Ca sensor proteins in spontaneous release and synaptic plasticity: Limited contribution of Doc2c, rabphilin-3a and synaptotagmin 7 in hippocampal glutamatergic neurons.

Presynaptic neurotransmitter release is strictly regulated by SNARE proteins, Ca and a number of Ca sensors including synaptotagmins (Syts) and Double C domain proteins (Doc2s). More than seventy years after the original description of spontaneous release, the mechanism that regulates this process is still poorly understood. Syt-1, Syt7 and Doc2 proteins contribute predominantly, but not exclusively, to synchronous, asynchronous and spontaneous phases of release.

Doc2 Proteins Are Not Required for the Increased Spontaneous Release Rate in Synaptotagmin-1-Deficient Neurons.

Regulated secretion is controlled by Ca sensors with different affinities and subcellular distributions. Inactivation of (synaptotagmin-1), the main Ca sensor for synchronous neurotransmission in many neurons, enhances asynchronous and spontaneous release rates, suggesting that Syt1 inhibits other sensors with higher Ca affinities and/or lower cooperativities. Such sensors could include Doc2a and Doc2b, which have been implicated in spontaneous and asynchronous neurotransmitter release and compete with Syt1 for binding SNARE complexes.

Doc2b Ca binding site mutants enhance synaptic release at rest at the expense of sustained synaptic strength.

Communication between neurons involves presynaptic neurotransmitter release which can be evoked by action potentials or occur spontaneously as a result of stochastic vesicle fusion. The Ca-binding double C proteins Doc2a and -b were implicated in spontaneous and asynchronous evoked release, but the mechanism remains unclear. Here, we compared wildtype Doc2b with two Ca binding site mutants named DN and 6A, previously classified as gain- and loss-of-function mutants.

SICT: automated detection and supervised inspection of fast Ca transients.

Recent advances in live Ca imaging with increasing spatial and temporal resolution offer unprecedented opportunities, but also generate an unmet need for data processing. Here we developed SICT, a MATLAB program that automatically identifies rapid Ca rises in time-lapse movies with low signal-to-noise ratios, using fluorescent indicators. A graphical user interface allows visual inspection of automatically detected events, reducing manual labour to less than 10% while maintaining quality control.

Doc2B acts as a calcium sensor for vesicle priming requiring synaptotagmin-1, Munc13-2 and SNAREs.

Doc2B is a cytosolic protein with binding sites for Munc13 and Tctex-1 (dynein light chain), and two C2-domains that bind to phospholipids, Ca and SNAREs. Whether Doc2B functions as a calcium sensor akin to synaptotagmins, or in other calcium-independent or calcium-dependent capacities is debated. We here show by mutation and overexpression that Doc2B plays distinct roles in two sequential priming steps in mouse adrenal chromaffin cells.

δ-Catenin () missense mutation in familial cortical myoclonic tremor and epilepsy.

Objective: To identify the causative gene in a large Dutch family with familial cortical myoclonic tremor and epilepsy (FCMTE).

Methods: We performed exome sequencing for 3 patients of our FCMTE family. Next, we performed knock-down (shRNA) and rescue experiments by overexpressing wild-type and mutant human δ-catenin (CTNND2) proteins in cortical mouse neurons and compared the results with morphologic abnormalities in the postmortem FCMTE brain.

Direct quantitative detection of Doc2b-induced hemifusion in optically trapped membranes.

Ca(2+)-sensor proteins control the secretion of many neuroendocrine substances. Calcium-secretion coupling may involve several mechanisms. First, Ca(2+)-dependent association of their tandem C2 domains with phosphatidylserine may induce membrane curvature and thereby enhance fusion.

Identification of a Dutch founder mutation in MUSK causing fetal akinesia deformation sequence.

Fetal akinesia deformation sequence (FADS) refers to a clinically and genetically heterogeneous group of disorders with congenital malformations related to impaired fetal movement. FADS can result from mutations in CHRNG, CHRNA1, CHRND, DOK7 and RAPSN; however, these genes only account for a minority of cases. Here we identify MUSK as a novel cause of lethal FADS.

Two male adults with pathogenic AUTS2 variants, including a two-base pair deletion, further delineate the AUTS2 syndrome.

AUTS2 syndrome is characterized by low birth weight, feeding difficulties, intellectual disability, microcephaly and mild dysmorphic features. All affected individuals thus far were caused by chromosomal rearrangements, variants at the base pair level disrupting AUTS2 have not yet been described. Here we present the full clinical description of two affected men with intragenic AUTS2 variants (one two-base pair deletion in exon 7 and one deletion of exon 6).

TRIM3 regulates the motility of the kinesin motor protein KIF21B.

Kinesin superfamily proteins (KIFs) are molecular motors that transport cellular cargo along the microtubule cytoskeleton. KIF21B is a neuronal kinesin that is highly enriched in dendrites. The regulation and specificity of microtubule transport involves the binding of motors to individual cargo adapters and accessory proteins.

Exonic deletions in AUTS2 cause a syndromic form of intellectual disability and suggest a critical role for the C terminus.

Genomic rearrangements involving AUTS2 (7q11.22) are associated with autism and intellectual disability (ID), although evidence for causality is limited. By combining the results of diagnostic testing of 49,684 individuals, we identified 24 microdeletions that affect at least one exon of AUTS2, as well as one translocation and one inversion each with a breakpoint within the AUTS2 locus.

Doc2b is a key effector of insulin secretion and skeletal muscle insulin sensitivity.

Exocytosis of intracellular vesicles, such as insulin granules, is carried out by soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) and Sec1/Munc18 (SM) proteins. An additional regulatory protein, Doc2b (double C2 domain), has recently been implicated in exocytosis from clonal β-cells and 3T3-L1 adipocytes. Here, we investigated the role of Doc2b in insulin secretion, insulin sensitivity, and the maintenance of whole-body glucose homeostasis.

Multiple Ca2+ sensors in secretion: teammates, competitors or autocrats?

Regulated neurotransmitter secretion depends on Ca(2+) sensors, C2 domain proteins that associate with phospholipids and soluble N-ethylmaleimide-sensitive fusion attachment protein receptor (SNARE) complexes to trigger release upon Ca(2+) binding. Ca(2+) sensors are thought to prevent spontaneous fusion at rest (clamping) and to promote fusion upon Ca(2+) activation. At least eight, often coexpressed, Ca(2+) sensors have been identified in mammals.