3136 RESEARCH REPORT
Development 139, 3136-3141 (2012) doi:10.1242/dev.078394
© 2012. Published by The Company of Biologists Ltd
Dopaminergic neurons modulate GABA neuron migration in
the embryonic midbrain
Anju Vasudevan1,*,‡, Chungkil Won1,2,3,*, Suyan Li1, Ferenc Erdélyi4, Gábor Szabó4 and Kwang-Soo Kim2,‡
SUMMARY
Neuronal migration, a key event during brain development, remains largely unexplored in the mesencephalon, where dopaminergic
(DA) and GABA neurons constitute two major neuronal populations. Here we study the migrational trajectories of DA and GABA
neurons and show that they occupy ventral mesencephalic territory in a temporally and spatially specific manner. Our results from
the Pitx3-deficient aphakia mouse suggest that pre-existing DA neurons modulate GABA neuronal migration to their final
destination, providing novel insights and fresh perspectives concerning neuronal migration and connectivity in the mesencephalon
in normal as well as diseased brains.
KEY WORDS: Midbrain, Neuronal migration, Parkinson’s disease
1
Angiogenesis and Brain Development Laboratory, Division of Basic Neuroscience,
McLean Hospital/Harvard Medical School, 115 Mill Street, Belmont, MA 02478,
USA. 2Molecular Neurobiology Laboratory and Program in Neuroscience, McLean
Hospital/Harvard Medical School, 115 Mill Street, Belmont, MA 02478, USA.
3
Institute of Life Science and College of Veterinary Medicine, Gyeongsang National
University, Jinju 660-701, Korea. 4Institute of Experimental Medicine, Department of
Gene Technology and Developmental Neurobiology, Laboratory of Molecular Biology
and Genetics, 1083 Budapest, Hungary.
*These authors contributed equally to this work
‡
Authors for correspondence ([email protected];
[email protected])
Accepted 11 June 2012
necessary for their proper migration and final connectivity that may
translate into novel understanding of potential etiology as well as
therapeutic development for many neurological diseases.
MATERIALS AND METHODS
Animals
Timed pregnant CD1 mice were purchased from Charles River
Laboratories. Colonies of GAD65-GFP and ak/ak mice were maintained in
our institutional animal facility. Day of plug discovery was designated
embryonic day (E) 0. Animal experiments were in full compliance with the
NIH Guide for the Care and Use of Laboratory Animals and were
approved by the McLean Institutional Animal Care and Use Committee.
BrdU labeling and immunohistochemistry
A single BrdU injection (50 g/g body weight) was administered to pregnant
dams carrying E10 or E11 embryos. Embryonic brains were removed after
2 hours, at E13, E15, E17 and postnatal (P) day 0 stages, immersed in zinc
fixative (BD Pharmingen) for 24 hours and processed for paraffin wax
histology. BrdU immunohistochemistry was performed on 10-m sections
with a mouse monoclonal anti-BrdU antibody (1:75, BD Pharmingen). Other
antibodies used were anti-TH (1:200, Millipore), anti-Otx2 (1:200,
Neuromics), anti-GAD65/67 (Gad2/1 – Mouse Genome Informatics) (1:400,
Millipore), anti-Lmx1b (1:100; Drs Carmen Birchmeier and Thomas Muller,
Max-Delbrück-Center for Molecular Medicine, Berlin, Germany), antiFoxa2 (1:100, Santa Cruz), anti-Lmx1a (1:100, Millipore), anti-Ki67 (1:30,
Sigma), anti-Pax6 (1:30, Sigma), anti-DAT (Slc6a3 – Mouse Genome
Informatics) (1:200, Millipore), anti-Helt (1:30, Sigma) and anti-calbindin
(1:100, Swant). BrdU+ cells in the red nucleus and BrdU+ GAD65/67+ colabeled cells in the VM were counted using ImageJ software (NIH).
Explant cultures
Basal plate (BP) and VM explants were dissected from mesencephalic slices
of E15 wild-type (WT) and ak/ak embryos. Explants were plated in Matrigel
(BD Biosciences) at a distance of 600 m, overlaid with Neurobasal medium
(1⫻, Invitrogen/Life Technologies) and co-cultured for 36 hours. Explants
were fixed in 4% paraformaldehyde, stained with Hoechst (Sigma) and
imaged. For quantification, BP explants were subdivided into proximal (P)
and distal (D) quadrants. The areas occupied by migrating cells in each
quadrant were determined using ImageJ. The P/D ratio was calculated and
used as a measure of chemoattraction in each case.
Heterochronic microtransplants
BP tissue obtained from E15 GAD65-GFP mesencephalic slices was
inserted into ak/ak mesencephalon using fine tungsten needles under a
high-magnification stereomicroscope. For some of these ak/ak slices (with
transplanted BP), the VM was discarded and substituted by VM from WT
DEVELOPMENT
INTRODUCTION
Neuronal migration is a fundamental process in the development
of the central nervous system because neurons eventually dwell in
regions distinct from their origin. From ventricular zones, neurons
and/or neuronal progenitors navigate along diverse courses, radially
and tangentially, to their final destination and integrate into specific
brain circuits (Corbin et al., 2001; Hatten, 2002; Marín and
Rubenstein, 2001; Parnavelas, 2000). A concerted and/or
sequentially regulated migration of both excitatory and inhibitory
neurons is essential for the emergence of their proper connectivity
and brain functions. Unlike in the telencephalon, where neuronal
migration has been well elucidated, in the mesencephalon this vital
event has been understudied and key factors remain to be defined.
Dopaminergic (DA) neurons located in the three anatomically
defined areas of the ventral mesencephalon (VM) – the substantia
nigra (SN), ventral tegmental area (VTA) and retrorubral field
(RRF) – are involved in controlling diverse brain functions,
including motor control and cognition, emotion and reward
behaviors (Björklund and Dunnett, 2007; Damier et al., 1999; Ding
et al., 2011; Lennington et al., 2011; Schultz, 2001; Seeman et al.,
1993; Smidt and Burbach, 2007). The migration routes of DA
neurons are not well understood and the related literature is
contradictory (Hanaway et al., 1971; Kawano et al., 1995), while
the route of GABA neurons to the VM is unknown.
Here, we study the migratory trajectories of DA and GABA
neurons and find that proper migration of GABA neurons to their
final location in the VM is dependent on the pre-existing DA
neuron palisade. These results provide several new concepts
regarding functional interactions between DA and GABA neurons
Mesencephalic neuronal migration
RESEARCH REPORT 3137
slices. Slices were transferred to polycarbonate membrane filters
(Invitrogen) in sterile six-well plates containing Neurobasal medium and
cultured for 48 hours. Slices were fixed and TH immunohistochemistry
performed. The number of GFP+ cells that migrated to the VM was
counted in all slices and average values obtained.
Statistics
Statistical significance of differences between groups was analyzed by twotailed Student’s t-test (Prism, GraphPad software). Results were expressed
as mean ± s.d. and statistical significance reported at P<0.05.
RESULTS AND DISCUSSION
Neuronal migration silhouette in the
mesencephalon
BrdU birthdating studies have been widely used to study neuronal
migration in the developing neocortex (López-Bendito et al.,
2008; Mathis et al., 2010; Ori-McKenney and Vallee, 2011;
Soriano and Del Rio, 1991; Supèr et al., 2000; Wines-Samuelson
et al., 2005). Because BrdU is integrated into the DNA of S-phase
progenitor cells, it serves as a stable marker for cells born around
DEVELOPMENT
Fig. 1. Neuronal migrational profiles in the mesencephalon. (A-G)E10 BrdU-labeled progenitors in the mesencephalon at 2 hours (A),
E13 (B), E15 (C), E17 (D) and P0 (E). Blue arrows in D point to ventral and perpendicular migration that depletes the red nucleus of BrdUlabeled cells (white asterisks, D-F) to form the anatomical architecture (arrowheads, D,E) of VTA and SN. Yellow arrows in E show dorsally and
ventrally segregated cells. (F)The anatomical architecture of SN and VTA confirmed by co-labeling of BrdU (red) and TH (green). (G)A 20⫻
magnification of F showing that some BrdU+ cells are TH+ (white arrows), whereas others are TH– (blue arrows). (H-K)GABA neurons are
absent from the VM in coronal (H-J) and sagittal (K) slices (30m) from E13 GAD65-GFP embryos. White asterisk indicates GABA neurons in
the basal plate (BP) (H,J) and pink arrows indicate possible ventral migration in a magnified BP (I). (J)No overlap of TH neurons (red) with
GABA neurons was seen. (K)Dashed circle indicates the absence of GABA neurons from VM. (L-O)GABA neurons appear in VM in coronal (LN) and sagittal (O) slices from E17 GAD65-GFP embryos. White asterisk indicates the GABA neuron stream from BP to VM (L), as magnified in
M (pink arrows). GABA neurons and TH neurons are in intimate contact (white arrows, N). (O)Dashed circle indicates GABA neurons in the
VM. (P,Q)GFP profiles of E17 mesencephalon collected from a second GAD65-GFP transgenic line (GAD65_Ncol/gfp/1e_6e) also showed a
similar picture. (P)White arrows indicate GABA neurons descending to VM and integrating with TH+ DA neurons (red). The boxed region in P
is magnified in Q and TH-GABA neuron contact is indicated (arrows). (R-U)Birthdating experiment in GAD65-GFP (R,T) and CD1 (S,U) mice.
Many of the BrdU+ cells that migrated into VM by E17 were GFP+ (R) or stained positively for GAD65/67 (S). VM regions of R and S are
magnified in T and U and co-expressing cell nuclei appear yellow (arrows). n5. aq, aqueduct; SN, substantia nigra; VTA, ventral tegmentum
area; VM, ventral mesencephalon; SC, superior colliculus. Scale bars: 100m in A-H,J-L,N-S; 50m in I,M,T,U.
3138 RESEARCH REPORT
Development 139 (17)
the time of injection. First, we performed a thorough and
systematic BrdU birthdating study to understand mesencephalic
neuronal migration in CD1 mice. We labeled neuronal
progenitors born at E10 with a single BrdU pulse and followed
their migration in the mesencephalon until P0 (Fig. 1A-G). BrdUlabeled cells first spread out uniformly in the mesencephalon
from E10-15 (Fig. 1A-C). However, a major change in neuronal
migration was observed at E17 (Fig. 1D), by which time neurons
had migrated both ventrally and perpendicular to the aqueduct to
form the distinct anatomical architecture of the boat-shaped SN
and VTA (Fig. 1D). The red nucleus area was significantly
depleted of E10-labeled neuronal progenitors by this
perpendicular migration. By P0, most of the neurons had
segregated to both dorsal and ventral mesencephalon (Fig. 1E).
The boat-shaped architecture was confirmed by tyrosine
hydroxylase (TH) staining (Fig. 1F,G). E11-labeled neuronal
progenitors followed the same route as E10-labeled neuronal
progenitors and formed the distinct anatomical architecture of SN
and VTA in VM (supplementary material Fig. S1A). Our results
corroborate those of previous studies indicating that neurons of
the SN and VTA in the mouse are generated on or before E12
(Bayer et al., 1995). E13-labeled neuronal progenitors migrated
predominantly to the dorsal mesencephalon and E15-labeled
progenitors gave rise to a limited number of lateral neurons
(supplementary material Fig. S1B,C).
Although many BrdU+ neurons in SN and VTA at P0 were
dopaminergic/TH+ (Fig. 1F,G), there were also many TH– neurons.
Given that DA and GABA neurons constitute two major neuronal
populations in the ventral midbrain, these neurons might be GABA
neurons. Although GAD mRNA expression starting at E10.5 has
been reported in BP, alar plate and dorsal mesencephalon (Guimera
et al., 2006; Katarova et al., 2000), and the number, frequency and
topography of GABA neurons in SN and VTA regions of the adult
brain have been characterized (Korotkova et al., 2004; Nair-Roberts
et al., 2008; Olson and Nestler, 2007), it is not known when and how
GABA neurons become admixed with ventral mesencephalic DA
neurons during development. Are GABA neurons of the VM born
elsewhere, then come to reside there to form the final connectivity?
To address these fundamental questions we used the GAD65-GFP
mouse model, in which GABA neurons can be clearly visualized
(López-Bendito et al., 2004). Strikingly, we found that whereas at
E13 the VM was completely devoid of GABA neurons (Fig. 1H-K),
by E17 GABA neurons were substantially intermingled with DA
neurons (Fig. 1L-Q). At E13, many BP GFP+ neurons were oriented
DEVELOPMENT
Fig. 2. Abnormal neuronal migration and
distribution of neurons in ak/ak
mesencephalon. (A-M)The migrational profile
of E11-labeled neuronal progenitors was
analyzed in WT (A-C,G) and ak/ak mutant (DF,H-M) mice at E17. White asterisks indicate
areas free of BrdU-labeled cells in WT
mesencephalon (A-C,G) and blue asterisks
indicate abnormal cell clusters in the red
nucleus of the ak/ak mutant (D-F,H).
(G,H)Higher magnifications of C and F
displaying failed perpendicular migration
(arrowheads) in the ak/ak mutant. (I-M)Stalled
cells in the ak/ak mutant are double positive for
BrdU/Otx2 (arrowheads, I), BrdU/Lmx1b (J,K)
and BrdU/Foxa2 (L,M). The boxed regions in J
and L are magnified in K and M, respectively,
and white arrows indicate double-positive cells.
(N)Quantification of E11 BrdU-labeled cells
distributed in the red nucleus (both
hemispheres) of WT and ak/ak mutant (mean
density of BrdU+ cells ± s.d.). A significant
increase in BrdU+ cells was observed in the
ak/ak mutant. *P<0.0001; n5. Scale bars:
100m in A-J,L; 50m in K,M.
Mesencephalic neuronal migration
RESEARCH REPORT 3139
ventrally (Fig. 1H,I) and by E17 a cohort of GFP+ neurons were
positioned in stream-like routes to the VM (Fig. 1L,M,P,Q). Further,
high-magnification images showed how GABA neurons of the VM
are in close physical contact with DA neurons (Fig. 1N,P,Q).
Birthdating experiments revealed that many E11-labeled neuronal
progenitors migrated to contribute to GABA neurons of the VM by
E17 (Fig. 1R-U).
Abnormal neuronal migration in the ak/ak
mesencephalon
This novel finding that DA and GABA neurons occupy separate
territories in the E13 mesencephalon (Fig. 1J) prompted us to
hypothesize that the early-formed DA neuron palisade might have
a role in GABA neuron migration into the VM at later
developmental stages. In line with this possibility, the direction and
entry of the GABA neuron stream were oriented towards VM
territory (Fig. 1H,I), leading to intimate contact with DA neurons
(Fig. 1L-Q). To address our hypothesis and to further investigate
mesencephalic neuron migration, we postulated that the Pitx3deficient aphakia (ak) mouse might provide an ideal animal model
with a defective DA neuron architecture as Pitx3 is one of the
crucial regulators of mesencephalic DA neuron development (Ding
et al., 2011; Kim et al., 2007; Nunes et al., 2003; Smidt et al., 2004;
van den Munckhof et al., 2003) and there is selective and early loss
of A9 DA neurons in the SN of ak/ak mice (Hwang et al., 2005;
Smidt et al., 2004; van den Munckhof et al., 2003).
Since expression of both Pitx3 and Th begins at E11, we
consistently studied the migration of E11-labeled neuronal progenitors
in both WT and ak/ak mice (Fig. 2). Mesencephalic sections were
analyzed at E17 with BrdU and TH markers (Fig. 2A-H). Strikingly,
in the ak/ak mutant, BrdU+ cells were scattered aberrantly in BP
regions and failed in their perpendicular migration to the SN. The
distinct anatomical architecture of the boat-shaped SN and VTA
outlined by BrdU+ cell migration did not form in the ak/ak mutant
(Fig. 2D), in contrast to WT (Fig. 2A; supplementary material Fig.
S1A). BrdU and TH double labeling revealed many E11-labeled cells
displaying a dopaminergic phenotype after arriving at their final
destination in both VTA and SN regions in WT mesencephalon (Fig.
2A-C,G), whereas in the ak/ak mutant the cells were unable to reach
the SN and display their full dopaminergic phenotype (Fig. 2D-F,H).
Instead, these E11-labeled cells appeared to be stuck or trailing in the
middle of their migratory trajectory and distributed abnormally in the
red nucleus area in the ak/ak mutant (Fig. 2F,H).
To further investigate the abnormally migrating cells, we tested
whether the stalled E11-labeled cells in the ak/ak red nucleus area
contain DA progenitor cells. Many cells were positive for Otx2
(Fig. 2I), a marker for DA progenitors (Chung et al., 2009; Vernay
et al., 2005), but never expressed the TH marker of DA neurons
(Fig. 2E,F,H), indicating impaired differentiation. The stalled cells
were also positive for the markers Lmx1b (Fig. 2J,K) and Foxa2
(Fig. 2L,M), confirming their DA progenitor identity. They were
positive for the proliferating progenitor markers Lmx1a, Ki67 and
DEVELOPMENT
Fig. 3. Impaired GABA neuron development in
ak/ak mesencephalon. (A-H)GAD65/67 and TH
labeling at E17 in WT (A-C,G) and ak/ak (D-F,H)
mouse mesencephalon. Higher magnification of VM
from C and F show intimate association of GABA
neurons and DA neurons in WT (co-label in yellow,
arrows in G) and decreased GAD65/67 label and
limited physical contact with TH neurons in the ak/ak
mutant (blue arrows, H). (I-O)WT BP explants
(outlined) show robust cell migration towards WT VM
(I-K,O), whereas WT BP explants fail to migrate
towards ak/ak VM (L-O) in proximal quadrants. WT BP
explants from I and L are magnified in J and M,
respectively. (K,N)Hoechst staining of WT BP explants
from I and L, respectively. (O)Quantification of
chemoattraction expressed as a ratio of the quadrant
(dotted lines) facing the VM explants (proximal, P)
relative to the area occupied by cells in the opposite
quadrant (distal, D). *P<0.01; n25; error bars
indicate s.d. Scale bars: 100m in A-H,J,K,M,N;
200m in I,L.
3140 RESEARCH REPORT
Development 139 (17)
Pax6 and negative for DAT, a marker of immature postmitotic DA
progenitors (supplementary material Fig. S2A-E). In addition,
many BrdU+ cells were observed along perpendicular migration
routes in a short-pulse experiment at E17 (supplementary material
Fig. S2F), confirming the presence of abnormally proliferating
progenitors in the ak/ak mesencephalon at late embryonic stages.
The mean density of BrdU+ cells in the red nucleus of the ak/ak
mutant was significantly higher than in WT (Fig. 2N).
Taken together, our data provide strong evidence of the
perpendicular migration of DA neurons to the VM and that this is
significantly disturbed in the ak/ak mutant. Thus, in the absence of
Pitx3, DA neuronal migration is impaired, contributing to severe
loss of A9 DA neurons in the SN. Interestingly, we also found that
migration of E13-labeled neuronal progenitors was similarly
affected in the ak/ak mutant (supplementary material Fig. S3).
Pre-existing DA neurons modulate GABA neuron
migration to ventral mesencephalon
GABA neuron development was also significantly affected in the
ak/ak mesencephalon. By E17, in WT mouse embryos GABA
neurons had settled together in close physical contact with TH
neurons (Fig. 3A-C,G). This profile was substantially altered in the
ak/ak mutant, leading to significantly limited contact of these
neurons in the VM (Fig. 3D-F,H). GABA neurogenesis was
unaffected in the ak/ak mutant (supplementary material Fig. S4). The
stalled cells on the route of perpendicular migration or in the VM
were not apoptotic (supplementary material Fig. S5), and so we
examined whether the decreased GABA neuron profile in the ak/ak
mutant by late embryonic stages was due to impaired migration. To
search for cellular sources of guidance cues in the VM for migratory
BP neurons, explants of VM were confronted with explants of BP
from WT mice. BP neurons were markedly attracted towards VM
(Fig. 3I-K,O). BP explants from WT mice, by contrast, showed no
attraction to VM from the ak/ak mutant (Fig. 3L-O).
Birthdating studies indicated that E11-labeled neuronal
progenitors contributed to GABA neurons of VM in WT
embryos and many BrdU+ GAD65/67+ co-labeled cells were
observed (Fig. 4A,C). In the ak/ak mutant, E11-labeled neuronal
progenitors did not contribute significantly to GABA neurons of
the VM, as illustrated by the significant decrease in BrdU
GAD65/67 co-labeling (Fig. 4B,D) and mean density of BrdU+
GAD65/67+ cells in the VM area (Fig. 4E). The stalled cells
along the perpendicular migration routes expressed the GABA
neuron progenitor markers Helt (Fig. 4F,G) and calbindin (Fig.
4H-J). Heterochronic microtransplants were also performed to
understand mesencephalic GABA neuron migration. When a BP
explant from a GAD65-GFP mouse was transplanted into ak/ak
mesencephalon, GFP+ cells appeared to be stalled around the
transplantation site and were unable to migrate and integrate into
VM (Fig. 4K,M,O). By contrast, when ak/ak VM was substituted
DEVELOPMENT
Fig. 4. DA neurons modulate GABA neuron
migration to ventral mesencephalon. (A-E)E11labeled neuronal progenitors were examined at E17 for
BrdU and GAD65/67 markers in WT (A,C) and ak/ak
mutant (B,D). VM from A and B is magnified in C and D,
respectively. White arrows show BrdU GAD65/67 colabeling in WT mouse and blue arrows indicate the lack
thereof in the ak/ak mutant. (E)BrdU+ GAD65/67+ cells in
the VM of WT and ak/ak mutant were quantified (mean
density of BrdU+ GAD65/67+ cells ± s.d.) and a significant
reduction was observed in the mutant. *P<0.0001; n5;
error bars indicate s.d. (F-J)The stalled cells in ak/ak
mesencephalon were Helt+ (F,G) and calbindin+ (H-J). The
boxed regions in F, H and I are magnified in G, I and J,
respectively. Arrows indicate BrdU+ Helt+ (G) and BrdU+
calbindin+ (J) co-labeled cells. (K,L) Scheme of
transplantation of GAD65-GFP BP (green circle) and WT
VM (pink shape) into ak/ak mesencephalon. Red crescent
marks the defective DA neuron architecture of the ak/ak
mesencephalon. (M,N)Blue arrows (M) indicate GFP+
cells close to site of transplantation (yellow dotted circle),
white asterisk (M) indicates the lack of migration to ak/ak
VM, and white arrows (N) indicate significant migration
and integration into transplanted WT VM (white border).
(O)Quantification of migrated GFP+ cells to ak/ak VM
(K,M) and ak/ak VM substituted with WT VM (ak/ak-WT,
L,N). *P<0.0001; n25; error bars indicate s.d.
(P,Q)Model of mesencephalic DA (blue arrows) and
GABA (green arrows) neuron migration in WT (P), which
involves ventral migration of VTA precursors (vertical
arrow) and perpendicular migration of SN precursors and
some VTA precursors (perpendicular arrows). In the ak/ak
mutant (Q), perpendicular migration of DA neurons to
VM is significantly affected (lower red cross) and cells
cluster abnormally in the red nucleus. Then, GABA
neurons also cannot migrate to VM (upper red cross). Aq,
aqueduct; BP, basal plate; VM, ventral mesencephalon.
Scale bars: 100m in A-D,F,H,M,N; 50m in G,I; 25m
in J.
with a VM from WT mouse, GFP+ cells exited the
transplantation site and migrated robustly to integrate with DA
neurons (Fig. 4L,N,O).
Together, these results strongly support our idea that the intact
DA system of the VM guides the GABA neuron system to descend
to VM and establish its connectivity with DA neurons.
Furthermore, the reduction in GABA neurons observed in the ak/ak
mesencephalon was reflected in adult (4 month old) mice as well
(supplementary material Fig. S6).
Our data provide novel insights into neuronal migration in the
embryonic mouse mesencephalon and its relevance for final ventral
mesencephalic neuronal population and connectivity. First, our data
support a model for DA and GABA neuron migration in the
mesencephalon that depicts vertical migration of VTA precursors
and perpendicular migration of both SN and VTA precursors (Fig.
4P). Second, our analysis of ak/ak mice indicates how A9 DA
progenitor cells show blocked perpendicular migration and
accumulate in the red nucleus area (Fig. 4Q). Perpendicular
migration is therefore essential to set up the proper anatomical
architecture of ventral mesencephalic structures. Third, we found
that DA and GABA neurons occupy VM in a temporally sequential
manner. Thus, at E13, the primary structure of DA neurons in the
VM is completely devoid of GABA neurons, whereas by E17
GABA neurons come to reside along with DA neurons.
Remarkably, proper migration of GABA neurons to their final
location is dependent on the complete DA neuron architecture in
the VM, strongly indicating an important interaction between
GABA and DA neurons for final location and connectivity.
Given that major brain disorders such as schizophrenia, attention
deficit hyperactivity disorder (ADHD) and Parkinson’s disease are
considered to be caused by abnormal early brain development, this
study will serve as a gateway to a whole new field of exploration
to identify substrates and mechanisms of neuronal migration in the
mesencephalon that might provide novel insights into the
underlying pathophysiology of these brain disorders.
Acknowledgements
We thank Drs Carmen Birchmeier and Thomas Müller for the generous gift of
Lmx1b antibody.
Funding
Supported by a National Alliance for Research on Schizophrenia and
Depression (NARSAD) Young Investigator Award to A.V. and National Institutes
of Health grants [NS064386, NS073635 to A.V., MH48866, MH087903 and
NS070577 to K.-S.K.]. Deposited in PMC for release after 12 months.
Competing interests statement
The authors declare no competing financial interests.
Supplementary material
Supplementary material available online at
http://dev.biologists.org/lookup/suppl/doi:10.1242/dev.078394/-/DC1
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DEVELOPMENT
Mesencephalic neuronal migration