The majority of axons in the central nervous system (CNS) are wrapped with compact layers of myelin sheaths to ensure the rapid transmission of neuronal signals over long distances. As myelin thickness and sheath length have profound effects on conduction velocity, myelination is also crucial to the precise control of spatiotemporal activity patterns in the CNS. Neuronal activity is known to positively regulate myelin development and induce adaptive myelin plasticity in adulthood, although the underlying mechanisms remain poorly understood. In the CNS, myelin sheaths are exclusively formed by oligodendrocytes, which are differentiated from oligodendrocyte precursor cells (OPCs). Neurons make bona fide synaptic contacts with OPCs in both grey and white matter, and OPCs lose those synaptic contacts once they differentiate into oligodendrocytes. These point-to-point synaptic contacts enable neuron-OPC communication with temporal and spatial precision, and genetically deletion or manipulation of OPC-expressed neurotransmitter receptors negatively impacted the OPC proliferation, differentiation, and subsequent myelination. Therefore, it is believed that neuron-OPC synaptic transmission provides instructive cues for oligodendrocyte lineage cells, and is an important regulator for activity-dependent myelination. In this talk, I will discuss how OPCs integrated neuronal synaptic inputs into intracellular Ca2+ signaling. I will also discuss our unpublished data on how we identify novel molecular mediators that promote myelin formation through regulating neuron-OPC synaptic transmission. Our findings provide new insights into the mechanisms underlying activity-dependent myelination.
Muscular dystrophy is a diverse group of disorders characterized by mutations in genes encoding key sarcolemmal, nucleoskeletal or nuclear envelope proteins. To gain new insights into the pathogenesis of Duchenne muscular dystrophy (DMD) and Emery-Dreifuss muscular dystrophy (EDMD) at the nanoscale we use single molecule optical microscopy in human cells and C. elegans animal models. We have characterized the in situ biomolecular properties of dystrophin, a key structural protein of muscle cells that is mutated in DMD patients. Using split-fluorescent proteins and a single molecule imaging technique called Complementation Activated Light Microscopy (CALM), we imaged individual Ca2+ channels at the muscle surface of live C. elegans worm models for DMD. I will discuss how diffusion measurements on single Ca2+ channels and spatial pattern analyses of their nanoscale distribution in vivo have allowed us to show that dystrophin acts as a load-bearing apparatus and a tension transducer that modulate the nanoconfinement of sarcolemmal Ca2+ channels in response to variation in muscle tone. We have also studied the diffusional mobility and the spatial distribution of the nuclear envelope protein emerin and a variety of EDMD-associated emerin mutants by sptPALM and dSTORM super-resolution imaging in cells from EDMD patients. I will discuss how the stepwise oligomerization of emerin in response to forces transmitted at the nuclear envelope by LINC complexes is central for nuclear adaptation against mechanical strains and how emerin mutations result in abnormal nuclear mechanics, in the context of EDMD. These single molecule imaging approaches provide new means not only to explore the basic principles of homeostatic controls for cells and tissues under mechanical strains, but also to understand the molecular basis of diseases at the nanoscale, that would otherwise remain undetected using traditional diffraction-limited microscopy.
Last update: 3/27/2023, Ralf Bundschuh