Biology subjects

Munns, J.

Publications and source records attributed to Munns, J..

4 recordsLinked to original sources

bioRxiv2024

The rhythmic transcriptional landscape in Caenorhabditis elegans: daily, circadian and novel 16-hour cycling gene expression revealed by RNA-sequencing

The nematode Caenorhabditis elegans is an unconventional model in chronobiology, reported to exhibit physiological and behavioural circadian rhythms while lacking a defined transcriptional oscillator. The extent and importance of circadian rhythms in C. elegans remain uncertain, given a probable lack of functional conservation of key circadian proteins, relatively non-robust reported rhythms and an ambiguous diel ecology. Here, we investigated the temporal coordination of gene expression in C. elegans post-development using RNA sequencing. Over a circadian time series, in which we synchronised nematodes to combined light and temperature cycles, we found clear evidence of daily oscillations in 343 genes using JTK_Cycle. However, rhythms were not well-sustained in constant conditions, with only 13 genes remaining significantly rhythmic. Reanalysis of previous transcriptomic data echoed this finding in identifying far fewer rhythmic genes in constant conditions, while also identifying a greater number of rhythmic genes overall. Weighted gene co-expression network analysis (WGCNA), a hierarchical clustering approach, further confirmed prevalent environmentally driven daily oscillations in the RNA-seq data. This analysis additionally revealed a novel co-expression trend in which over 1000 genes exhibited hitherto unreported 16-hour oscillations, highlighting a new facet of temporal gene expression coordination in C. elegans.

physiology↗

bioRxiv2020

Selective human tau protein expression in different clock circuits of the Drosophila brain disrupts different aspects of sleep and circadian rhythms

Circadian behavioural deficits, such as increased daytime naps and reduced night-time sleep, are common in Alzheimers disease and other tauopathies. But it has remained unclear whether these circadian abnormalities arise from tau pathology in either the master pacemaker or downstream neurons. Here we study this question by selectively expressing different human tau proteins in specific Drosophila brain circuits and monitoring locomotor activity under light-dark (LD) and in "free-running" dark-dark (DD) conditions. We show that expressing human tau proteins in the fly brain recapitulates faithfully several behavioural changes found in tauopathies. We identify discrete neuronal subpopulations within the clock network as the primary target of distinct circadian behavioural disturbances in different environmental conditions. Specifically, we show that the PDF-positive pacemaker neurons are the main site for night-activity gain and -sleep loss, whereas the non-PDF clock-neurons are the main site of reduced intrinsic behavioural rhythmicity. Bioluminescence measurements revealed that the molecular clock is intact despite the behavioural arrhythmia. Our results establish that dysfunction in both the central clock- and afferent clock-neurons jointly contribute to the circadian locomotor activity rhythm disruption in Drosophila expressing human tau. Significance StatementThis study directly links in vivo human tau protein expression in region-specific Drosophila clock-neurons with the resulting sleep and circadian rhythm deficits to extract new knowledge of how Alzheimers disease and other tauopathies perturb the balance of activity and sleep. We anticipate that this novel approach will provide a useful general template for other studies of neurodegeneration in model organisms, seeking to dissect the impact of neurodegenerative disease on circadian behaviour, and further deepening our understanding of how the clock-neuron network works.

neuroscience↗

bioRxiv2020

Multiple pathways of LRRK2-G2019S / Rab10 interaction in dopaminergic neurons

BackgroundInherited mutations in the LRRK2 protein are the most common known cause of Parkinsons, but the mechanisms by which increased kinase activity of mutant LRRK2 leads to pathological events remain to be determined. In vitro assays (heterologous cell culture, phospho-protein mass spectrometry) suggest that several Rab proteins might be directly phosphorylated by LRRK2-G2019S. Which Rabs interact with LRRK2 in dopaminergic neurons to facilitate normal and pathological physiological responses remains to be determined. An in vivo screen of Rab expression in dopaminergic neurons in young adult Drosophila demonstrated a strong genetic interaction between LRRK2-G2019S and Rab10. We now ask if Rab10 is required for LRRK2-induced physiological responses in DA neurons. MethodsLRRK2-G2019S was expressed in Drosophila dopaminergic neurons and the effects of Rab10 depletion on Proboscis Extension, vision, circadian activity pattern and courtship memory determined in aged flies. ResultsRab10 loss-of-function rescued bradykinesia of the Proboscis Extension Response (PER) and visual defects of aged flies expressing LRRK2-G2019S in DA neurons. Rab10 knock-down however, did not rescue the marked sleep phenotype which results from dopaminergic expression of LRRK2-G2019S. Courtship memory is not affected by LRRK2 expression, but is markedly improved by Rab10 depletion. Anatomically, both LRRK2-G2019S and Rab10 are seen in the cytoplasm and at the synaptic endings of dopaminergic neurons. ConclusionsWe conclude that, in Drosophila dopaminergic neurons, Rab10 is involved differentially in LRRK2-induced behavioral deficits. Therefore, variations in Rab expression may contribute to susceptibility of different dopaminergic nuclei to neurodegeneration seen in people with Parkinsons. Graphical AbstractRab10 depletion ameliorates the proboscis extension bradykinesia and loss of synaptic signalling in the retina induced by LRRK2-G2019S expression (magenta arrows / orange crosses). Rab10 manipulation does not affect the sleep phenotype from LRRK2-G2019S (magenta arrow). Reduction of Rab10 facilitates conditioned courtship memory, but LRRK2 has no effect (yellow arrow). All manipulations of Rab10 and G2019S in dopaminergic neurons, shown in the outline of the brain (filled cells have high levels of Rab10). We conclude that Rab10 and LRRK2 interact in some, but not all dopaminergic neurons. This may underlie differences in the susceptibility of different human striatal dopaminergic cells to Parkinsons and explain why different symptoms initiate particular ages. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=172 SRC="FIGDIR/small/316992v2_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@1e9a923org.highwire.dtl.DTLVardef@15f7135org.highwire.dtl.DTLVardef@101525borg.highwire.dtl.DTLVardef@1c5da02_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2019

Neurodegeneration caused by LRRK2-G2019S requires Rab10 in select dopaminergic neurons

Inherited mutations in the LRRK2 protein are the commonest known cause of Parkinsons, but the molecular link from increased kinase activity to pathological neurodegeneration remains to be determined. In vitro (biochemical and cell culture) assays led to the hypothesis that several Rab GTPases might be LRRK2 substrates. Here we show that Rab10 potently modifies LRRK2-G2019S mediated electrophysiological responses in an in vivo screen, in which each Rab was overexpressed in Drosophila dopaminergic neurons. We therefore tested the effect of Rab10 loss of function on three LRRK2-G2019S phenotypes (vision, movement and sleep) that rely on dopaminergic circuits in both flies and mammals. The knock-out of Rab10 in vivo fully rescues the reduced responses induced by dopaminergic LRRK2-G2019S in visual and motor (reaching, proboscis extension) assays, but the sleep phenotype is unaffected. We show that Rab10 is expressed in dopaminergic (tyrosine hydroxylase positive) neurons controlling vision and proboscis movement, but undetectable in those controlling sleep, indicating that anatomical and physiological patterns of Rab10 are related. Our results support the idea that LRRK2 phosphorylates separate targets in distinct neurons and confirm that one degenerative pathway starts with Rab10. Although Rab3 is another putative substrate of LRRK2, it shows no synergy with G2019S and localises to a different subset of dopaminergic neurons from Rab10. We propose that variations in Rab expression may contribute to differences in the rate of neurodegeneration seen in different dopaminergic nuclei in Parkinsons.\n\nSignificance StatementA key question in Parkinsons is why dopamine neurons die particularly fast in some parts of the substantia nigra. We focused on the commonest Parkinsons-related mutation, LRRK2-G2019S. In vitro assays suggested that neurodegeneration may start by LRRK2-G2019S increasing phosphorylation of Rab10. We found Rab10 in fly dopamine neurons in visual and motor pathways, but not in the sleep system. Rab10 knock-out rescues G2019S-induced visual and movement degeneration, leaving sleep dysfunction unaffected. Thus, LRRK2 activates at least two pathways, one Rab10-dependent, leading to neurodegeneration in vivo. Rab3 is found in a different subset of dopaminergic neurons and shows no synergy with LRRK2-G2019S. We propose that variations in Rab expression contribute to differences in neurodegeneration seen in Parkinsons.

neuroscience↗