stress tolerance

Insects successfully occupy most environmental niches and this success depends on surviving a broad range of environmental stressors including temperature, desiccation, xenobiotic, osmotic and infection stress. Epithelial tissues play key roles as barriers between the external and internal environments and therefore maintain homeostasis and organismal tolerance to multiple stressors. As such, the crucial role of epithelia in organismal stress tolerance cannot be underestimated. At a molecular level, multiple cell-specific signalling pathways including cyclic cAMP, cyclic cGMP and calcium modulate tissue, and hence, organismal responses to stress. Thus, epithelial cell-specific signal transduction can be usefully studied to determine the molecular mechanisms of organismal stress tolerance in vivo. This review will explore cell signalling modulation of stress tolerance in insects by focusing on cell signalling in a fluid transporting epithelium--the Malpighian tubule. Manipulation of specific genes and signalling pathways in only defined tubule cell types can influence the survival outcome in response to multiple environmental stressors including desiccation, immune, salt (ionic) and oxidative stress, suggesting that studies in the genetic model Drosophila melanogaster may reveal novel pathways required for stress tolerance.

Peroxisomes are required for lipid metabolism and muscle function in Drosophila melanogaster

Peroxisomes are ubiquitous organelles that perform lipid and reactive oxygen species metabolism. Defects in peroxisome biogenesis cause peroxisome biogenesis disorders (PBDs). The most severe PBD, Zellweger syndrome, is characterized in part by neuronal dysfunction, craniofacial malformations, and low muscle tone (hypotonia). These devastating diseases lack effective therapies and the development of animal models may reveal new drug targets. We have generated Drosophila mutants with impaired peroxisome biogenesis by disrupting the early peroxin gene pex3, which participates in budding of pre-peroxisomes from the ER and peroxisomal membrane protein localization. pex3 deletion mutants lack detectible peroxisomes and die before or during pupariation. At earlier stages of development, larvae lacking Pex3 display reduced size and impaired lipid metabolism. Selective loss of peroxisomes in muscles impairs muscle function and results in flightless animals. Although, hypotonia in PBD patients is thought to be a secondary effect of neuronal dysfunction, our results suggest that peroxisome loss directly affects muscle physiology, possibly by disrupting energy metabolism. Understanding the role of peroxisomes in Drosophila physiology, specifically in muscle cells may reveal novel aspects of PBD etiology.

Signaling by Drosophila capa neuropeptides

The capa peptide family, originally identified in the tobacco hawk moth, Manduca sexta, is now known to be present in many insect families, with increasing publications on capa neuropeptides each year. The physiological actions of capa peptides vary depending on the insect species but capa peptides have key myomodulatory and osmoregulatory functions, depending on insect lifestyle, and life stage. Capa peptide signaling is thus critical for fluid homeostasis and survival, making study of this neuropeptide family attractive for novel routes for insect control. In Dipteran species, including the genetically tractable Drosophila melanogaster, capa peptide action is diuretic; via elevation of nitric oxide, cGMP and calcium in the principal cells of the Malpighian tubules. The identification of the capa receptor (capaR) in several insect species has shown this to be a canonical GPCR. In D. melanogaster, ligand-activated capaR activity occurs in a dose-dependent manner between 10(-6) and 10(-12)M. Lower concentrations of capa peptide do not activate capaR, either in adult or larval Malpighian tubules. Use of transgenic flies in which capaR is knocked-down in only Malpighian tubule principal cells demonstrates that capaR modulates tubule fluid secretion rates and in doing so, sets the organismal response to desiccation. Thus, capa regulates a desiccation-responsive pathway in D. melanogaster, linking its role in osmoregulation and fluid homeostasis to environmental response and survival. The conservation of capa action between some Dipteran species suggests that capa's role in desiccation tolerance may not be confined to D. melanogaster.

Increased neuronal activity fragments the Golgi complex

The Golgi complex is essential for many aspects of cellular function, including trafficking and sorting of membrane and secretory proteins and posttranslational modification by glycosylation. We observed reversible fragmentation of the Golgi complex in cultured hippocampal neurons cultured in hyperexcitable conditions. In addition, Golgi fragmentation was found in cultured neurons with hyperactivity due to prolonged blockade of GABA(A)-mediated inhibition or withdrawal of NMDA receptor antagonism. The interplay between neuronal hyperactivity and Golgi structure established in this study thus reveals a previously uncharacterized impact of neuronal activity on organelle structure. This finding may have important roles in protein processing and trafficking in the Golgi as well as effects on neuronal signaling.

Peroxisome Ca(2+) homeostasis in animal and plant cells

Ca(2+) homeostasis in peroxisomes has been an unsolved problem for many years. Recently novel probes to monitor Ca(2+) levels in the lumen of peroxisomes in living cells of both animal and plant cells have been developed. Here we discuss the contrasting results obtained in mammalian cells with chemiluminecsent (aequorin) and fluorescent (cameleon) probes targeted to peroxisomes. We briefly discuss the different characteristics of these probes and the possible pitfalls of the two approaches. We conclude that the contrasting results obtained with the two probes may reflect a heterogeneity among peroxisomes in mammalian cells. We also discuss the results obtained in plant peroxisomes. In particular we demonstrate that Ca(2+) increases in the cytoplasm are mirrored by similar rises of Ca(2+) concentration the lumen of peroxisomes. The increases in peroxisome Ca(2+) level results in the activation of a catalase isoform, CAT3. Other functional roles of peroxisomal Ca(2+) changes in plant physiology are briefly discussed.

An inventory of peroxisomal proteins and pathways in Drosophila melanogaster

Peroxisomes are ubiquitous organelles housing a variety of essential biochemical pathways. Peroxisome dysfunction causes a spectrum of human diseases known as peroxisome biogenesis disorders (PBD). Although much is known regarding the mechanism of peroxisome biogenesis, it is still unclear how peroxisome dysfunction leads to the disease state. Several recent studies have shown that mutations in Drosophila peroxin genes cause phenotypes similar to those seen in humans with PBDs suggesting that Drosophila might be a useful system to model PBDs. We have analyzed the proteome of Drosophila to identify the proteins involved in peroxisomal biogenesis and homeostasis as well as metabolic enzymes that function within the organelle. The subcellular localization of five of these predicted peroxisomal proteins was confirmed. Similar to Caenorhabditis elegans, Drosophila appears to only utilize the peroxisome targeting signal type 1 system for matrix protein import. This work will further our understanding of peroxisomes in Drosophila and add to the usefulness of this emerging model system.

In vivo Drosophilia genetic model for calcium oxalate nephrolithiasis

Nephrolithiasis is a major public health problem with a complex and varied etiology. Most stones are composed of calcium oxalate (CaOx), with dietary excess a risk factor. Because of complexity of mammalian system, the details of stone formation remain to be understood. Here we have developed a nephrolithiasis model using the genetic model Drosophila melanogaster, which has a simple, transparent kidney tubule. Drosophilia reliably develops CaOx stones upon dietary oxalate supplementation, and the nucleation and growth of microliths can be viewed in real time. The Slc26 anion transporter dPrestin (Slc26a5/6) is strongly expressed in Drosophilia kidney, and biophysical analysis shows that it is a potent oxalate transporter. When dPrestin is knocked down by RNAi in fly kidney, formation of microliths is reduced, identifying dPrestin as a key player in oxalate excretion. CaOx stone formation is an ancient conserved process across >400 My of divergent evolution (fly and human), and from this study we can conclude that the fly is a good genetic model of nephrolithiasis.

Functional correlates of positional and gender-specific renal asymmetry in Drosophila

BACKGROUND

In humans and other animals, the internal organs are positioned asymmetrically in the body cavity, and disruption of this body plan can be fatal in humans. The mechanisms by which internal asymmetry are established are presently the subject of intense study; however, the functional significance of internal asymmetry (outside the brain) is largely unexplored. Is internal asymmetry functionally significant, or merely an expedient way of packing organs into a cavity?

METHODOLOGY/PRINCIPAL FINDINGS

Like humans, Drosophila shows internal asymmetry, with the gut thrown into stereotyped folds. There is also renal asymmetry, with the rightmost pair of renal (Malpighian) tubules always ramifying anteriorly, and the leftmost pair always sitting posteriorly in the body cavity. Accordingly, transcriptomes of anterior-directed (right-side) and posterior-directed (left-side) Malpighian (renal) tubules were compared in both adult male and female Drosophila. Although genes encoding the basic functions of the tubules (transport, signalling) were uniformly expressed, some functions (like innate immunity) showed positional or gender differences in emphasis; others, like calcium handling or the generation of potentially toxic ammonia, were reserved for just the right-side or left-side tubules, respectively. These findings correlated with the distinct locations of each tubule pair within the body cavity. Well known developmental genes (like dorsocross, dachshund and doublesex) showed continuing, patterned expression in adult tubules, implying that somatic tissues maintain both left-right and gender identities throughout life. Gender asymmetry was also noted, both in defence and in male-specific expression of receptors for neuropeptide F and sex-peptide: NPF elevated calcium only in male tubules.

CONCLUSIONS/SIGNIFICANCE

Accordingly, the physical asymmetry of the tubules in the body cavity is directly adaptive. Now that the detailed machinery underlying internal asymmetry is starting to be delineated, our work invites the investigation, not just of tissues in isolation, but in the context of their unique physical locations and milieux.

Inorganic polyphosphates are stored in spherites within the midgut of Anticarsia gemmatalis and play a role in copper detoxification

Inorganic polyphosphates (PolyP) are widespread molecules that have been shown to play a role in metal detoxification and heavy-metal tolerance. In the present report, we investigated the functional role of spherites as PolyP-metal binding stores in epithelial cells of the midgut of Anticarsia gemmatalis, a lepidopteran pest of soybean. PolyP stores were detected by DAPI staining and indirect immunohistochemistry as vesicles distributed in columnar cells and around goblet cell cavities. These PolyP vesicles were identified as spherites by their elemental profile in cell lysates that were partially modulated by P- or V-ATPases. PolyP levels along the midgut were detected using a recombinant exopolyphosphatase assay. When copper was added in the diet of larva, copper detection in spherites by X-ray microanalysis correlated with an increase in the relative phosphorous X-ray signal and with an increase in PolyP levels in epithelia cell lysate. Transmission electron microscopy of chemically fixed or cryofixed and freeze substituted tissues confirmed a preferential localization of spherites around the goblet cell cavity. Taken together, these results suggest that spherites store high levels of PolyP that are modulated during metal uptake and detoxification. The similarity between PolyP granules and spherites herein described also suggest that PolyP is one of the main phosphorous source of spherites found in different biological models. This suggests physiological roles played by spherites in the midgut of arthropods and mechanisms involved in heavy metal resistance among different insect genera.

Mechanism and function of Drosophila capa GPCR: a desiccation stress-responsive receptor with functional homology to human neuromedinU receptor

The capa peptide receptor, capaR (CG14575), is a G-protein coupled receptor (GPCR) for the D. melanogaster capa neuropeptides, Drm-capa-1 and -2 (capa-1 and -2). To date, the capa peptide family constitutes the only known nitridergic peptides in insects, so the mechanisms and physiological function of ligand-receptor signalling of this peptide family are of interest. Capa peptide induces calcium signaling via capaR with EC₅₀ values for capa-1 = 3.06 nM and capa-2 = 4.32 nM. capaR undergoes rapid desensitization, with internalization via a b-arrestin-2 mediated mechanism but is rapidly re-sensitized in the absence of capa-1. Drosophila capa peptides have a C-terminal -FPRXamide motif and insect-PRXamide peptides are evolutionarily related to vertebrate peptide neuromedinU (NMU). Potential agonist effects of human NMU-25 and the insect -PRLamides [Drosophila pyrokinins Drm-PK-1 (capa-3), Drm-PK-2 and hugin-gamma [hugg]] against capaR were investigated. NMU-25, but not hugg nor Drm-PK-2, increases intracellular calcium ([Ca²⁺]i) levels via capaR. In vivo, NMU-25 increases [Ca²⁺]i and fluid transport by the Drosophila Malpighian (renal) tubule. Ectopic expression of human NMU receptor 2 in tubules of transgenic flies results in increased [Ca²⁺]i and fluid transport. Finally, anti-porcine NMU-8 staining of larval CNS shows that the most highly immunoreactive cells are capa-producing neurons. These structural and functional data suggest that vertebrate NMU is a putative functional homolog of Drm-capa-1 and -2. capaR is almost exclusively expressed in tubule principal cells; cell-specific targeted capaR RNAi significantly reduces capa-1 stimulated [Ca²⁺]i and fluid transport. Adult capaR RNAi transgenic flies also display resistance to desiccation. Thus, capaR acts in the key fluid-transporting tissue to regulate responses to desiccation stress in the fly.

The genetics of calcium signaling in Drosophila melanogaster

BACKGROUND

Genetic screens for behavioral and physiological defects in Drosophila melanogaster, helped identify several components of calcium signaling of which some, like the Trps, were novel. For genes initially identified in vertebrates, reverse genetic methods have allowed functional studies at the cellular and systemic levels.

SCOPE OF REVIEW

The aim of this review is to explain how various genetic methods available in Drosophila have been used to place different arms of Ca2+ signaling in the context of organismal development, physiology and behavior.

MAJOR CONCLUSION

Mutants generated in genes encoding a range of Ca2+ transport systems, binding proteins and enzymes affect multiple aspects of neuronal and muscle physiology. Some also affect the maintenance of ionic balance and excretion from malpighian tubules and innate immune responses in macrophages. Aspects of neuronal physiology affected include synaptic growth and plasticity, sensory transduction, flight circuit development and function. Genetic interaction screens have shown that mechanisms of maintaining Ca2+ homeostasis in Drosophila are cell specific and require a synergistic interplay between different intracellular and plasma membrane Ca2+ signaling molecules.

GENERAL SIGNIFICANCE

Insights gained through genetic studies of conserved Ca2+ signaling pathways have helped understand multiple aspects of fly physiology. The similarities between mutant phenotypes of Ca2+ signaling genes in Drosophila with certain human disease conditions, especially where homologous genes are causative factors, are likely to aid in the discovery of underlying disease mechanisms and help develop novel therapeutic strategies. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signalling.

The Ca2+ pumps of the endoplasmic reticulum and Golgi apparatus

The various splice variants of the three SERCA- and the two SPCA-pump genes in higher vertebrates encode P-type ATPases of the P(2A) group found respectively in the membranes of the endoplasmic reticulum and the secretory pathway. Of these, SERCA2b and SPCA1a represent the housekeeping isoforms. The SERCA2b form is characterized by a luminal carboxy terminus imposing a higher affinity for cytosolic Ca(2+) compared to the other SERCAs. This is mediated by intramembrane and luminal interactions of this extension with the pump. Other known affinity modulators like phospholamban and sarcolipin decrease the affinity for Ca(2+). The number of proteins reported to interact with SERCA is rapidly growing. Here, we limit the discussion to those for which the interaction site with the ATPase is specified: HAX-1, calumenin, histidine-rich Ca(2+)-binding protein, and indirectly calreticulin, calnexin, and ERp57. The role of the phylogenetically older and structurally simpler SPCAs as transporters of Ca(2+), but also of Mn(2+), is also addressed.

The role of the Golgi apparatus in oxidative stress: is this organelle less significant than mitochondria?

Reactive oxygen species (ROS)/reactive nitrogen species (RNS) and ROS/RNS-mediated oxidative stress have well-established roles in many physiological and pathological processes and are associated with the pathogenesis of many diseases, such as hypertension, ischemia/reperfusion injury, diabetes mellitus, atherosclerosis, stroke, cancer, and neurodegenerative disorders. It is generally accepted that mitochondria play an essential role in oxidative stress because they are responsible for the primary generation of superoxide radicals. Little attention, however, has been paid to the importance of the Golgi apparatus (GA) in this process. The GA is a pivotal organelle in cell metabolism and participates in modifying, sorting, and packaging macromolecules for cell secretion or use within the cell. It is inevitably involved in the process of oxidative stress, which can cause modification and damage of lipids, proteins, DNA, and other structural constituents. Here we discuss the connections between the GA and oxidative stress and highlight the role of the GA in oxidative stress-related Ca(2+)/Mn(2+) homeostasis, cell apoptosis, sphingolipid metabolism, signal transduction, and antioxidation. We also provide a novel perspective on the subcellular significance of oxidative stress and its pathological implications and present "GA stress" as a new concept to explain the GA-specific stress response.

Drosophila provides rapid modeling of renal development, function, and disease

The evolution of specialized excretory cells is a cornerstone of the metazoan radiation, and the basic tasks performed by Drosophila and human renal systems are similar. The development of the Drosophila renal (Malpighian) tubule is a classic example of branched tubular morphogenesis, allowing study of mesenchymal-to-epithelial transitions, stem cell-mediated regeneration, and the evolution of a glomerular kidney. Tubule function employs conserved transport proteins, such as the Na(+), K(+)-ATPase and V-ATPase, aquaporins, inward rectifier K(+) channels, and organic solute transporters, regulated by cAMP, cGMP, nitric oxide, and calcium. In addition to generation and selective reabsorption of primary urine, the tubule plays roles in metabolism and excretion of xenobiotics, and in innate immunity. The gene expression resource FlyAtlas.org shows that the tubule is an ideal tissue for the modeling of renal diseases, such as nephrolithiasis and Bartter syndrome, or for inborn errors of metabolism. Studies are assisted by uniquely powerful genetic and transgenic resources, the widespread availability of mutant stocks, and low-cost, rapid deployment of new transgenics to allow manipulation of renal function in an organotypic context.

Cell-specific inositol 1,4,5 trisphosphate 3-kinase mediates epithelial cell apoptosis in response to oxidative stress in Drosophila

Organismal stress responses to oxidative stress are relevant to ageing and disease and involve key cell-/tissue-specific signal transduction mechanisms. Using Drosophila, an established in vivo model for stress studies, we show that cell-specific inositol phosphate signalling specifically via inositol 1,4,5 trisphosphate 3-kinase (InsP(3) 3-K, IP(3)K), negatively regulates organismal responses to oxidative stress. We demonstrate that the Drosophila Malpighian tubule (equivalent to vertebrate kidney and liver) is a key epithelial sensor for organismal oxidative stress responses: precise targeting of either gain-of-function constructs of Drosophila IP(3)Ks (IP(3)K-1 and IP(3)K-2), or loss-of-function (RNAi) constructs to only one cell type in tubule reversibly modulates survival of stress-challenged adult flies. In vivo, targeted IP(3)K-1 directly increases H(2)O(2) production, pro-apoptotic caspase-9 activity and mitochondrial membrane potential. The mitochondrial calcium load in tubule principal cells-assessed by luminescent and fluorescent genetically-encoded mitochondrial calcium reporters-is significantly increased by IP(3)K-1 under oxidative stress conditions, leading to apoptosis. The Drosophila orthologues of human apoptotic bcl-2 genes include debcl and buffy. Oxidative stress challenge does not modulate gene expression of either debcl or buffy in tubules; and altered debcl expression does not influence survival rates under oxidative stress challenge. Finally, targeted over-expression of either debcl or buffy to tubule principal cells does not impact on tubule caspase-9 activity. Thus, IP(3)K-1 modulates epithelial cell apoptosis without involvement of bcl-2-type proteins.

Mislocalization of mitochondria and compromised renal function and oxidative stress resistance in Drosophila SesB mutants

Mitochondria accumulate at sites of intense metabolic activity within cells, but the adaptive value of this placement is not clear. In Drosophila, sesB encodes the ubiquitous isoform of adenine nucleotide translocase (ANT, the mitochondrial inner membrane ATP/ADP exchanger); null alleles are lethal, whereas hypomorphic alleles display sensitivity to a range of stressors. In the adult renal tubule, which is densely packed with mitochondria and hence enriched for sesB, both hypomorphic alleles and RNA interference knockdowns cause the mitochondria to lose their highly polarized distribution in the tissue and to become rounded. Basal cytoplasmic and mitochondrial calcium levels are both increased, and neuropeptide calcium response compromised, with concomitant defects in fluid secretion. The remaining mitochondria in sesB mutants are overactive and maintain depleted cellular ATP levels while generating higher levels of hydrogen peroxide than normal. When sesB expression is knocked down in just tubule principal cells, the survival of the whole organism upon oxidative stress is reduced, implying a limiting role for the tubule in homeostatic response to stressors. The physiological impacts of defective ANT expression are thus widespread and diverse.

Organellar calcium signalling mechanisms in Drosophilaepithelial function

Calcium signalling and calcium homeostasis are essential for life. Studies of calcium signalling thus constitute a major proportion of research in the life sciences, although the majority of these studies are based in cell lines or isolated cells. Epithelial cells and tissues are essential in the regulation of critical physiological processes, including fluid transport; and so the modulation of such processes in vivo by cell-specific calcium signalling is thus of interest. In this review, we describe the approaches to measuring intracellular calcium in the genetically tractable fluid-transporting tissue, the Drosophila Malpighian tubule by targeting cell-specific protein-based calcium reporters to defined regions,cells and intracellular compartments of the intact Malpighian tubule. We also discuss recent findings on the roles of plasma membrane and intracellular calcium channels; and on organellar stores – including mitochondria,Golgi and peroxisomes – in Malpighian tubule function.

Golgi apparatus and neurodegenerative diseases

Neurodegenerative disorders are typically characterized by progressive and extensive neuronal loss in specific populations of neurons and brain areas which lead to the observed clinical manifestations. Despite the recent advances in molecular neuroscience, the subcellular bases such as Golgi apparatus (GA) for most neurodegenerative diseases are poorly understood. This review gives a brief overview of the contribution of the neuronal GA in the pathogeneses of neurodegeneration, summarizes what is known of the GA machinery in these diseases, and present the relationship between GA fragmentation and the aggregation and accumulation of misfolded or aberrant proteins including mutant SOD1, a-synuclein, tau, which is considered to be a key event in the pathogenic process, and perturbating in calcium homeostasis, regulation of hormones, lipid metabolism are also linkage to the function of the GA thought to underlie neurodegeneration. Although these precise diseases mechanisms remain to be clarified, more research is needed to better understand how GA function for it and to enable physicians to use this knowledge for the benefit of the patients.

Peroxisomes as novel players in cell calcium homeostasis

Ca2+ concentration in peroxisomal matrix ([Ca2+](perox)) has been monitored dynamically in mammalian cells expressing variants of Ca2+-sensitive aequorin specifically targeted to peroxisomes. Upon stimulation with agonists that induce Ca2+ release from intracellular stores, peroxisomes transiently take up Ca2+ reaching peak values in the lumen as high as 50-100 microm, depending on cell types. Also in resting cells, peroxisomes sustain a Ca2+ gradient, [Ca2+](perox) being approximately 20-fold higher than [Ca2+] in the cytosol ([Ca2+](cyt)). The properties of Ca2+ traffic across the peroxisomal membrane are different from those reported for other subcellular organelles. The sensitivity of peroxisomal Ca2+ uptake to agents dissipating H+ and Na+ gradients unravels the existence of a complex bioenergetic framework including V-ATPase, Ca2+/H+, and Ca2+/Na+ activities whose components are yet to be identified at a molecular level. The different [Ca2+](perox) of resting and stimulated cells suggest that Ca2+ could play an important role in the regulation of peroxisomal metabolism.

The GAL4 system : a versatile system for the expression of genes

Over the past decade the adoption and refinement of the GAL4 system by the Drosophila field has resulted in a wide array of tools with which the researcher can drive transgene expression in a precise spatiotemporal pattern. The GAL4 system relies on two components: (1) GAL4, a transcriptional activator from yeast, which is expressed in a tissue-specific manner and (2) a transgene under the control of the upstream activation sequence that is bound by GAL4 (UASG). The two components are brought together in a simple genetic cross. In the progeny of the cross, the transgene is only transcribed in those cells or tissues expressing the GAL4 protein. Recent modifications of the GAL4 system have improved the control of both the initiation and the spatial restriction of transgene expression. Here we describe the GAL4 system highlighting the properties that make it a powerful tool for the analysis of gene function in Drosophila and higher organisms.

Calcium in the Golgi apparatus

The secretory-pathway Ca2+-ATPases (SPCAs) represent a recently recognized family of phosphorylation-type ATPases that supply the lumen of the Golgi apparatus with Ca2+ and Mn2+ needed for the normal functioning of this structure. Mutations of the human SPCA1 gene (ATP2C1) cause Hailey-Hailey disease, an autosomal dominant skin disorder in which keratinocytes in the suprabasal layer of the epidermis detach. We will first review the physiology of the SPCAs and then discuss how mutated SPCA1 proteins can lead to an epidermal disorder.

Metabolite transport across the peroxisomal membrane

In recent years, much progress has been made with respect to the unravelling of the functions of peroxisomes in metabolism, and it is now well established that peroxisomes are indispensable organelles, especially in higher eukaryotes. Peroxisomes catalyse a number of essential metabolic functions including fatty acid beta-oxidation, ether phospholipid biosynthesis, fatty acid alpha-oxidation and glyoxylate detoxification. The involvement of peroxisomes in these metabolic pathways necessitates the transport of metabolites in and out of peroxisomes. Recently, considerable progress has been made in the characterization of metabolite transport across the peroxisomal membrane. Peroxisomes posses several specialized transport systems to transport metabolites. This is exemplified by the identification of a specific transporter for adenine nucleotides and several half-ABC (ATP-binding cassette) transporters which may be present as hetero- and homo-dimers. The nature of the substrates handled by the different ABC transporters is less clear. In this review we will describe the current state of knowledge of the permeability properties of the peroxisomal membrane.

Diseases involving the Golgi calcium pump

Secretory-pathway Ca2(+)-transport ATPases (SPCA) provide the Golgi apparatus with Ca2+ and Mn2+ needed for the normal functioning of this organelle. Loss of one functional copy of the human SPCA1 gene (ATP2C1) causes Hailey-Hailey disease, a rare skin disorder characterized by recurrent blisters and erosions in the flexural areas. Here, we will review the properties and functional role of the SPCAs. The relationship between Hailey-Hailey disease and its defective gene (ATP2C1) will be adressed as well.

The ins and outs of peroxisomes: Co-ordination of membrane transport and peroxisomal metabolism

Peroxisomes perform a range of metabolic functions which require the movement of substrates, co-substrates, cofactors and metabolites across the peroxisomal membrane. In this review, we discuss the evidence for and against specific transport systems involved in peroxisomal metabolism and how these operate to co-ordinate biochemical reactions within the peroxisome with those in other compartments of the cell.