Discovering how neurons form and maintain the membrane-associated periodic skeleton in vivo

• Applicant: Dr. Oliver Vinzenz Glomb
• Subject Area: Molecular Biology and Physiology of Neurons and Glial Cells ; Cell Biology
• Term: from 2021 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465611822

• Final Report Year: 2024

Final Report Abstract

Neurons contain long, thin axons that rely on a specialized cytoskeleton to function throughout life. A central component of the axonal cytoskeleton is the membrane associated periodic skeleton (MPS), which forms a continuous lattice throughout the entire axon consisting of periodic circumferential actin filament rings that are interspaced by spectrin tetramers. Although the ultrastructure and function of the MPS has been revealed, it remains unknown, how the MPS lattice forms. Mutations in spectrin result in axon breakage and an early onset of neurodegeneration from nematodes to humans. Consequently, identifying the mechanisms that regulate MPS formation is of great importance to understand how neurons can maintain functional throughout life - in health and disease. The difficulty in visualizing MPS lattice formation derives from the ubiquitous presence and high abundance of its components, which prevents the use of conventional labeling approaches to visualize their dynamics. To overcome this hurdle, I developed a temporally controlled labeling approach in nematodes. As most components of the MPS and its functions are conserved from nematodes to humans, I utilize C.elegans as a genetically tractable model to ask for the mechanisms that underly MPS formation. In the scope of this scholarship, I established a visualization strategy to study the formation process of the MPS lattice and addressed spectrins i) transport into the axon and uncovered first components that mediate this transport, ii) expansion into the outgrowing lattice, iii) turn-over from the lattice. Finally, we asked for the functional role of the MPS lattice by studying how the loss of its integrity impairs other cytoskeletal components in the axon. Our results provide first insights into the transport of spectrin, its expansion into the MPS lattice and its turn-over and revealed molecular mechanisms that underly its formation. Moreover, we revealed a Rho-1/RhoA dependent pathway through which the MPS lattice organizes microtubule distribution. Impaired MPS lattice formation resulted in a distal accumulation of microtubules, the occurrence of microtubule gaps along the axonal lattice and an early onset of neurodegeneration.

Publications

• Scaled-expansion of the membrane associated cytoskeleton requires conserved kinesin adaptors.
  Glomb, Oliver; Swaim, Grace; LLancao, Pablo Munoz; Lovejoy, Christopher; Sutradhar, Sabyasachi; Park, Junhyun; Wu, Youjun; Hammarlund, Marc; Howard, Jonathon; Ferguson, Shawn M. & Yogev, Shaul
  
• A kinesin-1 adaptor complex controls bimodal slow axonal transport of spectrin in Caenorhabditis elegans. Developmental Cell, 58(19), 1847-1863.e12.
  Glomb, Oliver; Swaim, Grace; Munoz, LLancao Pablo; Lovejoy, Christopher; Sutradhar, Sabyasachi; Park, Junhyun; Wu, Youjun; Cason, Sydney E.; Holzbaur, Erika L.F.; Hammarlund, Marc; Howard, Jonathon; Ferguson, Shawn M.; Gramlich, Michael W. & Yogev, Shaul
  
• Optimizing Visualization of Axonal Transport of Endogenous Cargo by Fluorescence Microscopy in Living Caenorhabditis elegans. Journal of Visualized Experiments(204).
  Glomb, Oliver; Lyu, Mengya & Yogev, Shaul