Biology subjects

Coakley, S.

Publications and source records attributed to Coakley, S..

4 recordsLinked to original sources

bioRxiv2025

A conserved Arf-GEF modulates axonal integrity through RAB-35 by altering neuron-epidermal attachment

Neurites of sensory neurons densely innervate the skin and are embedded within it. These delicate structures are exposed to acute and chronic mechanical strain and yet their integrity is maintained throughout life. Although evidence suggests a neuroprotective role for the skin, the molecular pathways involved are still poorly understood. In C. elegans, the cytoskeletal molecule UNC-70/{beta}-spectrin functions in synergy with the small GTPase RAB-35 within the skin to stabilize neuron-epidermal attachment structures against mechanical strain and prevent movement-induced damage to mechanosensitive axons. However, the full suite of molecules regulating these specialized attachments remains elusive. Here, through an unbiased forward genetic screen we have identified a guanine nucleotide exchange factor (GEF) previously associated with the endocytic-recycling machinery, AGEF-1a, that impacts axonal maintenance. We show that AGEF-1a functions selectively within the skin to regulate the integrity of the embedded axons. Mechanistically, we reveal that this effect is achieved through an interaction between AGEF-1a and epidermal RAB-35 to facilitate its activation, which in turn modulates the neuron-epidermal attachments. Finally, we demonstrate that the function of this GEF is highly conserved, with the expression of its human ortholog, BIG2 capable of replacing AGEF-1a. Together, we reveal the specific molecular machinery responsible for fine-tuning neuron-epidermal attachments and maintaining axonal integrity during life.

neuroscience↗

bioRxiv2022

Spectrin forms a periodic cytoskeleton within the epidermis to preserve axonal integrity.

Spectrins are highly conserved molecules that form a distinct membrane associated periodic scaffold within axons thought to provide mechanical resilience. In C. elegans, UNC-70/{beta}-Spectrin also functions outside the nervous system, within the epidermis, to maintain the integrity of sensory neurons. The precise molecular organization and cellular mechanisms that mediate this protection are unknown. Here, using 3D-structured illumination microscopy, we show that within the epidermis spectrins form a crescent-shaped scaffold with a periodicity of [~] 200 nm that embraces adjacent axons. This epidermal spectrin scaffold is induced by developing axons and reformed during axonal regeneration, and creates a "molecular imprint" of the adjacent nervous system. Disruption of this epidermal scaffold causes widespread axonal damage in sensory and motor neurons. These findings reveal the existence of a distinct and periodic spectrin framework within the epidermis that is molded by the developing nervous system and is necessary to protect it from mechanical damage. TeaserSpectrin forms a periodic scaffold in the epidermis that protects axons from damage.

neuroscience↗

bioRxiv2022

Dendrites use mechanosensitive channels to proofread ligand-mediated guidance during morphogenesis.

Ligand-receptor interactions guide axon navigation and dendrite arborization. Mechanical forces also influence guidance choices. However, the nature of such mechanical stimulations, the mechanosensors identity and how they interact with guidance receptors are unknown. Here, we demonstrate that mechanosensitive DEG/ENaC channels are required for dendritic arbor morphogenesis in Caenorhabditis elegans. Inhibition of DEG/ENaC channels causes reduced dendritic outgrowth and branching in vivo, a phenotype that is alleviated by overexpression of the mechanosensitive channels PEZO-1/Piezo or YVC1/TrpY1. DEG/ENaCs trigger local Ca2+ transients in growing dendritic filopodia via activation of L-type voltage-gated Ca2+ channels. Anchoring of filopodia by guidance ligand/receptor is required for the mechanical activation of DEG/ENaC channels. Therefore, mechanosensitive channels serve as a checkpoint for appropriate chemoaffinity by activating Ca2+ transients required for neurite growth.

neuroscience↗

bioRxiv2017

6-OHDA-induced dopaminergic neurodegeneration in C. elegans is promoted by the engulfment pathway and inhibited by the transthyretin-related protein TTR-33

Oxidative stress is linked to many pathological conditions including the loss of dopaminergic neurons in Parkinsons disease. The vast majority of disease cases appear to be caused by a combination of genetic mutations and environmental factors. We screened for genes protecting Caenorhabditis elegans dopaminergic neurons from oxidative stress induced by the neurotoxin 6-hydroxydopamine (6-OHDA) and identified the transthyretin-related gene ttr-33. The only described C. elegans transthyretin-related protein to date, TTR-52, has been shown to mediate corpse engulfment as well as axon repair. We demonstrate that TTR-52 and TTR-33 have distinct roles. TTR-33 is likely produced in the posterior arcade cells in the head of C. elegans larvae and is predicted to be a secreted protein. TTR-33 protects C. elegans from oxidative stress induced by paraquat or H2O2 at an organismal level. The increased oxidative stress sensitivity of ttr-33 mutants is alleviated by mutations affecting the KGB-1 MAPK kinase pathway, whereas it is enhanced by mutation of the JNK-1 MAPK kinase. Finally, we provide genetic evidence that the C. elegans cell corpse engulfment pathway is required for the degeneration of dopaminergic neurons after exposure to 6-OHDA. In summary, we describe a new neuroprotective mechanism and demonstrate that TTR-33 normally functions to protect dopaminergic neurons from oxidative stress-induced degeneration, potentially by acting as a secreted sensor or scavenger of oxidative stress.\n\nAuthor summaryAnimals employ multiple mechanisms to prevent their cells from damage by reactive oxygen species, chemically reactive molecules containing oxygen. Oxidative stress, caused by the overabundance of reactive oxygen species or a decreased cellular defence against these chemicals, is linked to a variety of neurodegenerative conditions, including the loss of dopaminergic neurons in Parkinsons disease. In this study, we discovered a novel protective molecule that functions to prevent dopaminergic neurodegeneration caused by oxidative stress induced by the neurotoxin 6-hydroxydopamine (6-OHDA). We used the nematode C. elegans, a well-characterised model in which mechanisms can be studied on an organismal level. When C. elegans is exposed to 6-OHDA, its dopaminergic neurons gradually die. Our major findings include (i) mutations of the transthyretin-related gene ttr-33 causes highly increased dopaminergic neurodegeneration after 6-OHDA exposure; (ii) TTR-33 is likely produced and secreted by several cells in the head of the animal; (iii) TTR-33 protects against oxidative stress induced by other compounds; (iv) mutations in the KGB-1 MAP kinase stress pathway alleviate dopaminergic neuron loss in the ttr-33 mutant; and (v) the cell corpse engulfment pathway is required for dopaminergic neurodegeneration. We hypothesise that TTR-33 protects dopaminergic neurons against 6-OHDA-induced oxidative stress by acting as an oxygen sensor or scavenger.

genetics↗