Isolation and Characteristics of Extracellular Vesicles Produced by Probiotics: Yeast Saccharomyces boulardii CNCM I-745 and Bacterium Streptococcus salivarius K12

Numerous probiotic microorganisms have repeatedly been shown to produce nanometer-sized structures named extracellular vesicles (EVs). Recently, it has been suggested that similarly to whole microbial cells, EVs produced by probiotics may also demonstrate health benefits to the host, while their application does not involve the risk of infection caused by live microorganisms. In this work, we isolated EVs from two probiotic species originating from different taxonomic domains - yeast Saccharomyces boulardii CNCM I-745 and bacterium Streptococcus salivarius K12. The diameters of S. boulardii EVs were about 142 nm and for S. salivarius EVs about 123 nm. For S. boulardii EVs, 1641 proteins and for S. salivarius EVs, 466 proteins were identified with a liquid chromatography-coupled tandem mass spectrometry and then functionally classified. In both microbial species, metabolic proteins significantly contributed to the cargo of EVs comprising 25% and 26% of all identified vesicular proteins for fungi and bacteria, respectively. Moreover, enzymes associated with cell wall rearrangement, including enzymatically active glucanases, were also identified in EVs. Furthermore, probiotic EVs were shown to influence host cells and stimulate the production of IL-1β and IL-8 by the human monocytic cell line THP-1, and, at the same time, did not cause any remarkable reduction in the survival rate of Galleria mellonella larvae in this invertebrate model commonly used to evaluate microbial EV toxicity. These observations suggest that the EVs produced by the investigated probiotic microorganisms may be promising structures for future use in pro-health applications.

Evolutionary formation of melatonin and vitamin D in early life forms: insects take centre stage

Melatonin, a product of tryptophan metabolism via serotonin, is a molecule with an indole backbone that is widely produced by bacteria, unicellular eukaryotic organisms, plants, fungi and all animal taxa. Aside from its role in the regulation of circadian rhythms, it has diverse biological actions including regulation of cytoprotective responses and other functions crucial for survival across different species. The latter properties are also shared by its metabolites including kynuric products generated by reactive oxygen species or phototransfomation induced by ultraviolet radiation. Vitamins D and related photoproducts originate from phototransformation of ∆5,7 sterols, of which 7-dehydrocholesterol and ergosterol are examples. Their ∆5,7 bonds in the B ring absorb solar ultraviolet radiation [290-315 nm, ultraviolet B (UVB) radiation] resulting in B ring opening to produce previtamin D, also referred to as a secosteroid. Once formed, previtamin D can either undergo thermal-induced isomerization to vitamin D or absorb UVB radiation to be transformed into photoproducts including lumisterol and tachysterol. Vitamin D, as well as the previtamin D photoproducts lumisterol and tachysterol, are hydroxylated by cyochrome P450 (CYP) enzymes to produce biologically active hydroxyderivatives. The best known of these is 1,25-dihydroxyvitamin D (1,25(OH)2D) for which the major function in vertebrates is regulation of calcium and phosphorus metabolism. Herein we review data on melatonin production and metabolism and discuss their functions in insects. We discuss production of previtamin D and vitamin D, and their photoproducts in fungi, plants and insects, as well as mechanisms for their enzymatic activation and suggest possible biological functions for them in these groups of organisms. For the detection of these secosteroids and their precursors and photoderivatives, as well as melatonin metabolites, we focus on honey produced by bees and on body extracts of Drosophila melanogaster. Common biological functions for melatonin derivatives and secosteroids such as cytoprotective and photoprotective actions in insects are discussed. We provide hypotheses for the photoproduction of other secosteroids and of kynuric metabolites of melatonin, based on the known photobiology of ∆5,7 sterols and of the indole ring, respectively. We also offer possible mechanisms of actions for these unique molecules and summarise differences and similarities of melatoninergic and secosteroidogenic pathways in diverse organisms including insects.

Autophagy as a new player in the regulation of clock neurons physiology of Drosophila melanogaster

Axonal terminals of the small ventral lateral neurons (sLNvs), the circadian clock neurons of Drosophila, show daily changes in their arborization complexity, with many branches in the morning and their shrinkage during the night. This complex phenomenon is precisely regulated by several mechanisms. In the present study we describe that one of them is autophagy, a self-degradative process, also involved in changes of cell membrane size and shape. Our results showed that autophagosome formation and processing in PDF-expressing neurons (both sLNv and lLNv) are rhythmic and they have different patterns in the cell bodies and terminals. These rhythmic changes in the autophagy activity seem to be important for neuronal plasticity. We found that autophagosome cargos are different during the day and night, and more proteins involved in membrane remodeling are present in autophagosomes in the morning. In addition, we described for the first time that Atg8-positive vesicles are also present outside the sLNv terminals, which suggests that secretory autophagy might be involved in regulating the clock signaling network. Our data indicate that rhythmic autophagy in clock neurons affect the pacemaker function, through remodeling of terminal membrane and secretion of specific proteins from sLNvs.

Stress Conditions Affect the Immunomodulatory Potential of Candida albicans Extracellular Vesicles and Their Impact on Cytokine Release by THP-1 Human Macrophages

Human immune cells possess the ability to react complexly and effectively after contact with microbial virulence factors, including those transported in cell-derived structures of nanometer sizes termed extracellular vesicles (EVs). EVs are produced by organisms of all kingdoms, including fungi pathogenic to humans. In this work, the immunomodulatory properties of EVs produced under oxidative stress conditions or at host concentrations of CO2 by the fungal pathogen Candida albicans were investigated. The interaction of EVs with human pro-monocytes of the U-937 cell line was established, and the most notable effect was attributed to oxidative stress-related EVs. The immunomodulatory potential of tested EVs against human THP-1 macrophages was verified using cytotoxicity assay, ROS-production assay, and the measurement of cytokine production. All fungal EVs tested did not show a significant cytotoxic effect on THP-1 cells, although a slight pro-oxidative impact was indicated for EVs released by C. albicans cells grown under oxidative stress. Furthermore, for all tested types of EVs, the pro-inflammatory properties related to increased IL-8 and TNF-α production and decreased IL-10 secretion were demonstrated, with the most significant effect observed for EVs released under oxidative stress conditions.

Candida albicans Biofilm-Derived Extracellular Vesicles Are Involved in the Tolerance to Caspofungin, Biofilm Detachment, and Fungal Proteolytic Activity

It has been repeatedly reported that the cells of organisms in all kingdoms of life produce nanometer-sized lipid membrane-enveloped extracellular vesicles (EVs), transporting and protecting various substances of cellular origin. While the composition of EVs produced by human pathogenic fungi has been studied in recent decades, another important challenge is the analysis of their functionality. Thus far, fungal EVs have been shown to play significant roles in intercellular communication, biofilm production, and modulation of host immune cell responses. In this study, we verified the involvement of biofilm-derived EVs produced by two different strains of Candida albicans-C. albicans SC5314 and 3147 (ATCC 10231)-in various aspects of biofilm function by examining its thickness, stability, metabolic activity, and cell viability in the presence of EVs and the antifungal drug caspofungin. Furthermore, the proteolytic activity against the kininogen-derived antimicrobial peptide NAT26 was confirmed by HPLC analysis for C. albicans EVs that are known to carry, among others, particular members of the secreted aspartic proteinases (Saps) family. In conclusion, EVs derived from C. albicans biofilms were shown to be involved in biofilm tolerance to caspofungin, biofilm detachment, and fungal proteolytic activity.

Changes in heme oxygenase level during development affect the adult life of Drosophila melanogaster

Heme oxygenase (HO) has been shown to control various cellular processes in both mammals and Drosophila melanogaster. Here, we investigated how changes in HO levels in neurons and glial cells during development affect adult flies, by using the TARGET Drosophila system to manipulate the expression of the ho gene. The obtained data showed differences in adult survival, maximum lifespan, climbing, locomotor activity, and sleep, which depended on the level of HO (after ho up-regulation or downregulation), the timing of expression (chronic or at specific developmental stages), cell types (neurons or glia), sex (males or females), and age of flies. In addition to ho, the effects of changing the mRNA level of the Drosophila CNC factor gene (NRF2 homolog in mammals and master regulator of HO), were also examined to compare with those observed after changing ho expression. We showed that HO levels in neurons and glia must be maintained at an appropriate physiological level during development to ensure the well-being of adults. We also found that the downregulation of ho in either neurons or glia in the brain is compensated by ho expressed in the retina.

Cecropin D-derived synthetic peptides in the fight against Candida albicans cell filamentation and biofilm formation

The recent progressive increase in the incidence of invasive fungal infections, especially in immunocompromised patients, makes the search for new therapies crucial in the face of the growing drug resistance of prevalent nosocomial yeast strains. The latest research focuses on the active compounds of natural origin, inhibiting fungal growth, and preventing the formation of fungal biofilms. Antimicrobial peptides are currently the subject of numerous studies concerning effective antifungal therapy. In the present study, the antifungal properties of two synthetic peptides (ΔM3, ΔM4) derived from an insect antimicrobial peptide - cecropin D - were investigated. The fungicidal activity of both compounds was demonstrated against the yeast forms of Candida albicans, Candida tropicalis, and Candida parapsilosis, reaching a MFC_99.9 in the micromolar range, while Candida glabrata showed greater resistance to these peptides. The scanning electron microscopy revealed a destabilization of the yeast cell walls upon treatment with both peptides; however, their effectiveness was strongly modified by the presence of salt or plasma in the yeast environment. The transition of C. albicans cells from yeast to filamentous form, as well as the formation of biofilms, was effectively reduced by ΔM4. Mature biofilm viability was inhibited by a higher concentration of this peptide and was accompanied by increased ROS production, activation of the GPX3 and SOD5 genes, and finally, increased membrane permeability. Furthermore, both peptides showed a synergistic effect with caspofungin in inhibiting the metabolic activity of C. albicans cells, and an additive effect was also observed for the mixtures of peptides with amphotericin B. The results indicate the possible potential of the tested peptides in the prevention and treatment of candidiasis.

Light exposure during development affects physiology of adults in Drosophila melanogaster

Light is one of most important factors synchronizing organisms to day/night cycles in the environment. In Drosophila it is received through compound eyes, Hofbauer-Buchner eyelet, ocelli, using phospholipase C-dependent phototransduction and by deep brain photoreceptors, like Cryptochrome. Even a single light pulse during early life induces larval-time memory, which synchronizes the circadian clock and maintains daily rhythms in adult flies. In this study we investigated several processes in adult flies after maintaining their embryos, larvae and pupae in constant darkness (DD) until eclosion. We found that the lack of external light during development affects sleep time, by reduction of night sleep, and in effect shift to the daytime. However, disruption of internal CRY- dependent photoreception annuls this effect. We also observed changes in the expression of genes encoding neurotransmitters and their receptors between flies kept in different light regime. In addition, the lack of light during development results in decreasing size of mushroom bodies, involved in sleep regulation. Taking together, our results show that presence of light during early life plays a key role in brain development and affects adult behavior.

The Role of Glia Clocks in the Regulation of Sleep in Drosophila melanogaster

In Drosophila melanogaster, the pacemaker located in the brain plays the main role in maintaining circadian rhythms; however, peripheral oscillators including glial cells, are also crucial components of the circadian network. In the present study, we investigated an impact of oscillators located in astrocyte-like glia, the chiasm giant glia of the optic lobe, epithelial and subperineurial glia on sleep of Drosophila males. We described that oscillators located in astrocyte-like glia and chiasm giant glia are necessary to maintain daily changes in clock neurons arborizations, while those located in epithelial glia regulate amplitude of these changes. Finally, we showed that communication between glia and neurons through tripartite synapses formed by epithelial glia and, in effect, neurotransmission regulation plays important role in wake-promoting during the day.SIGNIFICANCE STATEMENT Circadian clock or pacemaker regulates many aspects of animals' physiology and behavior. The pacemaker is located in the brain and is composed of neurons. However, there are also additional oscillators, called peripheral clocks, which synchronize the main clock. Despite the critical role of glia in the clock machinery, little is known which type of glia houses peripheral oscillators and how they affect neuronal clocks. This study using Drosophila shows that oscillators in specific glia types maintain awakeness during the day by regulating the daily plasticity of clock neurons.

Insight Into the Properties and Immunoregulatory Effect of Extracellular Vesicles Produced by Candida glabrata, Candida parapsilosis, and Candida tropicalis Biofilms

Currently, non-albicans Candida species, including C. tropicalis, C. glabrata, and C. parapsilosis, are becoming an increasing epidemiological threat, predominantly due to the distinct collection of virulence mechanisms, as well as emerging resistance to antifungal drugs typically used in the treatment of candidiasis. They can produce biofilms that release extracellular vesicles (EVs), which are nanometric spherical structures surrounded by a lipid bilayer, transporting diversified biologically active cargo, that may be involved in intercellular communication, biofilm matrix production, and interaction with the host. In this work, we characterize the size and protein composition of these structures for three species of non-albicans Candida fungi forming biofilm, indicating considerable heterogeneity of the investigated population of fungal EVs. Examination of the influence of EVs on cytokine production by the human monocytic cell line THP-1 differentiated into macrophage-like cells revealed that the tested vesicles have a stimulating effect on the secretion of tumor necrosis factor α and interleukin 8, while they reduce the production of interleukin 10. This may indicate the proinflammatory nature of the effect of EVs produced by these species on the host immune cells. Moreover, it has been indicated that vesicles may be involved in C. tropicalis biofilm resistance to fluconazole and caspofungin. This reveals the important role of EVs not only in the physiology of C. tropicalis, C. glabrata, and C. parapsilosis fungi but also in the pathogenesis of infections associated with the production of fungal biofilm.

Glia-Neurons Cross-Talk Regulated Through Autophagy

Autophagy is a self-degradative process which plays a role in removing misfolded or aggregated proteins, clearing damaged organelles, but also in changes of cell membrane size and shape. The aim of this phenomenon is to deliver cytoplasmic cargo to the lysosome through the intermediary of a double membrane-bound vesicle (autophagosome), that fuses with a lysosome to form autolysosome, where cargo is degraded by proteases. Products of degradation are transported back to the cytoplasm, where they can be re-used. In the present study we showed that autophagy is important for proper functioning of the glia and that it is involved in the regulation of circadian structural changes in processes of the pacemaker neurons. This effect is mainly observed in astrocyte-like glia, which play a role of peripheral circadian oscillators in the Drosophila brain.

Secretory Leukocyte Protease Inhibitor Is Present in Circulating and Tissue-Recruited Human Eosinophils and Regulates Their Migratory Function

Eosinophils and secretory leukocyte protease inhibitor (SLPI) are both associated with Th2 immune responses and allergic diseases, but whether the fact that they are both implicated in these conditions is pathophysiologically related remains unknown. Here we demonstrate that human eosinophils derived from normal individuals are one of the major sources of SLPI among circulating leukocytes. SLPI was found to be stored in the crystalline core of eosinophil granules, and its dislocation/rearrangement in the crystalline core likely resulted in changes in immunostaining for SLPI in these cells. High levels of SLPI were also detected in blood eosinophils from patients with allergy-associated diseases marked by eosinophilia. These include individuals with eosinophilic granulomatosis with polyangiitis (EGPA) and atopic dermatitis (AD), who were also found to have elevated SLPI levels in their plasma. In addition to the circulating eosinophils, diseased skin of AD patients also contained SLPI-positive eosinophils. Exogenous, recombinant SLPI increased numbers of migratory eosinophils and supported their chemotactic response to CCL11, one of the key chemokines that regulate eosinophil migratory cues. Together, these findings suggest a role for SLPI in controlling Th2 pathophysiologic processes via its impact on and/or from eosinophils.

Characterization of age-dependent decline in spontaneous running performance in the heart failure Tgαq*44 mice

In this study we characterize the impact of aging on the spontaneous running performance of the Tgα_q*44 mice (transgenic murine model of chronic heart failure) as compared to the wild-type FVB mice. In 166 mice we have recorded the following parameters of their physical activities in the running wheels: the total distance covered during the experiment (D_sum), the maximal distance covered in single-effort (D_max), mean time spent on running per 24 h (T_mean), mean running speed (ν_mean), the maximum instantaneous speed of run (ν_max) and the number of efforts (i.e. the number of running events undertaken by the mice) during 54 days, in four age groups ~4, ~10, ~12 and ≥12.5 months of age. The level of spontaneous running performance of the FVB mice remained essentially unchanged, but a strong impact of aging in the Tgα_q*44 mice on their running performance was found. Namely, the D_sum, D_max, T_mean and ν_mean in the Tgα_q*44 mice at the age of ≥12.5 months decreased by ~50%, when compared to its level corresponding level at the age of ~4 months, with far lesser effect of aging on their V_max. Surprisingly, the number of attempts to perform running by the Tgαq*44 mice at the age of 4 - 12 months remained essentially unchanged. This suggests that the exercise intolerance of the aging heart failure (HF) mice seems to be more dependent on deterioration of heart and muscles function linked to HF than on a possible ageing-related impairment of the 'willngness' to initiate running, generated by the central nervous system.

Expression of antimicrobial peptide genes oscillates along day/night rhythm protecting mice skin from bacteria

Antimicrobial peptides (AMPs) are important components of the innate immune system and are involved in skin protection against environmental insults and in wound healing. Herein, we assessed the gene expression of chemerin (Rarres2), cathelicidin CRAMP (Camp), and three β-defensins (Defb1, Defb3, and Defb14) in mouse skin during light/dark cycle (LD 12:12) and constant darkness (DD). Next, we examined the survival of bacteria applied on the skin at specific times during the day. We found that the expression of Rarres2, Camp, and Defb1 was the highest at 4 h after the beginning of darkness, during high activity of mice. These rhythms, however, were not maintained under DD in the skin but were present in the liver. This indicated that in the case of skin, a circadian input was masked by daily changes of light in the environment. In contrast, Defb3 and Defb14 showed the highest mRNA levels when the mice slept, and these rhythmic mRNA oscillations were maintained under DD. This shows that Rarres2, Camp, and Defb1 levels in the skin are correlated with high locomotor activity in mice and they are controlled by daily changes of light and dark. Alternatively, oscillations in the mRNA levels of Defb3 and Defb14 seem to protect skin and heal wounds during sleep. These rhythms are maintained under DD, indicating that they are regulated by a circadian clock. Our study suggests that daily AMP expression affects the survival of bacteria on the surface of skin, which depends on the phase of AMP cycling.

Circadian Changes of Dendritic Spine Geometry in Mouse Barrel Cortex

The circadian rhythmicity changes the density and shape of dendritic spines in mouse somatosensory barrel cortex, influencing their stability and maturation. In this study, we analyzed the main geometric parameters of dendritic spines reflecting the strength of synapses located on these spines under light/dark (12:12) and constant darkness conditions, in order to distinguish between endogenously regulated and light-driven parameters. Using morphological analysis of serial electron micrographs, as well as three-dimensional reconstructions, we found that the light induces elongation of single-synapse spine necks and increases in the diameter of double-synapse spine necks, increasing and decreasing the isolation of synapses from the parent dendrite, respectively. During the subjective night of constant darkness, we observed an enlargement of postsynaptic density area in inhibitory synapses and an increase in the number of polyribosomes inside double-synapse spines. The results show that both endogenous effect (circadian clock/locomotor activity) and light affect the morphological parameters of single- and double-synapse spines in the somatosensory cortex: light reduces the efficiency of excitatory synapses on single-synapse spines, increases the effect of synaptic transmission in double-synapse spines, and additionally masks the endogenous clock-driven enlargement of inhibitory synapses located on double-synapse spines. This indicates a special role of double-synapse spines and their inhibitory synapses in the regulation of synaptic transmission during both circadian and diurnal cycles in the mouse somatosensory cortex.

Bacteria Modify Their Sensitivity to Chemerin-Derived Peptides by Hindering Peptide Association With the Cell Surface and Peptide Oxidation

Chronic inflammatory skin diseases like psoriasis alter the local skin microbiome and lead to complications such as persistent infection with opportunistic/pathogenic bacteria. Disease-associated changes in microbiota may be due to downregulation of epidermal antimicrobial proteins/peptides, such as antimicrobial protein chemerin. Here, we show that chemerin and its bioactive derivatives have differential effects on the viability of different genera of cutaneous bacteria. The lethal effects of chemerin are enhanced by bacterial-derived ROS-induced chemerin peptide oxidation and suppressed by stationary phase sigma factor RpoS. Insight into the mechanisms underlying changes in the composition of cutaneous bacteria during autoreactive skin disease may provide novel ways to mobilize chemerin and its peptide derivatives for maximum antimicrobial efficacy.

Characteristics of Extracellular Vesicles Released by the Pathogenic Yeast-Like Fungi Candida glabrata, Candida parapsilosis and Candida tropicalis

Candida spp. yeast-like fungi are opportunistic pathogens in humans and have been recently found to release extracellular vesicles (EVs) that are involved in many vital biological processes in fungal cells. These include communication between microorganisms and host–pathogen interactions during infection. The production of EVs and their content have been significantly characterized in the most common candidal species Candida albicans, including the identification of numerous virulence factors and cytoplasmic proteins in the EV cargo. We have here conducted the isolation and proteomic characterization of EVs produced by the clinically important non-albicans Candida species C. glabrata, C. tropicalis and C. parapsilosis. With the use of ultracentrifugation of the cell-free culture supernatant, the candidal EVs were collected and found to be a heterogeneous population of particles for each species with sizes ranging from 60–280 nm. The proteinaceous contents of these vesicles were analyzed using LC-MS/MS, with particular attention paid to surface-expressed proteins that would come into immediate and direct contact with host cells. We thereby identified 42 extracellular and surface-connected proteins from C. glabrata, 33 from C. parapsilosis, and 34 from C. tropicalis, including membrane-associated transporters, glycoproteins and enzymes involved in the organization of the fungal cell wall, as well as several cytoplasmic proteins, including alcohol dehydrogenase, enolase, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase and pyruvate kinase, for which the vesicular transport is a possible mechanism underlying their non-classical secretion.

Circadian clock regulates the shape and content of dendritic spines in mouse barrel cortex

Circadian rhythmicity affects neuronal activity induced changes in the density of synaptic contacts and dendritic spines, the most common location of synapses, in mouse somatosensory cortex. In the present study we analyzed morphology of single- and double-synapse spines under light/dark (12:12) and constant darkness conditions. Using serial electron micrographs we examined the shape of spines (stubby, thin, mushroom) and their content (smooth endoplasmic reticulum, spine apparatus), because these features are related to the maturation and stabilization of spines. We observed significant diurnal and circadian changes in the shape of spines that are differentially regulated: single-synapse spines remain under circadian clock regulation, while changes of double-synapse spines are driven by light. The thin and mushroom single-synapse spines, regardless of their content, are more stable comparing with the stubby single-synapse spines that show the greatest diversity. All types of double-synapse spines demonstrate a similar level of stability. In light/dark regime, formation of new mushroom single-synapse spines occurs, while under constant darkness new stubby single-synapse spines are formed. There are no shape preferences for new double-synapse spines. Diurnal and circadian alterations also concern spine content: both light exposure and the clock influence translocation of smooth endoplasmic reticulum from dendritic shaft to the spine. The increasing number of mushroom single-synapse spines and the presence of only those mushroom double-synapse spines that contain spine apparatus in the light phase indicates that the exposure to light, a stress factor for nocturnal animals, promotes enlargement and maturation of spines to increase synaptic strength and to enhance the effectiveness of neurotransmission.

Overexpression of Mitochondrial Ligases Reverses Rotenone-Induced Effects in a Drosophila Model of Parkinson's Disease

Mul1 and Park are two major mitochondrial ligases responsible for mitophagy. Damaged mitochondria that cannot be removed are a source of an increased level of free radicals, which in turn can destructively affect other cell organelles as well as entire cells. One of the toxins that damages mitochondria is rotenone, a neurotoxin that after exposure displays symptoms typical of Parkinson’s disease. In the present study, we showed that overexpressing genes encoding mitochondrial ligases protects neurons during treatment with rotenone. Drosophila strains with overexpressed mul1 or park show a significantly reduced degeneration of dopaminergic neurons, as well as normal motor activity during exposure to rotenone. In the nervous system, rotenone affected synaptic proteins, including Synapsin, Synaptotagmin and Disk Large1, as well as the structure of synaptic vesicles, while high levels of Mul1 or Park suppressed degenerative events at synapses. We concluded that increased levels of mitochondrial ligases are neuroprotective and could be considered in developing new therapies for Parkinson’s disease.

The antimicrobial activity of chemerin-derived peptide p4 requires oxidative conditions

Chemerin is a leukocyte attractant, adipokine, and antimicrobial protein abundantly produced in the skin epidermis. Despite the fact that most of the bactericidal activity present in human skin exudates is chemerin-dependent, just how chemerin shapes skin defenses remains obscure. Here we demonstrate that p4, a potent antimicrobial human chemerin peptide derivative, displays killing activity against pathogenic methicillin-resistant Staphylococcus aureus strains and suppresses microbial growth in a topical skin infection model. Mechanistically, we show that p4 homodimerization is required for maximal bactericidal activity and that an oxidative environment, such as at the skin surface, facilitates p4 disulfide bridge formation, required for the dimerization. p4 led to rapid damage of the bacterial internal membrane and inhibited the interaction between the membranous cytochrome bc ₁ complex and its redox partner, cytochrome c These results suggest that a chemerin p4-based defense strategy combats bacterial challenges at the skin surface.

Role of Nrf2/HO-1 system in development, oxidative stress response and diseases: an evolutionarily conserved mechanism

The multifunctional regulator nuclear factor erythroid 2-related factor (Nrf2) is considered not only as a cytoprotective factor regulating the expression of genes coding for anti-oxidant, anti-inflammatory and detoxifying proteins, but it is also a powerful modulator of species longevity. The vertebrate Nrf2 belongs to Cap 'n' Collar (Cnc) bZIP family of transcription factors and shares a high homology with SKN-1 from Caenorhabditis elegans or CncC found in Drosophila melanogaster. The major characteristics of Nrf2 are to some extent mimicked by Nrf2-dependent genes and their proteins including heme oxygenase-1 (HO-1), which besides removing toxic heme, produces biliverdin, iron ions and carbon monoxide. HO-1 and their products exert beneficial effects through the protection against oxidative injury, regulation of apoptosis, modulation of inflammation as well as contribution to angiogenesis. On the other hand, the disturbances in the proper HO-1 level are associated with the pathogenesis of some age-dependent disorders, including neurodegeneration, cancer or macular degeneration. This review summarizes our knowledge about Nrf2 and HO-1 across different phyla suggesting their conservative role as stress-protective and anti-aging factors.

Circadian rhythmicity of synapses in mouse somatosensory cortex

The circadian rhythmicity displayed by motor behavior of mice: activity at night and rest during the day; and the associated changes in the sensory input are reflected by cyclic synaptic plasticity in the whisker representations located in the somatosensory (barrel) cortex. It was not clear whether diurnal rhythmic changes in synapse density previously observed in the barrel cortex resulted from changes in the activity of the animals, from daily light/dark (LD) rhythm or are driven by an endogenous clock. These changes were investigated in the barrel cortex of C57BL/6 mouse strain kept under LD 12 : 12 h conditions and in constant darkness (DD). Stereological analysis of serial electron microscopic sections was used to assess numerical density of synapses. In mice kept under LD conditions, the total density of synapses and the density of excitatory synapses located on dendritic spines was higher during the light period (rest phase). In contrast, the density of inhibitory synapses located on dendritic spines increased during the dark period (activity phase). Under DD conditions, the upregulation of the inhibitory synapses during the activity phase was retained, but the cyclic changes in the density of excitatory synapses were not observed. The results show that the circadian plasticity concerns only synapses located on spines (and not those on dendritic shafts), and that excitatory and inhibitory synapses are differently regulated during the 24 h cycle: the excitatory synapses are influenced by light, whilst the inhibitory synapses are driven by the endogenous circadian clock.

Clock and clock-controlled genes are differently expressed in the retina, lamina and in selected cells of the visual system of Drosophila melanogaster

The retina and the first optic neuropil (lamina) of Drosophila show circadian rhythms in various processes. To learn about the regulation of circadian rhythms in the retina and lamina and in two cell types, glial and the lamina L2 interneurons, we examined expression of the following clock genes; per, tim, clk, and cry and clock-controlled genes (ccgs); Atpα, nrv2, brp, Pdfr. We found that the expression of gene studied is specific for the retina and lamina. The rhythms of per and tim expression in the retina and glial cells are similar to that observed in the whole head and in clock neurons, while they differ in the lamina and L2 cells. In both the retina and lamina, CRY seems to be a repressor of clk expression. In L2 interneurons per expression is not cyclic indicating the other function of PER in those cells than in the circadian molecular clock. In contrast to per and tim, the pattern of clk and cry expression is similar in both the retina and lamina. The retina holds the autonomous oscillators but the expression of cry and ccgs, Atpα and nrv2, is also regulated by inputs from the pacemaker transmitted by PDF and ITP neuropeptides.

Daily rhythm of synapse turnover in mouse somatosensory cortex

The whisker representations in the somatosensory barrel cortex of mice are modulated by sensory inputs associated with animal motor behavior which shows circadian rhythmicity. In a C57/BL mouse strain kept under a light/dark (LD 12:12) regime, we observed daily structural changes in the barrel cortex, correlated with the locomotor activity level. Stereological analysis of serial electron microscopic sections of the barrel cortex of mice sacrificed during their active or rest period, revealed an increase in the total numerical density of synapses and in the density of excitatory synapses located on dendritic spines during the rest, as well as an increase in the density of inhibitory synapses located on double-synapse spines during the active period. This is the first report demonstrating a daily rhythm in remodeling of the mammalian somatosensory cortex, manifested by changes in the density of synapses and dendritic spines. Moreover, we have found that the excitatory and inhibitory synapses are differently regulated during the day/night cycle.

Effects triggered by platinum nanoparticles on primary keratinocytes

The platinum (Pt)-group elements (PGEs) represent a new kind of environmental pollutant and a new hazard for human health. Since their introduction as vehicle-exhaust catalysts, their emissions into the environment have grown considerably compared with their low natural concentration in the earth crust. PGE emissions from vehicle catalysts can be also in the form of nanometer-sized particles (Pt nanoparticles [PtNPs]). These elements, both in their metallic form or as ions solubilized in biological media, are now recognized as potent allergens and sensitizers. Human skin is always exposed to toxic particles; therefore, in the present study we addressed the question of whether polyvinylpyrrolidone-coated PtNPs may have any negative effects on skin cells, including predominantly epidermal keratinocytes. In this study, PtNPs of two sizes were used: 5.8 nm and 57 nm, in concentrations of 6.25, 12.5, and 25 μg/mL. Both types of NPs were protected with polyvinylpyrrolidone. Primary keratinocytes were treated for 24 and 48 hours, then cytotoxicity, genotoxicity, morphology, metabolic activity, and changes in the activation of signaling pathways were investigated in PtNP-treated cells. We found that PtNPs trigger toxic effects on primary keratinocytes, decreasing cell metabolism, but these changes have no effects on cell viability or migration. Moreover, smaller NPs exhibited more deleterious effect on DNA stability than the big ones. Analyzing activation of caspases, we found changes in activity of caspase 9 and caspase 3/7 triggered mainly by smaller NPs. Changes were not so significant in the case of larger nanoparticles. Importantly, we found that PtNPs have antibacterial properties, as is the case with silver NPs (AgNPs). In comparison to our previous study regarding the effects of AgNPs on cell biology, we found that PtNPs do not exhibit such deleterious effects on primary keratinocytes as AgNPs and that they also can be used as potential antibacterial agents, especially in the treatment of Escherichia coli, representing a group of Gram-negative species.

Circadian regulation of the Na+/K+-ATPase alpha subunit in the visual system is mediated by the pacemaker and by retina photoreceptors in Drosophila melanogaster

We investigated the diurnal oscillation in abundance of the catalytic α subunit of the sodium/potassium pump (ATPα) in the brain of Drosophila melanogaster. This rhythm is bimodal and is particularly robust in the glia cells of the lamina, the first optic neuropil. We observed loss of ATPα cycling in lamina glia in behaviourally arrhythmic per⁰¹ and tim⁰¹ mutants and in flies overexpressing the pro-apoptotic gene hid in the PDF-positive clock neurons. Moreover, the rhythm of ATPα abundance was altered in cry⁰¹ and Pdf⁰ mutants, in flies with a weakened clock mechanism in retina photoreceptor cells and in those subject to downregulation of the neuropeptide ITP by RNAi. This complex, rhythmic regulation of the α subunit suggests that the sodium/potassium pump may be a key target of the circadian pacemaker to impose daily control on brain activities, such as rhythmic changes in neuronal plasticity, which are best observed in the visual system.

Fear learning increases the number of polyribosomes associated with excitatory and inhibitory synapses in the barrel cortex

Associative fear learning, resulting from whisker stimulation paired with application of a mild electric shock to the tail in a classical conditioning paradigm, changes the motor behavior of mice and modifies the cortical functional representation of sensory receptors involved in the conditioning. It also induces the formation of new inhibitory synapses on double-synapse spines of the cognate barrel hollows. We studied density and distribution of polyribosomes, the putative structural markers of enhanced synaptic activation, following conditioning. By analyzing serial sections of the barrel cortex by electron microscopy and stereology, we found that the density of polyribosomes was significantly increased in dendrites of the barrel activated during conditioning. The results revealed fear learning-induced increase in the density of polyribosomes associated with both excitatory and inhibitory synapses located on dendritic spines (in both single- and double-synapse spines) and only with the inhibitory synapses located on dendritic shafts. This effect was accompanied by a significant increase in the postsynaptic density area of the excitatory synapses on single-synapse spines and of the inhibitory synapses on double-synapse spines containing polyribosomes. The present results show that associative fear learning not only induces inhibitory synaptogenesis, as demonstrated in the previous studies, but also stimulates local protein synthesis and produces modifications of the synapses that indicate their potentiation.

Genetic variability and changes of elemental concentrations in cells of Tetrix tenuicornis (orthoptera: tetrigidae) from polluted and unpolluted areas

Genetic variability between populations of the orthopteran insect Tetrix tenuicornis, collected from six locations in Poland, was assayed by using the random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) method. The results show that insects in a population from metal polluted areas in Bolesław have reduced genetic variability in contrast to five other populations located in unpolluted areas. The insects from polluted sites also showed significant changes in elemental concentrations in nerve and muscle cells, measured by X-ray spectroscopy, when compared to insects of the same species collected from unpolluted sites.

Zinc induces caspase-dependent mitochondrial pathway of the programmed cell death in haemocytes of Drosophila melanogaster

Zinc is an essential trace element in cells. However, its high level in cytoplasm promotes activation of stress signaling pathways and may lead to cell death. In the present study we used Drosophila melanogaster blood cells (haemocytes), obtained from the third instar larvae, to study the effects of high concentrations of Zn(2+) on programmed cell death (PCD). We analyzed the activity of caspases, the level of caspase inhibitor protein DIAP1 and metallothioneins, as well as calcium concentrations and activity of mitochondria in haemocytes exposed to 0.35 and 1.7 mM concentrations of Zn. The obtained results showed that rapid increase of [Zn(2+)]( i ) in the cytoplasm up-regulates metallothionein MtnB but not MtnA gene expression in cells treated with Zn(2+) in both concentrations. Excess of Zn(2+) also induced activation of the initiator caspase Dronc, associated with the mitochondrial pathway of PCD, and the effector caspase DrICE. In turn, the activity of receptor-regulated Dredd caspase was not changed. The level of DIAP1 decreased significantly in haemocytes in the presence of high Zn(2+) concentration in comparison to untreated cells. Moreover, mitochondrial membrane potential was significantly decreased after exposure to Zn ions. These results indicate that high concentration of Zn(2+) in the cytoplasm of haemocytes induces PCD via a mitochondrial pathway and that caspases play a pivotal role in this process.

The clock input to the first optic neuropil of Drosophila melanogaster expressing neuronal circadian plasticity

In the first optic neuropil (lamina) of the fly's visual system, two interneurons, L1 and L2 monopolar cells, and epithelial glial cells show circadian rhythms in morphological plasticity. These rhythms depend on clock gene period (per) and cryptochrome (cry) expression. In the present study, we found that rhythms in the lamina of Drosophila melanogaster may be regulated by circadian clock neurons in the brain since the lamina is invaded by one neurite extending from ventral lateral neurons; the so-called pacemaker neurons. These neurons and the projection to the lamina were visualized by green fluorescent protein (GFP). GFP reporter gene expression was driven by the cry promotor in cry-GAL4/UAS-GFP transgenic lines. We observed that the neuron projecting to the lamina forms arborizations of varicose fibers in the distal lamina. These varicose fibers do not form synaptic contacts with the lamina cells and are immunoreactive to the antisera raised against a specific region of Schistocerca gregaria ion transport peptide (ITP). ITP released in a paracrine way in the lamina cortex, may regulate the swelling and shrinking rhythms of the lamina monopolar cells and the glia by controlling the transport of ions and fluids across cell membranes at particular times of the day.

Effects of zinc on programmed cell death of Musca domestica and Drosophila melanogaster blood cells

Programmed cell death (PCD) and phagocytotic activity of immune cells play a pivotal role in insect development. We examined the influence of Zn(2+), an important element to fundamental biological processes, on phagocytosis and apoptosis of hemocytes in two fly species: Musca domestica and Drosophila melanogaster. Hemocytes were isolated from the third instar larvae of both species and treated for 3h with zinc chloride solutions, containing 0.35 mM or 1.7 mM of Zn(2+), and untreated as control. Phagocytotic activity of hemocytes was examined by flow cytometry after adding latex fluorescent beads to the medium, while apoptosis was evaluated by application of annexinV-FITC and pan-caspase-FITC inhibitor. Mitochondrial viability was determined by measuring resazurin absorbancy in the cell medium. The obtained results showed that Zn(2+) increases phagocytosis and affects PCD of both species hemocytes but each in a different way. Zinc decreases fraction of annexin-positive hemocytes in M. domestica but increases it in D. melanogaster. The pan-caspase analysis revealed low and high activity of caspases in hemocytes of M. domestica and D. melanogaster, respectively. Zn(2+) also decreased the viability of hemocyte mitochondria but only in D. melanogaster. It suggests that flies use different pathways of PCD, or that Zn plays a different role in this process in M. domestica than in D. melanogaster.

Cyclical expression of Na+/K+-ATPase in the visual system of Drosophila melanogaster

In the first (lamina) and second (medulla) optic neuropils of Drosophila melanogaster, sodium pump subunit expression changes during the day and night, controlled by a circadian clock. We examined alpha-subunit expression from the intensity of immunolabeling. For the beta-subunit, encoded by Nervana 2 (Nrv2), we used Nrv2-GAL4 to drive expression of GFP, and measured the resultant fluorescence in whole heads and specific optic lobe cells. All optic neuropils express the alpha-subunit, highest at the beginning of night in both lamina and medulla in day/night condition and the oscillation was maintained in constant darkness. This rhythm was lacking in the clock arrhythmic per(0) mutant. GFP driven by Nrv2 was mostly detected in glial cells, mainly in the medulla. There, GFP expression occurs in medulla neuropil glia (MNGl), which express the clock gene per, and which closely contact the terminals of clock neurons immunoreactive to pigment dispersing factor. GFP fluorescence exhibited circadian oscillation in whole heads from Nrv2-GAL4+UAS-S65T-GFP flies, although significant GFP oscillations were lacking in MNGl, as they were for both subunit mRNAs in whole-head homogenates. In the dissected brain tissues, however, the mRNA of the alpha-subunit showed a robust daily rhythm in concentration changes while changes in the beta-subunit mRNA were weaker and not statistically significant. Thus in the brain, the genes for the sodium pump subunits, at least the one encoding the alpha-subunit, seem to be clock-controlled and the abundance of their corresponding proteins mirrors daily changes in mRNA, showing cyclical accumulation in cells.

External and internal inputs affecting plasticity of dendrites and axons of the fly's neurons

Neurons and glial cells in the fly's visual system exhibit circadian rhythms through changes in shape and size. Moreover, the number of synaptic contacts between these cells changes during the day and night and in the case of one type of synapses, feedback synapses, is maintained under constant conditions indicating an endogenous origin of this rhythm. The structural changes described above, involving the oscillations in the number of synapses and the size of interneurons and glial cells, are examples of plasticity in the central nervous system driven by internal inputs from a circadian clock and by external stimuli such as light. They are also modulated by visual and other sensory stimuli and by motor activity.

Effects of locomotor stimulation and protein synthesis inhibition on circadian rhythms in size changes of L1 and L2 interneurons in the fly's visual system

Axons of monopolar cell interneurons L1 and L2 in the first optic lobe (lamina) of the fly Musca domestica undergo cyclical changes in diameter. These axons swell during the day and shrink during the night. In addition, the axons' size depends on light conditions since they are largest in continuous light (LL), somewhat smaller under day/night (LD) conditions, and smallest under constant darkness (DD). In this study we found that sizes of both cells can further increase in free flying flies under LD conditions, while the visual stimulation alone does not have significant effect on the cross-sectional area of L1 and L2 axons. The stimulation of free flying had no effect on L1 and L2 sizes if it was performed at the beginning of subjective day in LL or DD. Our results indicate that a maximal increase in size of L1 and L2 is observed when stimulation of free flying is synchronized with a fly' daily peak of activity. We also found that protein synthesis is needed to increase size of monopolar cell axons during the day when they normally swell.

Neurotoxic protein expression reveals connections between the circadian clock and mating behavior in Drosophila

To investigate the functions of circadian neurons, we added two strategies to the standard Drosophila behavioral genetics repertoire. The first was to express a polyglutamine-expanded neurotoxic protein (MJDtr78Q; MJD, Machado-Joseph disease) in the major timeless (tim)-expressing cells of the adult brain. These Tim-MJD flies were viable, in contrast to the use of cell-death gene expression for tim neuron inactivation. Moreover, they were more arrhythmic than flies expressing other neurotoxins and had low but detectable tim mRNA levels. The second extended standard microarray technology from fly heads to dissected fly brains. By combining the two approaches, we identified a population of Tim-MJD-affected mRNAs. Some had been previously identified as sex-specific and relevant to courtship, including mRNAs localized to brain-proximal fat-body tissue and brain courtship centers. Finally, we found a decrease in the number of neurons that expressed male-specific forms of the fruitless protein in the laterodorsal region of the brain. The decrease was not a consequence of toxic protein expression within these specialized cells but a likely effect of communication with neighboring TIM-expressing neurons. The data suggest a functional interaction between adjacent circadian and mating circuits within the fly brain, as well as an interaction between circadian circuits and brain-proximal fat body.

PDF cycling in the dorsal protocerebrum of the Drosophila brain is not necessary for circadian clock function

In Drosophila, the neuropeptide pigment-dispersing factor (PDF) is a likely circadian molecule, secreted by central pacemaker neurons (LNvs). PDF is expressed in both small and large LNvs (sLNvs and lLNvs), and there are striking circadian oscillations of PDF staining intensity in the small cell termini, which require a functional molecular clock. This cycling may be relevant to the proposed role of PDF as a synchronizer of the clock system or as an output signal connecting pacemaker cells to locomotor activity centers. In this study, the authors use a generic neuropeptide fusion protein (atrial natriuretic factor-green fluorescent protein [ANF-GFP]) and show that it can be expressed in the same neurons as PDF itself. Yet, ANF-GFP as well as PDF itself does not manifest any cyclical accumulation in sLNv termini in adult transgenic flies. Surprisingly, the absence of detectable PDF cycling is not accompanied by any detectable behavioral pheno-type, since these transgenic flies have normal morning and evening anticipation in a light-dark cycle (LD) and are fully rhythmic in constant darkness (DD). The molecular clock is also not compromised. The results suggest that robust PDF cycling in sLNv termini plays no more than a minor role in the Drosophila circadian system and is apparently not even necessary for clock output function.

Characterization and plasticity of the double synapse spines in the barrel cortex of the mouse

The somatosensory barrel cortex of rodents and its afferent pathway from the facial vibrissae is a very useful model for studying neuronal plasticity. Dendritic spines are the most labile elements of synaptic circuitry and the most likely substrate of experience-dependent alterations in neuronal circuits in cerebral cortex. We characterized morphologically and numerically a specific population of spines, i.e. double synapse spines, which have two different inputs--one excitatory and the other inhibitory, in the B2 barrel of mouse somatosensory cortex. We also described changes in morphology of double synapse spines induced by classical conditioning in which stimulation of vibrissae was paired with a tail shock. The analysis was carried out by means of serial EM micrograph reconstruction. We showed that double spines account for about 10% of all analyzed spines. The morphology of a typical double synapse spine is similar to the morphology of single synapse spine and both consist of two parts--a large head and a narrow, long neck. Excitatory synapses are preferentially located on the head of double synapse spines and inhibitory synapses are usually located on the neck of these spines. The length of the double synapse spine neck decreases and the cross-section area of the spine neck increases significantly as a result of sensory conditioning.

Structural daily rhythms in GFP-labelled neurons in the visual system of Drosophila melanogaster

In the visual system of Drosophila melanogaster, two classes of interneurons in the first optic neuropil, or lamina, the monopolar cells L1 and L2, show rhythmic circadian changes in the shape and size of their axons. In the present study we have used the GAL4-UAS system to target the GFP expression to the L2 cells in D. melanogaster and to examine morphological changes in the cell body, nucleus, axon and dendritic spines. Our results showed that in addition to changes in the caliber of its axon, L2 also shows daily changes in the morphology of its dendritic spines, differences which are most pronounced at the beginning of the night. There are also changes in the sizes of the cells' nuclei in the lamina cortex, which are largest at the beginning and in the middle of day, in females and males, respectively. In contrast to the axon and dendrites, L2's soma does not change size significantly during the day or night. The observed changes clearly indicate the cyclical modulation of the structure of the L2 interneurons. These changes seem to be regulated by a circadian clock, which exhibits certain differences between the sexes.

Heavy metal accumulation, heat shock protein expression and cytogenetic changes in Tetrix tenuicornis (L.) (Tetrigidae, Orthoptera) from polluted areas

The orthopteran insect Tetrix tenuicornis, collected from polluted and unpolluted areas, was used to study heavy metal accumulation and its impact on stress protein levels and on changes in the number and morphology of chromosomes in mitotic and meiotic cells. During two consecutive years, insects were collected from polluted areas of zinc-lead mine spoils near Bolesław (Poland) and from unpolluted areas near Busko and Staszów (Poland). T. tenuicornis from the polluted area showed 1.5, 4.03, 4.32 and 41.73 times higher concentrations of copper (Cu), zinc (Zn), lead (Pb) and cadmium (Cd), respectively, than insects of the same species collected from unpolluted areas. Insects exposed to heavy metals showed only small changes, and rather a decrease in the concentration of constitutive and inducible heat shock proteins Hsp70, the level of which increases under stress conditions. A cytogenetic study of T. tenuicornis revealed intra-population anomalies in chromosome number and morphology in mitotic and meiotic cells and the presence of an additional B chromosome in germinal cells. In 50% of females collected from polluted areas, mosaic oogonial mitotic chromosome sets and diploid, hypo- or hypertetraploid, tetraploid, and octoploid chromosome numbers were detected. In turn, 14.6% of males showed a heterozygous deficiency of chromatin in L2 and M3 bivalents in addition to the presence of B chromosomes.

Elemental changes in the brain, muscle, and gut cells of the housefly,Musca domestica, exposed to heavy metals

The toxic effects of heavy metals on organisms are well established. However, their specific action at the cellular level in different tissues is mostly unknown. We have used the housefly, Musca domestica, as a model organism to study the toxicity of four heavy metals: copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb). These have been fed to larvae at low and high, semi-lethal concentrations, and their accumulation in the head, thorax, and abdomen was subsequently measured in adult flies. In addition, their impact on the cellular concentration of several elements important for cell metabolism-sodium (Na+), magnesium (Mg++), phosphorous (P), sulphur (S), chloride (Cl-) and potassium (K+)-were measured in neural cells, muscle fibers, and midgut epithelial cells. Our study showed that the heavy metals accumulate mainly in the abdomen, in which the concentrations of two of the xenobiotic metals, Cd and Pb, were 213 and 23 times more concentrated, respectively, than in controls. All the heavy metals affected the cellular concentration of light elements in all cell types, but the changes observed were dependent on tissue type and were specific for each heavy metal, and its concentration.

Reduced plasticity of cortical whisker representation in adult tenascin-C-deficient mice after vibrissectomy

The effect of the extracellular matrix recognition molecule tenascin-C on cerebral plasticity induced by vibrissectomy was investigated with 2-deoxyglucose (2DG) brain mapping in tenascin-C-deficient mice. Unilateral vibrissectomy sparing row C of vibrissae was performed in young adult mice. Two months later, cortical representations of spared row C vibrissae and control row C on the other side of the snout were visualized by [(14)C]2DG autoradiography. In both wild-type and tenascin-C-deficient mice, cortical representation of the spared row was expanded in all layers of the barrel cortex. However, the effect was significantly more extensive in wild-type animals than in the mutant. Elimination of tenascin-C by genetic manipulation thus reduces the effect of vibrissectomy observed in the somatosensory cortex. No increase in number of fibres in the vibrissal nerve of spared vibrissae was seen, and occurrence of additional nerve to the spared follicle was very rare. Thus, in tenascin-C-deficient mice functional plasticity seems to be impaired within the CNS.

Involvement of V-ATPase in the regulation of cell size in the fly's visual system

In the fly's visual system, two classes of lamina interneuron, L1 and L2, cyclically change both their size and shape in a rhythm that is circadian. Several neurotransmitters and the lamina's glial cells are known to be involved in regulating these rhythms. Moreover, vacuolar-type H+-ATPase (V-ATPase) in the optic lobe is thought also to participate in such regulation. We have detected V-ATPase-like immunoreactivity in the heads of both Drosophilla melanogaster and Musca domestica using antibodies raised against either the B- or H-subunits of V-ATPase from D. melanogaster or against the B-subunit from two other insect species Culex quinquefasciatus and Manduca sexta. In the visual systems of both fly species V-ATPase was localized immunocytochemically to the compound eye photoreceptors. In D. melanogaster immunoreactivity oscillated during the day and night and under constant darkness the signal was stronger during the subjective night than the subjective day. In turn, blocking V-ATPase by injecting a V-ATPase blocker, bafilomycin, in M. domestica increased the axon sizes of L1 and L2, but only when bafilomycin was applied during the night. As a result bafilomycin abolished the day/night difference in axon size in L1 and L2, their sizes being similar during the day and night.

Ultrastructural characteristics of circadian pacemaker neurones, immunoreactive to an antibody against a pigment-dispersing hormone in the fly's brain

Neurones immunoreactive to an antibody against a pigment-dispersing hormone (PDH-ir) are considered to be pacemaker cells in the neuronal circadian system of flies. We investigated the ultrastructure of PDH-ir varicosities, possible releasing sites of the PDH-like peptide, in the distal medulla of the optic lobe and in the dorsal protocerebrum of the two fly species Drosophila melanogaster and Musca domestica. In both species PDH-ir varicosities show accumulation of dense core vesicles (DCVs). PDH-like peptide is localized in the DCVs as shown by post-embedding immuno-electron microscopy. Localization of PDH-like peptide in DCVs and normally lacking synaptic specializations at PDH-ir varicosities in the medulla are interpreted as a non-synaptic paracrine release of peptide.

Involvement of glial cells in rhythmic size changes in neurons of the housefly's visual system

In the housefly's first optic neuropile, or lamina, the axons of two classes of monopolar cell interneurons, L1 and L2, exhibit a daily rhythm of size changes: swelling during the day, and shrinking by night. At least for the L2 cells this rhythm is circadian. Moreover, epithelial glial cells that enwrap each lamina cartridge, its monopolar cell axons, and their surrounding crown of input photoreceptor terminals also change size, but in the opposite direction to the changes in L1 and L2-swelling by night and shrinking by day. The rhythmic changes in glia indicate the possible involvement of these cells in the lamina's circadian system. To examine their role in regulating the rhythmic changes of L1 and L2's axon sizes we have injected three chemicals into the haemolymph of the fly's head: fluorocitrate (FL) and iodoacetate (IAA), which affect the metabolism of glial cells, and octanol (OC), which closes gap junction channels. All chemicals exerted an effect on L1 and L2, which depended on the time of injection, the drug concentration, and the postinjection times at which we examined the fly's brains. Moreover, day/night changes in the axon sizes of L1 and L2 were increased in FL- and IAA-treated flies, indicating that glial cells may normally inhibit these changes by regulating the sizes of L1 and L2's axons during the day and night. In turn, lack of a day/night rhythm in L1 and L2 after OC injections shows that the rhythm's persistence depends on communication between the lamina cells through gap junction channels.

Development of PDF-immunoreactive cells, possible clock neurons, in the housefly Musca domestica

Even though the housefly Musca domestica shows clear circadian rhythms in its behavioural and physiological processes, a circadian pacemaker system controlling these rhythms has not yet been described morphologically in this species. In M. domestica, neurons immunoreactive to pigment-dispersing factor (PDF), a neurotransmitter/neuromodulator of circadian information arising from a circadian clock and transmitted to target cells, are similar in their number and distribution to the PDF neurons of Drosophila melanogaster. In D. melanogaster these neurons co-localize PER protein and have been identified as clock neurons in that species. Here we report PDF-immunoreactive cells in the housefly's brain during postembryonic development in the larval and pupal stages, as well as in the adult fly soon after eclosion. In the housefly's brain, there are three groups of PDF-immunoreactive neurons: two groups with small (sPDFMe) and large (lPDFMe) cell bodies in the proximal medulla of the optic lobe; and one group in the dorsal protocerebrum (PDFD). Three out of four sPDFMe can be detected during the first hour of larval development, but the fourth sPDFMe is observed in the larva only from 48 hours after hatching, along with five lPDFMe neurons, seen first as two subgroups, and three out of four PDFD neurons. During postembryonic development these neurons show changes in their structure and immunoreactivity. New PDF neurons are observed during pupal development but these neurons mostly do not survive into adulthood. In the adult fly's brain, the PDF neurons have also been examined in double-labelled preparations made with a second antibody directed against the product of one of several clock genes: period (per), timeless (tim), or cryptochrome (cry). Among them, only immunoreactivity to CRY-like protein has been detected in the brain of M. domestica and has shown a daily rhythm in its concentration, as examined immunocytochemically. CRY was co-localized with PDF in the sPDFMe of the housefly's brain fixed during the day. The possibility that the sPDFMe neurons are the housefly's clock neurons is discussed.

The regulation of circadian rhythms in the fly's visual system: involvement of FMRFamide-like neuropeptides and their relationship to pigment dispersing factor in Musca domestica and Drosophila melanogaster

The cross-sectional area of axon profiles in two classes of interneuron, L1 and L2, in the fly's lamina, exhibits a circadian rhythm of swelling and shrinking; axon caliber also changes after microinjecting putative lamina neurotransmitters. Among these, the neuropeptide pigment-dispersing factor, PDF, is proposed to transmit circadian information from the housefly's (Musca domestica) clock to L1 and L2, increasing axon caliber during the day. Testing whether other neurotransmitters may modulate this effect we have: (1) examined optic lobe cell immunoreactivity to FMRFamide peptides and its co-immunolocalization to PDF in M. domestica and Drosophila melanogaster, and to the product of the circadian clock gene PER in D. melanogaster; and (2) made microinjections of FMRFamide and related neuropeptides into the second neuropil, or medulla. In M. domestica, nine groups of optic lobe cells, several cells in the lateral and dorsal protocerebrum, and in the subesophageal ganglion, together contribute dense FMRFamide immunoreactive arborizations in almost all central brain and optic lobe neuropils. In D. melanogaster a similar pattern of labeling arises from fewer cells. Daytime microinjections show that another neuropeptide, similar to molluscan FMRFamide, shrinks M. domestica's L1 and L2 axons, thus opposing the action of PDF. We discuss evidence for a medulla site of action for a released FMRFamide-like peptide, either from: MeRF2 cells, acting directly on L1 and L2's medulla terminals; or MeRF1 cells, acting indirectly via medulla centrifugal cells C2 and C3.

Dynamic structural changes of synaptic contacts in the visual system of insects

The visual system of insects provides an excellent model to study processes of transduction and transmission of photic information, synaptogenesis, synaptic plasticity, and wiring between photoreceptors and their visual interneurons in the optic lobe. This review describes synaptic contacts between photoreceptors and other neurons in the visual system of insects, especially in the fly's first optic neuropile (the lamina), and summarizes changes observed in the synapses of visual cells that have been reported both in phylogeny and ontogeny, and also examples of synaptic plasticity in adult insects that have been evoked by intrinsic and extrinsic factors. Plasticity observed in synapses of the insect's visual system seems to exemplify not only synaptic contacts in insects but, given that similar examples of plasticity have been found in other animal groups, may also be a general phenomenon in the nervous system.

Localization of the clock controlling circadian rhythms in the first neuropile of the optic lobe in the housefly

The visual system of a fly expresses several circadian rhythms that have been detected in the photoreceptors of the compound eye and in the first neuropile, the lamina, of the underlying optic lobe. In the lamina, axons of two classes of interneuron, L1 and L2, exhibit cyclical size changes, swelling by day and shrinking by night. These rhythmic size changes may be generated by circadian oscillators located inside and/or outside the optic lobe. To localize such oscillators, we have examined changes in the axonal cross-sectional areas of L1 and L2 within the lamina of the housefly (Musca domestica) under conditions of 12 h of light and 12 h of darkness (LD12:12), constant darkness (DD) or continuous light (LL) 24 h after the medulla was severed from the rest of the brain. After the lesion, the axon size changes of L1 and L2 were maintained only in LD conditions, but were weaker than in control flies. In DD and LL conditions, they were eliminated. This indicates that circadian rhythms in the lamina of a fly are generated central to the lamina and medulla neuropiles of the optic lobe. Cyclical changes of light and darkness in LD conditions are still able, however, to induce a weak daily rhythm in the axon sizes of L1 and L2.