Biology subjects

Scholz, N.

Publications and source records attributed to Scholz, N..

10 recordsLinked to original sources

bioRxiv2026

Restoration of (nor)adrenergic-like Ca2+ signalling counteracts age-related motor decline

Aging disrupts neural function, but whether impaired noradrenergic control of brain metabolism contributes to functional decline remains unclear. Using genetically encoded fluorescent sensors we measured metabolic and signaling responses in neurons and glia of living Drosophila brains following stimulation with octopamine, the invertebrate analogue of noradrenaline. Aging was accompanied by neurodegeneration, reduced locomotion and enhanced oxidative whole-brain metabolism. Octopamine increased D-glucose uptake selectively in astrocytes and elevated L-lactate in both astrocytes and neurons, consistent with astrocytic glycolysis coupled to neuronal L-lactate uptake; monocarboxylate transporter inhibition caused selective astrocytic L-lactate accumulation. In aged animals octopamine-evoked metabolic responses in astrocytes and neural Ca2+ transients were markedly reduced. This impairment was associated with lower expression of adrenoceptor-like tyramine 1 receptor (Tyr1R). Selective Tyr1R overexpression in (nor)adrenergic-like Tdc2 neurons prolonged lifespan, restored Ca2+ signalling and improved locomotor performance. These findings identify Tyr1R-dependent Ca2+ signalling as an age-sensitive regulator of brain metabolism and motor function.

neuroscience↗

bioRxiv2025

Polycystin-1 acts as an atypical adhesion GPCR that responds to novel Wnt signaling and mechanical stimuli

Mutations in the genes encoding Polycystin-1 and 2 cause autosomal dominant polycystic kidney disease (ADPKD). These proteins cellular functions and the mechanisms through which their absence causes disease are unknown. We find that the behavior of the 11 transmembrane domain polycystin-1 protein resembles that of an adhesion G protein-coupled receptor when activated by Wnt ligands. Exposure to Wnt ligands causes shedding of the polycystin-1 N terminal region, exposing a tethered agonist that activates G protein-dependent functions of the membrane-associated C terminal fragment. Activated polycystin-1 communicates through G13 to activate RhoA, leading in turn to the ROCK-dependent phosphorylation and inactivation of GSK3{beta}. Activated polycystin-1 traffics out of the primary cilium through an arrestin-dependent mechanism, and arrestin involvement is required for signaling to occur. These data elaborate a function for polycystin-1 that is structurally non-canonical and that is directly connected to pathways whose perturbation results in cystic disease. SummaryThe polycystin-1 protein can activate a signaling pathway resembling those employed by non-canonical adhesion G protein coupled receptors, which is induced by Wnt9b binding and which leads to leads to inhibition of the GSK3{beta} kinase and removal of polycystin-1 from the primary cilium. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC="FIGDIR/small/655326v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1b32dc1org.highwire.dtl.DTLVardef@80ee43org.highwire.dtl.DTLVardef@9aa441org.highwire.dtl.DTLVardef@95ceb1_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract PC1 resides at baseline in the primary cilium. PC1 behaves as an aGPCR that responds to Wnt9b and to flow-induced ATP release by departing from the cilium and initiating the inhibition of GSK3. The schematic diagram presents a model that integrates the findings presented here. Wnt9b binding to the PC1 NTF leads to shedding of the NTF, exposing the tethered agonist to activate the PC1 receptor-mediated signaling cascade, which involves triggering G13 binding and the subsequent nucleotide exchange and GTP-loading of RhoA. GTP-bound RhoA stimulates the kinase activity of ROCK, which phosphorylates and inhibits GSK3. C_FIG

cell biology↗

bioRxiv2024

Mechanical load conditions the spectrin network to `run-on' proteolysis and promotes early onset neurodegeneration

The correct homeostasis of the neuronal cytoskeleton and its dynamics is important for health and disease. Forces constantly act on the neurons in our body, leading to subtle axonal deformations and length changes. The spectrin cytoskeleton is known as a key player that protects neurons against mechanical damage. How the spectrin cytoskeleton changes with age and how it influences mechanoprotection in aging animals is not well understood. Using an interdisciplinary approach, we show that age causes a loss of proprioception during the first few days of adulthood in C. elegans via spectrin unfolding, loss of mechanical tension and degradation of the spectrin cytoskeleton. Guided by a proteomic screen to identify potential spectrin binding partners, we found that this early-onset neurodegeneration can be suppressed in clp-1 mutants and by targeted expression of an engineered chaperone derived from human B-crystallin. Our data suggest that the spectrin cytoskeleton is sensitized to proteolytic damage by calcium-sensitive proteases when mechanical stresses conspires with high-calcium concentrations as in proprioceptive signaling. These results may have implications for the etiology of diseases in which high calcium dynamics and mechanical stress co-incide.

neuroscience↗

bioRxiv2023

Drosophila Bchs overexpression recapitulates human WDFY3 neurodevelopmental phenotypes with implications for glial cell involvement in altered head circumference

The autophagy adaptor WDFY3 is linked to neurodevelopmental delay and altered brain size. Loss-of-function variants are associated with an increased brain size in both humans and mice. We thus, hypothesized that the microcephaly observed in some of the patients may be related to a gain-of-function of the WDFY3 gene product. While the role of WDFY3 loss-of-function has been studied extensively in neurons, little is known about the effects of WDFY3 overexpression in different neural cell types. We utilized a Drosophila melanogaster overexpression model to investigate the effect of the WDFY3 ortholog Bchs (blue cheese) on development, CNS size, and gene expression profiles. Glial and neuronal overexpression of Bchs impaired CNS development, locomotion and autophagy. Glial overexpression of Bchs also altered CNS size significantly. We identified 79 genes that were differentially expressed and overlapped in flies that overexpress Bchs in glial and neuronal cells, respectively. Additionally, upon neuronal Bchs overexpression differentially expressed genes clustered in gene ontology categories associated with autophagy and mitochondria. Our data indicate that WDFY3/Bchs overexpression in both neurons and glial cells results in impaired neural development, which corresponds to symptoms observed in WDFY3-related neurodevelopmental delay.

neuroscience↗

bioRxiv2023

HECTD1 is both a positive regulator and substrate of caspase-3 activity during apoptotic cell death

Programmed cell death is a complex and tightly regulated sequence of events that determines cell fate during tissue homeostasis, development, and pathogenesis. The small protein modifier ubiquitin mediates important regulatory functions during cell death by regulating the stability and activity of checkpoint proteins and the assembly of cell death signalling complexes. The caspase family of cysteine aspartases are essential effectors of apoptotic cell death. Components of the ubiquitin system including RING ubiquitin ligases XIAP, MDM2, RBX1; RBR E3 ubiquitin ligases Parkin and LUBAC; and HECT E3 ubiquitin ligases NEDD4 and Itch are also substrates of caspase-mediated cleavage. In the case of NEDD4 and Itch, the single cleavage event occurs outside of the catalytic HECT domain and it remains unclear whether such cleavage events impact on ubiquitin ligase activity and/or function. Here, we identified the E3 ubiquitin ligase HECTD1 as the third HECT E3 cleaved by caspase-mediated cleavage during apoptotic cell death, in a manner which does not affect the integrity of the catalytic C-ter HECT domain. We mapped the single cleavage event to DFLD1664{downarrow}S and showed that the cleaved C-ter product, which contains the HECT ligase domain, is as stable as the endogenous full length protein. We also found that HECTD1 transient depletion led to reduced caspase-3 activity, but not caspase 8 nor 9. Furthermore, we also identified caspase-3 as the protease responsible for HECTD1 cleavage at Asp1664 suggesting that HECTD1 and caspase-3 might be part of a novel feedback loop mechanism during apoptotic cell death. This study highlight novel crosstalk between cell death mechanisms and the ubiquitin system and raises important questions on whether proteolytic cleavage of E3 ubiquitin ligases might represent an underappreciated mode of regulation during cell death mechanisms.

cell biology↗

bioRxiv2023

Intron retention of an adhesion GPCR generates single transmembrane-helix isoforms to enable 7TM-adhesion GPCR function

Adhesion G protein-coupled receptors (aGPCR) function as metabotropic mechanosensors in the nervous system and other organs. aGPCR are heavily spliced forecasting an extraordinary molecular structural diversity. Many predicted isoforms lack the transmembrane (7TM) signaling subunit, but to what extent these non-GPCR isoforms are produced and what physiological purpose they serve is unknown. Alternative splicing through intron retention of ADGRL/Latrophilin/Cirl mRNA in Drosophila generates transcripts encoding unconventional proteins with an extracellular domain anchored by a single transmembrane helix (Cirl1TM). Here, we show that Cirl1TM transcripts are translated in vivo and that Cirl1TM binds Cirl7TM N-terminal fragment-dependently. This interaction enables mechanosensory neurons to distinguish input intensities through Go-dependent signaling. Similarly, a direct interaction was found for mammalian GPR126/ADGRG6 isoforms. Together, our findings define intron retention and isoform-specific heteromerization as extraordinary molecular strategies to adjust Cirl-dependent mechanosensation and demonstrate physiological relevance of versatile aGPCR isoform repertoire to tune cellular responsiveness.

neuroscience↗

bioRxiv2022

High-resolution analysis of individual Drosophila melanogaster larvae within groups uncovers inter- and intra-individual variability in locomotion and its neurogenetic modulation

Neuronally orchestrated muscular movement and locomotion are defining faculties of multicellular animals. Due to its numerically simple brain and neuromuscular system and its genetic accessibility, the larva of the fruit fly Drosophila melanogaster is an established model to study these processes at tractable levels of complexity. However, although the faculty of locomotion clearly pertains to the individual animal, present studies of locomotion in larval Drosophila mostly use group assays and measurements aggregated across individual animals. The alternative is to measure animals one at a time, an extravagance for larger-scale analyses. In principle or in practice, this in particular rules out grasping the inter- and intra-individual variability in locomotion and its genetic and neuronal determinants. Here we present the IMBA (Individual Maggot Behaviour Analyser) for tracking and analysing the behaviour of individual larvae within groups. Using a combination of computational modelling and statistical approaches, the IMBA reliably resolves individual identity across collisions. It does not require specific hardware and can therefore be used in non-expert labs. We take advantage of the IMBA first to systematically describe the inter- and intra-individual variability in free, unconstrained locomotion in wild-type animals. We then report the discovery of a novel, complex locomotion phenotype of a mutant lacking an adhesion-type GPCR. The IMBA further allows us to determine, at the level of individual animals, the modulation of locomotion across repeated activations of dopamine neurons. Strikingly, IMBA can also be used to analyse silly walks, that is patterns of locomotion it was not originally designed to investigate. This is shown for the transient backward locomotion induced by brief optogenetic activation of the brain-descending mooncrawler neurons, and the variability in this behaviour. Thus, the IMBA is an easy-to-use toolbox allowing an unprecedentedly rich view of the behaviour and behavioural variability of individual Drosophila larvae, with utility in multiple biomedical research contexts.

neuroscience↗

bioRxiv2021

The E3 ubiquitin ligase HECTD1 contributes to cell cycle progression through an effect on mitosis

Mechanistic studies of how protein ubiquitylation regulates the cell cycle, in particular during mitosis, has provided unique insights which have contributed to the emergence of the Ubiquitin code. In contrast to RING E3 ubiquitin ligases such as the APC/c ligase complex, the contribution of other E3 ligase families during cell cycle progression remains less well understood. Similarly, the contribution of ubiquitin chain types beyond homotypic K48 chains in S-phase or branched K11/K48 chains assembled by APC/c during mitosis, also remains to be fully determined. Our recent findings that HECTD1 ubiquitin ligase activity assembles branched K29/K48 ubiquitin linkages prompted us to evaluate its function during the cell cycle. We used transient knockdown and genetic knockout to show that HECTD1 depletion in HEK293T and HeLa cells decreases cell proliferation and we established that this is mediated through loss of its ubiquitin ligase activity. Interestingly, we found that HECTD1 depletion increases the proportion of cells with aligned chromosomes (Prometa/Metaphase). We confirmed this molecularly using phospho-Histone H3 (Ser28) as a marker of mitosis. Time-lapse microscopy of NEBD to anaphase onset established that HECTD1-depleted cells take on average longer to go through mitosis. To explore the mechanisms involved, we used proteomics to explore the endogenous HECTD1 interactome in mitosis and validated the Mitosis Checkpoint Complex protein BUB3 as a novel HECTD1 interactor. In line with this, we found that HECTD1 depletion reduces the activity of the Spindle Assembly Checkpoint. Overall, our data suggests a novel role for HECTD1 ubiquitin ligase activity in mitosis.

cell biology↗

bioRxiv2020

Functional diversity of PFKFB3 splice variants in glioblastomas

Tumor cells tend to metabolize glucose through aerobic glycolysis instead of oxidative phosphorylation in mitochondria. One of the rate limiting enzymes of glycolysis is 6-phosphofructo-1-kinase, which is allosterically activated by fructose 2,6-bisphosphate which in turn is produced by 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2 or PFKFB). Mounting evidence suggests that cancerous tissues overexpress the PFKFB isoenzyme, PFKFB3, being causing enhanced proliferation of cancer cells. Initially, six PFKFB3 splice variants with different C-termini have been documented in humans. More recently, additional splice variants with varying N-termini were discovered the functions of which are to be uncovered. Glioblastoma is one of the deadliest forms of brain tumors. Up to now, the role of PFKFB3 splice variants in the progression and prognosis of glioblastomas is only partially understood. In this study, we first re-categorized the PFKFB3 splice variant repertoire to simplify the denomination. We investigated the impact of increased and decreased levels of PFKFB3-4 (former UBI2K4) and PFKFB3-5 (former variant 5) on the viability and proliferation rate of glioblastoma U87 and HEK-293 cells. The simultaneous knock-down of PFKFB3-4 and PFKFB3-5 led to a decrease in viability and proliferation of U87 and HEK-293 cells as well as a reduction in HEK-293 cell colony formation. Overexpression of PFKFB3-4 but not PFKFB3-5 resulted in increased cell viability and proliferation. This finding contrasts with the common notion that overexpression of PFKFB3 enhances tumor growth, but instead suggests splice variant-specific effects of PFKFB3, apparently with opposing effects on cell behaviour. Strikingly, in line with this result, we found that in human IDH-wildtype glioblastomas, the PFKFB3-4 to PFKFB3-5 ratio was significantly shifted towards PFKFB3-4 when compared to control brain samples. Our findings indicate that the expression level of distinct PFKFB3 splice variants impinges on tumorigenic properties of glioblastomas and that splice pattern may be of important diagnostic value for glioblastoma.

cancer biology↗

bioRxiv2018

Complexin cooperates with Bruchpilot to tether synaptic vesicles to the active zone cytomatrix

Information processing by the nervous system depends on the release of neurotransmitter from synaptic vesicles (SVs) at the presynaptic active zone. Molecular components of the cytomatrix at the active zone (CAZ) regulate the final stages of the SV cycle preceding exocytosis and thereby shape the efficacy and plasticity of synaptic transmission. Part of this regulation is reflected by a physical association of SVs with filamentous CAZ structures. However, our understanding of the protein interactions underlying SV tethering by the CAZ is far from complete. The very C-terminal region of Bruchpilot (Brp), a key component of the Drosophila CAZ, participates in SV tethering. Yet so far, no vesicular or cytoplasmic molecules have been reported to engage in an interaction with Brps C-terminus. Here, we carried out an in vivo screen for molecules that link the Brp C-terminus to SVs. This strategy identified the conserved SNARE (soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor) regulator Complexin (Cpx) as a vesicular interaction partner of Brp. We show that Brp and Cpx interact genetically and functionally. Interfering with Cpx targeting to SVs mirrored distinctive features of a C-terminal Brp truncation: impaired SV recruitment to the CAZ and enhanced short-term synaptic depression. Extending the study beyond Drosophila synapses, we interrogated active zones of mouse rod bipolar cells. Here, too, we collected evidence for an evolutionarily conserved role of Cpx upstream of SNARE complex assembly where it participates in SV tethering to the CAZ.

neuroscience↗