Synapsin I is expressed in epithelial cells: localization to a unique trans-Golgi compartment

Abstract

Synapsin I is abundant in neural tissues. Its phosphorylation is thought to regulate synaptic vesicle exocytosis in the pre-synaptic terminal by mediating vesicle tethering to the cytoskeleton. Using anti-synapsin antibodies, we detected an 85 kDa protein in liver cells and identified it as synapsin I. Like brain synapsin I, non-neuronal synapsin I is phosphorylated in vitro by protein kinase A and yields identical 32P-peptide maps after limited proteolysis. We also detected synapsin I mRNA in liver by northern blot analysis. These results indicate that the expression of synapsin I is more widespread than previously thought. Immunofluorescence analysis of several non-neuronal cell lines localizes synapsin I to a vesicular compartment adjacent to trans-elements of the Golgi complex, which is also labeled with antibodies against myosin II; no sub-plasma membrane synapsin I is evident. We conclude that synapsin I is present in epithelial cells and is associated with a trans-Golgi network-derived compartment; this localization suggests that it plays a role in modulating post-TGN trafficking pathways.

Improving adeno-associated viral (AAV) vector-mediated transgene expression in retinal ganglion cells: comparison of five promoters

“…We found that all promoters initiate transgene expression in cultured HEK293T cells, including weak expression by SYN. There are a few possible explanations why this neuronal-specific promoter still initiated weak expression in these cells derived from humanembryonic kidney: (1) the high copy-number of the transgene due to the plasmid DNA transfection may be responsible for leaky expression; (2) ITR sequences in the plasmid DNA have weak promoter activity themselves [65,66] and may cause expression in these non-neuronal cells; (3) there are reports that the SYN promoter can initiate expression in non-neuronal cells such as hepatocytes after high-dose and systemic administration [67][68][69]. In contrast to observations in HEK293T cells, we've previously demonstrated that the SYN promoter does initiate strong transgene expression in cultured CNS neurons [45].…”

The synapsins: Key actors of synapse function and plasticity

“…Syn I has been also found in osteoblasts, which are able to trigger glutamate release via molecular mechanisms strikingly similar to those of synaptic neurotransmission (Bhangu et al, 2001), and synapsin-like proteins have been identified on rat liver endosomes (Matovcik et al, 1994). In epithelial cells, syn I localises on a trans-Golgi network (TGN)-associated compartment, where it might mediate post-TGN trafficking routes (Bustos et al, 2001). Finally, syn I is also present in non-neuronal cell lines such as HeLa or NIH/3T3, where it is associated with cytoskeletal components, in particular to the actin cytoskeleton (Hurley et al, 2004).…”

BDNF Spinal Overexpression after Spinal Cord Injury Partially Protects Soleus Neuromuscular Junction from Disintegration, Increasing VAChT and AChE Transcripts in Soleus but Not Tibialis Anterior Motoneurons

“…A second possibility is that the AAV-BDNF spreads through the blood system. The expression of BDNF in the blood vessels was proposed by Cefis et al [ 76 ], and should be taken into consideration in our experimental model, as we used the synapsin promoter to express BDNF, and synapsin-1 has also been reported to be expressed in the epithelial cells of blood vessels [ 80 ].…”