Synapto-pHluorin is a genetically encoded optical indicator of vesicle release and recycling. It is used in
neuroscience
Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions, and its disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, ...
to study transmitter release. It consists of a pH-sensitive form of
green fluorescent protein
The green fluorescent protein (GFP) is a protein that exhibits green fluorescence when exposed to light in the blue to ultraviolet range. The label ''GFP'' traditionally refers to the protein first isolated from the jellyfish ''Aequorea victo ...
(GFP) fused to the luminal side of a
vesicle-associated membrane protein (VAMP). At the acidic pH inside transmitter vesicles, synapto-pHluorin is non-fluorescent (
quenched). When vesicles get released, synapto-pHluorin is exposed to the neutral extracellular space and the presynaptic terminal becomes brightly fluorescent. Following
endocytosis
Endocytosis is a cellular process in which Chemical substance, substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a Vesicle (biology and chem ...
, vesicles become re-acidified and the cycle can start again. Chemical
alkalinization of all vesicles is often used for normalization of the synapto-pHluorin signals. Synapto-pHluorin sometimes consists of
yellow fluorescent protein (YFP) to monitor the cytoplasm because its
pKa is higher than GFP (7.1 versus 6.0).
History
Synapto-pHluorin was invented by
Gero Miesenböck in 1998. In 2006, an improved version was published, using
synaptophysin
Synaptophysin, also known as the major synaptic vesicle protein p38, is a protein that in humans is encoded by the ''SYP'' gene.
Gene
The gene is located on the short arm of X chromosome (Xp11.23-p11.22). It is 12,406 bases in length and li ...
to target the GFP to vesicles. In 2013, a two-color release sensor (ratio-sypHy) was introduced to determine the size of the
recycling pool at individual synapses.
Applications
Synapto-pHluorin is mainly used by neurobiologists to study transmitter release and
recycling
Recycling is the process of converting waste materials into new materials and objects. This concept often includes the recovery of energy from waste materials. The recyclability of a material depends on its ability to reacquire the propert ...
at
presynaptic terminals.
It has also been applied to the study of
insulin
Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the insulin (''INS)'' gene. It is the main Anabolism, anabolic hormone of the body. It regulates the metabol ...
secretion in
beta cells
Beta cells (β-cells) are specialized endocrine cells located within the pancreatic islets of Langerhans responsible for the production and release of insulin and amylin. Constituting ~50–70% of cells in human islets, beta cells play a vit ...
of the
pancreas
The pancreas (plural pancreases, or pancreata) is an Organ (anatomy), organ of the Digestion, digestive system and endocrine system of vertebrates. In humans, it is located in the abdominal cavity, abdomen behind the stomach and functions as a ...
.
References
{{Optogenetics
Protein methods
Recombinant proteins
Cell imaging
Fluorescent proteins