Biology subjects

Morgan, J. R.

Publications and source records attributed to Morgan, J. R..

5 recordsLinked to original sources

bioRxiv2024

High-speed 3D Imaging with 25-Camera Multifocus Microscope

We here report an aberration-corrected 25-plane camera array Multifocus microscope (M25) for high-speed, high-resolution wide-field optical microscopy in three spatial dimensions (3D). We demonstrate live imaging of 25-plane 3D volumes of up to 180x180x50um at >100 volumes per second. 3D data is recorded simultaneously by an array of 25 small, sensitive, synchronized machine-vision cameras. M25 employs aberration-corrected Multifocus microscopy--an optical method where diffractive Fourier optics are used for multiplexing and refocusing light-- with a simplified design for chromatic dispersion correction where a corrective diffractive gratings is placed on each camera in the array. This elegant architecture for chromatic correction will be applicable in a broad range of diffractive imaging applications. M25 is a powerful optical tool for high-speed 3D microscopy in that it allows both non-invasive, label-free bright-field and highly sensitive fluorescence microscopy. We showcase M25 capabilities in 3D particle tracking, bright-field, and fluorescence imaging in D. melanogaster, and locomotion and neural activity studies in C. elegans.

neuroscience↗

bioRxiv2021

Swimming kinematics and performance of spinal transected lampreys with different levels of axon regeneration

Neural and functional recovery in lampreys from spinal cord transection has been well documented. However, the extent of axon regeneration is highly variable and it is not known whether it is related to the level of behavioral recovery. To address this, we examined how swimming kinematics were related to axon regeneration by quantifying the relationship between swimming performance and percent axon regeneration of transected lampreys after 11 weeks of recovery. We found that swimming speed was not related to percent axon regeneration but it was closely related to body wave frequency and speed. However, wave frequency and speed varied greatly within individuals which resulted in swimming speed also varying within individuals. In fact, most recovered individuals, regardless of percent axon regeneration, could swim at fast and slow speeds. However, none of the transected individuals were able to generate body waves as large as the control lampreys. In order to swim faster, transected lampreys increased their wave frequencies and, as a result, transected lampreys had much higher frequencies than control lamprey at comparable swimming velocities. These data suggest that the control lampreys swam more efficiently than transected lampreys. In conclusion, there appears to be a minimal recovery threshold in terms of percent axon regeneration required for lampreys to be capable of swimming, however, there also seems to be a limit to how much they can behaviorally recover.

animal behavior and cognition↗

bioRxiv2020

α-Synuclein-112 impairs synaptic vesicle recycling consistent with its enhanced membrane binding properties

Synucleinopathies are neurological disorders associated with -synuclein overexpression and aggregation. While it is well established that overexpression of wild type -synuclein (-syn-140) leads to cellular toxicity and neurodegeneration, much less is known about other naturally occurring -synuclein splice isoforms. In this study we provide the first detailed examination of the synaptic effects caused by one of these splice isoforms, -synuclein-112 (-syn-112). -Syn-112 is produced by an in-frame excision of exon 5, resulting in deletion of amino acids 103-130 in the C-terminal region. -Syn-112 is upregulated in the substantia nigra, frontal cortex, and cerebellum of parkinsonian brains and is correlated with susceptibility to sporadic Parkinsons disease (PD), dementia with Lewy bodies (DLB) and multiple systems atrophy (MSA). We report here that -syn-112 binds strongly to anionic phospholipids when presented in highly-curved liposomes, similar to -syn-140. However, -syn-112 bound significantly stronger to all phospholipids tested, including the phosphoinositides. -Syn-112 also dimerized and trimerized on isolated synaptic membranes, while -syn-140 remained largely monomeric. When introduced acutely to lamprey synapses, -syn-112 robustly inhibited synaptic vesicle recycling. Interestingly, -syn-112 produced effects on the plasma membrane and clathrin-mediated synaptic vesicle endocytosis that were phenotypically intermediate between those caused by monomeric and dimeric -syn-140. These findings indicate that -syn-112 exhibits enhanced phospholipid binding and oligomerization in vitro and consequently interferes with synaptic vesicle recycling in vivo in ways that are consistent with its biochemical properties. This study provides additional evidence suggesting that impaired vesicle endocytosis is a cellular target of excess -synuclein and advances our understanding of potential mechanisms underlying disease pathogenesis in the synucleinopathies.

neuroscience↗

bioRxiv2019

Hsc70 Ameliorates the Vesicle Recycling Defects Caused by Excess -Synuclein at Synapses

-Synuclein overexpression and aggregation are linked to Parkinsons disease (PD), dementia with Lewy bodies (DLB), and several other neurodegenerative disorders. In addition to effects in the cell body, -synuclein accumulation occurs at presynapses where the protein is normally localized. While it is generally agreed that excess -synuclein impairs synaptic vesicle trafficking, the underlying mechanisms are unknown. We show here that acute introduction of excess human -synuclein at a classic vertebrate synapse, the lamprey reticulospinal synapse, selectively impaired the uncoating of clathrin-coated vesicles (CCVs) during synaptic vesicle recycling, leading to a severe depletion of synaptic vesicles. Furthermore, human -synuclein and lamprey {gamma}-synuclein both interact in vitro with Hsc70, the chaperone protein that uncoats CCVs at synapses. After introducing excess -synuclein to lamprey axons, Hsc70 availability was reduced at the synapses, suggesting Hsc70 sequestration as a possible mechanism underlying the synaptic vesicle trafficking defects. In support of this hypothesis, increasing the levels of exogenous Hsc70 together with -synuclein ameliorated the CCV uncoating and vesicle recycling defects. These experiments identify a reduction in Hsc70 availability at synapses, and consequently its function, as the mechanism by which -synuclein induces synaptic vesicle recycling defects. To our knowledge, this is the first report of a viable chaperone-based strategy for reversing the toxic impacts of excess -synuclein at synapses, which may be of value for ameliorating synaptic defects in PD and other synuclein-linked diseases.\n\nSIGNIFICANCE STATEMENTSynaptic defects caused by -synuclein overexpression are linked to cognitive deficits in PD and other diseases. However, the mechanisms by which excess -synuclein impairs synaptic vesicle trafficking are unknown. Data presented here demonstrate that acute introduction of excess -synuclein at a classical vertebrate synapse selectively inhibits CCV uncoating, leading to impaired vesicle recycling. Furthermore, increasing -synuclein reduced synaptic levels of Hsc70, the clathrin uncoating ATPase. Subsequently increasing Hsc70 restored CCV uncoating and improved vesicle recycling. This study identifies a novel molecular mechanism underlying the -synuclein-induced synaptic defects and presents one viable strategy for reversing them.

neuroscience↗

bioRxiv2018

GABA promotes survival and axonal regeneration in identifiable descending neurons after spinal cord injury in larval lampreys

In mammals, spinal cord injury (SCI) causes permanent disability. The poor regenerative capacity of descending neurons is one of the main causes of the lack of recovery after SCI. In addition, the prevention of retrograde degeneration leading to the atrophy or death of descending neurons is an obvious prerequisite for the activation of axonal regeneration. Lampreys show an amazing regenerative capacity after SCI. Recent histological work in lampreys suggested that GABA, which is massively released after a SCI, could promote the survival of descending neurons. Here, we aimed to study if GABA, acting through GABAB receptors, promotes the survival and axonal regeneration of descending neurons of larval sea lampreys after a complete SCI. First, we used in situ hybridization to confirm that identifiable descending neurons of late stage larvae express the gabab1 subunit of the sea lamprey GABAB receptor. We also observed an acute increase in the expression of this subunit in descending neurons after a complete SCI, which further supported the possible role of GABA and GABAB receptors in promoting the survival and regeneration of these neurons. So, we performed gain and loss of function experiments to confirm this hypothesis. Treatments with GABA and baclofen (GABAB agonist) significantly reduced caspase activation in descending neurons 2 weeks after a complete SCI. Long-term treatments with GABOB (a GABA analogue) and baclofen significantly promoted axonal regeneration of descending neurons after SCI. These data indicate that GABAergic signalling through GABAB receptors promotes the survival and regeneration of descending neurons after SCI. Finally, we used morpholinos against the gabab1 subunit to specifically knockdown the expression of the GABAB receptor in descending neurons. Long-term morpholino treatments caused a significant inhibition of axonal regeneration, which shows that endogenous GABA promotes axonal regeneration after a complete SCI in lampreys by activating GABAB receptors expressed in descending neurons. These data implicate GABAB receptors in spinal cord regeneration in lampreys and further provide a new target of interest for SCI.

neuroscience↗