Neuronal compartments and axonal transport of synapsin I

Mol Neurobiol. Summer-Fall 1992;6(2-3):239-51. doi: 10.1007/BF02780556.

Abstract

Studies on the transport kinetics and the posttranslational modification of synapsin I in mouse retinal ganglion cells were performed to obtain an insight into the possible factors involved in forming the structural and functional differences between the axon and its terminals. Synapsin I, a neuronal phosphoprotein associated with small synaptic vesicles and cytoskeletal elements at the presynaptic terminals, is thought to be involved in modulating neurotransmitter release. The state of phosphorylation of synapsin I in vitro regulates its interaction with both synaptic vesicles and cytoskeletal components, including microtubules and microfilaments. Here we present the first evidence that in the mouse retinal ganglion cells most synapsin I is transported down the axon, together with the cytomatrix proteins, at the same rate as the slow component b of axonal transport, and is phosphorylated at both the head and tail regions. In addition, our data suggest that, after synapsin I has reached the nerve endings, the relative proportions of variously phosphorylated synapsin I molecules change, and that these changes lead to a decrease in the overall content of phosphorus. These results are consistent with the hypothesis that, in vivo, the phosphorylation of synapsin I along the axon prevents the formation of a dense network that could impair organelle movement. On the other hand, the dephosphorylation of synapsin I at the nerve endings may regulate the clustering of small synaptic vesicles and modulate neurotransmitter release by controlling the availability of small synaptic vesicles for exocytosis.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Axonal Transport*
  • Kinetics
  • Male
  • Methionine / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Nerve Endings / physiology
  • Neurons / metabolism
  • Neurons / physiology*
  • Optic Nerve / physiology*
  • Phosphates / metabolism
  • Phosphorus Radioisotopes
  • Phosphorylation
  • Retinal Ganglion Cells / metabolism
  • Retinal Ganglion Cells / physiology*
  • Sulfur Radioisotopes
  • Superior Colliculi / physiology*
  • Synapsins / biosynthesis
  • Synapsins / isolation & purification
  • Synapsins / metabolism*
  • Visual Pathways / physiology*

Substances

  • Phosphates
  • Phosphorus Radioisotopes
  • Sulfur Radioisotopes
  • Synapsins
  • Methionine