© 2006 Nature Publishing Group
A brain-specific microRNA regulates
dendritic spine development
Gerhard M. Schratt1,2,3, Fabian Tuebing4, Elizabeth A. Nigh1,2,3, Christina G. Kane1,2,3, Mary E. Sabatini3,
Michael Kiebler4& Michael E. Greenberg1,2,3
MicroRNAs are small, non-coding RNAs that control the translation of target messenger RNAs, thereby regulating
critical aspects of plant and animal development. In the mammalian nervous system, the spatiotemporal control of
mRNA translation has an important role in synaptic development and plasticity. Although a number of microRNAs have
been isolated from the mammalian brain, neither the specific microRNAs that regulate synapse function nor their target
mRNAs have been identified. Here we show that a brain-specific microRNA, miR-134, is localized to the synapto-
dendritic compartment of rat hippocampal neurons and negatively regulates the size of dendritic spines—postsynaptic
sites of excitatory synaptic transmission. This effect is mediated by miR-134 inhibition of the translation of an mRNA
encoding a protein kinase, Limk1, that controls spine development. Exposure of neurons to extracellular stimuli such as
brain-derived neurotrophic factor relieves miR-134 inhibition of Limk1 translation and in this way may contribute to
synaptic development, maturation and/or plasticity.
Highly orchestrated programmes of gene expression act to shape the
developing nervous system. This tight regulation is mediated by a
the expression of individual gene products1,2. The discovery of small,
non-coding RNAs has greatly expanded our understanding of the
cellular mechanisms that regulate gene expression at the post-
transcriptional level. MicroRNAs (miRNAs) act by binding to target
mRNAs and initiating either cleavage or a reduction in the trans-
lational efficiency of the target mRNA, depending on the degree
of sequence complementarity3–5. Biochemical and genetic studies
have revealed important functions for specific miRNAs in a variety
of cellular processes, including differentiation, apoptosis and
A number of miRNAs have been isolated from the vertebrate
nervous system11–13, and a recent study has demonstrated a crucial
role for the miRNA pathway in early zebrafish brain development14.
Expression analysis also supports a role for miRNAs in later stages of
neuronal maturation and synapse development12,15,16. A potential
role for miRNAs in synaptic function is particularly intriguing given
the evidence that selected mRNAs in neurons are transported to sites
of synaptic contact that are quite distant from the cell body17–19.
Within dendrites, and at synapses, the translation of these mRNAs
may be inhibited until neurons are exposed to appropriate extra-
cellular stimuli such as a neurotrophic factor (for example, brain-
derived neurotrophic factor (BDNF)) or neurotransmitter release at
the synapse. Local translation of these previously dormant mRNAs
plasticity20–22. Whether miRNAs might inhibit the translation of
synaptically localized mRNAs in neurons until their translation is
activated by neurotrophic factors or neuronal activity remains to be
miR-134 expression during synapse development
Toidentify miRNAsthatmightfunction indendriticand/or synaptic
development, we investigated the expression and localization of
candidate miRNAs that had been previously isolated from mouse
revealed that the expression of microRNA-134 (miR-134) is
restricted to the brain, similar to the expression pattern of the
previously characterized miR-124a (Fig. 1a and Supplementary Fig.
1a, b). Unlike miR-124a, however, miR-134 levels in the hippo-
campus gradually increase with development, reaching maximum
levels at postnatal day 13 (P13), the time at which synaptic matu-
ration occurs (Fig. 1b). A similar developmental expression profile
was also observed in dissociated hippocampal neurons that were
allowed to mature over time in culture (Fig. 1c). Moreover, mem-
brane depolarization of cortical neurons induced a significant
increase in the level of the miR-134 precursor (Supplementary Fig.
1c). Taken together, these results suggested a potential role for miR-
134 in dendritic and/or synaptic development.
We used an in situ hybridization (ISH) protocol to examine the
subcellular localization of the miR-134 RNA within cultured hippo-
campal neurons. Unlike the mismatch control probe, hybridization
with the miR-134-specific probe revealed the presence of miR-134
within dendrites, where it is present in a punctate pattern (Fig. 1d and
Supplementary Fig. 1d). Quantification of the two signal intensities
(miR-134-specific versus the mismatch probe) along the length of
multiple dendrites confirmed significantly higher levels of miR-134-
specific signal within dendrites as compared to that obtained with the
mismatch control (Supplementary Fig. 1e) or the U6 small nuclear
134 was found to partially co-localize with synapsin immunostaining,
indicating that miR-134 is present near synaptic sites on dendrites
(Fig. 1d, lower panel and inset at higher magnification). The presence
of miR-134 in synaptic compartments was also corroborated by
subcellular fractionation experiments; miR-134 was enriched in syn-
aptoneurosome preparations (Fig. 1e), which represent membrane
preparations highly enriched for synaptic terminals23. The presence of
miR-134 within dendrites near synapses suggested a possible func-
tional role for this miRNA at post-synaptic sites.
1Neurobiology Program, Children’s Hospital,2Department of Neurology,3Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.4Division of
Neuronal Cell Biology, Center for Brain Research, Medical University of Vienna, A-1090 Vienna, Austria.
Vol 439|19 January 2006|doi:10.1038/nature04367
© 2006 Nature Publishing Group
miR-134 regulates dendritic spine morphology
To investigate a possible function of miR-134 at the synapse, we
examined the effects of modulating miR-134 activity on dendritic
spine development. Dendritic spines are actin-rich protrusions from
contact24,25. The size of dendritic spines is a good correlate of the
strength of excitatory synapses26–28. To achieve miR-134 overexpres-
sion, we designed a vector that permits efficient expression of
exogenous miR-134 (Supplementary Fig. 2a). Alternatively, miR-
134 function in neurons was suppressed by introducing a 2
methylated antisense oligonucleotide that interferes with endogen-
ous miR-134 activity in a sequence-specific manner29,30. The efficacy
of these approaches was confirmed in neurons using a previously
described miRNA sensor assay (Supplementary Fig. 2b)31.
An analysis of dendritic spines in cultured hippocampal neurons
(cultured for a total of 18days, transfected at day 8: 8 þ 10days
in vitro (DIV)) overexpressing miR-134 showed a significantly
decreased spine volume as compared to the spines of neurons
transfected with empty vector or overexpressing the unrelated let-
7c miRNA (Fig. 2a (bottom panel), b (bottom panel), e and
Supplementary Fig. 3a–c).
Further analysis revealed that this decrease in spine volume was
mainly a consequence of a reduction in spine width (216.9 ^ 5.8%,
n ¼ 3, P ¼ 0.02) as opposed to a change in spine length
(23.5 ^ 7.1%, n ¼ 3, P ¼ 0.23, Fig. 2f). A similar reduction in
dendritic spine size was observed when synthetic miR-134 was
introduced into neurons at a later stage (15DIV) and for shorter
times (72h, Supplementary Fig. 3d). Because hippocampal neurons
at 15DIV have already developed the vast majority of their spines,
these findings suggest that miR-134 may perturb the morphology of
In contrast to the effect of miR-134 overexpression, sequence-
specific inhibition of endogenous miR-134 function using a 2
methylated antisense oligonucleotide29,30(2
but statistically significant increases in spine volume and width
(7.6 ^ 3.7%, n ¼ 3, P ¼ 0.03) when compared to neurons trans-
fected with an unrelated 2
(bottom panel), d (bottom panel), e, f). No significant effects on
spine length were observed in the presence of 2
(2.6 ^ 5.6%, n ¼ 3, P ¼ 0.25). Neither miR-134 overexpression
nor theuse of2
effect on spine density or overall dendritic complexity (Supplemen-
taryFig. 3e,f).Weconcludethat miR-134actsas anegativeregulator
of dendritic spine volume in hippocampal neurons, raising the
development and/or function.
0-O-Me-134) led to small
0-O-Me-control oligonucleotide (Fig. 2c
0-O-methylated oligonucleotides had any measurable
miR-134 inhibits translation of Limk1 mRNA
To gain insight into the mechanisms by which miR-134 regulates
dendritic spine morphology, we sought to identify miR-134 target
mRNAs. Towards this end, we scanned the 3
(UTRs) of mRNAs for potential miR-134 binding sites. For this
analysis, we focused on a set of 48 genes that we recently identified in
a screen for mRNAs for which translation is enhanced in neurons
upon treatment with BDNF32. As BDNF promotes dendritic spine
growth33and regulates synaptic function, at least in part, by activat-
ing dendritic protein synthesis21, we reasoned that mRNAs for which
translation is regulated by BDNF might also represent miR-134
targets. Three of the BDNF-regulated mRNAs (discs large homol-
1 (Limk1)) were found to contain conserved 3
elements that were partially complementary to mouse miR-134
(Fig. 3a and data not shown). Among these potential miR-134 target
mRNAs, Limk1 was of particular interest. Limk1 regulates actin
filament dynamics through inhibition of ADF/cofilin34, and Limk1
knockout mice show abnormalities in dendritic spine structure
similar to those observed upon miR-134 overexpression35.
Using an electrophoretic mobility shift assay, we demonstrated
that Limk1 mRNA and miR-134 interact in vitro (Supplementary
Fig. 4). We next determined whether the Limk1 mRNA co-localized
miR-134 was introduced into hippocampal neurons by micro-injec-
134 binding site. Both miR-134 and the Limk1 3
the non-dendritic Gapdh and histone H3 mRNAs, were found to be
present within dendrites in a granular pattern (Fig. 3b, upper two
panels and data not shown). Moreover, miR-134- and Limk1 3
UTR-positive granules were co-localized within dendrites (Fig. 3b,
lower panel). Furthermore, efficient co-localization of miR-134 and
within the Limk1 3
localization of endogenous Limk1 mRNA was further confirmed
by ISH in cultured neurons and by subcellular fractionation
(Supplementary Fig. 5a, b).
In mammalian cells, miRNAs are thought to regulate the
expression of target mRNAs predominantly through the inhibition
of productive translation3. We therefore hypothesized that miR-134
binding to the Limk1 mRNA might act to inhibit Limk1 translation.
In support of this idea, miR-134 overexpression in both 293T cells
a luciferase reporter gene fused to the wild-type Limk1 3
whereas expression of the unrelated let-7c miRNA had no significant
0UTR, in contrast to
0UTR (Fig. 3b, bar graph). The dendritic
Figure 1 | miR-134 is specifically expressed in the brain and localized to
neuronal dendrites. a, Northern blot of adult tissues was probed for the
indicated miRNAs or U6 snRNA. b, RNase protection assay (RPA) to detect
the indicated miRNAsin postnatal (P1–P19) hippocampus. c, RPAto detect
the indicated miRNAs in hippocampal neurons cultured for 4–18DIV.
Asterisk indicates an unknown protected fragment. d, Co-staining of the
presynaptic marker protein synapsin (red) together with miR-134 ISH
(green) in 14DIV hippocampal neurons (upper left). The boxed area in the
upper-left panel is shown at greater magnification in the bottom panel,
which also has a higher-magnification inset. Arrows point to synapses that
partially overlap with miR-134-positive puncta. Scale bars, 10mm. e,
Northern blot of P15 whole brain or synaptoneurosomes (syn.) probed for
indicated miRNAsor U6 snRNA. Fold enrichment in synaptoneurosomes is
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effect on the expression of this reporter construct (Fig. 4a and
Supplementary Fig. 6a, b). The steady-state levels of the reporter
gene mRNAwere unaffected by miR-134 overexpression, suggesting
that the observed effect of miR-134 on luciferase expression does not
reflect a change in the stability of the luciferase mRNA (Supplemen-
tary Fig. 6c). The effect of miR-134 on translation of the luciferase
mRNA is dependent onthe presence of the miR-134 cognate binding
site within the 3
binding site) was unaffected by the presence of exogenous miR-134
(Fig. 4a, white bars). In contrast to the effect on Limk1 mRNA
translation, mutation of the miR-134 binding site did not affect
dendritic targeting of a Gfp–Limk1 reporter RNA (Supplementary
The inhibition of endogenous miR-134 in neurons by 2
134 led to a statistically significant increase in the expression of the
luciferase reporter fused to the wild-type Limk1 3
black bars), but had no significant effect on expression of the m191
mutant reporter that is incapable of binding miR-134 (Fig. 4b, white
bars). By contrast, an antisense oligonucleotide directed against let-
Peptide-mediated delivery of miR-134 into neurons led to a dose-
dependent decrease in the level of endogenous Limk1 protein,
whereas delivery of its inhibitor 2
of the endogenous Limk1 mRNA. Taken together, these data suggest
that endogenous miR-134 inhibits Limk1 mRNA translation in
neurons by binding to a single site present in the Limk1 3
Although these studies provide evidence that miR-134 acts to
repress Limk1 mRNA translation, they do not distinguish whether
the inhibition occurs within the cell body and/or dendrites. To
address this issue, we generated a GFP-based protein synthesis
reporter (myr-d1Gfp) with limited diffusion and a shortened half-
life (1h). Results from a previous study using a similar construct
0UTR, as expression of a luciferase reporter contain-
0UTR (Fig. 4b,
0-O-Me-let-7c) had no effect on Limk1 reporter gene activity.
0-O-Me-134 led to an increase in
neurons. a–d, Representative neurons (18DIV) transfected with control
vector (a), miR-134 expression vector (b), 2
134 oligonucleotide (d). Bottom panels (insets of boxed areas) illustrate
higher frequencyofthinnerspinesinmiR-134-expressingcells(arrows inb)
bars, 10mm. e, Normalized average volume of spines (n . 600) from
0-O-Me control (c) or 2
neurons (n ¼ 15) transfected as in a–d. Data are presented as average spine
volume ^s.d. from three independent experiments. Asterisk, P , 0.05
(n . 600) in neurons (n ¼ 15) expressing miR-134 or 2
compared to GFP. Data are presented as mean change in spine length/width
^s.d from three independent experiments. Asterisk, P , 0.05 (paired
Figure 3 | Limk1 mRNA is a putative miR-134 target. a, Upper panel:
(bottom). Middle panel: Sequence conservation of the miR-134 binding site
within the Limk1 3
134 binding site (red). b, Localization of microinjected miR-134 (red) and
Limk1 RNA (green) in hippocampal neurons. Arrows indicate miR-134 and
Limk1 co-localization in granule-like structures. Bar graph: quantification of
dendritic co-localization events between microinjected miR-134 and either
Limk1 m191 or Limk1 wild-type (WT) RNA. Data represent the mean of
n ¼ 12 cells per condition counted in triplicate ^s.d. Asterisk, P , 0.05.
0UTR of mouse (mm), rat (rn) and human (hs). Lower
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demonstrated that GFP expressed from the reporter gene allows for
the study of local protein synthesis within intact dendrites36. The
myr-d1GFP reporter was fused to either wild-type or m191 mutant
expression was monitored by confocal microscopy, and the intensity
varying distances from the cell body (Fig. 4e). This analysis revealed
that the average expression of the wild-type Limk1 reporter was
significantly reduced (by 18–28%) along the entire length of the
dendrites compared to that of the m191 reporter (Fig. 4f). Given the
dendritic localization of endogenous Limk1 mRNA and miR-134,
these findings suggest that miR-134 partially inhibits Limk1 mRNA
translation locally within dendrites.
0UTR and introduced into hippocampal neurons. GFP
miR-134 regulates spine size through Limk1
Because both overexpression of miR-134 and disruption of Limk1
function lead to decreased spine size35, we next investigated whether
miR-134-mediated repression of Limk1 mRNA translation might be
an explanation for the observed reduction in dendritic spine size
upon miR-134 overexpression. Towards this end, we expressed miR-
134 in hippocampal neurons together with constructs expressing
either awild-type Limk1 mRNAor mutant m191 Limk1 mRNA, and
of miR-134 on spine morphology occurs through suppression of
endogenous Limk1 mRNA translation, ectopically expressed Limk1
mRNA that is incapable of interacting with miR-134 (m191) should
be able to rescue the spine defect. In contrast, co-expression of the
wild-type Limk1 mRNA, which is still subject to miR-134-mediated
translational inhibition, might be expected to prove less effective in
the rescue of the dendritic spine phenotype caused by miR-134
overexpression. Consistent with this idea, we found that the m191
mutant Limk1 mRNA efficiently rescued both the spine volume and
width decrease imposed by miR-134 overexpression, whereas the
wild-type Limk1 mRNAwas not as effective at rescuing the decrease
in spine volume and width (Fig. 5a, upper and lower left panels).
Both Limk1 constructs had no effect on dendritic spine length (Fig.
5a, lower right). In addition, the observed difference between the
effect of the wild-type and m191 mutant Limk1 mRNA on spine
width was not due to intrinsic differences in the ability of the two
mRNAs to be translated, because in the absence of miR-134, Limk1
protein levels were equivalent in 293Tcells transfected with the wild-
typeand mutant Limk1 constructs (Fig. 5b). Immunohistochemistry
revealed that in neurons, overexpressed Limk1 protein was targeted
that an increased level of Limk1 protein within spines might be
together, these results suggest that Limk1 is a downstream effector of
miR-134 in the control of dendritic spine development.
miR-134 functions in BDNF-stimulated Limk1 synthesis
ment within RNA granules. During their transport and once they
have arrived at synaptic sites, the translation of dendritic mRNAs
may be suppressed until extracellular factors such as those released
upon synaptic stimulation activate the translation of these dormant
mRNAs17,19. We asked whether the suppression of Limk1 translation
bymiR-134is relieved byextracellularstimuli such as BDNF. Wefirst
assessed whether the translation of Limk1 mRNA is regulated by
BDNF. Towards this end, synaptoneurosomes prepared from P15 rat
brainwere incubated with35S-methionine to label newly synthesized
Figure 4 | miR-134 inhibits Limk1 mRNA translation in neurons.
UTR reporter genes in the absence (control) or presence of the indicated
miRNAs (10mM). Data represent the mean from three independent
experiments ^s.d. Asterisk, P , 0.05 (paired Student’s t-test). b, Luciferase
activity of reporter genes described in a in the presence of the indicated
threeindependentexperiments^s.d.Limk1wild-typecontrol ¼ 1;asterisk,
P , 0.05 (paired Student’s t-test). c, Western blot analysis of endogenous
Limk1 (upper panel) and actin (lower panel) expression in lysates from
corticalneurons(12 þ 2DIV)transducedwithpenetratin-coupledmiR-134
or mismatch (mism.) control. d, Western blot analysis as in c, except that
penetratin-coupled antisense 2
0-O-Meoligonucleotides (20mM). Data represent the mean from
0-O-Me oligonucleotides were used. e, Local
translation assay in hippocampal neurons (12 þ 2DIV) using destabilized,
membrane-anchored myr-d1GFP reporter genes (green) harbouring
either the wild type (left panel) or m191 (right panel) Limk1 3
Co-transfected dsRed was used to track dendrites. Three representative
dendrites are shown per experimental condition. Arrows point to dendritic
regions of myr-d1GFP-Limk1 wild-type UTR transfected neurons where
little GFP signal is detectable. Scale bar, 20mm. f, Average normalized GFP
intensity in dendritic segments (n . 60) depicted in e. Data are from three
independent experiments and presented as mean ^s.d. at 30-mm dendritic
intervals.The averageGFPintensityoftheLimk1 m191reporter at themost
proximal part of the dendrite was set to 100. Asterisk, P , 0.05 (paired
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proteins, and the amount of newly synthesized Limk1 protein
was monitored by radio-immunoprecipitation. BDNF treatment
significantly increased synthesis of Limk1 protein within isolated
synaptoneurosomes as indicated by an increase in35S-methionine-
labelled protein in Limk1 immunoprecipitates. This increase was
sensitive to treatment with rapamycin, an inhibitor of the mTOR
kinase pathway, which we and others have shown to mediate BDNF
signalling to the translational machinery (Fig. 6a)32,37.
We next asked whether the ability of BDNF to induce Limk1
mRNA translation reflects the ability of BDNF to relieve miR-134-
dependent repression of Limk1 translation. Towards this end, we
examined the effect ofBDNF treatment on the translation of aLimk1
endogenous miR-134 is highly expressed (14DIV). When cells
were transfected with luciferase mRNA fused to the wild-type
0UTR luciferase reporter mRNA in neurons at a time when
0UTR, BDNF led to a statistically significant induction of
translation of the reporter mRNA (Fig. 6b). Expression of the m191
luciferase reporter mRNA was derepressed relative to the wild-type
reporter in the absence of BDNF treatment, presumably due to the
failure of endogenous miR-134 to bind to the m191 reporter gene
(Fig. 6b). BDNF treatment did not lead to a further increase in the
expression of the m191 reporter gene. To investigate the effect of
miR-134 on BDNF-induced Limk1 translation more directly, we
introduced synthetic miR-134 into neurons that express little
endogenous miR-134 (4DIV, Fig. 1c). We found that miR-134
partially interferes with BDNF induction of the wild-type, but not
the m191 mutant, reporter mRNA (Fig. 6c). These findings suggest
that miR-134 represses Limk1 mRNA translation and that BDNF
treatment relieves this repression. However, the observation that
there is still residual BDNF induction of reporter mRNA translation
Figure 5 | Limk1 expression rescues miR-134-mediated reduction in spine
size. a, Cumulative percentage plots of spine volume, width and length in
hippocampal neurons (18DIV) transfected with miR-134 alone or together
with the indicated Limk1 expression constructs (n . 500 spines per
condition from two independent experiments, five neurons per
experiment). Spines of miR-134-transfected neurons have a significantly
decreased volume compared to GFP (P , 0.001) or Limk1 m191 3
(P , 0.001)—but not Limk1 wild-type 3
neurons, and are significantly thinner than those of GFP (P , 0.001) or
Limk1 m191 3
(P ¼ 0.189)—transfected neurons. Statistical significance was assessed by
Kolmogorov–Smirnov test. b, Anti-Limk1 western blot of 293Twhole-cell
lysates transfected with vector alone or the indicated Limk1 expression
constructs.c,ImmunocytochemistryofGFP (green), Limk1 expressedfrom
the Limk1 m191 3
hippocampal neurons. Arrows point to the co-localization of Limk1 and
synapsin in GFP-positive dendritic spine heads. Scale bar, 10mm.
0UTR (P ¼ 0.229)—transfected
0UTR (P ¼ 0.006)—but not Limk1 wild-type 3
0UTR construct (red) and synapsin (blue) in 18DIV
Figure 6 | miR-134 is involved in BDNF-induced Limk1 mRNA
translation. a, Left panel: immunoprecipitation (IP) of Limk1 from P15
rapamycin (rap). Right panel: average of the Limk1 immunoprecipitation
signal intensities from three independent experiments ^s.d. Unstim. ¼ 1.
Asterisk, P , 0.05. b, Relative luciferase activity in 14DIV cortical neurons
transfected with Limk wild type (black bars) or Limk1 m191 (white bars)
reporter mRNAs. Neurons were either unstimulated or treated with
100ngml21BDNF for 4h. Data represent the average of three independent
experiments ^s.d. Asterisk, P , 0.05. c, Relativeluciferase activity in 4DIV
(white bars) reporter mRNAs treated as in b together with miR-134 where
indicated. Data represent the average of three independent experiments
^s.d. Asterisk, P , 0.005. d, Model for the role of miR-134 (green) in the
regulation of Limk1 synthesis and spine growth. For details, see text.
NATURE|Vol 439|19 January 2006
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when miR-134 cannot bind to the Limk1 3
involvement of additional miR-134-independent mechanism(s) in
BDNF-induced Limk1 translation.
0UTR suggests an
We have identified a dendritically localized miRNAthat regulates the
expression of the synaptic Limk1 protein, thereby controlling den-
with miR-134 keeps the Limk1 mRNA in a dormant state while it is
being transported within dendrites to synaptic sites (Fig. 6d). In the
that has a key role in repressing Limk1 mRNA translation. This then
limits the synthesis of new Limk1 protein and restricts the growth of
dendritic spines. Upon synaptic stimulation, the release of BDNF
may trigger activation of the TrkB/mTOR signalling pathway, which
inactivates the miR-134-associated silencing complex by an as-yet-
unknown mechanism, leading to enhanced Limk1 protein synthesis
and spine growth. Our preliminary finding that miR-134 moves to
the polysome-associated mRNA pool upon BDNF stimulation (G.S.
and M.E.G., unpublished observations) suggests that miR-134 itself
to BDNF. Instead, we speculate that BDNF alters the activityof other
translational regulators within the miR-134-containing complex. In
bind the Limk1 3
multiple miRNAs on the Limk1 3
vation that miR-134 only partially inhibits Limk1 mRNA translation
A recent bioinformatics approach predicted several additional
neuronal mRNAs that may also represent miR-134 targets39. Given
that BDNF has important roles at multiple steps of synaptic devel-
We propose that miRNA regulation of the translation of a variety
of neuronal mRNAs will be found to contribute in an important way
to synaptic function42. It is tempting to speculate that miRNAs act
locally at individual synapses, thereby contributing to synapse-
specific modifications that occur during synaptic plasticity. A future
challenge will be to identify the full complement of dendritic
miRNAs as well as their target mRNAs, and to determine their role
in synaptic development.
0UTR38. Therefore, the combinatorial action of
0UTR might explain our obser-
DNA constructs. The rat Limk1 3
polymerase chain reaction (PCR) from rat brain cDNA (P15). Mutation of the
miR-134 binding site (m191) was achieved using the Quick Changesite directed
mutagenesis kit (Stratagene). PCR products were cloned into pGL3 basic
(Promega), pBSK (Stratagene) or myr-d1GFP (gift of B. Sabatini) for constructs
For Limk1 expression constructs, the Limk1 cDNA (gift of K. Mizuno) was
cloned into pcDNA3 (Promega) together with rat Limk1 3
m191). For the miR-134 expression construct, a genomic sequence spanning
150base pairs 3
PCR-amplified and cloned into pcDNA3. See Supplementary Information for
Cell culture, transfection and stimulation. Cultures of dissociated primary
cortical and hippocampal neurons were prepared as described32. Hippocampal
neurons were maintained in Neurobasal plus B27 supplement; cortical neurons
in Basal Medium Eagle plus 5% FBS. Neuronal transfections were performed
with LipofectAmine 2000 (Invitrogen). For BDNF stimulation, neurons were
starved overnightin thepresenceof UO126(1mM) andthen treatedwith BDNF
(Preprotech, 100ngml21) for 4h before cell harvest.
Northern blotting and RNase protection assays. RNA was isolated from
synaptoneurosomes or cultured neurons by phenol/chloroform extraction
using RNA Stat-60 (Tel-Test). For northern blots, 30mg of total RNA was
resolved on 15% urea/polyacrylamide gels and transferred to Hybond Nþ
membrane (Amersham). See Supplementary Information for further details.
RNase protection assays were performed with the mirVana miRNAdetection kit
(Ambion) as per the manufacturers’ recommendations.
0UTR (1,171base pairs) was amplified by
0UTR (wild type or
0of the miR-134 sequence (Supplementary Fig. S1c) was
In situ hybridization. In situ hybridization of endogenous mRNAs and GFP
reporter mRNAs was as described32. For the detection of small RNAs, a
digoxigenin tail was added to antisense-locked nucleic acid (LNA) oligonucleo-
tides (Exiqon) with the DIG tailing kit (Roche). Tailed LNA oligonucleotides
were purified and used for overnight hybridization at 428C. All other steps were
the same as for mRNAs.
Microinjection. Mature hippocampal neurons43were microinjected using an
AIS2 microinjection system (Cellbiology Trading) attached to a Zeiss Axiovert
200M. Annealed 3
vitro transcription in the presence of Alexa-488-5
used at 200ngml21. Microinjection needles with a tip size between 0.2 and
0.3mm were used (P-87, Sutter Instruments) with a holding pressure of 40hPa
randomly selected images were analysed by three independent observers in a
Peptide-mediated delivery. Double-stranded small RNA or 2
DNA oligonucleotides containing a 5
with TCEP (80mm, Sigma) at room temperature for 15min. Penetratin (80mm,
Qbiogene) was added and the mixture was incubated at 658C followed by 1h at
cells at the indicated concentrations for 4h. Neurons were harvested for western
analysis 48h after transduction.
Image analysis. For spine analysis, neurons were transfected at 8DIVor 15DIV
confocal microscopy at 18DIV. See Supplementary Information for further
details on spine analysis.
For Sholl analysis, a series of concentric circles of 10-mm increments was
manuallydrawn around the cell body, andthe numberof dendriticintersections
at each individual circle was counted. At least ten individual neurons were
measured for each experimental condition. To quantify dendritic GFP levels in
thelocalreporterassay, randomdendriteswere selectedbasedondsRedstaining
and plot profiles of the GFP intensity of the same dendrites were derived using
ImageJ (NIH). The obtained values were background corrected and normalized
to the respective signal in theredchannel.At least 20 dendrites perexperimental
condition of a total of three independent experiments were measured.
Quantitative real-time PCR. Quantitative real-time PCR was performed on a
(PE Applied Biosystems) as described32.
Preparation of synaptoneurosomes and radio-immunoprecipitation. Syn-
aptoneurosomes were prepared from P15 long-Evans rat pups (Charles River)
as described32. For radio-immunoprecipitation, a mouse monoclonal anti-
Limk1 antibody (Pharmingen) was used.
Immunocytochemistry. Hippocampal neurons (18DIV) were immunostained
as described32, using a mouse monoclonal anti-Limk1 (Pharmingen) or a rabbit
anti-synapsin (Chemicon) antibody as primary antibody.
Luciferase assay. Cortical neurons were transfected at 4DIV or 12DIV, and
luciferase assays were performed 2days later with the Dual-Luciferase Reporter
Assay System (Promega).
0-end labelled (Alexa-546) sense and unmodified antisense
0UTP (Molecular Probes) and
0thiol group (80mm, IDT) were reduced
Received 15 August; accepted 25 October 2005.
1.West, A. E., Griffith, E. C. & Greenberg, M. E. Regulation of transcription
factors by neuronal activity. Nature Rev. Neurosci. 3, 921– -931 (2002).
Kelleher, R. J. III, Govindarajan, A. & Tonegawa, S. Translational regulatory
mechanisms in persistent forms of synaptic plasticity. Neuron 44, 59– -73 (2004).
Bartel, D. P. MicroRNAs: genomics, biogenesis, mechanism, and function. Cell
116, 281– -297 (2004).
He, L. & Hannon, G. J. MicroRNAs: small RNAs with a big role in gene
regulation. Nature Rev. Genet. 5, 522– -531 (2004).
Ambros, V. The functions of animal microRNAs. Nature 431, 350– -355 (2004).
Chen, C. Z., Li, L., Lodish, H. F. & Bartel, D. P. MicroRNAs modulate
hematopoietic lineage differentiation. Science 303, 83– -86 (2004).
Brennecke, J., Hipfner, D. R., Stark, A., Russell, R. B. & Cohen, S. M. bantam
encodes a developmentally regulated microRNA that controls cell proliferation
and regulates the proapoptotic gene hid in Drosophila. Cell 113, 25– -36 (2003).
Poy, M. N. et al. A pancreatic islet-specific microRNA regulates insulin
secretion. Nature 432, 226– -230 (2004).
Chang, S., Johnston, R. J. Jr, Frokjaer-Jensen, C., Lockery, S. & Hobert, O.
MicroRNAs act sequentially and asymmetrically to control chemosensory
laterality in the nematode. Nature 430, 785– -789 (2004).
10. Johnston, R. J. & Hobert, O. A microRNA controlling left/right neuronal
asymmetry in Caenorhabditis elegans. Nature 426, 845– -849 (2003).
11.Kim, J. et al. Identification of many microRNAs that copurify with
polyribosomes in mammalian neurons. Proc. Natl Acad. Sci. USA 101, 360– -365
NATURE|Vol 439|19 January 2006
© 2006 Nature Publishing Group Download full-text
12. Krichevsky, A. M., King, K. S., Donahue, C. P., Khrapko, K. & Kosik, K. S. A
microRNA array reveals extensive regulation of microRNAs during brain
development. RNA 9, 1274– -1281 (2003).
13. Lagos-Quintana, M. et al. Identification of tissue-specific microRNAs from
mouse. Curr. Biol. 12, 735– -739 (2002).
14. Giraldez, A. J. et al. MicroRNAs regulate brain morphogenesis in zebrafish.
Science 308, 833– -838 (2005).
15. Miska, E. A. et al. Microarray analysis of microRNA expression in the
developing mammalian brain. Genome Biol. 5, R68 (2004).
16. Sempere, L. F. et al. Expression profiling of mammalian microRNAs uncovers a
subset of brain-expressed microRNAs with possible roles in murine and human
neuronal differentiation. Genome Biol. 5, R13 (2004).
17. Kiebler, M. A. & DesGroseillers, L. Molecular insights into mRNA transport and
local translation in the mammalian nervous system. Neuron 25, 19– -28 (2000).
18. Steward, O. & Schuman, E. M. Protein synthesis at synaptic sites on dendrites.
Annu. Rev. Neurosci. 24, 299– -325 (2001).
19. Eberwine, J., Miyashiro, K., Kacharmina, J. E. & Job, C. Local translation of
classes of mRNAs that are targeted to neuronal dendrites. Proc. Natl Acad. Sci.
USA 98, 7080– -7085 (2001).
20. Campbell, D. S. & Holt, C. E. Chemotropic responses of retinal growth cones
mediated by rapid local protein synthesis and degradation. Neuron 32,
1013– -1026 (2001).
21. Kang, H. & Schuman, E. M. A requirement for local protein synthesis in
neurotrophin-induced hippocampal synaptic plasticity. Science 273, 1402– -1406
22. Zhang, X. & Poo, M. Localized synaptic potentiation by BDNF requires local
protein synthesis in the developing axon. Neuron 36, 675– -688 (2002).
23. Rao, A. & Steward, O. Evidence that protein constituents of postsynaptic
membrane specializations are locally synthesized: analysis of proteins
synthesized within synaptosomes. J. Neurosci. 11, 2881– -2895 (1991).
24. Bonhoeffer, T. & Yuste, R. Spine motility. Phenomenology, mechanisms, and
function. Neuron 35, 1019– -1027 (2002).
25. Hering, H. & Sheng, M. Dendritic spines: structure, dynamics and regulation.
Nature Rev. Neurosci. 2, 880– -888 (2001).
26. Matsuzaki, M., Honkura, N., Ellis-Davies, G. C. & Kasai, H. Structural basis of
long-term potentiation in single dendritic spines. Nature 429, 761– -766 (2004).
27. Nagerl, U. V., Eberhorn, N., Cambridge, S. B. & Bonhoeffer, T. Bidirectional
activity-dependent morphological plasticity in hippocampal neurons. Neuron
44, 759– -767 (2004).
28. Zito, K., Knott, G., Shepherd, G. M., Shenolikar, S. & Svoboda, K. Induction of
spine growth and synapse formation by regulation of the spine actin
cytoskeleton. Neuron 44, 321– -334 (2004).
29. Meister, G., Landthaler, M., Dorsett, Y. & Tuschl, T. Sequence-specific
inhibition of microRNA- and siRNA-induced RNA silencing. RNA 10, 544– -550
30. Hutvagner, G., Simard, M. J., Mello, C. C. & Zamore, P. D. Sequence-specific
inhibition of small RNA function. PLoS Biol. 2, E98 (2004).
31. Mansfield, J. H. et al. MicroRNA-responsive ‘sensor’ transgenes uncover Hox-
like and other developmentally regulated patterns of vertebrate microRNA
expression. Nature Genet. 36, 1079– -1083 (2004).
32. Schratt, G. M., Nigh, E. A., Chen, W. G., Hu, L. & Greenberg, M. E. BDNF
regulates the translation of a select group of mRNAs by a mammalian target of
rapamycin– -phosphatidylinositol 3-kinase-dependent pathway during neuronal
development. J. Neurosci. 24, 9366– -9377 (2004).
33. Ji, Y., Pang, P. T., Feng, L. & Lu, B. Cyclic AMP controls BDNF-induced TrkB
phosphorylation and dendritic spine formation in mature hippocampal neurons.
Nature Neurosci. 8, 164– -172 (2005).
34. Bamburg, J. R. Proteins of the ADF/cofilin family: essential regulators of actin
dynamics. Annu. Rev. Cell Dev. Biol. 15, 185– -230 (1999).
35. Meng, Y. et al. Abnormal spine morphology and enhanced LTP in LIMK-1
knockout mice. Neuron 35, 121– -133 (2002).
36. Aakalu, G., Smith, W. B., Nguyen, N., Jiang, C. & Schuman, E. M. Dynamic
visualization of local protein synthesis in hippocampal neurons. Neuron 30,
489– -502 (2001).
37. Takei, N., Kawamura, M., Hara, K., Yonezawa, K. & Nawa, H. Brain-derived
neurotrophic factor enhances neuronal translation by activating multiple
initiation processes: comparison with the effects of insulin. J. Biol. Chem. 276,
42818– -42825 (2001).
38. Rusinov, V., Baev, V., Minkov, I. N. & Tabler, M. MicroInspector: a web tool for
detection of miRNA binding sites in an RNA sequence. Nucleic Acids Res. 33,
W696– -W700 (2005).
39. John, B. et al. Human microRNA targets. PLoS Biol. 2, e363 (2004).
40. McAllister, A. K., Katz, L. C. & Lo, D. C. Neurotrophins and synaptic plasticity.
Annu. Rev. Neurosci. 22, 295– -318 (1999).
41. Lu, B. BDNF and activity-dependent synaptic modulation. Learn. Mem. 10,
86– -98 (2003).
42. Martin, K. C. & Kosik, K. S. Synaptic tagging—who’s it? Nature Rev. Neurosci. 3,
813– -820 (2002).
43. Goetze, B., Grunewald, B., Kiebler, M. A. & Macchi, P. Coupling the iron-
responsive element to GFP—an inducible system to study translation in a
single living cell. Sci. STKE 2003, PL12 (2003).
Supplementary Information is linked to the online version of the paper at
Acknowledgements We thank D. Bartel for providing the lin-41 reporter
constructs and northern blot protocols, K. Mizuno for the rat Limk1 cDNA,
G. Corfas for initial help with ISH, Y. Lin and A. West for reagents, J. Bikoff,
E. Griffith, E. Hong, S. Paradis and B. Sabatini for critically reading the
manuscript, and all the members of the Greenberg laboratory for support and
discussion. This work was supported by grants from the NINDS and NICHD
(M.E.G.), HFSP (G.S. and M.K.), the Charles Hood Foundation (G.S.), the Hertie-
Foundation (M.K.), the Schram-Stiftung (M.K.) and a Boehringer Ingelheim
Fonds fellowship (F.T.). M.E.G. acknowledges the generous support of the
F. M. Kirby Foundation to the Neurobiology Program of Children’s Hospital.
Author Information Reprints and permissions information is available at
npg.nature.com/reprintsandpermissions. The authors declare no competing
financial interests. Correspondence and requests for materials should be
addressed to M.E.G. (Michael.Greenberg@childrens.harvard.edu).
NATURE|Vol 439|19 January 2006