Publications by year
In Press
Shahidi R, Williams E, Conzelmann M, Asadulina A, Veraszto C, Jasek S, Bezares-Calderon LA, Jekely G (In Press). A Serial Multiplex Immunogold Labeling Method for Identifying Peptidergic Neurons in Connectomes.
Abstract:
A Serial Multiplex Immunogold Labeling Method for Identifying Peptidergic Neurons in Connectomes
Electron microscopy-based connectomics aims to comprehensively map synaptic connections in neural tissue. However, current approaches are limited in their capacity to directly assign molecular identities to neurons. Here, we use serial multiplex immunogold labeling (siGOLD) and serial-section transmission electron microscopy (ssTEM) to identify multiple peptidergic neurons in a connectome. The high immunogenicity of neuropeptides and their broad distribution along axons, allowed us to identify distinct neurons by immunolabeling small subsets of sections within larger series. We demonstrate the scalability of siGOLD by using 11 neuropeptide antibodies on a full-body larval ssTEM dataset of the annelid Platynereis. We also reconstruct a peptidergic circuitry comprising the sensory nuchal organs, found by siGOLD to express pigment-dispersing factor, a circadian neuropeptide. Our approach enables the direct overlaying of chemical neuromodulatory maps onto synaptic connectomic maps in the study of nervous systems.
Abstract.
Verasztó C, Gühmann M, Jia H, Rajan VBV, Bezares-Calderón LA, Lopez CP, Randel N, Shahidi R, Michiels NK, Yokoyama S, et al (In Press). Ciliary and rhabdomeric photoreceptor-cell circuits form a spectral depth gauge in marine zooplankton.
Abstract:
Ciliary and rhabdomeric photoreceptor-cell circuits form a spectral depth gauge in marine zooplankton
AbstractCiliary and rhabdomeric photoreceptor cells represent two main lines of photoreceptor evolution in animals. The two photoreceptor-cell types coexist in some animals, however how they functionally integrate is unknown. We used connectomics to map synaptic paths between ciliary and rhabdomeric photoreceptors in the planktonic larva of the annelidPlatynereisand found that ciliary photoreceptors are presynaptic to the rhabdomeric circuit. The behaviors mediated by the ciliary and rhabdomeric cells also interact hierarchically. The ciliary photoreceptors are UV-sensitive and mediate downward swimming to non-directional UV light, a behavior absent in ciliary-opsin knockouts. UV avoidance antagonizes positive phototaxis mediated by the rhabdomeric eyes so that vertical swimming direction is determined by the ratio of blue/UV light. Since this ratio increases with depth,Platynereislarvae may use it as a depth gauge during planktonic migration. Our results revealed a functional integration of ciliary and rhabdomeric photoreceptors with implications for eye and photoreceptor evolution.
Abstract.
Verasztó C, Ueda N, Bezares-Calderón LA, Panzera A, Williams EA, Shahidi R, Jékely G (In Press). Ciliomotor circuitry underlying whole-body coordination of ciliary activity in the<i>Platynereis</i>larva.
Abstract:
Ciliomotor circuitry underlying whole-body coordination of ciliary activity in thePlatynereislarva
AbstractCiliated surfaces harbouring synchronously beating cilia can generate fluid flow or drive locomotion. In ciliary swimmers, ciliary beating, arrests, and changes in beat frequency are often coordinated across extended or discontinuous surfaces. To understand how such coordination is achieved, we studied the ciliated larvae ofPlatynereis dumerilii, a marine annelid.Platynereislarvae have segmental multiciliated cells that regularly display spontaneous coordinated ciliary arrests. We used whole-body connectomics, activity imaging, transgenesis, and neuron ablation to characterize the ciliomotor circuitry. We identified cholinergic, serotonergic, and catecholaminergic ciliomotor neurons. The synchronous rhythmic activation of cholinergic cells drives the coordinated arrests of all cilia. The serotonergic cells are active when cilia are beating. Serotonin inhibits the cholinergic rhythm, and increases ciliary beat frequency. Based on their connectivity and alternating activity, the catecholaminergic cells may generate the rhythm. The ciliomotor circuitry thus constitutes a stop-and-go pacemaker system for the whole-body coordination of ciliary locomotion.
Abstract.
Jasek S, Verasztó C, Brodrick E, Shahidi R, Kazimiers T, Kerbl A, Jékely G (In Press). Desmosomal connectomics of all somatic muscles in an annelid larva.
Abstract:
Desmosomal connectomics of all somatic muscles in an annelid larva
AbstractCells form networks in animal tissues through synaptic, chemical and adhesive links. Invertebrate muscle cells often connect to other cells through desmosomes, adhesive junctions anchored by intermediate filaments. To study desmosomal networks, we skeletonised 853 muscle cells and their desmosomal partners in volume electron microscopy data covering an entire larva of the annelidPlatynereis. Muscle cells adhere to each other, to epithelial, glial, ciliated, and bristle-producing cells and to the basal lamina, forming a desmosomal connectome of over 2,000 cells. The aciculae – chitin rods that form an endoskeleton in the segmental appendages – are highly connected hubs in this network. This agrees with the many degrees of freedom of their movement, as revealed by video microscopy. Mapping motoneuron synapses to the desmosomal connectome allowed us to infer the extent of tissue influenced by motoneurons. Our work shows how cellular-level maps of synaptic and adherent force networks can elucidate body mechanics.
Abstract.
Bezares-Calderón LA, Berger J, Jasek S, Verasztó C, Mendes S, Gühmann M, Almeda R, Shahidi R, Jékely G (In Press). Neural circuitry of a polycystin-mediated hydrodynamic startle response for predator avoidance.
Abstract:
Neural circuitry of a polycystin-mediated hydrodynamic startle response for predator avoidance
AbstractStartle responses triggered by aversive stimuli including predators are widespread across animals. These coordinated whole-body actions require the rapid and simultaneous activation of a large number of muscles. Here we study a startle response in a planktonic larva to understand the whole-body circuit implementation of the behavior. Upon encountering water vibrations, larvae of the annelidPlatynereisclose their locomotor cilia and simultaneously contract the body and raise the parapodia. The startle response is mediated by collar receptor neurons expressing the polycystins PKD1-1 and PKD2-1. CRISPR-generatedPKD1-1andPKD2-1mutant larvae do not startle and fall prey to a copepod predator at a higher rate. Reconstruction of the whole-body connectome of the collar-receptor-cell circuitry revealed converging feedforward circuits to the ciliary bands and muscles. The wiring diagram suggests circuit mechanisms for the intersegmental and left-right coordination of the response. Our results reveal how polycystin-mediated mechanosensation can trigger a coordinated whole-body effector response involved in predator avoidance.Short SummaryThe neuronal circuitry of thePlatynereisstartle response links polycystin-dependent hydrodynamic sensors to muscle and ciliary effector cells
Abstract.
Williams EA, Verasztó C, Jasek S, Conzelmann M, Shahidi R, Bauknecht P, Jékely G (In Press). Synaptic and peptidergic connectome of a neurosecretory centre in the annelid brain.
Abstract:
Synaptic and peptidergic connectome of a neurosecretory centre in the annelid brain
AbstractNeurosecretory centres in animal brains use peptidergic signalling to influence physiology and behaviour. Understanding neurosecretory centre function requires mapping cell types, synapses, and peptidergic networks. Here we use electron microscopy and gene expression mapping to analyse the synaptic and peptidergic connectome of an entire neurosecretory centre. We mapped 78 neurosecretory neurons in the brain of larval Platynereis dumerilii, a marine annelid. These neurons form an anterior neurosecretory organ expressing many neuropeptides, including hypothalamic peptide orthologues and their receptors. Analysis of peptide-receptor pairs revealed sparsely connected networks linking specific neuronal subsets. We experimentally analysed one peptide-receptor pair and found that a neuropeptide can couple neurosecretory and synaptic brain signalling. Our study uncovered extensive non-synaptic signalling within a neurosecretory centre and its connection to the synaptic brain.
Abstract.
Verasztó C, Jasek S, Gühmann M, Shahidi R, Ueda N, Beard JD, Mendes S, Heinz K, Bezares-Calderón LA, Williams E, et al (In Press). Whole-animal connectome and cell-type complement of the three-segmented <i>Platynereis dumerilii</i> larva.
Abstract:
Whole-animal connectome and cell-type complement of the three-segmented Platynereis dumerilii larva
AbstractNervous systems coordinate effectors across the body during movements. We know little about the cellular-level structure of synaptic circuits for such body-wide control. Here we describe the whole-body synaptic connectome and cell-type complement of a three-segmented larva of the marine annelid Platynereis dumerilii. We reconstructed and annotated over 1,500 neurons and 6,500 non-neuronal cells in a whole-body serial electron microscopy dataset. The differentiated cells fall into 180 neuronal and 90 non-neuronal cell types. We analyse the modular network architecture of the entire nervous system and describe polysynaptic pathways from 428 sensory neurons to four effector systems – ciliated cells, glands, pigment cells and muscles. The complete somatic musculature and its innervation will be described in a companion paper. We also investigated intersegmental differences in cell-type complement, descending and ascending pathways, and mechanosensory and peptidergic circuits. Our work provides the basis for understanding whole-body coordination in annelids.
Abstract.
2019
Buchholz TO, Krull A, Shahidi R, Pigino G, Jékely G, Jug F (2019). Content-aware image restoration for electron microscopy. In (Ed)
Methods in Cell Biology, 277-289.
Abstract:
Content-aware image restoration for electron microscopy
Abstract.
2018
Verasztó C, Gühmann M, Jia H, Rajan VBV, Bezares-Calderón LA, Piñeiro-Lopez C, Randel N, Shahidi R, Michiels NK, Yokoyama S, et al (2018). Ciliary and rhabdomeric photoreceptor-cell circuits form a spectral depth gauge in marine zooplankton.
Elife,
7Abstract:
Ciliary and rhabdomeric photoreceptor-cell circuits form a spectral depth gauge in marine zooplankton.
Ciliary and rhabdomeric photoreceptor cells represent two main lines of photoreceptor-cell evolution in animals. The two cell types coexist in some animals, however how these cells functionally integrate is unknown. We used connectomics to map synaptic paths between ciliary and rhabdomeric photoreceptors in the planktonic larva of the annelid Platynereis and found that ciliary photoreceptors are presynaptic to the rhabdomeric circuit. The behaviors mediated by the ciliary and rhabdomeric cells also interact hierarchically. The ciliary photoreceptors are UV-sensitive and mediate downward swimming in non-directional UV light, a behavior absent in ciliary-opsin knockout larvae. UV avoidance overrides positive phototaxis mediated by the rhabdomeric eyes such that vertical swimming direction is determined by the ratio of blue/UV light. Since this ratio increases with depth, Platynereis larvae may use it as a depth gauge during vertical migration. Our results revealed a functional integration of ciliary and rhabdomeric photoreceptor cells in a zooplankton larva.
Abstract.
Author URL.
Bezares-Calderón LA, Berger J, Jasek S, Verasztó C, Mendes S, Gühmann M, Almeda R, Shahidi R, Jékely G (2018). Neural circuitry of a polycystin-mediated hydrodynamic startle response for predator avoidance.
Elife,
7Abstract:
Neural circuitry of a polycystin-mediated hydrodynamic startle response for predator avoidance.
Startle responses triggered by aversive stimuli including predators are widespread across animals. These coordinated whole-body actions require the rapid and simultaneous activation of a large number of muscles. Here we study a startle response in a planktonic larva to understand the whole-body circuit implementation of the behaviour. Upon encountering water vibrations, larvae of the annelid Platynereis close their locomotor cilia and simultaneously raise the parapodia. The response is mediated by collar receptor neurons expressing the polycystins PKD1-1 and PKD2-1. CRISPR-generated PKD1-1 and PKD2-1 mutant larvae do not startle and fall prey to a copepod predator at a higher rate. Reconstruction of the whole-body connectome of the collar-receptor-cell circuitry revealed converging feedforward circuits to the ciliary bands and muscles. The wiring diagram suggests circuit mechanisms for the intersegmental and left-right coordination of the response. Our results reveal how polycystin-mediated mechanosensation can trigger a coordinated whole-body effector response involved in predator avoidance.
Abstract.
Author URL.
2017
Verasztó C, Ueda N, Bezares-Calderón LA, Panzera A, Williams EA, Shahidi R, Jékely G (2017). Ciliomotor circuitry underlying whole-body coordination of ciliary activity in the Platynereis larva.
Elife,
6Abstract:
Ciliomotor circuitry underlying whole-body coordination of ciliary activity in the Platynereis larva.
Ciliated surfaces harbouring synchronously beating cilia can generate fluid flow or drive locomotion. In ciliary swimmers, ciliary beating, arrests, and changes in beat frequency are often coordinated across extended or discontinuous surfaces. To understand how such coordination is achieved, we studied the ciliated larvae of Platynereis dumerilii, a marine annelid. Platynereis larvae have segmental multiciliated cells that regularly display spontaneous coordinated ciliary arrests. We used whole-body connectomics, activity imaging, transgenesis, and neuron ablation to characterize the ciliomotor circuitry. We identified cholinergic, serotonergic, and catecholaminergic ciliomotor neurons. The synchronous rhythmic activation of cholinergic cells drives the coordinated arrests of all cilia. The serotonergic cells are active when cilia are beating. Serotonin inhibits the cholinergic rhythm, and increases ciliary beat frequency. Based on their connectivity and alternating activity, the catecholaminergic cells may generate the rhythm. The ciliomotor circuitry thus constitutes a stop-and-go pacemaker system for the whole-body coordination of ciliary locomotion.
Abstract.
Author URL.
Williams EA, Verasztó C, Jasek S, Conzelmann M, Shahidi R, Bauknecht P, Mirabeau O, Jékely G (2017). Synaptic and peptidergic connectome of a neurosecretory center in the annelid brain.
Elife,
6Abstract:
Synaptic and peptidergic connectome of a neurosecretory center in the annelid brain.
Neurosecretory centers in animal brains use peptidergic signaling to influence physiology and behavior. Understanding neurosecretory center function requires mapping cell types, synapses, and peptidergic networks. Here we use transmission electron microscopy and gene expression mapping to analyze the synaptic and peptidergic connectome of an entire neurosecretory center. We reconstructed 78 neurosecretory neurons and mapped their synaptic connectivity in the brain of larval Platynereis dumerilii, a marine annelid. These neurons form an anterior neurosecretory center expressing many neuropeptides, including hypothalamic peptide orthologs and their receptors. Analysis of peptide-receptor pairs in spatially mapped single-cell transcriptome data revealed sparsely connected networks linking specific neuronal subsets. We experimentally analyzed one peptide-receptor pair and found that a neuropeptide can couple neurosecretory and synaptic brain signaling. Our study uncovered extensive networks of peptidergic signaling within a neurosecretory center and its connection to the synaptic brain.
Abstract.
Author URL.
2015
Shahidi R, Williams EA, Conzelmann M, Asadulina A, Verasztó C, Jasek S, Bezares-Calderón LA, Jékely G (2015). A serial multiplex immunogold labeling method for identifying peptidergic neurons in connectomes.
Elife,
4Abstract:
A serial multiplex immunogold labeling method for identifying peptidergic neurons in connectomes.
Electron microscopy-based connectomics aims to comprehensively map synaptic connections in neural tissue. However, current approaches are limited in their capacity to directly assign molecular identities to neurons. Here, we use serial multiplex immunogold labeling (siGOLD) and serial-section transmission electron microscopy (ssTEM) to identify multiple peptidergic neurons in a connectome. The high immunogenicity of neuropeptides and their broad distribution along axons, allowed us to identify distinct neurons by immunolabeling small subsets of sections within larger series. We demonstrate the scalability of siGOLD by using 11 neuropeptide antibodies on a full-body larval ssTEM dataset of the annelid Platynereis. We also reconstruct a peptidergic circuitry comprising the sensory nuchal organs, found by siGOLD to express pigment-dispersing factor, a circadian neuropeptide. Our approach enables the direct overlaying of chemical neuromodulatory maps onto synaptic connectomic maps in the study of nervous systems.
Abstract.
Author URL.
Randel N, Shahidi R, Verasztó C, Bezares-Calderón LA, Schmidt S, Jékely G (2015). Inter-individual stereotypy of the Platynereis larval visual connectome.
Elife,
4Abstract:
Inter-individual stereotypy of the Platynereis larval visual connectome.
Developmental programs have the fidelity to form neural circuits with the same structure and function among individuals of the same species. It is less well understood, however, to what extent entire neural circuits of different individuals are similar. Previously, we reported the neuronal connectome of the visual eye circuit from the head of a Platynereis dumerilii larva (Randel et al. 2014). We now report a full-body serial section transmission electron microscopy (ssTEM) dataset of another larva of the same age, for which we describe the connectome of the visual eyes and the larval eyespots. Anatomical comparisons and quantitative analyses of the two circuits reveal a high inter-individual stereotypy of the cell complement, neuronal projections, and synaptic connectivity, including the left-right asymmetry in the connectivity of some neurons. Our work shows the extent to which the eye circuitry in Platynereis larvae is hard-wired.
Abstract.
Author URL.
2014
Randel N, Asadulina A, Bezares-Calderón LA, Verasztó C, Williams EA, Conzelmann M, Shahidi R, Jékely G (2014). Neuronal connectome of a sensory-motor circuit for visual navigation.
Elife,
3Abstract:
Neuronal connectome of a sensory-motor circuit for visual navigation.
Animals use spatial differences in environmental light levels for visual navigation; however, how light inputs are translated into coordinated motor outputs remains poorly understood. Here we reconstruct the neuronal connectome of a four-eye visual circuit in the larva of the annelid Platynereis using serial-section transmission electron microscopy. In this 71-neuron circuit, photoreceptors connect via three layers of interneurons to motorneurons, which innervate trunk muscles. By combining eye ablations with behavioral experiments, we show that the circuit compares light on either side of the body and stimulates body bending upon left-right light imbalance during visual phototaxis. We also identified an interneuron motif that enhances sensitivity to different light intensity contrasts. The Platynereis eye circuit has the hallmarks of a visual system, including spatial light detection and contrast modulation, illustrating how image-forming eyes may have evolved via intermediate stages contrasting only a light and a dark field during a simple visual task.
Abstract.
Author URL.
2013
Conzelmann M, Williams EA, Tunaru S, Randel N, Shahidi R, Asadulina A, Berger J, Offermanns S, Jékely G (2013). Conserved MIP receptor-ligand pair regulates Platynereis larval settlement.
Proc Natl Acad Sci U S A,
110(20), 8224-8229.
Abstract:
Conserved MIP receptor-ligand pair regulates Platynereis larval settlement.
Life-cycle transitions connecting larval and juvenile stages in metazoans are orchestrated by neuroendocrine signals including neuropeptides and hormones. In marine invertebrate life cycles, which often consist of planktonic larval and benthic adult stages, settlement of the free-swimming larva to the sea floor in response to environmental cues is a key life cycle transition. Settlement is regulated by a specialized sensory-neurosecretory system, the larval apical organ. The neuroendocrine mechanisms through which the apical organ transduces environmental cues into behavioral responses during settlement are not yet understood. Here we show that myoinhibitory peptide (MIP)/allatostatin-B, a pleiotropic neuropeptide widespread among protostomes, regulates larval settlement in the marine annelid Platynereis dumerilii. MIP is expressed in chemosensory-neurosecretory cells in the annelid larval apical organ and signals to its receptor, an orthologue of the Drosophila sex peptide receptor, expressed in neighboring apical organ cells. We demonstrate by morpholino-mediated knockdown that MIP signals via this receptor to trigger settlement. These results reveal a role for a conserved MIP receptor-ligand pair in regulating marine annelid settlement.
Abstract.
Author URL.
Randel N, Bezares-Calderón LA, Gühmann M, Shahidi R, Jékely G (2013). Expression dynamics and protein localization of rhabdomeric opsins in Platynereis larvae.
Integr Comp Biol,
53(1), 7-16.
Abstract:
Expression dynamics and protein localization of rhabdomeric opsins in Platynereis larvae.
The larval stages of polychaete annelids are often responsive to light and can possess one to six eyes. The early trochophore larvae of the errant annelid Platynereis dumerilii have a single pair of ventral eyespots, whereas older nectochaete larvae have an additional two pairs of dorsal eyes that will develop into the adult eyes. Early Platynereis trochophores show robust positive phototaxis starting on the first day of development. Even though the mechanism of phototaxis in Platynereis early trochophore larvae is well understood, no photopigment (opsin) expression has yet been described in this stage. In late trochophore larvae, a rhabdomeric-type opsin, r-opsin1, expressed in both the eyespots and the adult eyes has already been reported. Here, we identify another Platynereis rhabdomeric opsin, r-opsin3, that is expressed in a single photoreceptor in the eyespots in early trochophores, suggesting that it mediates early larval phototaxis. We also show that r-opsin1 and r-opsin3 are expressed in adjacent photoreceptor cells in the eyespots in later stages, indicating that a second eyespot-photoreceptor differentiates in late trochophore larvae. Using serial transmission electron microscopy (TEM), we identified and reconstructed both photoreceptors and a pigment cell in the late larval eyespot. We also characterized opsin expression in the adult eyes and found that the two opsins co-express there in several photoreceptor cells. Using antibodies recognizing r-opsin1 and r-opsin3 proteins, we demonstrate that both opsins localize to the rhabdomere in all six eyes. In addition, we found that r-opsin1 mRNA is localized to, and translated in, the projections of the adult eyes. The specific changes we describe in opsin transcription and translation and in the cellular complement suggest that the six larval eyes undergo spectral and functional maturation during the early planktonic phase of the Platynereis life cycle.
Abstract.
Author URL.
2004
Noseda M, McLean G, Niessen K, Chang L, Pollet I, Montpetit R, Shahidi R, Dorovini-Zis K, Li L, Beckstead B, et al (2004). Notch activation results in phenotypic and functional changes consistent with endothelial-to-mesenchymal transformation.
Circ Res,
94(7), 910-917.
Abstract:
Notch activation results in phenotypic and functional changes consistent with endothelial-to-mesenchymal transformation.
Various studies have identified a critical role for Notch signaling in cardiovascular development. In this and other systems, Notch receptors and ligands are expressed in regions that undergo epithelial-to-mesenchymal transformation. However, there is no direct evidence that Notch activation can induce mesenchymal transdifferentiation. In this study we show that Notch activation in endothelial cells results in morphological, phenotypic, and functional changes consistent with mesenchymal transformation. These changes include downregulation of endothelial markers (vascular endothelial [VE]-cadherin, Tie1, Tie2, platelet-endothelial cell adhesion molecule-1, and endothelial NO synthase), upregulation of mesenchymal markers (alpha-smooth muscle actin, fibronectin, and platelet-derived growth factor receptors), and migration toward platelet-derived growth factor-BB. Notch-induced endothelial-to-mesenchymal transformation does not seem to require external regulation and is restricted to cells expressing activated Notch. Jagged1 stimulation of endothelial cells induces a similar mesenchymal transformation, and Jagged1, Notch1, and Notch4 are expressed in the ventricular outflow tract during stages of endocardial cushion formation. This is the first evidence that Jagged1-Notch interactions induce endothelial-to-mesenchymal transformation, and our findings suggest that Notch signaling may be required for proper endocardial cushion differentiation and/or vascular smooth muscle cell development.
Abstract.
Author URL.
2000
Duriez PJ, Wong F, Dorovini-Zis K, Shahidi R, Karsan A (2000). A1 functions at the mitochondria to delay endothelial apoptosis in response to tumor necrosis factor.
J Biol Chem,
275(24), 18099-18107.
Abstract:
A1 functions at the mitochondria to delay endothelial apoptosis in response to tumor necrosis factor.
Tumor necrosis factor (TNF) does not cause endothelial apoptosis unless the expression of cytoprotective genes is blocked. We have previously demonstrated that one of the TNF-inducible cytoprotective genes is the Bcl-2 family member, A1. A1 is induced by the action of the transcription factor, NFkappaB, in response to inflammatory mediators. In this report we demonstrate that, as with other cell types, inhibition of NFkappaB initiates microvascular endothelial apoptosis in response to TNF. A1 is able to inhibit this apoptosis over 24 h. We demonstrate that A1 is localized to and functions at the mitochondria. Whereas A1 is able to inhibit mitochondrial depolarization, loss of cytochrome c, cleavage of caspase 9, BID, and poly(ADP-ribose) polymerase, it does not block caspase 8 or caspase 3 cleavage. In contrast, A1 is not able to prevent endothelial apoptosis by TNF over 72 h, when NFkappaB signaling is blocked. On the other hand, the caspase inhibitor, benzyloxycarbonyl-VAD-formylmethyl ketone, completely blocks TNF-induced endothelial apoptosis over 72 h. Our findings indicate that A1 is able to maintain temporary survival of endothelial cells in response to TNF by maintaining mitochondrial viability and function. However, a mitochondria-independent caspase pathway eventually results in endothelial death despite mitochondrial protection by A1.
Abstract.
Author URL.
