@phdthesis{Deng2023,
  author    = {Deng, Chunchu},
  title     = {Dynamic remodeling of endoplasmic reticulum and ribosomes in axon terminals of wildtype and Spinal Muscular Atrophy motoneurons},
  doi       = {10.25972/OPUS-26495},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-264954},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2023},
  abstract  = {In highly polarized neurons, endoplasmic reticulum (ER) forms a dynamic and continuous network in axons that plays important roles in lipid synthesis, Ca2+ homeostasis and the maintenance of synapses. However, the mechanisms underlying the regulation of axonal ER dynamics and its function in regulation of local translation still remain elusive. In the course of my thesis, I investigated the fast dynamic movements of ER and ribosomes in the growth cone of wildtype motoneurons as well as motoneurons from a mouse model of Spinal Muscular Atrophy (SMA), in response to Brain-derived neurotrophic factor (BDNF) stimulation. Live cell imaging data show that ER extends into axonal growth cone filopodia along actin filaments and disruption of actin cytoskeleton by cytochalasin D treatment impairs the dynamic movement of ER in the axonal filopodia. In contrast to filopodia, ER movements in the growth cone core seem to depend on coordinated actions of the actin and microtubule cytoskeleton. Myosin VI is especially required for ER movements into filopodia and drebrin A mediates actin/microtubule coordinated ER dynamics. Furthermore, we found that BDNF/TrkB signaling induces assembly of 80S ribosomes in growth cones on a time scale of seconds. Activated ribosomes relocate to the presynaptic ER and undergo local translation. These findings describe the dynamic interaction between ER and ribosomes during local translation and identify a novel potential function for the presynaptic ER in intra-axonal synthesis of transmembrane proteins such as the α-1β subunit of N-type Ca2+ channels in motoneurons. In addition, we demonstrate that in Smn-deficient motoneurons, ER dynamic movements are impaired in axonal growth cones that seems to be due to impaired actin cytoskeleton. Interestingly, ribosomes fail to undergo rapid structural changes in Smn-deficient growth cones and do not associate to ER in response to BDNF. Thus, aberrant ER dynamics and ribosome response to extracellular stimuli could affect axonal growth and presynaptic function and maintenance, thereby contributing to the pathology of SMA.},
  subject      = {Motoneuron},
  language  = {en}
}
@phdthesis{Moradi2017,
  author    = {Moradi, Mehri},
  title     = {Differential roles of α-, β- and γ-actin isoforms in regulation of cytoskeletal dynamics and stability during axon elongation and collateral branch formation in motoneurons},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-147453},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {In highly polarized cells like neurons, cytoskeleton dynamics play a crucial role in establishing neuronal connections during development and are required for adult plasticity. Actin turnover is particularly important for neurite growth, axon path finding, branching and synaptogenesis. Motoneurons establish several thousand branches that innervate neuromuscular synapses (NMJs). Axonal branching and terminal arborization are fundamental events during the establishment of synapses in motor endplates. Branching process is triggered by the assembly of actin filaments along the axon shaft giving rise to filopodia formation. The unique contribution of the three actin isoforms, α-, β- and γ-actin, in filopodia stability and dynamics during this process is not well characterized. Here, we performed high resolution in situ hybridization and qRT-PCR and showed that in primary mouse motoneurons α-, β- and γ-actin isoforms are expressed and their transcripts are translocated into axons. Using FRAP experiments, we showed that transcripts for α-, β- and γ-actin become locally translated in axonal growth cones and translation hot spots of the axonal branch points. Using live cell imaging, we showed that shRNA depletion of α-actin reduces dynamics of axonal filopodia which correlates with reduced number of collateral branches and impairs axon elongation. Depletion of β-actin correlates with reduced dynamics of growth cone filopoida, disturbs axon elongation and impairs presynaptic differentiation. Also, depletion of γ-actin impairs axonal growth and decreases axonal filopodia dynamics. These findings implicate that actin isoforms accomplish unique functions during development of motor axons. Depletions of β- and γ-actin lead to compensatory upregulation of other two isoforms. Consistent with this, total actin levels remain unaltered and F-actin polymerization capacity is preserved. After the knockdown of either α- or γ-actin, the levels of β-actin increase in the G-actin pool indicating that polymerization and stability of β-actin filaments depend on α- or γ-actin. This study provides evidence both for unique and overlapping function of actin isoforms in motoneuron growth and differentiation. In the soma of developing motoneurons, actin isoforms act redundantly and thus could compensate for each other's loss. In the axon, α-, β- and γ-actin accomplish specific functions, i.e. β-actin regulates axon elongation and plasticity and α- and γ-actin regulate axonal branching. Furthermore, we show that both axonal transport and local translation of α-, β- and γ-actin isoforms are impaired in Smn knockout motoneurons, indicating a role for Smn protein in RNA granule assembly and local translation of these actin isoforms in primary mouse motoneurons.},
  subject      = {Motoneuron},
  language  = {en}
}
@phdthesis{Lechner2009,
  author    = {Lechner, Barbara Dorothea},
  title     = {Modulation des axonalen Wachstums prim{\"a}rer Motoneurone durch cAMP in einem Mausmodell f{\"u}r die Spinale Muskelatrophie},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-39585},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2009},
  abstract  = {Die Spinale Muskelatrophie (SMA) ist eine h{\"a}ufige autosomal-rezessiv vererbte Erkrankung des motorischen Nervensystems bei Kindern. Ursache der Degeneration von spinalen Motoneuronen ist der homozygote Verlust des SMN- (survival of motoneuron) Gens und ein dadurch bedingter Mangel an SMN-Protein. Untersuchungen an Motoneuronen von Smn-defizienten M{\"a}usen ergaben St{\"o}rungen des axonalen L{\"a}ngenwachstums aufgrund einer Fehlverteilung des Zytoskelettproteins beta-Aktin und seiner mRNA in den Axonterminalen. Das Axonwachstum wird durch Aktin-Polymerisierung im Wachstumskegel gesteuert. beta-Aktin-mRNA findet sich auch in Axonen, und die lokale Proteinsynthese kann durch neuronale Aktivierung gesteigert werden. Das SMN-Protein ist am axonalen Transport von beta-Aktin beteiligt. In der vorliegenden Arbeit ergaben Western Blot-Analysen in neuralen Stammzellen (NSC) sowie spinalen Motoneuronen in vitro eine Steigerung der SMN-Proteinexpression durch 8-CPT-cAMP. Zur Untersuchung der Auswirkungen der erh{\"o}hten SMN-Proteinmenge auf die Pathologie der Motoneurone wurde ein in-vitro-Assay entwickelt, mit dessen Hilfe gezeigt werden konnte, dass eine Behandlung mit 100 µM 8-CPT-cAMP die axonalen Ver{\"a}nderungen isolierter embryonaler Smn-defizienter Motoneurone kompensieren kann. Motoneurone von 14 Tage alten Smn-defizienten und Kontroll-Mausembryonen wurden {\"u}ber sieben Tage hinweg auf einer Matrix aus Poly-Ornithin und Laminin-111 bzw. Laminin-121/221 kultiviert und mit 100µM cAMP und neurotrophen Faktoren behandelt. Nach Fixierung wurden die Zellen mit Antik{\"o}rpern gegen Islet-1/2, tau und beta-Aktin gef{\"a}rbt, mit Hilfe eines konfokalen Mikroskops fotografiert und digital vermessen. 8-CPT-cAMP erh{\"o}ht den beta-Aktin-Gehalt in den axonalen Wachstumskegeln von Smn-defizienten Motoneuronen. Die Gr{\"o}ße der Wachstumskegel nimmt durch die Behandlung um das 2-3fache zu und erreicht normale Werte. Auf Laminin-111 bleibt das L{\"a}ngenwachstum der Axone durch 100µM 8-CPT-cAMP unbeeinflusst, auf Laminin-121/221 wird das L{\"a}ngenwachstum normalisiert. Die beta-Aktin-Verteilung innerhalb der Axone und Wachstumskegel von Smn-defizienten Motoneuronen erscheint durch die cAMP-Behandlung nahezu normalisiert. Die Wiederherstellung der beta-Aktin-Verteilung in Wachstumskegeln durch cAMP kann große Auswirkungen auf die Funktionalit{\"a}t der Motoneurone haben. Die Ergebnisse sind m{\"o}glicherweise ein erster Schritt auf dem Weg zu einer Therapie f{\"u}r die Spinale Muskelatrophie.},
  subject      = {Spinale Muskelatrophie},
  language  = {de}
}