ABSTRACTIn vitro, developing neurons progress through well-defined stages to form an axon and mul... more ABSTRACTIn vitro, developing neurons progress through well-defined stages to form an axon and multiple dendrites.In vivo, neurons are derived from progenitors within a polarised neuroepithelium and it is not clear how axon initiation observedin vitrorelates to what occurs in a complex, three-dimensionalin vivoenvironment. Here we show that the position of axon initiation in embryonic zebrafish spinal neurons is extremely consistent across neuronal sub-types. We investigated what mechanisms may regulate axon positioningin vivoand found that microtubule organising centres are located distant from the site of axon initiation in contrast to that observedin vitro, and that microtubule plus-ends are not enriched in the axon during axon initiation. F-actin accumulation precedes axon formation and nascent axons form but are not stabilised in the absence of microtubules. Laminin depletion removes a spatial cue for axon initiation but axon initiation remains robust.
Building arborisations of the right size and shape is fundamental for neural network function. Li... more Building arborisations of the right size and shape is fundamental for neural network function. Live imaging studies in vertebrate brains strongly suggest that nascent synapses are critical for branch growth during the development of axonal and dendritic arborisations. The molecular mechanisms underlying such ‘synaptotropic’ events are largely unknown.Here we present a novel system inDrosophilafor studying the development of complex axonal arborisations live,in vivoduring metamorphosis. In these growing axonal arborisations we see a relationship between the punctate localisations of presynaptic components and branch dynamics that is very similar to synaptotropic growth described in fish and frogs. These presynaptic components however do not appear to represent functional presynaptic release sites and are not paired with clusters of neurotransmitter receptors. Pharmacological and genetic knockdowns of evoked and spontaneous neurotransmission do not impact the outgrowth of these neuron...
Our understanding of the cell behaviours and cytoskeletal requirements of axon formation is large... more Our understanding of the cell behaviours and cytoskeletal requirements of axon formation is largely derived from in vitro models but how these relate to axon formation in vivo is not clear. In vitro, neurons progress through a well-defined multineurite stage to form an axon and both actin and microtubules cooperate to drive the first steps in neurite and axon morphogenesis. However, these steps are not recapitulated in vivo, and it is not clear whether the underlying cell biological mechanisms may differ also. Here, we investigate the mechanisms that regulate axon formation in embryonic zebrafish spinal neurons in vivo. We find microtubule organising centres are located distant from the site of axon initiation, and microtubule plus-ends are not enriched in the axon during axon initiation. Focal F-actin accumulation precedes axon formation, and we find that nocodazole-treated neurons with no detectable microtubules are still able to form nascent axonal protrusions that are approximately 10-lm long, dilated and relatively long-lived. We suggest spinal axon formation in vivo is fundamentally different from axon formation in in vitro models.
ABSTRACTIn vitro, developing neurons progress through well-defined stages to form an axon and mul... more ABSTRACTIn vitro, developing neurons progress through well-defined stages to form an axon and multiple dendrites.In vivo, neurons are derived from progenitors within a polarised neuroepithelium and it is not clear how axon initiation observedin vitrorelates to what occurs in a complex, three-dimensionalin vivoenvironment. Here we show that the position of axon initiation in embryonic zebrafish spinal neurons is extremely consistent across neuronal sub-types. We investigated what mechanisms may regulate axon positioningin vivoand found that microtubule organising centres are located distant from the site of axon initiation in contrast to that observedin vitro, and that microtubule plus-ends are not enriched in the axon during axon initiation. F-actin accumulation precedes axon formation and nascent axons form but are not stabilised in the absence of microtubules. Laminin depletion removes a spatial cue for axon initiation but axon initiation remains robust.
Building arborisations of the right size and shape is fundamental for neural network function. Li... more Building arborisations of the right size and shape is fundamental for neural network function. Live imaging studies in vertebrate brains strongly suggest that nascent synapses are critical for branch growth during the development of axonal and dendritic arborisations. The molecular mechanisms underlying such ‘synaptotropic’ events are largely unknown.Here we present a novel system inDrosophilafor studying the development of complex axonal arborisations live,in vivoduring metamorphosis. In these growing axonal arborisations we see a relationship between the punctate localisations of presynaptic components and branch dynamics that is very similar to synaptotropic growth described in fish and frogs. These presynaptic components however do not appear to represent functional presynaptic release sites and are not paired with clusters of neurotransmitter receptors. Pharmacological and genetic knockdowns of evoked and spontaneous neurotransmission do not impact the outgrowth of these neuron...
Our understanding of the cell behaviours and cytoskeletal requirements of axon formation is large... more Our understanding of the cell behaviours and cytoskeletal requirements of axon formation is largely derived from in vitro models but how these relate to axon formation in vivo is not clear. In vitro, neurons progress through a well-defined multineurite stage to form an axon and both actin and microtubules cooperate to drive the first steps in neurite and axon morphogenesis. However, these steps are not recapitulated in vivo, and it is not clear whether the underlying cell biological mechanisms may differ also. Here, we investigate the mechanisms that regulate axon formation in embryonic zebrafish spinal neurons in vivo. We find microtubule organising centres are located distant from the site of axon initiation, and microtubule plus-ends are not enriched in the axon during axon initiation. Focal F-actin accumulation precedes axon formation, and we find that nocodazole-treated neurons with no detectable microtubules are still able to form nascent axonal protrusions that are approximately 10-lm long, dilated and relatively long-lived. We suggest spinal axon formation in vivo is fundamentally different from axon formation in in vitro models.
Uploads
Papers by Sînziana Pop