A Subtype-Specific Function for the Extracellular
Domain of Neuroligin 1 in Hippocampal LTP
Seth L. Shipman1,2and Roger A. Nicoll1,*
1Departments of Cellular and Molecular Pharmacology and Physiology, University of California, San Francisco, San Francisco,
CA 94158, USA
2Neuroscience Graduate Program, University of California, San Francisco, San Francisco, CA 94158, USA
of the synaptic adhesion molecule neuroligin are
present. These subtypes, neuroligin 1 and neuroligin
3, have roles in synaptogenesis and synaptic mainte-
nance that appear largely overlapping. In this study,
we combine electrophysiology with molecular dele-
tion and replacement of these proteins to identify
similarities and differences between these subtypes.
Indoing so,weidentify asubtype-specific roleinLTP
for neuroligin 1 in young CA1, which persists into
adulthood in the dentate gyrus. As neuroligin 3
showed no requirement for LTP, we constructed
chimeric proteins of the two excitatory neuroligin
subtypes to identify the molecular determinants
particular to the unique function of neuroligin 1.
Using in vivo molecular replacement experiments,
we find that these unique functions depend on a
region in its extracellular domain containing the B
site splice insertion previously shown to determine
specificity of neurexin binding.
As a class of cells, neurons are unmatched in the variety of
cellular processes that they display—from migration, dendrite
and axon development, and targeting, to synaptogenesis,
spiking, synaptic homeostasis, and plasticity. Diversity within
the proteome of a neuron is central to this wide range of abilities,
with proteins specialized for each individual function. Yet, within
the milieu of the proteome are families of related proteins, similar
in sequence, but encoded by distinct genes. Determining redun-
dancy and specialization within these families of proteins can be
a challenge, as the presence of a shared function among a family
of proteins under experimental constraints does not prove the
lack of endogenous specialization in vivo any more than the
presence of a unique response to an experimental constraint
proves that specialization necessarily exists.
In humans, four major genes encode for a family of proteins
termed neuroligins. These single-pass transmembrane proteins
are found at postsynaptic sites, where they support the forma-
tion and maintenance of synapses through both intracellular,
as well as trans-synaptic interactions (Washbourne et al.,
2004). A cursory look at the neuroligins reveals high sequence
and structural homology and a shared major binding partner in
presynaptic neurexin (Ichtchenko et al., 1996). Indeed, this simi-
larity is borne out functionally, as all of the neuroligins promote
the formation and maintenance of synapses (Chih et al., 2005;
Levinson et al., 2005). However, some notable differences
have begun to emerge between the neuroligins, suggesting
divergent roles for the individual members of this family.
Most dramatically, differences exist between neuroligin
subtypes with regard to expression patterns at excitatory and
inhibitory synapses, with neuroligin 1 (NLGN1) and neuroligin 3
(NLGN3) found at excitatory synapses and neuroligin 2
(NLGN2) and NLGN3 found at inhibitory synapses (Budreck
and Scheiffele, 2007; Song et al., 1999; Varoqueaux et al.,
2004). However, beyond the broad excitatory/inhibitory divide,
subtle differences exist specifically between the two major
neuroligin subtypes found endogenously at excitatory synapses,
NLGN1 and NLGN3. Notably, NLGN1 knockout animals have
been shown to have deficits in memory (Blundell et al., 2010;
Kim et al., 2008), while NLGN3 has been more strongly linked
to autism and impairments in social behavior (Radyushkin
et al., 2009). Yet, little has been done to directly compare the
physiological roles of these two proteins.
ences between NLGN1 and NLGN3. Using a variety of in vivo
and in vitro techniques combining both knockdown and molec-
ular replacement of the subtypes, we present differences in the
physiological roles of these two proteins, most strikingly with
respect to plasticity. Specifically, we find that NLGN1 has a clear
role in the support of LTP in the hippocampus—in young CA1,
but extending into adulthood in the dentate gyrus—a role that
is not shared by NLGN3. We provide the first molecular dissec-
tion of the physiological differences between these neuroligin
subtypes at excitatory synapses and find that the unique func-
tions of NLGN1, both the potency of its synaptogenic phenotype
and its role in LTP, depend on the inclusion of the B splice
insertion site in its extracellular domain.
NLGN1 Is Exclusively Required for LTP in the Adult
We began this subtype comparison of the excitatory neuroligins
by testing for a differential role in the support of adult plasticity.
Neuron 76, 309–316, October 18, 2012 ª2012 Elsevier Inc. 309
Supplemental Information includes four figures and Supplemental Experi-
mental Procedures and can be found with this article online at http://dx.doi.
This work was supported by grants from the US NIMH. We wish to thank
K. Bjorgan and M. Cerpas for technical assistance and J. Levy for comments
on the manuscript. We are additionally grateful for assistance provided by the
R. Malenka laboratory in lentiviral production methodology.
Accepted: July 19, 2012
Published: October 17, 2012
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A Role for the NLGN1 Extracellular Domain in LTP
316 Neuron 76, 309–316, October 18, 2012 ª2012 Elsevier Inc.