Schram Foundation Neuroscience Grant

Schram Foundation Neuroscience Grant is sponsored by Schram Foundation. This grant supports early-career researchers at German universities and research institutions working in basic neuroscience, especially molecular and cellular neurobiology.

## Dorothea Schulte*, Christian Rosenmund and Eckart D. Gundel fi nger # Synapses, networks, brain development – funding basic neuroscience research in Germany by the Schram Foundation https://doi. org/10.

1515/nf-2020-0027 Abstract: Research driven solely by curiosity and the desire to understand fundamental principles of brain function. The freedom to address important questions with bold, sometimes risky experiments. A platform for open scientific exchange and discussions at highest academic level to provide new impulses to the field.

And a growing number of scientists who share the passion for neurosci-ence and who join forces to tackle some of the big mysteries that surround the brain. These visions together with the deep conviction that basic research is the fundament needed for any progress in applied science motivated Dr. Armin Schram to create the foundation that carries his name.

They are also the ideals that the foundation still pursues, and to date, 26 research proposals designed by individual researchers or small teams have been, or are, supported in this spirit.

Here, we introduce the reader to the individual scientists who were awarded grants by the Schram Foundation over the years, highlight some of the many discoveries made in the course of their studies and list some of the key publications that arose from this work. Keywords: basic neuroscience research; brain develop-ment; network; Schram Foundation; synapse.

Zusammenfassung: Forschungsförderung, die sich der neurobiologischen Grundgenforschung auf höchstem wissenschaftlichem Niveau verp fl ichtet sieht, sowie ein Forum, das offene wissenschaftliche Diskussionen fördert, Impulse setzt und die Forschungslandschaft in Deutsch-land nachhaltig stärkt – das waren die Visionen, die Dr. Armin Schram zur Gründung der nach ihm benannten Stiftung bewegten.

In diesem Geiste wurden seither 26 Projekte gefördert, die sich aus den unterschiedlichsten Blickwinkeln der Erforschung von Entwicklung, Funktion, Homöostase und Altern des Gehirns widmen. Im Folgen-den umreißen wir einige der wichtigsten Entdeckungen, die dank Förderung durch die Schram-Stiftung möglich wurden, und stellen die vielfältigen Förderaktivitäten der Stiftung kurz vor.

Schlüsselwörter: Neurowissenschaftliche Grundlagenfor-schung; Hirnentwicklung; Synapse; Netzwerk; Schram Stiftung. Working with animal models as diverse as mice, rats, chick, Mongolian gerbils, the fruit fly D. melanogaster or the nematode C.

elegans , and drawing on a broad spectrum of techniques, projects supported by the Schram Founda-tion have tackled some of the central questions in molec-ular neuroscience: How is neuronal activity modulated at the level of individual synapses? How do neuronal net-works form, become stabilized or adapt to ever-changing environmental conditions?

How do genetic and epigenetic mechanisms in fl uence nervous system development, ho-meostasis and aging? How do these building blocks cooperate to create what we call behavior? And fi nally, which techniques and methods are needed to accelerate neuroscienti fi c research and how can they be developed?

Below, we have selected some of the most prominent discoveries, which were made with support of the Schram Foundation. This collection gives a good impression of the many activities of the foundation, yet it is far from com-plete.

For a more comprehensive overview of the scientific output of research projects that had received support from *Corresponding author: Dorothea Schulte , Neurologisches Institut (Edinger Institut), Universitätsklinikum Frankfurt, Goethe Universität, Heinrich-Hoffmann-Str. 7, 60528 Frankfurt, Germany, E-mail: dorothea. schulte@kgu.

de Christian Rosenmund, Institut für Neurophysiologie, Charite Universitätsmedizin Berlin, 10117 Berlin, Germany. https://orcid. org/ 0000-0002-3905-2444 Eckart D.

Gundel fi nger, Abteilung Neurochemie und Molekularbiologie, Leibniz-Institut für Neurobiologie, 39118 Magdeburg, Germany Neuroforum 2020; 26(4): 195 –207 the Schram Foundation, the reader is invited to visit the foundation ’s homepage at https://www. schram-stiftung. de/ (see Table 1).

# The basic interface of neuronal communication: the synapse The central units for information transmission and process-ing in the brain are the chemical synapses, the contacts be-tween neurons, which allow regulated neurotransmitter release from the presynapse and detection at the postsynaptic site.

Several of the projects that were supported by grants from the Schram Foundation addressed the question of how synapses operate and how their activity changes to allow for plasticity and ultimately learning and memory. Many excit-atory transmitter release sites utilizing glutamate as neuro-transmitter contact spines, small protrusions from neuronal dendrites.

Focusing on the BAR (Bin/Amphiphysin/Rvs)-domain protein syndapin I, the project led by Britta Qual-mann (Figure 1) took a cell biological approach and exam-ined how membrane shaping at these spines can be mediated by cytoskeletal forces and membrane-associated proteins. Syndapins partially insert into one lea fl et of the cell mem-brane and can remodel membranes by scaffolding.

They thus combine cytoskeletal and membrane shaping mechanisms. Britta Qualmann and her coworkers identi fi ed syndapin I as a crucial postsynaptic coordinator in the formation of excit-atory synapses. Syndapin I–enriched membrane nano-domains thereby serve as important organizing platforms, which shape dendritic membrane areas into synaptic sub-compartments (Schwintzer et al.

, 2011; Schneider et al. , 2014). The project led by Volker Hauke dealt with the long-standing question of how synapses are kept up to speed (see also this issue).

He and his coworkers focused on two com-plementary questions: First, how are key presynaptic com-ponents such as synaptic vesicles and active zone proteins formed, transported and assembled into nascent synapses? Second, how are synaptic vesicles regenerated after fusion?

Among others, their work established that synaptic vesicles locally reform by adapter proteins that recognize speci fi ccomponents of the vesicle and sort them in a coordinated manner. Synapses thereby capitalize on clathrin-indepen-dent endocytosis and clathrin/AP-2 –dependent reformation of synaptic vesicles from endosome-like vacuoles to maintain excitability (Kononenko et al. , 2014).

The regulation of synaptic vesicle biogenesis and degradation is also addressed by the newly awarded grant to Eugenio Fornasiero . This project will develop new tools, based on protein stability measurements, imaging technologies and computational modeling, to decipher the precise molecular composition of synaptic vesicles and apply this knowledge to questions related to neuronal aging.

Membrane recycling mechanisms at the synapse were also at the center of the project headed by Ira Milosevic (see also this issue). Focusing on the key endocytic protein endophilin-A, she and her team described that, in addition to its essential role in endocytosis, endophilin-A has a role in the priming and fusion of secretory vesicles (Gow-risankaran et al. , 2020).

Endophilin-A de fi ciency causes dysregulation of autophagy and the ubiquitin-proteasome system (Murdoch et al. , 2016). Synapses without endophi-lin-A accumulate clathrin-coated vesicles, an observation that led to the discovery that clathrin can control vesicle acidi fi cation by sterically blocking vacuolar ATPase activ-ity (Farsi et al.

2018). Besides membrane dynamics, the composition of the local extracellular matrix (ECM) at the synapse also pro-foundly influences synaptic function. Renato Frisch-knecht investigated the contribution of the perisynaptic ECM to network activity and memory formation.

He and his colleagues observed that the perisynaptic ECM is modi fi ed during homeostatic plasticity and discovered activity-dependent mechanisms of ECM turnover . By training Mongolian gerbils in an auditory cortex –dependent discrimination and reversal learning task, they found that ECM removal promoted performance during reversal learning (Happel et al. , 2014; Valenzuela et al.

, 2014). The local ECM at synapses thus contributes to neuronal network performance and memory consolidation. Our ability to learn and memorize depends on internal brain states, such as attention and arousal, which are mediated by the action of neuromodulators.

One such neuromodulator, noradrenaline, has long been known to facilitate NMDA ( N-Methyl-D-Aspartat) receptor –dependent long-term synaptic potentiation (LTP), yet the precise mechanisms behind this effect have remained elusive. Supported by the Schram Foundation, Oliver Schlüter unraveled the identity of the potassium channel in the dendrite on which noradrenaline acts.

Speci fi cally, he discovered that the signaling scaffold protein SAP97 links the noradrenaline receptor beta2-adrenergic receptor to the inactivation of voltage-gated Kv1. 1 potassium channels in the dendrite of hippocampal CA1 pyramidal neurons. This study provides a nice demonstration of how local changes in dendritic excitability can support the impact of NMDA-receptor activation during LTP (Liu et al.

, 2017). Synapses do not work as isolated entities but must engage in continuous communication with the cell body and cell nucleus. Two of the first projects funded by the Schram Foundation addressed the mechanisms involved.

196 D. Schulte et al. : Synapses, networks, brain development Table : Research projects funded by the Schram-Foundation.

Sox  vermittelte Genexpressionsänderungen als Ursache der Differenzierung neuraler Stammzellen zu zentralnervösen Gliazellen Prof. Dr. Michael Wegner , Friedrich-Alexander-Universität Erlangen-Nürnberg, Emil-Fischer-Zentrum/Institut für Biochemie. Caldendrin und Jacob – Eine Protein-Interaktion zur Kopplung synaptischer Ca +- Signale an die dendritische Morphogenese? Prof. Dr. Michael R.

Kreutz und Dr. Christina Spilker , Leibniz-Institut für Neurobiologie, Magdeburg, Projektgruppe Neuroplastizität; aktuell: Leibniz-Institut für Neurobiologie Magdeburg und Zentrum für Molekulare Neurobiologie Hamburg (ZMNH). RNA-Transport in Dendriten Prof. Dr. Michael Kiebler , Medizinische Universität Wien, Abteilung für neuronale Zellbiologie; aktuell Biomedizinisches Zentrum München, Ludwig-Maximilians-Universität München.

Die Rolle von Genexpressionsprogrammen beim Aufbau neuronaler Verschaltungen Prof. Dr. Bernd Knöll , Eberhard-Karls-Universität Tübingen, Interfakultäres Institut für Zellbiologie, Abteilung Molekularbiologie; aktuell: Universität Ulm, Institut für Physiologische Chemie.

Regulation der molekularen, strukturellen und physiologischen Differenzierung durch physiologische elektrische Aktivitätsmuster im neo-natalen Säugercortex Prof. Dr. Heiko J. Luhmann , Johannes-Gutenberg-Universität Mainz, Institut für Physiologie und Pathophysiologie. Prof. Dr. Volkmar Leßmann , Otto-von- Guericke-Universität Magdeburg, Institut für Physiologie.

Prof. Dr. Petra Wahle und Dr. Silke Patz , Ruhr-Universität Bochum, Allgemeine Zoologie und Neurobiologie. Untersuchungen zur strukturellen Plastizität von Nervenzellverbindungen als Basis für Lern- und Gedächtnisprozesse Prof. Dr. Britta Qualmann ; Friedrich-Schiller-Universität Jena, Institut für Biochemie I.

Transkriptionelle Kontrolle der Entwicklung sympatischer und parasympatische Nervenzellen Prof. Dr. Hermann Rohrer , Max-Planck-Institut für Hirnforschung, Frankfurt am Main. Visit our websites for more information or send an email to info@ThomasRECORDING. com ## www.

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Schulte et al. : Synapses, networks, brain development 197 Table : (continued) Molecular mechanisms underlying region-speci fi c microcircuit formation in the brain Prof. Dr. Thomas Hummel , Westfälische Wilhelms-Universität Münster, Institute of Neuro- and Behavior Biology und Universität Wien, Abteilung für Neurowissenschaften und Entwicklungsbiologie.

Rolle endozytischer Adaptor- und akzessorischer Proteine bei der Sortierung und Rezyklierung synaptischer Vesikelproteine Prof. Dr. Volker Haucke , Freie Universität Berlin, Institut für Chemie und Biochemie; aktuell: Leibniz Forschungsinstitut für molekulare Phar-makologie, Berlin.

Optogenetics-assisted analysis of small neuronal networks and identi fi cation of novel proteins affecting recycling of synaptic vesicles in Caenorhabditis elegans Prof. Dr. Alexander Gottschalk , Goethe-Universität Frankfurt am Main, Institut für Biochemie, Molekulare Membranbiologie und Neurobiologie.

The cellular mechanisms by which chromatin plasticity affects neuronal gene-expression in the ageing brain Prof. Dr. André Fischer , European Neuroscience Institute (ENI) Göttingen; aktuell: Universitätsmedizin Göttingen und Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE) Göttingen. Kerntranslokation als Mechanismus der neuronalen Differenzierung Prof. Dr. Jens C.

Schwamborn , Universitätsklinikum Münster, Institut für Zellbiologie (ZMBE); aktuell: Universit e du Luxembourg, LCSB, Department of Developmental and Cellular Biology, Luxemburg. Poly ADP Ribosylierung as novel control mechanism in adult and embryonic neurogenesis Prof. Dr. Dorothea Schulte , Klinikum der Goethe-Universität Frankfurt am Main, Neurologisches Institut (Edinger Institut).

Role of the Perisynaptic Extracellular Matrix in Synaptic Plasticity and Network Activity Dr. Renato Frischknecht , Leibniz-Institut für Neurobiologie (IfN) Magdeburg; aktuell: Friedrich-Alexander-Universität Erlangen-Nürnberg, Abteilung für Tierphysiologie.

Dissecting the dentate gyrus circuitry: In fl uence of dendritic versus perisomatic inhibition on network oscillations Prof. Dr. Marlene Bartos , Albert-Ludwigs-Universität Freiburg i. B. , Physiologisches Institut, Lichtenberg-Professur.

Angiopoietine und ihre Tie-Rezeptoren in der Entwicklung neuronaler Netzwerke im Hippocampus Prof. Dr. Carmen Ruiz de Almodovar , Ruprecht-Karls-Universität Heidelberg, Biochemiezentrum; aktuell: Medizinische Fakultät Mannheim der Universität Heidelberg. Dynamische Membranen der Synapse: die Rolle subkompartimentaler Endosome in gesunden und kranken Nervenzellen Dr. Ira Milosevic , European Neuroscience Institute (ENI) Göttingen.

Mechanismen von dendritischer Kv . -Inaktivierung, um “spike-timing ”-abhängige synaptische Potenzierung zu bahnen Prof. Dr. Oliver Marcus Schlüter , European Neuroscience Institute (ENI) Göttingen; aktuell: Universitätsmedizin Göttingen, Abteilung für Psychiatrie und Psychotherapie und Department of Neuroscience, University of Pittsburgh, Pittsburgh, PA, USA.

Neuronale Schaltkreise für Erleichterungslernen bei Drosophila Dr. Ayse Yarali , Leibniz-Institut für Neurobiologie (IfN) Magdeburg. Regulierung der Genexpression in humanen induzierten Neuronen durch Faktoren der Musterbildung Prof. Dr. Marisa Karow , Ludwig-Maximilians-Universität München, Biomedizinisches Centrum (BMC), Physiologische Genomik; aktuell: Friedrich-Alexander-Universität Erlangen-Nürnberg, Institut für Biochemie.

Determining the function of local inhibitory circuits in the synaptic dynamics of hippocampal pyramidal neurons during learning and memory Dr. Alessio Attardo , Max-Planck-Institut für Psychiatrie, Dept. Stress Neurobiologie und Neurogenetik, München.

Chromatin und epigenetische Regulation während der neuronalen Migration Dr. Tran Tuoc , Universitätsmedizin Göttingen, Institut für Neuroanatomie, Göttingen; aktuell: Ruhr-Universität Bochum, Medizinische Fakultät, Abteilung für Humangenetik.

αδ-Untereinheiten spannungsgesteuerter Kalziumkanäle bestimmen die erregende und hemmende Konnektivität in neuronalen Netzwerken Prof. Dr. Martin Heine , Leibniz-Institut für Neurobiologie (IfN), Magdeburg; aktuell: Johannes-Gutenberg-Universität Mainz, Institut für Entwicklungsbiologie und Neurobiologie.

Untersuchung der Genregulation durch Polycomb-Proteine in neuralen Vorläuferzellen während der Entwicklung des humanen Neocortex Dr. Mareike Albert , CRTD / DFG – Forschungszentrum, für Regenerative Therapien Dresden. Regulation of synaptic vesicle biogenesis and degradation in neuronal transport: novel tools for studying the vesicle life cycle Dr. Eugenio F.

Fornasiero , Universitätsmedizin Göttingen, Institut für Neuro- und Sinnesphysiologie. Structural, Molecular, and Functional determinants of enteroendocrine cell mediated gut-to-brain signaling Dr. Cordelia Imig und Dr. Benjamin H. Cooper , Max-Planck-Institut für Experimentelle Medizin / Molecular Neurobiology, Göttingen, und University of Copenhagen, Department of Neuroscience, Kopenhagen, Dänemark.

198 D. Schulte et al. : Synapses, networks, brain development Michael Kiebler discovered homologs of the invertebrate RNA-binding protein Staufen in mammals and made sig-ni fi cant contributions to understanding their function at synapses.

Supported by the Schram Foundation, he and his coworkers found that in rodent hippocampal neurons, Staufen 2 is critically involved in dendritic spine morpho-genesis and contributes to memory formation and plas-ticity. Mechanistically, Staufen controls the transport and activity-dependent translation of mRNAs in distinct re-gions of the cell.

Staufen proteins thereby facilitate locally restricted protein synthesis and consequently allow for spatially controlled adaptations within the cell (Fritzsche et al. , 2013; Goetze et al. , 2006; Heraud-Farlow et al.

, 2013). Cellular events that lead to long-lasting memories require processes that occur in seconds but also on very long-time scales. That gene expression changes are involved has long been postulated.

The project led by Michael Kreutz and Christina Spilker asked how synaptic events couple to transcriptional responses in the cell nucleus . They identi fi ed the neuronal Ca 2+ sensor caldendrin, a post-synaptic density component, and Jacob, a caldendrin-bind-ing partner, as key players in the communication from the dendrite to cell nucleus (Figure 2).

Upon activation of NMDA-type glutamate receptors, Jacob is recruited to neuronal cell nuclei where it induces rapid transcriptional > Figure 1: Prof. Britta Qualmann discussing her results with Dr. Armin Schram during his visit at University Hospital Jena in 2011. Picture courtesy of Britta Qualmann (Foto: Riese/UKJ). > Phone: +49-(0)7141-97302-30 http://www.

npielectronic. com support@npielectronic. com # Automated Stereotax Complete Anesthesia Solutions Tilt Stereotax Animal Heatpads Laser Speckle Contrast Imaging System > D.

Schulte et al. : Synapses, networks, brain development 199 changes, which ultimately result in synaptic scaling and a drastically altered morphology of the dendritic tree. Calden-drin binds to Jacob ’s nuclear localization signal in a Ca 2+-dependent manner, thereby controlling Jacob ’s ability to enter the cell nucleus.

In addition, Michael Kreutz and his colleagues established that Jacob is phosphorylated by syn-aptic, but not extrasynaptic, NMDA-receptor activation and that Jacob ’s differential phosphorylation determines whether NMDA-receptor activation promotes cell survival and en-hances synaptic plasticity or induces cell death (Dieterich et al. , 2008; Karpova et al. , 2013).

While the work highlighted above deals with the events taking place at synapses in the central nervous system, the grant recently awarded to the research team of Cordelia Imig and Benjamin H. Cooper enters truly new territories by dissecting fundamental synaptic signaling mechanisms at the synapse formed between enteroendocrine cells and sen-sory neurons.

Enteroendocrine cells sense nutrients and metabolites in the gut and produce a range of gut hormones. Information exchange along the gut –brain axis is receiving increasing attention recently as it is crucial not only for feeding-related physiological responses, like appetite and satiety, but has also been linked to more complex traits such as anxiety-like behaviors.

# You never walk alone: neuronal networks Although the events taking place at individual synapses are the basis of learning and memory, it is the orchestrated activity of many neurons and the computational capacity of the resulting neuronal network that drives information processing and higher cognitive functions.

Formation and stabilization of neuronal networks in rodents was investi-gated by several projects and from very different angles. The strength of a given synapse in its neuronal network is primarily shaped by two parameters: the release probability of individual synaptic vesicles and the number of release sites that exist within each active zone.

In his currently ongoing project, Martin Heine in-vestigates how the composition and biochemical proper-ties of voltage-gated calcium channels affect these processes. Focusing on CaV2. 1, one of the major voltage-gated calcium channels responsible for fast synaptic transmission in the mammalian nervous system, he re-ported on the physiological consequences of alternative splicing of CaV2.

1 transcripts, leading to channel isoforms with different intracellular domains. Depending on the nature of their intracellular domain, these alternative CaV2. 1 isoforms exhibit diverse mobilities and dynamic organization within the presynaptic membrane, which alters the release probability of synaptic vesicles from these sites.

This in turn profoundly affects the strength of synaptic transmission and consequently short-term plasticity and network properties (Heck et al. , 2019).

This study demonstrated not only that calcium channels at the presynapse are mobile and undergo permanent move-ments within nanodomains of the presynaptic membrane but also that alternative splicing of a single exon can have far-reaching consequences for the performance of the neuronal network as a whole (Heck et al. , 2019; Figure 3).

Calcium channels are crucial for neurotransmission, but are they also utilized to tune how excitation and inhibi-tion in networks interact? Martin Heine and his team found that in the developing network the balance of excitation and inhibition is indeed regulated through varying the speci fi c content of voltage-gated calcium channels (Bikbaev et al. , 2020).

GABAergic inhibitory interneurons play a key role in sculpting the representation of afferent information in principal cells. They are highly diverse and include the diversification in perisoma-inhibiting GABAergic in-terneurons, which control the timing and frequency of action potential generation in their target cells, and dendrite-targeting GABAergic cells whose functional char-acterization is lacking behind.

Supported by the Schram Foundation, Marlene Bartos examined how dendrite-tar-geting GABAergic interneurons shape synaptic output prop-erties in the dentate gyrus of mice (see also this issue). She and her coworkers discovered that one subtype of dendrite-targeting GABAergic interneurons, somatostatin-expressing > Figure 2: Communication between postsynapse and nucleus illuminated.

3D Imaris reconstruction of a dendritic segment filled with a volume marker (shown in gray) of a hippocampal pyramidal neuron. In red transport packages for importin-mediated long-dis-tance transport are shown, and in green the synaptonuclear protein messenger Jacob can be seen on the way to the nucleus. Picture courtesy of Anna Karpova and Michael Kreutz, LIN, Magdeburg.

200 D. Schulte et al. : Synapses, networks, brain development cells, fall into different classes with distinct functional and dynamic synaptic output properties, which relate to the na-ture of their target cells.

They undergo synaptic plasticity at their glutamatergic inputs, and the long-lasting potentiation of their inputs plays a key role in cognitive functions, like the recognition of replaced objects in the environment (Booker et al. , 2020; Elgueta and Bartos, 2019).

In keeping with the saying ‘seeing is believing, ’ Alessio Attardo has developed deep-brain 2-photon microscopy as a tool to visualize the dynamics of neuronal connections in living mice over weeks to months (Ulivi et al. , 2019).

Supported by the Schram Foundation, he currently applies this technique to the CA1 region of the hippocampal formation and tracks how the connectivity of excitatory and inhibitory neurons changes when animals undergo hippocampus-dependent learning tasks.

Including optogenetics and chemogenetics, he also probes the effect of activation or inactivation of different classes of genetically de fi ned local inhibitory neurons on synaptic dynamics, learning and memory. Network formation viewed from a very different perspective was the topic of the project headed by Carmen Ruiz de Almodovar (see also this issue).

As has become increasingly clear during the past decades, classical molecules that regulate neurodevelopment also play an important role in regulating the development of the vascular system. Adopting a converse approach, Carmen Ruiz de Almodovar asked whether angiogenic factors may also impinge on the nervous system.

Although vascular endothelial growth factor (VEGF) and its receptor VEGFR2 were originally identi fi ed as angiogenesis-regulating receptor –ligand pair, VEGFR2 exhibits surprisingly restricted and dynamic expression on neurons of the CA3 region of the developing mouse hippocampus.

Stimulation of VEGFR2 -expressing hippocampal neurons with VEGF or targeted deletion of VEGFR2 in developing neurons both altered axonal branching and synapse formation. This fi nding established the prototypical angiogenic receptor VEGF as an important regulator of neuronal network for-mation (Luck et al. , 2019).

A grant given to Petra Wahle , Silke Patz , Heiko Luh-mann and Volkmar Leßmann dealt with the molecular, structural and physiological differentiation of the neonatal mammalian cortex. The Wahle and Patz groups identi fi ed which subunits of the AMPA ( α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)-type glutamate receptors promote dendritic growth of cortical pyramidal cells and interneurons > D. Schulte et al.

: Synapses, networks, brain development 201 (Hamad et al. , 2011) and showed that elevated levels of the proin fl ammatory cytokine Leukemia inhibitory factor (LIF) during brain development cause malfunctions of GABAergic neurons (Engelhardt et al. , 2018).

The Lessmann and Luh-mann laboratories focused on the interplay of programmed cell death and developmental survival of neurons. Work on organotypic cultures showed that the activation of ionotropic glutamate receptors, GABA-A receptors, voltage-controlled calcium channels and electrical synapses (gap junctions) promotes the survival of neonatal cortical neurons (Golbs et al. , 2011).

This survival is mainly mediated by the brain-derived neurotrophic factor (BDNF) (Kuczewski et al. , 2008). Owing to the relative simplicity and accessibility of their nervous systems, invertebrates are excellent models to study neuronal network formation.

The fruit fly D. melanogaster and the nematode C. elegans have so far taken the center stage in research projects funded by the Schram Foundation.

In sharp contrast to the complex nervous systems of vertebrates, the nervous system of the adult C. elegans hermaphrodite has been fully mapped and the complete wiring diagram is known. Supported by funds from the Schram Foundation, Alexander Gottschalk developed a multispectral optical illumination system that allows precise spatiotemporal control over the activation of optogenetic tools in freely behaving animals (Stirman et al.

, 2012) (see also this issue). The term optogenetics refers to the targeted expression of genetically encoded light-sensitive ion channels or proton pumps, with the aim to functionally characterize single neurons or neuronal networks.

Applying these tools to a nociceptive treatment regime, Alexander Gottschalk and his team dissected a neural circuit surrounding the neuron termed PVD and identi fi ed the channels, which by acting on PVD regulate behavioral outputs (Husson et al. , 2012). Painful events not only are answered by avoidance reactions but also establish memories.

A neutral stim-ulus given close to a noxious experience can be remembered in opposite ways: Cues that precede pain or overlap with it are remembered as predictors of pun-ishment and are later avoided. Cues that follow pain are perceived as relief and are therefore recalled positively.

The project headed by Ayse Yarali examined the mini-mal circuit that supports the formation, storage and retrieval of these opposite memories in the mushroom > Figure 3: Local organization of voltage-gated calcium channels (CaV2. 1) within the axonal membrane. (A) Axonal segments of rat hippocampal neurons expressing GCamp5::synaptophysin, the stimulation with four extracellular Action potential-like stimulations (scale bars 0.

1 F/ΔF,400 ms). (B) Trajectories of CaV2. 1 channels; indicated are the synaptic locations (scale bar 2 μm).

(B ′– B′′′ ) higher magni fi cations of the synaptic regions marked in (B), demonstrating a mixed population of highly con fi ned and mobile channels (scale bar 0. 5 μm). (C) Examples of local con fi ned CaV2.

1 channels within energy wells keeping channels for a few 100 ms within the well. (D) In addition to motion inside the well, CaV2. 1 channel wells move within the presynaptic membrane, disappearing and reappearing again.

Picture courtesy of Martin Heine, Gutenberg University, Mainz. 202 D. Schulte et al.

: Synapses, networks, brain development bodies of D. melanogaster . These paired structures integrate multimodal inputs and ful fi ll important func-tions in learning and memory.

Applying an optogenetic approach in fruit fl ies, Ayse Yarali ’s team identi fi ed two types of dopaminergic neurons, each comprising one paired cell per hemisphere, which upon photo-stimulation evoke a reaction resembling the punish-ment-versus-relief memories that are reinforced by real noxious events (König et al. , 2018).

While the two projects above dealt with the plasticity of already established neuronal networks, the project led by Thomas Hummel investigated the fi rst steps of neuronal circuit formation during development. Among the great wonders of embryogenesis are the apparently self-orga-nizing processes through which structure, order and complexity emerge.

Thomas Hummel and coworkers discovered a simple but ingenious principle that drives this process. Opting for the D. melanogaster visual system as model, they found that the afferents of photoreceptor cells sequentially segregate into distinct layers of their target region depending on the relative time when the cells had undergone their fi nal division.

They identi fi ed a tran-scription factor, Sequoia, whose absolute protein load in individual photoreceptor cells re fl ects their relative birth order and which organizes growth cones in a dosage-sen-sitive manner. Small differences in the amount of Sequoia protein between individual photoreceptors organize their growth cones within the same layer, whereas large differ-ences segregate growth cones between layers.

The birth order of photoreceptor neurons thus establishes a pre-pattern, which dictates the assembly of synaptic connec-tions during visual map formation (Kulkarni et al. , 2016). # Finding one ’s identity: cell fate specification The performance of a neuronal network not only depends on the size, strength and kind of its synapses or the number and nature of its connections.

Critically important for every network are the types of neurons it consists of and the glia that associate with them. Neuronal and glial cell types are highly diverse, differing in their size, morphology, and physiological and molecular properties. Understanding how individual cell types are produced at the right time and place and in the right relative proportions is therefore a key ques-tion in developmental neurobiology.

Having been awarded one of the first Schram grants, Michael Wegner set out to decipher the transcription factors that control the generation of oligodendrocytes, the myelin-forming macroglia that facilitate the fast, saltatory nerve conduction characteristic of the vertebrate central nervous system.

He uncovered a network of Sox-type transcription factors, centered around the Sox-family member SOX9, that allows for the timely progression of oligodendrocyte development in the spinal cord. He established that SOX9 is essential for gliogenesis and that it is required, jointly with SOX10, for survival and migration of oligodendroglial precursor cells (Finzsch et al. , 2008).

SOX9 and SOX10 regulate expression of the distantly related Sox5 and Sox6 genes, which in turn modulate the activity of Sox9 and Sox10 in a negative feedback loop and thereby determine the timing of oligodendroglial differenti-ation (Stolt et al. , 2006). These studies shed light on the interdependent levels of transcriptional regulation that are needed to advance the production of a single cell type, myelinating oligodendrocytes.

A rather unexpected mechanism by which the devel-opment of myelinating oligodendrocytes is regulated in the corpus callosum of juvenile mice was revealed by the work of Bernd Knöll . He and his coworkers observed that targeted deletion of the transcription factor SRF in neurons interfered with oligodendrocyte development in a non – cell autonomous manner.

Consistently, neuronal deletion of SRF resulted in myelination defects and axon degener-ation, whereas forced activation of SRF in neurons affected the maturation of neighboring oligodendrocytes.

Paracrine regulation of oligodendrogliogenesis by neuronal SRF in-volves two secreted molecules, connective tissue growth factor (CTGF), which is repressed by SRF , and insulin like growth factor 1 (IGF-1), which stimulates oligodendrocyte maturation but is antagonized by CTGF. This double-negative regulation places oligodendrocyte maturation under the control of nearby neurons (Stritt et al. , 2009).

The network of transcription factors controlling autonomous nervous system development was investi-gated in the project led by Hermann Rohrer . The auton-omous nervous system is derived from a transient cell population called neural crest. It regulates involuntary physiologic processes and contains three anatomical dis-tinctions, the sympathetic, parasympathetic and enteric nervous system.

Hermann Rohrer and his team demon-strated that the transcription factors AP-2 α/AP-2 β exert an early prespecifying function for sympathetic progenitor cells and a later survival function for sympathetic neurons (Schmidt et al. , 2011).

Likewise, transcription factors of the HoxB cluster exert an early in fl uence on the pre-speci fi cation of the sympathetic versus sensory neuron lin-eages of the neural crest and support and maintain the expression of sympathetic neuron genes (Huber et al. , 2012). Transcription factors bind enzymes, which chemically alter DNA or proteins, and recruit these enzymes to specific > D.

Schulte et al. : Synapses, networks, brain development 203 sites in the genome. This process, known as epigenetic modification, introduces heritable but reversible changes in DNA or histones, the building blocks of nucleosomes.

For transcription to occur, nucleosomes must be destabi-lized on DNA by the activity of nucleosome-remodeling ATPases. Nucleosome remodeling and histone modifying activities jointly reorganize the chromatin structure in a way that either facilitates or inhibits gene expression. The Schram Foundation supported several projects that examined the effect of these activities on development and aging of the nervous system.

Studying the role of the BAF (BRG1- or BRM-associated factor) nucleosome-remodeling complex in the developing mouse neocortex, Tran Tuoc discovered that nucleosome remodeling is closely inte-grated with the activity of histone demethylases during corticogenesis.

He found that BAF complexes can simul-taneously silence the expression of genes required for the proliferation of cortical progenitor cells and stimulate the expression of genes associated with the differentiation and migration of young neurons. Mechanistically, this involved recruitment of histone-demethylating enzymes with opposing functions, KDM6A/B and KDM1A, respectively.

By acting both as activators and repressors of gene expression, BAF complexes thus ensure the generation of the appropriate numbers