The Journal of Neuroscience, August 15, 1998, 18(16):6331-6339
Innervation and Target Tissue Interactions Induce Rab-GDP
Dissociation Inhibitor (GDI) Expression during Peripheral Synapse
Formation in Developing Chick Ciliary Ganglion Neurons In
Situ
Ognian C.
Ikonomov1,
Marianne C.
Kulesa1,
Assia
C.
Shisheva2, and
Michele H.
Jacob1
1 Worcester Foundation for Biomedical Research,
Shrewsbury, Massachusetts 01545, and 2 Program in Molecular
Medicine, Department of Biochemistry and Molecular Biology, University
of Massachusetts Medical Center, Worcester, Massachusetts 01605
Regulated exocytosis of neurotransmitter from synaptic vesicles
involves the function of a small GTP-binding protein, Rab3A. Rab-GDP dissociation inhibitor (GDI) is an important modulator of Rab
function and subcellular distribution. We have characterized the
respective roles of innervation and target tissue interactions in
regulating GDI expression during synapse formation in chick ciliary
ganglion (CG) neurons developing in situ. Here we report the first full-length chick GDI cDNA sequence. It is highly homologous to mammalian GDI isoforms and includes all of the sequence-conserved regions critical for Rab3A binding. This chick GDI mRNA is
predominantly expressed in neurons as judged by Northern blot analysis
of tissue distribution and by in situ hybridization of
CG sections. Developmental increases in CG GDI mRNA levels occur in two
phases as determined by reverse transcription (RT)-PCR and by
Northern analysis of both normal-developing and input- or target
tissue-deprived ganglia. The initial phase appears to be independent of
cell-cell interactions. In contrast, the second, larger increase is
induced by both presynaptic inputs and postganglionic target tissues
but does not occur until target tissue innervation. Synaptic
interaction with the target seems necessary for the regulatory response
to both inputs and target tissues. GDI protein levels show similar
changes. The developmentally delayed ability of inputs and targets to
influence GDI levels differs from the regulation of neurotransmitter
receptor expression in CG neurons. These results suggest that distinct
extrinsic regulatory signals influence the expression of
synapse-related components at the presynaptic axon terminal versus
postsynaptic membrane in an individual neuron.
Key words:
chick Rab-GDP dissociation inhibitor (GDI); embryonic
chick ciliary ganglion; neuronal synapse formation; neuron-specific
gene expression; induction; regulation; innervation; target tissue
interactions; presynaptic terminal differentiation; synaptic vesicle
exocytosis
Copyright © 1998 Society for Neuroscience 0270-6474/98/18166331-09$05.00/0