Synaptotagmins are trafficked to distinct subcellular domains including the postsynaptic compartment

Abstract

The synaptotagmin family has been implicated in calcium-dependent neurotransmitter release, although Synaptotagmin 1 is the only isoform demonstrated to control synaptic vesicle fusion. Here, we report the characterization of the six remaining synaptotagmin isoforms encoded in the Drosophila genome, including homologues of mammalian Synaptotagmins 4, 7, 12, and 14. Like Synaptotagmin 1, Synaptotagmin 4 is ubiquitously present at synapses, but localizes to the postsynaptic compartment. The remaining isoforms were not found at synapses (Synaptotagmin 7), expressed at very low levels (Synaptotagmins 12 and 14), or in subsets of putative neurosecretory cells (Synaptotagmins α and β). Consistent with their distinct localizations, overexpression of Synaptotagmin 4 or 7 cannot functionally substitute for the loss of Synaptotagmin 1 in synaptic transmission. Our results indicate that synaptotagmins are differentially distributed to unique subcellular compartments. In addition, the identification of a postsynaptic synaptotagmin suggests calcium-dependent membrane-trafficking functions on both sides of the synapse.

Peptidergic Cell-Specific Synaptotagmins inDrosophila: Localization to Dense-Core Granules and Regulation by the bHLH Protein DIMMED

“…We emphasize that SYT-␣ and SYT-␤ antibody stains were not restricted to DIMM cells. For example, Kenyon Cells of the Mushroom Body (which contain the neuropeptide short NPF) (Johard et al, 2008) are DIMM Ϫ , but they are both SYT-␣ ϩ and SYT-␤ ϩ (Adolfsen et al, 2004). Outside the larval CNS, we observed coexpression of DIMM with SYT-␣ and SYT-␤ in peripheral NE centers, such as the corpora cardiaca of the Ring Gland (data not shown).…”

“…For primary antibodies, we used affinity-purified guinea pig anti-DIMM (1: 200) (Allan et al, 2005); rabbit anti-SYT␣ (1:500) and rabbit anti-SYT␤ (1:1000) (Adolfsen et al, 2004) (anti-SYT antibodies were gifts from Dr. Troy Littleton, MIT); rabbit anti-dGM130 (1:1000; Nakamura et al, 1995), rabbit anti-Lava Lamp (lva; 1:500; Sisson et al, 2000) and rabbit anti-Sec16 (1:500; Ivan et al, 2008) (all three were gifts from Dr. Aaron DiAntonio, Washington University); mouse monoclonal anti-myc (1: 1000, Sigma); mouse monoclonal anti-GFP 3E6 (1:800, Invitrogen); and rabbit anti-GFP (1:500; rabbit polyclonal, #AB3080 Millipore Bioscience Research Reagents).…”

“…Outside the larval CNS, we observed coexpression of DIMM with SYT-␣ and SYT-␤ in peripheral NE centers, such as the corpora cardiaca of the Ring Gland (data not shown). Also, Adolfsen et al (2004) reported SYT-␣ is selectively present in the embryonic LBD neuron and that SYT-␤ is selectively expressed in the embryonic Inka cells, both of which are DIMM ϩ peripheral peptidergic cells (Hewes et al, 2003;Park et al, 2011). Together, these results indicate extensive coexpression of either, or both, SYT-␣ and SYT-␤ with DIMM.…”

“…Several SYT isoforms have been associated with LDCVs in diverse tissues (e.g., Fukuda et al, 2004;Gustavsson et al, 2008;Schonn et al, 2008). In the Drosophila genome, there are seven annotated SYT isoforms (Adolfsen et al, 2004); and of these, two (syt-␣, CG5559 and syt-␤, CG3020) appear enriched in NE cells. Whether syt-␣ and syt-␤ has NE-specific physiological roles remains to be determined.…”

Transmission, Development, and Plasticity of Synapses

“…The molecular machinery for DCV fusion is still being elucidated, but is thought to have some overlap with SV pathways. For example, SNAREs are thought to be required, as well as additional members of the Synaptotagmin family, including Syta and Sytb (Adolfsen et al 2004;Park et al 2014). In addition, one wellcharacterized DCV-specific regulator of release has been identified-the Ca 2+ -activated protein for secretion (CAPS).…”