Speakers

Selected speakers for the afternoon session

15 minutes presentations with 5 min Q&A

Christian F. Christensen

Presynaptic Active Zones Tune to Nutrient Availability

Christian F. Christensen, Vera Kovaleva, Natalie Blaum, Alexander M. Walter.

Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen.

Synaptic plasticity, the change of the connection strength between nerve cells, enables an organism to adapt to environmental changes. While its roles in learning and memory are well appreciated, its involvement in metabolic adaptation remains poorly understood. Using quantitative imaging of endogenously tagged synaptic proteins in the genetically tractable model organism; Drosophila melanogaster, we find that brain-wide levels of key targets for presynaptic plasticity are shifted upon metabolic challenge in adult flies. We observe that nutrient deprivation selectively alters the abundance of presynaptic components, including the voltage-gated Ca2+ channel Cacophony and the essential release-factor Unc-13. In contrast, levels of the core active zone scaffold Bruchpilot (mammalian ELKS family) and the postsynaptic marker Dlg1 (mammalian PSD95) remain stable, suggesting a targeted remodeling of presynaptic active zones in response to shifts in metabolic state. Furthermore, introduction of a human disease-associated gain-of-function mutation in unc-13 (Lipstein et al., 2017) enhances neurotransmitter release in flies. We find that the mutation is associated with elevated in-vivo brain-wide activity, impaired internal energy homeostasis and that it renders flies more susceptible to starvation-induced lethality. These findings implicate presynaptic plasticity in metabolic adaptation and highlight a potential vulnerability conferred by synaptic mutations. Ongoing work aims to elucidate the molecular mechanisms underlying this adaptive remodeling and its disruption in disease contexts.

Presenting at: 13:30 - 13:50

Kerttu Kotala

Lubel-induced Met1-ubiquitination activates the Drosophila caspase Dredd and NF-κB signalling

Kerttu Kotala1,2, Veera Luukkonen1, Anna M. Dahlström1,2, Anna L. Aalto1,2, Fanny Ehrström1, Aravind K. Mohan1,2, Luis Alberto Baena-Lopez3, Annika Meinander1,2

1 Faculty of Science and Engineering, Cell Biology, Åbo Akademi University, Turku, Finland

2 InFlames Research Flagship, Åbo Akademi University, Turku, Finland

3 Center of Molecular Biology Severo Ochoa, Madrid, Spain

Inflammatory intestinal diseases, caused by dysregulation of innate immune signalling, are an escalating global health problem and a major risk factor for the development of colorectal cancer. These diseases result from prolonged inflammation and dysregulation of innate immune signalling in the intestinal epithelium. The intestinal epithelium is a key immune barrier that must balance rapid antimicrobial defence with tolerance to commensal microbes. A key signalling pathway involved in controlling this balance is the nuclear factor kappa B (NF-κB) pathway. This pathway is activated in response to pathogenic signals, and upon activation, it regulates the production of proinflammatory cytokines, the recruitment of immune cells, and promotes cell survival. In Drosophila, a conserved version of the NF-κB pathway is known as the immune deficiency (Imd) pathway. While linear ubiquitination has emerged as an important regulator of intestinal Imd signalling, its molecular targets and mechanisms remain poorly understood. Here, we show that the initiator caspase and caspase-8 homologue Dredd is a direct substrate of the linear ubiquitin E3 ligase Lubel. Our results indicate that Met1-ubiquitination of Dredd is signal-dependent in cultured cells and in vivo, and that this modification occurs on its first death effector domain. Furthermore, Met1-ubiquitination of Dredd is enhanced through Lys63-linked chains synthesized by Death-associated inhibitor of apoptosis 2 Diap2, suggesting the formation of heterotypic ubiquitin chains. Disruption of Dredd Met1-ubiquitination compromises host survival following oral infection with Gram-negative bacteria, highlighting its functional relevance in intestinal immunity. To study when and in which cells Dredd is activated during inflammation in vivo, we have developed a transgenic fly line carrying a Dredd-specific QF-reporter. Using this tool, we show that Dredd is activated in intestinal epithelial cells upon infection in a Met1-ubiquitination-dependent manner, and that Dredd activation occurs in parallel with NF-κB transcription factor nuclear translocation. Loss of Lubel markedly reduces both Dredd activation and NF-κB signalling in the gut. In addition to gut activation, we visualise Dredd activation in the fatbody in response to systemic infection. Together, our findings identify Met1-ubiquitination as a key regulatory switch that licenses non-apoptotic Dredd activity and NF-κB activation in barrier epithelia. This work reveals a conserved mechanism by which linear ubiquitination fine-tunes inflammatory caspase signalling to promote effective local immune responses without compromising tissue integrity.

Presenting at 13:50-14:10

Silas Boye Nissen

Cluster Assembly Dynamics Drive Fidelity of Planar Cell Polarity Polarization

Silas Boye Nissen1,2,3, Alexis T. Weiner1, Kaye Suyama1, Pablo Sanchez Bosch1, Maiya Yu1,4, Song Song1, Yuan Gu5, Alexander R. Dunn3,*, Jeffrey D. Axelrod1,*

1 Department of Pathology, Stanford University School of Medicine, Stanford, CA, USA

2 The Novo Nordisk Foundation Center for Stem Cell Medicine (reNEW), University of Copenhagen, Copenhagen, Denmark

3 Department of Chemical Engineering, Stanford University, Stanford, CA, USA

4. Departments of Structural Biology and Molecular and Cellular Physiology, and Graduate program in Structural Biology, Stanford University School of Medicine, Stanford, CA, USA

5 Quantitative Science Unit, Stanford University School of Medicine, Stanford, CA, USA

* These authors contributed equally

Planar cell polarity (PCP) signaling orients epithelial cells along an in-plane axis and is required for embryogenesis. In PCP signaling, distinct molecular subcomplexes segregate to opposite sides of cells, forming polarized clusters. Using quantitative photobleaching and mathematical modeling, we show that clusters become increasingly polarized and correctly oriented as they grow, indicating a general mechanism by which clustering amplifies weak and noisy inputs into robust signaling output.

Presenting at 14:10-14:30

Sylvana Tabone

From Genetic Association to Mechanism: Investigating a Novel ALS Genetic Risk Factor

Sylvana Tabone, BSc. (Hons), MSc.1

1University of Malta

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease driven by complex gene-environment interactions. This study characterises a novel GWAS-identified risk factor involved in vesicle trafficking. Using Drosophila models, we investigate this gene’s role in motor circuits and the cellular mechanisms underlying progressive motor deficits. Our findings link genetic susceptibility to neuronal dysfunction and highlight potential avenues for disease prevention and targeted therapies for ALS.

Presenting at 15:00-15:20

Lea Fischbach

Coordinated mitochondrial dynamics coupled with a microtubule-based membrane protrusion network in the Drosophila pupal wing

Lea Fischbach¹, Osamu Shimmi ¹ ²

1 University of Helsinki,

2 University of Tartu

In the pupal wing, we uncover a membrane‑protrusion network that links the two epithelial layers and keeps their growth synchronized. Within this network, mitochondria move and cell shape changes occur in step with microtubule dynamics. Blocking mitochondrial movement disrupts the lattice and distorts the final wing architecture, revealing a previously unrecognized protrusion‑mediated communication system that couples the cytoskeleton and organelles to coordinate epithelial morphogenesis.

Presenting at 15:20-15:40

Samuel W. Vernon

Spontaneous neurotransmitter release is regulated by Unc-5

Samuel W. Vernon, Evelyne Ruchti, Chiara Paolantoni, Rebecca Smith, Marine V. Campenhoudt and Brian D. McCabe.

Brain Mind Institute, EPFL - Swiss Federal Institute of Technology Lausanne, Lausanne, Switzerland.

✉email: brian.mccabe@epfl.ch

The spontaneous quantal release of single vesicles of neurotransmitter in the absence of an action potential is a universal feature of all neuronal chemical synapses. These ‘miniature events’ have long been thought to be stochastic and unregulated, leading to measurement of their frequency as a widely employed estimate of the number of synaptic connections within neuronal networks. Here we show using high resolution live imaging of Drosophila adult glutamatergic synapses that the spontaneous release of neurotransmitters occurs only from a subset of synaptic release sites. We discover that the proportion of release sites participating in spontaneous neurotransmitter release is regulated by a novel synaptic function of the transmembrane signalling receptor Unc-5 which is heparan sulfate proteoglycan dependent, but Netrin independent. We show that synaptic Unc-5 forms a complex with the SNARE protein Syntaxin to regulate neurotransmitter release. The depletion of Unc-5 in adult synapses diminishes miniature events, inducing terminal degeneration and behavioural decline. Our results reveal that ‘spontaneous’ neurotransmitter release is a singular, essential and independently regulated property of synapses that is critical for the structural integrity and behavioural capability of synaptic connections.

Presenting at 15:40-16:00

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