Synchronous neurotransmitter release is triggered by Ca2+ binding to the synaptic vesicle protein Synaptotagmin 1, while asynchronous fusion and short-term facilitation is hypothesized to be mediated by plasma membrane-localized Synaptotagmin 7 (SYT7). We generated mutations in Drosophila Syt7 to determine if it plays a conserved role as the Ca2+ sensor for these processes. Electrophysiology and quantal imaging revealed evoked release was elevated 2-fold. Syt7 mutants also had a larger pool of readily-releasable vesicles, faster recovery following stimulation, and intact facilitation. Syt1/Syt7 double mutants displayed more release than Syt1 mutants alone, indicating SYT7 does not mediate the residual asynchronous release remaining in the absence of SYT1. SYT7 localizes to an internal membrane tubular network within the peri-active zone, but does not enrich at active zones. These findings indicate the two Ca2+ sensor model of SYT1 and SYT7 mediating all phases of neurotransmitter release and facilitation is not applicable at Drosophila synapses.

The Golgi apparatus (GA) is the hub of intracellular trafficking, but selectively targeting GA remains a challenge. We show an unconventional types of peptide thioesters, consisting of an aminoethyl thioester and acting as substrates of thioesterases, for instantly targeting the GA of cells. The peptide thioesters, above or below their critical micelle concentrations, enter cells mainly via caveolin-mediated endocytosis or macropinocytosis, respectively. After being hydrolyzed by GA-associated thioesterases, the resulting thiopeptides form dimers and accumulate in the GA. After saturating the GA, the thiopeptides are enriched in the endoplasmic reticulum (ER). Their buildup in ER and GA disrupts protein trafficking, thus leading to cell death via multiple pathways. The peptide thioesters target the GA of a wide variety of cells, including human, murine, and Drosophila cells. Changing d-diphenylalanine to l-diphenylalanine in the peptide maintains the GA-targeting ability. In addition, targeting GA redirects protein (e.g., NRAS) distribution. This work illustrates a thioesterase-responsive and redox-active molecular platform for targeting the GA and controlling cell fates.

The Synaptotagmin (SYT) family of proteins play key roles in regulating membrane trafficking at neuronal synapses. Using both Ca2+-dependent and Ca2+-independent interactions, several SYT isoforms participate in synchronous and asynchronous fusion of synaptic vesicles (SVs) while preventing spontaneous release that occurs in the absence of stimulation. Changes in the function or abundance of the SYT1 and SYT7 isoforms alter the number and route by which SVs fuse at nerve terminals. Several SYT family members also regulate trafficking of other subcellular organelles at synapses, including dense core vesicles (DCV), exosomes, and postsynaptic vesicles. Although SYTs are linked to trafficking of multiple classes of synaptic membrane compartments, how and when they interact with lipids, the SNARE machinery and other release effectors are still being elucidated. Given mutations in the SYT family cause disorders in both the central and peripheral nervous system in humans, ongoing efforts are defining how these proteins regulate vesicle trafficking within distinct neuronal compartments. Here, we review the Drosophila SYT family and examine their role in synaptic communication. Studies in this invertebrate model have revealed key similarities and several differences with the predicted activity of their mammalian counterparts. In addition, we highlight the remaining areas of uncertainty in the field and describe outstanding questions on how the SYT family regulates membrane trafficking at nerve terminals.

SummaryExtracellular matrix remodeling is an essential component of regenerative processes in metazoans. Among these animals, holothurians (sea cucumbers) are distinguished by their great regenerative capacities. We have previously shown that fibrous collagen as well as other fibrous components disappear from the connective tissue (CT) early during intestinal regeneration, and later return as the organ primordia form. We now report on changes of the nonfibrous component of the CT. We have used Alcian Blue staining and an antibody, Proteoglycan Like-1 (PGL-1), that recognizes a proteoglycanlike antigen to identify the presence of proteoglycans in normal and regenerating intestines. Our results show that early in regeneration, the ground substance resembles that of the mesentery, the structure from where the new intestine originates. As regeneration proceeds, Alcian Blue staining and PGL-1 labeling reorganize, so that by 4 weeks the normal intestinal CT pattern is achieved. Together with our previous findings, the data suggest that CT components that might be detrimental to regeneration disappear early on, while those that might be beneficial to regeneration, such as proteoglycans, are present throughout the regenerative process. (J Histochem Cytochem 64:381-393, 2016)