The EHD protein Past1 controls postsynaptic membrane elaboration and synaptic function

Membranes form elaborate structures that are highly tailored to their specialized cellular functions, yet the mechanisms by which these structures are shaped remain poorly understood. Here, we show that the conserved membrane-remodeling C-terminal Eps15 Homology Domain (EHD) protein Past1 is required for the normal assembly of the subsynaptic muscle membrane reticulum (SSR) at the Drosophila melanogaster larval neuromuscular junction (NMJ). past1 mutants exhibit altered NMJ morphology, decreased synaptic transmission, reduced glutamate receptor levels, and a deficit in synaptic homeostasis. The membrane-remodeling proteins Amphiphysin and Syndapin colocalize with Past1 in distinct SSR subdomains and collapse into Amphiphysin-dependent membrane nodules in the SSR of past1 mutants. Our results suggest a mechanism by which the coordinated actions of multiple lipid-binding proteins lead to the elaboration of increasing layers of the SSR and uncover new roles for an EHD protein at synapses.

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Characterization of postsynaptic Ca2+ signals at the Drosophila larval NMJ

Journal of Neurophysiology ◽

10.1152/jn.00045.2011 ◽

2011 ◽

Vol 106 (2) ◽

pp. 710-721 ◽

Cited By ~ 9

Author(s):

Sunil A. Desai ◽

Gregory A. Lnenicka

Keyword(s):

Transmitter Release ◽

Postsynaptic Membrane ◽

Synaptic Activity ◽

Synaptic Efficacy ◽

Single Action ◽

Synaptic Homeostasis ◽

Multiple Transcripts ◽

Quantal Size ◽

Intracellular Ca ◽

Larval Neuromuscular Junction

Postsynaptic intracellular Ca2+ concentration ([Ca2+]i) has been proposed to play an important role in both synaptic plasticity and synaptic homeostasis. In particular, postsynaptic Ca2+ signals can alter synaptic efficacy by influencing transmitter release, receptor sensitivity, and protein synthesis. We examined the postsynaptic Ca2+ transients at the Drosophila larval neuromuscular junction (NMJ) by injecting the muscle fibers with Ca2+ indicators rhod-2 and Oregon Green BAPTA-1 (OGB-1) and then monitoring their increased fluorescence during synaptic activity. We observed discrete postsynaptic Ca2+ transients along the NMJ during single action potentials (APs) and quantal Ca2+ transients produced by spontaneous transmitter release. Most of the evoked Ca2+ transients resulted from the release of one or two quanta of transmitter and occurred largely at synaptic boutons. The magnitude of the Ca2+ signals was correlated with synaptic efficacy; the Is terminals, which produce larger excitatory postsynaptic potentials (EPSPs) and have a greater quantal size than Ib terminals, produced a larger Ca2+ signal per terminal length and larger quantal Ca2+ signals than the Ib terminals. During a train of APs, the postsynaptic Ca2+ signal increased but remained localized to the postsynaptic membrane. In addition, we showed that the plasma membrane Ca2+-ATPase (PMCA) played a role in extruding Ca2+ from the postsynaptic region of the muscle. Drosophila melanogaster has a single PMCA gene, predicted to give rise to various isoforms by alternative splicing. Using RT-PCR, we detected the expression of multiple transcripts in muscle and nervous tissues; the physiological significance of the same is yet to be determined.

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Synaptic excitation is regulated by the postsynaptic dSK channel at the Drosophila larval NMJ

Journal of Neurophysiology ◽

10.1152/jn.00903.2013 ◽

2014 ◽

Vol 111 (12) ◽

pp. 2533-2543 ◽

Cited By ~ 10

Author(s):

Daniel M. Gertner ◽

Sunil Desai ◽

Gregory A. Lnenicka

Keyword(s):

Transmitter Release ◽

Membrane Conductance ◽

Postsynaptic Membrane ◽

Synaptic Activity ◽

Muscle Membrane ◽

Resting Membrane Potential ◽

Excitatory Postsynaptic Potential ◽

Synaptic Excitation ◽

Sk Channel ◽

Larval Neuromuscular Junction

In the mammalian central nervous system, the postsynaptic small-conductance Ca2+-dependent K+ (SK) channel has been shown to reduce postsynaptic depolarization and limit Ca2+ influx through N-methyl-d-aspartate receptors. To examine further the role of the postsynaptic SK channel in synaptic transmission, we studied its action at the Drosophila larval neuromuscular junction (NMJ). Repetitive synaptic stimulation produced an increase in postsynaptic membrane conductance leading to depression of excitatory postsynaptic potential amplitude and hyperpolarization of the resting membrane potential (RMP). This reduction in synaptic excitation was due to the postsynaptic Drosophila SK (dSK) channel; synaptic depression, increased membrane conductance and RMP hyperpolarization were reduced in dSK mutants or after expressing a Ca2+ buffer in the muscle. Ca2+ entering at the postsynaptic membrane was sufficient to activate dSK channels based upon studies in which the muscle membrane was voltage clamped to prevent opening voltage-dependent Ca2+ channels. Increasing external Ca2+ produced an increase in resting membrane conductance and RMP that was not seen in dSK mutants or after adding the glutamate-receptor blocker philanthotoxin. Thus it appeared that dSK channels were also activated by spontaneous transmitter release and played a role in setting membrane conductance and RMP. In mammals, dephosphorylation by protein phosphatase 2A (PP2A) increased the Ca2+ sensitivity of the SK channel; PP2A appeared to increase the sensitivity of the dSK channel since PP2A inhibitors reduced activation of the dSK channel by evoked synaptic activity or increased external Ca2+. It is proposed that spontaneous and evoked transmitter release activate the postsynaptic dSK channel to limit synaptic excitation and stabilize synapses.

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β-Synuclein: An Enigmatic Protein with Diverse Functionality

Biomolecules ◽

10.3390/biom12010142 ◽

2022 ◽

Vol 12 (1) ◽

pp. 142

Author(s):

Junna Hayashi ◽

John A. Carver

Keyword(s):

Molecular Chaperone ◽

Lewy Bodies ◽

Lipid Binding ◽

Synaptic Function ◽

Cellular Functions ◽

Post Translational Modifications ◽

Metal Levels ◽

And Function ◽

Presynaptic Protein

α-Synuclein (αS) is a small, unstructured, presynaptic protein expressed in the brain. Its aggregated form is a major component of Lewy bodies, the large proteinaceous deposits in Parkinson’s disease. The closely related protein, β-Synuclein (βS), is co-expressed with αS. In vitro, βS acts as a molecular chaperone to inhibit αS aggregation. As a result of this assignation, βS has been largely understudied in comparison to αS. However, recent reports suggest that βS promotes neurotoxicity, implying that βS is involved in other cellular pathways with functions independent of αS. Here, we review the current literature pertaining to human βS in order to understand better the role of βS in homeostasis and pathology. Firstly, the structure of βS is discussed. Secondly, the ability of βS to (i) act as a molecular chaperone; (ii) regulate synaptic function, lipid binding, and the nigrostriatal dopaminergic system; (iii) mediate apoptosis; (iv) participate in protein degradation pathways; (v) modulate intracellular metal levels; and (vi) promote cellular toxicity and protein aggregation is explored. Thirdly, the P123H and V70M mutations of βS, which are associated with dementia with Lewy bodies, are discussed. Finally, the importance of post-translational modifications on the structure and function of βS is reviewed. Overall, it is concluded that βS has both synergistic and antagonistic interactions with αS, but it may also possess important cellular functions independent of αS.

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Acid Sphingomyelinase, a Lysosomal and Secretory Phospholipase C, Is Key for Cellular Phospholipid Catabolism

International Journal of Molecular Sciences ◽

10.3390/ijms22169001 ◽

2021 ◽

Vol 22 (16) ◽

pp. 9001

Author(s):

Bernadette Breiden ◽

Konrad Sandhoff

Keyword(s):

Membrane Lipids ◽

Potential Effect ◽

Lipid Binding ◽

Acid Sphingomyelinase ◽

Cellular Functions ◽

Physiological Processes ◽

Niemann Pick Disease ◽

Niemann Pick ◽

Lipid Binding Proteins

Here, we present the main features of human acid sphingomyelinase (ASM), its biosynthesis, processing and intracellular trafficking, its structure, its broad substrate specificity, and the proposed mode of action at the surface of the phospholipid substrate carrying intraendolysosomal luminal vesicles. In addition, we discuss the complex regulation of its phospholipid cleaving activity by membrane lipids and lipid-binding proteins. The majority of the literature implies that ASM hydrolyses solely sphingomyelin to generate ceramide and ignores its ability to degrade further substrates. Indeed, more than twenty different phospholipids are cleaved by ASM in vitro, including some minor but functionally important phospholipids such as the growth factor ceramide-1-phosphate and the unique lysosomal lysolipid bis(monoacylglycero)phosphate. The inherited ASM deficiency, Niemann-Pick disease type A and B, impairs mainly, but not only, cellular sphingomyelin catabolism, causing a progressive sphingomyelin accumulation, which furthermore triggers a secondary accumulation of lipids (cholesterol, glucosylceramide, GM2) by inhibiting their turnover in late endosomes and lysosomes. However, ASM appears to be involved in a variety of major cellular functions with a regulatory significance for an increasing number of metabolic disorders. The biochemical characteristics of ASM, their potential effect on cellular lipid turnover, as well as a potential impact on physiological processes will be discussed.

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