Periodic Reporting for period 2 - SynapseBuild (Mechanisms of Presynaptic Biogenesis and Dynamic Remodeling)
Reporting period: 2022-07-01 to 2023-12-31
Our ability to move, to process sensory information or to form, store and retrieve memories crucially depends on the function of neuronal synapses. Synapses comprise a presynaptic compartment harboring the machinery for neurotransmitter release and an associated postsynaptic compartment that processes the neurotransmitter signal. During decades of research, the field has acquired a wealth of knowledge regarding the mechanisms of neurotransmitter release and information processing in the postsynaptic compartment. In great contrast, we know surprisingly little about the pathways that direct the formation, transport, and assembly of the complex molecular machines that make up a functional presynapse. The main overall objective of the project is to obtain groundbreaking new insights into the mechanisms of presynaptic biogenesis and remodeling. Specifically, we will tackle the following questions 1. Which mechanisms and machinery direct the formation of SV precursor organelles in the soma? 2. How is the axonal transport of SV precursors coordinated with the delivery of large AZ scaffold proteins synthesized on cytoplasmic ribosomes? 3. How are SV precursor organelles assembled into synapses? 4. How is SV precursor and AZ protein assembly at the synapse controlled to set synaptic weight?
During the reporting period we have focussed on two major aspects of the project: The implementation of an experimental model system based on genome engineered stem cell-derived induced human glutamatergic neurons to analyze the formation of the presynaptic compartment in human neurons in vitro. Moreover, we have developed a methodology that allows us to visualize the morphology of the transported presynaptic organelles in the axons of living human neurons. In addition, we have begun to track down the mechanisms by which the various components of the presynapse are transported and eventually assembled into nascent synapses. Our major findings can be summarized as follows: We found that presynaptic biogenesis involves the axonal transport of precursor vesicles harboring multiple newly synthesized presynaptic components including synaptic vesicle and active zone proteins. Moreover, we could show using correlative light and electron microscopy that axonally transported precursor vesicles are distinct from other organelles and from SVs. Instead, we postulate that precursor vesicles represent a neuron-specific biogenesis organelle, which may derive from a pathway that sorts lysosomal membrane proteins. These findings have just been accepted for publication in Science (Rizalar et al, Haucke (2023), Science, in press).
We predict that this pathway is not only used in development but also in the mature nervous system to set and alter synaptic strength over time periods well beyond the classical paradigms of long-term plasticity.
We predict that this pathway is not only used in development but also in the mature nervous system to set and alter synaptic strength over time periods well beyond the classical paradigms of long-term plasticity.
We expect our studies to yield groundbreaking new insights into the mechanisms that mediate the formation, maintenance, and dynamic remodeling of the presynaptic compartment during development and thereby fill a crucial knowledge gap in neuroscience. Furthermore, we hope to pave the way for the development of therapeutics to cure nerve injury or neurological disorders linked to synaptic dysfunction.