A selection from Stockholm University publication database

• Time- and temperature-dependent dynamics of prothoracicotropichormone and ecdysone sensitivity co-regulate pupal diapause in thegreen-veined white butterfly Pieris napi

  2022. Philip Süess (et al.). Insect Biochemistry and Molecular Biology 149

  Article

  Diapause, a general shutdown of developmental pathways, is a vital adaptation allowing insects to adjust their life cycle to adverse environmental conditions such as winter. Diapause in the pupal stage is regulated by the major developmental hormones prothoracicotropic hormone (PTTH) and ecdysone. Termination of pupal diapause in the butterfly Pieris napi depends on low temperatures; therefore, we study the temperature-dependence of PTTH secretion and ecdysone sensitivity dynamics throughout diapause, with a focus on diapause termination. While PTTH is present throughout diapause in the cell bodies of two pairs of neurosecretory cells in the brain, it is absent in the axons, and the PTTH concentration in the haemolymph is significantly lower during diapause than during post diapause development, indicating that the PTTH signaling is reduced during diapause. The sensitivity of pupae to ecdysone injections is dependent on diapause stage. While pupae are sensitive to ecdysone during early diapause initiation, they gradually lose this sensitivity and become insensitive to non-lethal concentrations of ecdysone about 30 days into diapause. At low temperatures, reflecting natural overwintering conditions, diapause termination propensity after ecdysone injection is precocious compared to controls. In stark contrast, at high temperatures reflecting late summer and early autumn conditions, sensitivity to ecdysone does not return. Thus, here we show that PTTH secretion is reduced during diapause, and additionally, that the low ecdysone sensitivity of early diapause maintenance is lost during termination in a temperature dependent manner. The link between ecdysone sensitivity and low-temperature dependence reveals a putative mechanism of how diapause termination operates in insects that is in line with adaptive expectations for diapause.

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• Local olfactory interneurons provide the basis for neurochemical regionalization of olfactory glomeruli in crustaceans

  2021. Steffen Harzsch, Heinrich Dircksen, Bill S. Hansson. Journal of Comparative Neurology

  Article

  The primary olfactory centers of metazoans as diverse as arthropods and mammals consist of an array of fields of dense synaptic neuropil, the olfactory glomeruli. However, the neurochemical structure of crustacean olfactory glomeruli is largely understudied when compared to the insects. We analyzed the glomerular architecture in selected species of hermit crabs using immunohistochemistry against presynaptic proteins, the neuropeptides orcokinin, RFamide and allatostatin, and the biogenic amine serotonin. Our study reveals an unexpected level of structural complexity, unmatched by what is found in the insect olfactory glomeruli. Peptidergic and aminergic interneurons provide the structural basis for a regionalization of the crustacean glomeruli into longitudinal and concentric compartments. Our data suggest that local olfactory interneurons take a central computational role in modulating the information transfer from olfactory sensory neurons to projection neurons within the glomeruli. Furthermore, we found yet unknown neuronal elements mediating lateral inhibitory interactions across the glomerular array that may play a central role in modulating the transfer of sensory input to the output neurons through presynaptic inhibition. Our study is another step in understanding the function of crustacean olfactory glomeruli as highly complex units of local olfactory processing. 

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• Orcokinin in the central complex of the locust Schistocerca gregaria

  2021. Uwe Homberg (et al.). Journal of Comparative Neurology 529 (8), 1876-1894

  Article

  The central complex is a group of highly interconnected neuropils in the insect brain. It is involved in the control of spatial orientation, based on external compass cues and various internal needs. The functional and neurochemical organization of the central complex has been studied in detail in the desert locust Schistocerca gregaria. In addition to classical neurotransmitters, immunocytochemistry has provided evidence for a major contribution of neuropeptides to neural signalling within the central complex. To complement these data, we have identified all orcokinin‐immunoreactive neurons in the locust central complex and associated brain areas. About 50 bilateral pairs of neurons innervating all substructures of the central complex exhibit orcokinin immunoreactivity. Among these were about 20 columnar neurons, 33 bilateral pairs of tangential neurons of the central body, and seven pairs of tangential neurons of the protocerebral bridge. In silico transcript analysis suggests the presence of eight different orcokinin‐A type peptides in the desert locust. Double label experiments showed that all orcokinin‐immunostained tangential neurons of the lateral accessory lobe cluster were also immunoreactive for GABA and the GABA‐synthesizing enzyme glutamic acid decarboxylase. Two types of tangential neurons of the upper division of the central body were, furthermore, also labeled with an antiserum against Dip‐allatostatin I. No colocalization was found with serotonin immunostaining. The data provide additional insights into the neurochemical organization of the locust central complex and suggest that orcokinin‐peptides of the orcokinin‐A gene act as neuroactive substances at all stages of signal processing in this brain area.

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• Pigment dispersing factors and their cognate receptors in a crustacean model, with new insights into distinct neurons and their functions

  2020. Jodi Alexander (et al.). Frontiers in Neuroscience 14, 1-16

  Article

  Pigment dispersing factors (PDFs, or PDHs in crustaceans) form a structurally related group of neuropeptides found throughout the Ecdysozoa and were first discovered as pigmentary effector hormones in crustaceans. In insects PDFs fulfill crucial neuromodulatory roles, most notably as output regulators of the circadian system, underscoring their central position in physiological and behavioral organization of arthropods. Intriguingly, decapod crustaceans express multiple isoforms of PDH originating from separate genes, yet their differential functions are still to be determined. Here, we functionally define two PDH receptors in the crab Carcinus maenas and show them to be selectively activated by four PDH isoforms: PDHR 43673 was activated by PDH-1 and PDH-2 at low nanomolar doses whilst PDHR 41189 was activated by PDH-3 and an extended 20 residue e-PDH. Detailed examination of the anatomical distribution of all four peptides and their cognate receptors indicate that they likely perform different functions as secreted hormones and/or neuromodulators, with PDH-1 and its receptor 43,673 implicated in an authentic hormonal axis. PDH-2, PDH-3, and e-PDH were limited to non-neurohemal interneuronal sites in the CNS; PDHR 41189 was largely restricted to the nervous system suggesting a neuromodulatory function. Notably PDH-3 and e-PDH were without chromatophore dispersing activity. This is the first report which functionally defines a PDHR in an endocrine system in a crustacean and to indicate this and other putative roles of this physiologically pivotal peptide group in these organisms. Thus, our findings present opportunities to further examine the endocrine and circadian machinery in this important arthropod phylum.

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• Functional morphology of the primary olfactory centers in the brain of the hermit crab Coenobita clypeatus (Anomala, Coenobitidae)

  2020. Martha A. Polanska (et al.). Cell and Tissue Research

  Article

  Terrestrial hermit crabs of the genus Coenobita display strong behavioral responses to volatile odors and are attracted by chemical cues of various potential food sources. Several aspects of their sense of aerial olfaction have been explored in recent years including behavioral aspects and structure of their peripheral and central olfactory pathway. Here, we use classical histological methods and immunohistochemistry against the neuropeptides orcokinin and allatostatin as well as synaptic proteins and serotonin to provide insights into the functional organization of their primary olfactory centers in the brain, the paired olfactory lobes. Our results show that orcokinin is present in the axons of olfactory sensory neurons, which target the olfactory lobe. Orcokinin is also present in a population of local olfactory interneurons, which may relay lateral inhibition across the array of olfactory glomeruli within the lobes. Extensive lateral connections of the glomeruli were also visualized using the histological silver impregnation method according to Holmes-Blest. This technique also revealed the structural organization of the output pathway of the olfactory system, the olfactory projection neurons, the axons of which target the lateral protocerebrum. Within the lobes, the course of their axons seems to be reorganized in an axon-sorting zone before they exit the system. Together with previous results, we combine our findings into a model on the functional organization of the olfactory system in these animals.

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• Unprecedented reorganization of holocentric chromosomes provides insights into the enigma of lepidopteran chromosome evolution

  2019. Jason Hill (et al.). Science Advances 5 (6)

  Article

  Chromosome evolution presents an enigma in the mega-diverse Lepidoptera. Most species exhibit constrained chromosome evolution with nearly identical haploid chromosome counts and chromosome-level gene collinearity among species more than 140 million years divergent. However, a few species possess radically inflated chromosomal counts due to extensive fission and fusion events. To address this enigma of constraint in the face of an exceptional ability to change, we investigated an unprecedented reorganization of the standard lepidopteran chromosome structure in the green-veined white butterfly (Pieris napi). We find that gene content in P. napi has been extensively rearranged in large collinear blocks, which until now have been masked by a haploid chromosome number close to the lepidopteran average. We observe that ancient chromosome ends have been maintained and collinear blocks are enriched for functionally related genes suggesting both a mechanism and a possible role for selection in determining the boundaries of these genome-wide rearrangements.

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• Reproductive fitness of Drosophila is maximised by optimal developmental temperature

  2019. Peter Klepsatel (et al.). Journal of Experimental Biology 222 (10)

  Article

  Whether the character of developmental plasticity is adaptive or non-adaptive has often been a matter of controversy. Although thermal developmental plasticity has been studied in Drosophila for several traits, it is not entirely clear how it affects reproductive fitness. We, therefore, investigated how developmental temperature affects reproductive performance (early fecundity and egg-to-adult viability) of wild-caught Drosophila melanogaster. We have tested competing hypotheses on the character of developmental thermal plasticity using a full factorial design with three developmental and adulthood temperatures within the natural thermal range of this species. To account for potential intraspecific differences, we examined flies from tropical (India) and temperate (Slovakia) climate zones. Our results show that flies from both populations raised at intermediate developmental temperature (25°C) have comparable or higher early fecundity and fertility at all tested adulthood temperatures, while lower (17°C) or higher developmental temperatures (29°C) did not entail any advantage under the tested thermal regimes. Importantly, the superior thermal performance of flies raised at 25°C is apparent even after taking two traits positively associated with reproductive output into account – body size and ovariole number. Thus, in Drosophila melanogaster, development at a given temperature does not necessarily provide any advantage at this thermal environment in terms of reproductive fitness. Our findings strongly support the optimal developmental temperature hypothesis which claims that at different thermal environments the highest fitness is achieved when an organism is raised at its optimal developmental temperature.

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• Cyanobacterial neurotoxin beta-methyl-amino-L-alanine affects dopaminergic neurons in optic ganglia and brain of Daphnia magna

  2018. Megan Brooke-Jones, Martina Gáliková, Heinrich Dircksen. Toxins 10 (527)

  Article

  The non-proteinogenic amino acid beta-methyl-amino-l-alanine (BMAA) is a neurotoxin produced by cyanobacteria. BMAA accumulation in the brain of animals via biomagnification along the food web can contribute to the development of neurodegenerative diseases such as Amyotrophic lateral sclerosis/Parkinsonism dementia complex (ALS/PDC), the latter being associated with a loss of dopaminergic neurons. Daphnia magna is an important microcrustacean zooplankton species that plays a key role in aquatic food webs, and BMAA-producing cyanobacteria often form part of their diet. Here, we tested the effects of BMAA on putative neurodegeneration of newly identified specific dopaminergic neurons in the optic ganglia/brain complex of D. magna using quantitative tyrosine-hydroxylase immunohistochemistry and fluorescence cytometry. The dopaminergic system was analysed in fed and starved isogenic D. magna adults incubated under different BMAA concentrations over 4 days. Increased BMAA concentration showed significant decrease in the stainability of dopaminergic neurons of D. magna, with fed animals showing a more extreme loss. Furthermore, higher BMAA concentrations tended to increase offspring mortality during incubation. These results are indicative of ingested BMAA causing neurodegeneration of dopaminergic neurons in D. magna and adversely affecting reproduction. This may imply similar effects of BMAA on known human neurodegenerative diseases involving dopaminergic neurons.

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• The thirsty fly: Ion transport peptide (ITP) is a novel endocrine regulator of water homeostasis in Drosophila

  2018. Martina Gáliková, Heinrich Dircksen, Dick R. Nässel. PLOS Genetics

  Article

  Animals need to continuously adjust their water metabolism to the internal and external conditions. Homeostasis of body fluids thus requires tight regulation of water intake and excretion, and a balance between ingestion of water and solid food. Here, we investigated how these processes are coordinated in Drosophila melanogaster. We identified the first thirst-promoting and anti-diuretic hormone of Drosophila, encoded by the gene Ion transport peptide (ITP). This endocrine regulator belongs to the CHH (crustacean hyperglycemic hormone) family of peptide hormones. Using genetic gain- and loss-of-function experiments, we show that ITP signaling acts analogous to the human vasopressin and renin-angiotensin systems; expression of ITP is elevated by dehydration of the fly, and the peptide increases thirst while repressing excretion, promoting thus conservation of water resources. ITP responds to both osmotic and desiccation stress, and dysregulation of ITP signaling compromises the fly’s ability to cope with these stressors. In addition to the regulation of thirst and excretion, ITP also suppresses food intake. Altogether, our work identifies ITP as an important endocrine regulator of thirst and excretion, which integrates water homeostasis with feeding of Drosophila.

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• Prey selection of the swimming crab Portunus trituberculatus (Miers, 1876) (Brachyura: Portunidae) foraging on bivalves

  2017. Yunfei Sun (et al.). Journal of Crustacean Biology 37 (5), 521-528

  Article

  Predators may be exposed to different prey types simultaneously, and so may select certainprey types over others. We examined prey selection, predation rate, and foraging behaviourof the swimming crab Portunus trituberculatus (Miers, 1876) provided with three types of clams, the Manila Ruditapes philippinarum (Adams & Reeve, 1850), bloody Scapharca subcrenata (Lischke,1896), and hard Meretrix meretrix (Linnaeus, 1758) clams in laboratory experiments. When provided will all three possible prey simultaneously, crabs exhibited higher preference for R. philippinarum over S. subcrenata and M. meretrix (Chesson’s selectivity index; P = 0.003). In the single-prey experiments, predation rates were signifcantly higher on R. philippinarum and S. subcrenata than on M. meretrix (P = 0.002). Video analysis revealed that prey type signifcantly affected both the proportion of time crabs spent on searching, and the probability of consumption upon capture. The proportion of time crabs spent on handling (P = 0.171), the encounter rate (P = 0.918), and the probability of capture upon encounter (P = 0.456), however, were not signifcantly affected by prey types. Handling time per prey was not signifcantly different among clam species. For the crab, prey proftability (energy intake perunit handling time) of R. philippinarum was similar to that of S. subcrenata, in both cases being signifcantly higher than that of M. meretrix (P ﹤ 0.001). The relative frequencies of changing from searching to handling were significantly higher for M. meretrix than for R. philippinarum and S. subcrenata (P = 0.007). These results suggest that the probability of consumption upon capture explained the observed selection by crabs. Furthermore, prey proftability, shell strength, and shell width, are important elements to affect prey selection of the crab.

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• Depressing antidepressant

  2016. Bruno Campos (et al.). Environmental Science and Technology 50 (11), 6000-6007

  Article

  Selective serotonin reuptake inhibitors (SSRIs) are widely used antidepressants. As endocrine disruptive contaminants in the environment, SSRIs affect reproduction in aquatic organisms. In the water flea Daphnia magna, SSRIs increase offspring production in a food ration-dependent manner. At limiting food conditions, females exposed to SSRIs produce more but smaller offspring, which is a maladaptive life-history strategy. We asked whether increased serotonin levels in newly identified serotonin-neurons in the Daphnia brain mediate these effects. We provide strong evidence that exogenous SSRI fluoxetine selectively increases serotonin-immunoreactivity in identified brain neurons under limiting food conditions thereby leading to maladaptive offspring production. Fluoxetine increases serotonin-immunoreactivity at low food conditions to similar maximal levels as observed under high food conditions and concomitantly enhances offspring production. Sublethal amounts of the neurotoxin 5,7-dihydroxytryptamine known to specifically ablate serotonin-neurons markedly decrease serotonin-immunoreactivity and offspring production, strongly supporting the effect to be serotonin-specific by reversing the reproductive phenotype attained under fluoxetine. Thus, SSRIs impair serotonin-regulation of reproductive investment in a planktonic key organism causing inappropriately increased reproduction with potentially severe ecological impact.

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• Neuroanatomy of the optic ganglia and central brain of the water flea Daphnia magna (Crustacea, Cladocera)

  2016. Timm Kress, Steffen Harzsch, Heinrich Dircksen. Cell and Tissue Research 363 (3), 649-677

  Article

  We reveal the neuroanatomy of the optic ganglia and central brain in the water flea Daphnia magna by use of classical neuroanatomical techniques such as semi-thin sectioning and neuronal backfilling, as well as immunohistochemical markers for synapsins, various neuropeptides and the neurotransmitter histamine. We provide structural details of distinct neuropiles, tracts and commissures, many of which were previously undescribed. We analyse morphological details of most neuron types, which allow for unravelling the connectivities between various substructural parts of the optic ganglia and the central brain and of ascending and descending connections with the ventral nerve cord. We identify 5 allatostatin-A-like, 13 FMRFamide-like and 5 tachykinin-like neuropeptidergic neuron types and 6 histamine-immunoreactive neuron types. In addition, novel aspects of several known pigment-dispersing hormone-immunoreactive neurons are re-examined. We analyse primary and putative secondary olfactory pathways and neuronal elements of the water flea central complex, which displays both insect- and decapod crustacean-like features, such as the protocerebral bridge, central body and lateral accessory lobes. Phylogenetic aspects based upon structural comparisons are discussed as well as functional implications envisaging more specific future analyses of ecotoxicological and endocrine disrupting environmental chemicals.

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• Evolution of pigment-dispersing factor neuropeptides in panarthropoda

  2015. Georg Mayer (et al.). Journal of Comparative Neurology 523 (13), 1865-1885

  Article

  Pigment-dispersing factor (PDF) denotes a conserved family of homologous neuropeptides present in several invertebrate groups, including mollusks, nematodes, insects and crustaceans (referred to here as pigment-dispersing hormone, PDH). Regarding their encoding genes (pdf, pdh), insects possess only one, nematodes two, and decapod crustaceans up to three, but their phylogenetic relationship is unknown. To shed light on the origin and diversification of pdf/pdh homologs in Panarthropoda (Onychophora + Tardigrada + Arthropoda) and other molting animals (Ecdysozoa), we analyzed the transcriptomes of five distantly related onychophorans and a representative tardigrade and searched for putative pdf homologs in publically available genomes of other protostomes. This revealed only one pdf homolog in several mollusk and annelid species, two in Onychophora, Priapulida and Nematoda, and three in Tardigrada. Phylogenetic analyses suggest that the last common ancestor of Panarthropoda possessed two pdf homologs, one of which was lost in the arthropod or arthropod/tardigrade lineage, followed by subsequent duplications of the remaining homolog in some taxa. Immunolocalization of PDF-like peptides in six onychophoran species, using a broadly reactive antibody that recognizes PDF/PDH peptides in numerous species, revealed an elaborate system of neurons and fibers in their central and peripheral nervous systems. Large varicose projections in the heart suggest that the PDF neuropeptides functioned as both circulating hormones and locally released transmitters in the last common ancestor of Onychophora and Arthropoda. The lack of PDF-like immunoreactive somata associated with the onychophoran optic ganglion conforms to the hypothesis that onychophoran eyes are homologous to the arthropod median ocelli.

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• The Ion Transport Peptide Is a New Functional Clock Neuropeptide in the Fruit Fly Drosophila melanogaster

  2014. Christiane Hermann-Luibl (et al.). Journal of Neuroscience 34 (29), 9522-9536

  Article

  The clock network of Drosophila melanogaster expresses various neuropeptides, but a function in clock-mediated behavioral control was so far only found for the neuropeptide pigment dispersing factor (PDF). Here, we propose a role in the control of behavioral rhythms for the ion transport peptide (ITP), which is expressed in the fifth small ventral lateral neuron, one dorsal lateral neuron, and in only a few nonclock cells in the brain. Immunocytochemical analyses revealed that ITP, like PDF, is most probably released in a rhythmic manner at projection terminals in the dorsal protocerebrum. This rhythm continues under constant dark conditions, indicating that ITP release is clock controlled. ITP expression is reduced in the hypomorph mutant Clk^AR, suggesting that ITP expression is regulated by CLOCK. Using a genetically encoded RNAi construct, we knocked down ITP in the two clock cells and found that these flies show reduced evening activity and increased nocturnal activity. Overexpression of ITP with two independent timeless-GAL4 lines completely disrupted behavioral rhythms, but only slightly dampened PER cycling in important pacemaker neurons, suggesting a role for ITP in clock output pathways rather than in the communication within the clock network. Simultaneous knockdown (KD) of ITP and PDF made the flies hyperactive and almost completely arrhythmic under constant conditions. Under light-dark conditions, the double-KD combined the behavioral characteristics of the single-KD flies. In addition, it reduced the flies' sleep. We conclude that ITP and PDF are the clock's main output signals that cooperate in controlling the flies' activity rhythms.

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