Kiss-and-run fusion: Difference between revisions

'''Kiss-and-run fusion''' is a type of [[synaptic vesicle]] release where the [[vesicle (biology and chemistry)|vesicle]] opens and closes transiently. In this form of [[exocytosis]], the vesicle formsdocks aand fusiontransiently pore or [[porosome]]fuses inat the presynaptic membrane and releases its [[neurotransmitters]] across the [[synapse]], after which the vesicle can then be reused. <ref>{{cite pmid | 15048116}}</ref><refname="Ceccarelli">{{citeCite pmid | 19213879}}</ref>journal

Kiss-and-Runrun differs from full fusion, where the vesicle collapses fully into the [[plasma membrane]] and is then later retrieved by a [[clathrin]]-coat-dependent process. <ref name="Jahn">{{cite pmidjournal|last1=Heuser|first1=JE|last2=Reese|first2=TS|title=Evidence for recycling of synaptic vesicle membrane during transmitter release at the frog neuromuscular junction.|journal=J. 17645434Cell Biol.|date=1973|volume=57|issue=2|pages=315–344|pmid=4348786|pmc=2108984|doi=10.1083/jcb.57.2.315}}</ref> The idea ofthat kiss-and-runneurotransmitter might be released in "quanta" by the fusion of synaptic vesicles with the presynaptic membrane was first introduced by [[Bernard Katz]] and Jose del Castillo in 1955, whowhen togetherthe hypothesizedfirst thatEM synapticimages vesiclesof fusenerve transientlyterminals withfirst the plasma membraneappeared. <refThe name="Jahn"></ref>possibility Theof actualtransient term,fusion kiss-and-run, originatedrapid fromretrieval Brunoof Ceccarellivesicle inmembrane 1973,was whenproposed heby sawBruno similarCeccarelli resultsin to1973, Katzafter andexamining delin Castillo using anthe [[electron microscropemicroscope]] examiningstrongly astimulated frog [[neuromuscular junction]].junctions, <ref>{{citeand pmidindirectly |supported 17765328}}</ref>by Todaythe work of his group in the following years, thereusing iselectrophysiology, electron backmicroscopy and forthquick debatefreezing overtechniques. full fusion andThe actual term, kiss-and-run, fusionwas andintroduced whichby modelCeccarelli's portrayscollaborators a<ref morename="Fesce" accurate/> after the first picturestudies of thesimultaneous mechanismsmembrane behindcapacitance synapticand amperometric transmitter release measurements were performed and indicated that secretory products could actually be released during transient vesicle fusion.<ref name="ADT">{{cite journal|last1=Alvarez de Toledo|first1=G|last2=Fernàndez-Chacòn|first2=R|last3=Fenràndez|first3=JM|title=Release of secretory products during transient vesicle fusion.|journal=Nature|date=1993|volume=363|issue=6429|pages=554–558|pmid=8505984|doi=10.1038/363554a0|bibcode=1993Natur.363..554D|s2cid=4316497}}</ref>

Kiss-and-runTransient vesicle fusion was first observedhypothesized by Katz and del Castillo in 1955.{{Citation needed|date=February 2014}} However, the first systematic studies were conducted by Ceccarelli et al. in 1973. Ceccarelli et al. studied frog neuromuscular junctions, stimulating them with markers such as [[horseradish peroxidase]] to identify endocytosed organelles., <refand name="Jahn"></ref> Ceccarelli et al. stimulated nerve-muscle preparations atusing either lowmild stimulation (2 &nbsp;Hz) or highstrong stimulation (10 &nbsp;Hz) protocols for periods ranging from 20 minutes to 4 hours. <ref name="MauroCeccarelli">{{cite pmid | 4348791}}</ref><ref>{{citeCite pmid | 4338962}}</ref> At low stimulation for a period of 4 hours, Ceccarelli et al. found that there was an increase in horseradish peroxidase labeled vesicles over time, and no increases in large organelles, indicative of the vesicles fusing quickly with the presynaptic membrane and then separating from it after releasing its neurotransmitters. <ref name="Mauro"></ref> They hypothesized that at low frequencies of stimulation, most of the vesicles are quickly re-formed from the presynaptic membrane during and after stimulation. <ref name="Mauro"></ref> This gave rise to the term kiss-and-run.journal

==Evidence for Kisskiss-and-Runrun==

With the discovery of the kiss-and-run mechanism by Katz and del Castillo and Ceccarelli et al., there have been many subsequent studies done that give evidence supporting kiss-and-run fusion. All studies have suggested that there are two main advantages kiss-and-run fusion has over full fusion: 1) kiss-and-run enables more efficient vesicle recycling and 2) kiss-and-run can limit how much neurotransmitter is released due to a smaller fusion pore and a shorter time during which neurotransmitters can actually be released. One of the major problems of kiss-and-run evidence, and subsequently the basis for many counterarguments against kiss-and-run, is that because fusion is so short, it is very hard to capture an actual kiss-and-run event. <ref name="Jahn"></ref>{{Cite journal

[[Mitochondria]] demonstrate kiss-and-run fusion in exchanging [[Inner mitochondrial membrane|inner membrane]] materials. Studies using [[mitochondrial matrix]]-targeted green-photoactivated, red-fluorescent KFP and cyan-photoactivated, green-fluorescence PAGFP in rat cells have shown interactions where the KFP and PAGFP were transferred from one mitochondrion to another mitochondrion through transient fusion, suggesting a kiss-and-run mechanism. <ref name="Liu">{{cite pmidCite journal
| 19745815}}</ref>last1 Unlike= fullLiu fusion| offirst1 mitochonrdia,= whichX.
| resultedlast2 in= aWeaver single| organelle,first2 transient= kiss-and-runD.
| fusionlast3 of= twoShirihai mitochondria| resultedfirst3 in= two distinct membranesO. <ref name="Liu"></ref>

Manipulation of the [[optic atrophy 1]] (Opa1) gene had interesting effects on fusion between mitochondria. Silencing the Opa1 gene decreased full fusion activity of mitochondria after 24 hours, and full fusion activity was completely eliminated after the Opa1 gene was silenced for 48 hours. <ref name="Liu">< /ref> Transient kiss-and-run fusion activity remained the same after 24 hours of Opa1 silencing. <ref name="Liu">< /ref> Kiss-and-run fusion is most common with low levels of Opa1 [[gene expression]] and extremely high levels of Opa1 gene expression. As a result, Opa1 expression governs fusion in mitochondria with regard to kiss-and-run.

Kiss-and-run fusion in mitochondria help to keep mitochondria in a reduced motility state for shorter period of time compared to full fusion. Liu et al. tested both kiss-and-run and full fusion and their effects on mitochondrial motility, and found that both forms of fusion resulted in decreased mitochondrial motility at first, but kiss-and-run fusion restored, and even increased, mitochondrial motility immediately after the kiss-and-run event was over. <ref name="Liu">< /ref> Kiss-and-run fusion provides a better mechanism to control mitochondrial [[bioenergetics]] than full fusion.

===Calcium-Dependentdependent Actinactin Coatingcoating===

Kiss-and-run fusion has been thought to be stabilized by an [[actin]] coating of vesicles. Testing for the vesicle uptake of FM1-43 to note when vesicles fused with the membrane allowed researchers to notice that actin coating is a necessary step for the kiss-and-run mechanism. Vesicles labelled with the Beta-actin-[[Greengreen Fluorescentfluorescent Proteinprotein]] (GFP) fluoresced seconds after fusing with the presynaptic membrane (as shown by FM1-43 uptake), but non-fused vesicles never fluoresced, suggesting that an actin coating is required for kiss-and-run. <ref name="Dietl">{{citeCite pmid | 19161375}}</ref> This actin coating came from the [[polymerization]] of actin monomers.journal

The actin coating process necessary for transient kiss-and-run fusion is mediated by calcium. Actin coating of vesicles was inhibited by BAPTA-AM, which removes calcium. With the absence of calcium through the use of BAPTA-AM, all fused vesicles remained attached to the presynaptic membrane but did not release its neurotransmitters, suggesting that calcium is required to make the actin coating, and that the actin coating is responsible in the mechanism for vesicle unloading or vesicle release. <ref name="Dietl">< /ref>

Kiss-and-run exocytosis is regulated by [[myosin]] II. Studies using [[total internal reflection fluorescence microscopy]] (TIRFM) in neuroendocrine [[PC12 cells]] showed that myosin II regulates fusion pore dynamics during kiss-and-run exocytosis. <ref name="Aoki">{{cite pmid | 20528772}}</ref> Over-expression of normal myosin II regulatory light chain (RLC) in mRFP (monomeric red fluorescent protein) tagged tissue and Venus-tagged brain tissue resulted in prolonged release kinetics, while over-expression of a mutant form of myosin II RLC short shortened release kinetics. <ref name="Aoki"></ref> Prolonged release kinetics is indicative of a slower closing of the fusion pore, so myosin II also regulates how much neurotransmitter is released during kiss-and-runCite exocytosis.journal