Axonal and dendritic synaptotagmin isoforms revealed by a pHluorin-syt functional screen

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Synaptotagmins (syts) are key regulators of membrane fusion, with 17 mammalian isoforms.
• Most syt isoforms are expressed in the brain, but their neuronal functions and subcellular localization remain largely uncharacterized due to a lack of specific antibodies.

Purpose of the Study:

• To investigate the subcellular localization and functional dynamics of various synaptotagmin isoforms in neurons.
• To characterize the exocytosis and endocytosis kinetics of different syt isoforms in distinct neuronal compartments.

Main Methods:

• Generation of pHluorin-syt fusion constructs with a luminal pH sensor.
• Utilizing pHluorin-syt to track syt localization, organelle pH, and membrane trafficking events (exocytosis/endocytosis) in neurons.

Main Results:

• Synaptotagmin-1 and -2 are localized to synaptic vesicles.
• Other syt isoforms exhibit selective recycling in dendrites (syt-3, -11), axons (syt-5, -7, -10, -17), or both (syt-4, -6, -9, -12).
• Distinct exocytosis and endocytosis kinetics were observed for different syt isoforms in their respective compartments.

Conclusions:

• The majority of synaptotagmin isoforms are targeted to distinct secretory organelles within axons and dendrites.
• These isoforms likely play crucial roles in regulating neuropeptide and neurotrophin release, thereby modulating neuronal function.