The Journal of Neuroscience, August 1, 2002, 22(15):6587-6595
Regulation of Synaptic Connectivity: Levels of Fasciclin II
Influence Synaptic Growth in the Drosophila CNS
Richard A.
Baines1,
Laurent
Seugnet2,
Annemarie
Thompson2,
Paul M.
Salvaterra3, and
Michael
Bate2
1 Department of Biological Sciences, University of
Warwick, Coventry, CV4 7AL, United Kingdom, 2 Department of
Zoology, University of Cambridge, Cambridge, CB2 3EJ, United Kingdom,
and 3 Division of Neurosciences, City of Hope, Beckman
Research Institute, Duarte, California 91010-0269
Much of our understanding of synaptogenesis comes from studies that
deal with the development of the neuromuscular junction (NMJ). Although
well studied, it is not clear how far the NMJ represents an adequate
model for the formation of synapses within the CNS. Here we investigate
the role of Fasciclin II (Fas II) in the development of synapses
between identified motor neurons and cholinergic interneurons in
the CNS of Drosophila. Fas II is a neural cell adhesion
molecule homolog that is involved in both target selection and
synaptic plasticity at the NMJ in Drosophila. In this
study, we show that levels of Fas II are critical determinants of
synapse formation and growth in the CNS. The initial establishment of
synaptic contacts between these identified neurons is seemingly independent of Fas II. The subsequent proliferation of these synaptic connections that occurs postembryonically is, in contrast,
significantly retarded by the absence of Fas II. Although the initial
formation of synaptic connectivity between these neurons is seemingly
independent of Fas II, we show that their formation is, nevertheless,
significantly affected by manipulations that alter the relative balance
of Fas II in the presynaptic and postsynaptic neurons. Increasing
expression of Fas II in either the presynaptic or postsynaptic neurons,
during embryogenesis, is sufficient to disrupt the normal level of
synaptic connectivity that occurs between these neurons. This effect of Fas II is isoform specific and, moreover, phenocopies the disruption to
synaptic connectivity observed previously after tetanus toxin light
chain-dependent blockade of evoked synaptic vesicle release in these neurons.
Key words:
aCC; neural activity; RP2; synaptic activity; synaptogenesis; tetanus toxin
Copyright © 2002 Society for Neuroscience 0270-6474/02/22156587-09$05.00/0