Biology subjects

Melland, H.

Publications and source records attributed to Melland, H..

3 recordsLinked to original sources

bioRxiv2023

Adaptive functions correlate with evoked neurotransmitter release in SYT1-associated neurodevelopmental disorder

Pathogenic missense variants in the essential synaptic vesicle protein synaptotagmin-1 (SYT1) cause a neurodevelopmental disorder that is characterised by motor delay and intellectual disability, hyperkinetic movement disorder, episodic agitation, and visual impairments. SYT1 is the presynaptic calcium sensor that both triggers and drives synchronous neurotransmitter release. We have previously shown that pathogenic variants around the calcium-sensing region of the critical C2B domain decrease synaptic vesicle exocytosis in neurons. Here we show that recently identified variants within the facilitatory C2A domain of the protein (L159R, T196K, E209K, E219Q), as well as additional variants in the C2B domain (M303V, S309P, Y365C, G369D), share this underlying pathogenic mechanism, causing a graded and variant-dependent dominant-negative impairment in exocytosis. We establish that the extent of disruption to exocytosis in vitro correlates with neurodevelopmental impacts of this disorder. Specifically, the severity of motor and communication impairments exhibited by individuals harbouring these variants correlates with multiple measures of exocytic impairment. Together, this suggests that there is a genotype-function-phenotype relationship in SYT1-associated neurodevelopmental disorder, centring impaired evoked neurotransmitter release as a common pathogenic driver of this disorder. Moreover, this points toward a direct link between control of neurotransmitter release and development of adaptive functions, and provides a tractable target for therapeutic amelioration.

neuroscience↗

bioRxiv2023

Delineation of the pathogenic presynaptic mechanisms of synaptotagmin-1 variants

Missense variants in the presynaptic calcium sensor synaptotagmin-1 (SYT1) are associated with an autosomal dominant neurodevelopmental disorder (NDD). These cause dominant-negative impairment of evoked neurotransmitter release in a mutation-specific manner; however, whether NDD-associated variants also perturb the auxiliary functions of SYT1 remains unknown. We investigated whether the expression of SYT1 variants in cultured hippocampal neurons altered either action potential-independent spontaneous synaptic vesicle exocytosis or synaptic vesicle endocytosis. SYT1 variants did not induce dominant-negative impairment of either process, confirming that defective evoked exocytosis is the major pathogenic mechanism of SYT1-associated NDD. To examine the differential impacts of human variants on evoked exocytosis, both NDD-associated and strategic mutations were used to explore the functional importance of two distinct Ca2+-binding residues in the C2B domain. We show that both the nature of the amino acid change and the specific residues targeted determine the severity of exocytic disturbance. Together, this work informs understanding of SYT1 function and further clarifies potential mechanistic targets for treating SYT1-associated NDD.

neuroscience↗

bioRxiv2021

Postsynaptic neuroligin-1 mediates presynaptic endocytosis during neuronal activity

Fast, high-fidelity neurotransmission and synaptic efficacy requires tightly regulated coordination of pre- and postsynaptic compartments and alignment of presynaptic release sites with postsynaptic receptor nanodomains. Neuroligin-1 (Nlgn-1) is a postsynaptic cell-adhesion protein exclusively localised to excitatory synapses that is crucial for coordinating the transsynaptic alignment of presynaptic release sites with postsynaptic AMPA receptors as well as postsynaptic transmission and plasticity. However, little is understood about whether the postsynaptic machinery can mediate the molecular architecture and activity of the presynaptic nerve terminal, and thus it remains unclear whether there are presynaptic contributions to Nlgn1-dependent control of signalling and plasticity. Here, we employed a presynaptic reporter of neurotransmitter release and synaptic vesicle dynamics, synaptophysin-pHluorin (sypHy), to directly assess the presynaptic impact of loss of Nlgn1. We show that lack of Nlgn1 had no effect on the size of the readily releasable or entire recycling pool of synaptic vesicles, nor did it impact exocytosis. However, we observed significant changes in the retrieval of synaptic vesicles by compensatory endocytosis, specifically during activity. Our data extends growing evidence that synaptic adhesion molecules critical for forming transsynaptic scaffolds are also important for regulating activity-induced endocytosis at the presynapse.

neuroscience↗