34 research outputs found
Two specific populations of GABAergic neurons originating from the medial and the caudal ganglionic eminences aid in proper navigation of callosal axons
No full text<div>Post-print of original paper "Two specific populations of GABAergic neurons originating from the medial and</div><div>the caudal ganglionic eminences aid in proper navigation of callosal axons".</div><div><br></div
Author response: Neurogliaform cortical interneurons derive from cells in the preoptic area
No full textDelineating the basic cellular components of cortical inhibitory circuits remains a fundamental issue in order to understand their specific contributions to microcircuit function. It is still unclear how current classifications of cortical interneuron subtypes relate to biological processes such as their developmental specification. Here we identified the developmental trajectory of neurogliaform cells (NGCs), the main effectors of a powerful inhibitory motif recruited by long-range connections. Using in vivo genetic lineage-tracing in mice, we report that NGCs originate from a specific pool of 5-HT3AR-expressing Hmx3+ cells located in the preoptic area (POA). Hmx3-derived 5-HT3AR+ cortical interneurons (INs) expressed the transcription factors PROX1, NR2F2, the marker reelin but not VIP and exhibited the molecular, morphological and electrophysiological profile of NGCs. Overall, these results indicate that NGCs are a distinct class of INs with a unique developmental trajectory and open the possibility to study their specific functional contribution to cortical inhibitory microcircuit motifs.</jats:p
Two specific populations of GABAergic neurons originating from the medial and the caudal ganglionic eminences aid in proper navigation of callosal axons.
No full textThe corpus callosum (CC) plays a crucial role in interhemispheric communication. It has been shown that CC formation relies on the guidepost cells located in the midline region that include glutamatergic and GABAergic neurons as well as glial cells. However, the origin of these guidepost GABAergic neurons and their precise function in callosal axon pathfinding remain to be investigated. Here, we show that two distinct GABAergic neuronal subpopulations converge toward the midline prior to the arrival of callosal axons. Using in vivo and ex vivo fate mapping we show that CC GABAergic neurons originate in the caudal and medial ganglionic eminences (CGE and MGE) but not in the lateral ganglionic eminence (LGE). Time lapse imaging on organotypic slices and in vivo analyses further revealed that CC GABAergic neurons contribute to the normal navigation of callosal axons. The use of Nkx2.1 knockout (KO) mice confirmed a role of these neurons in the maintenance of proper behavior of callosal axons while growing through the CC. Indeed, using in vitro transplantation assays, we demonstrated that both MGE- and CGE-derived GABAergic neurons exert an attractive activity on callosal axons. Furthermore, by combining a sensitive RT-PCR technique with in situ hybridization, we demonstrate that CC neurons express multiple short and long range guidance cues. This study strongly suggests that MGE- and CGE-derived interneurons may guide CC axons by multiple guidance mechanisms and signaling pathways.Mathieu Niquille and Shilpi Minocha contributed equally to this work.
*Correspondence to: C. Lebrand ([email protected]).
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DATASET of Two specific populations of GABAergic neurons originating from the medial and the caudal ganglionic eminences aid in proper navigation of callosal axons
No full text<h2>Confocal Time-Lapse Microscopy</h2>
<p>For imaging neurons, slices were cultured on nucleopore
Track-Etch membranes (1 mm pore size; Whatman) in tissue dishes
containing 3ml of SCM medium (BME/HBSS supplemented with glutamine, 5% horse
serum and Pen/Strep). CC GABAergic interneuron migration paths and dynamics
were studied in<b> </b>coronal CC slices of GAD67-GFP<b> </b>transgenic mice from E14.5 to E18.5. To
visualize callosal axons, the plasmid encoding the red fluorescent protein (<i>pCAG-IRES-Tomato) </i>was electroporated <i>in utero</i>
into the dorsal pallium progenitors of E14.5 embryos that generate callosally
projecting neurons. In some additional experiments,
small dye crystals were implanted within the frontal cortex of GAD67-GFP<b> </b>sections made from E16.5
to E18.5. We imaged growth cone dynamics and outgrowth
properties of frontal callosal axons that were found to grow continuously from
the lateral extension of the CC to the midline after E16.5. After
15-20 hrs in culture, slices were placed in an open perfusion chamber on the
stage of an upright Leica SP5 confocal microscope. Temperature was maintained
at 37ºC with the aid of a microscope incubator system (Life Scientific,
Switzerland) and slices were perfused with SCM medium containing a gas mixture
of 5% CO2/ 95% O2. GAD67-GFP positive CC neurons and callosal axons labelled
with Tomato were imaged with a 20X, a 40X, or a 60X immersion lens at 15 or 20
minute intervals using the fast scan function of the Leica SP5 confocal microscope
resonant scanner. Image captures and all peripherals were controlled with Leica
software. Pictures were processed and converted into *.AVI movies using
Imaris and Metamorph 6.0. Migration parameters (basal rate of migration, frequency
and duration of the intervening pauses) were determined by measuring movements
every 15-20 minutes during 5 hours while the neurons were migrating through the
CC white matter. Using the tracking function of Metamorph software 6.0, a total
of 70 GAD67-GFP neuron traces were analyzed at E14.5 and at E16.5; and 35
traces at E17.5.</p><p><b>Movies 1 and 2. <i>Reduced motility of CC
GABAergic guidepost neurons after E16.5</i></b></p><p>
<i>In
vitro</i> time-lapse sequences over a period of around
three hours (sequential pictures taken at regular intervals) of GAD67-GFP<sup>+</sup> neuron dynamics in<b> </b>coronal CC slices of E14.5 <b>(A1-A6) </b>and
E16.5 <b>(B1-B6) </b>GAD67-GFP<sup>+</sup><b> </b>transgenic mice. Open arrowheads
indicate the progression of neurons between sequential pictures while arrowheads
highlight immobilized neurons. <b>(A1-A6) </b>At
E14.5, the majority of the GAD67-GFP<sup>+ </sup>neurons exhibit rapid
movements within the white matter of the CC (open arrowheads). <b>(B1-B6) </b>By contrast, at E16.5, nearly
all the GAD67-GFP<sup>+</sup> neurons exhibit a reduced motility within the
white matter of the CC <b>(</b>arrowheads<b>)</b>.</p><p><b>Movies 3 and 4. <i>Dynamic
interactions between CC GABAergic neurons and callosal axons between E16.5 to
E18.5.</i></b></p><p><b>(A)</b> Experimental<b> </b>paradigm
used to study cell interactions between callosal pioneering axons labelled with
the red fluorescent protein Tomato and GAD67-GFP<sup>+</sup> CC neurons. For
this purpose, a plasmid encoding the Tomato (<i>pCAG-Ires-Tomato</i>) was electroporated into the dorsal pallium of E14.5 GAD67-GFP<sup>+</sup> living embryos to label neuronal precursors of
pyramidal neurons that migrate to the cortex and differentiate for a part into
callosal projecting neurons. DNA solution
containing the <i>pCAG-Ires-Tomato</i>
plasmid was pressure-injected
focally into the lateral ventricle of E14.5 embryos. Each
embryo, while still within the uterine horn, was placed between tweezers-type
electrodes. After <i>in utero</i>
electroporation, the embryos were quickly placed back into the abdominal cavity
and allowed to develop until E16.5. </p><p>
<b>(B1</b> and<b> B2)</b>
<i>In vitro</i> time-lapse sequences over a
period of 100 minutes (at 20 minute intervals) of Tomato-labelled
callosal axons and GAD67-GFP<sup>+</sup> neurons on<b> </b>coronal CC slices of E16.5 GAD67-GFP<sup>+</sup><i> </i>embryos.<b> (B1)</b> Low power view of the CC showing the region of interest where
the video imaging was done. <b>(B2)</b> High power views of Tomato<sup>+</sup>
callosal axon growing through the CC and making branch extensions and
retractions at different time points <b>(</b>t:0
min-t:100 min<b>)</b>. Callosal axon
branches are seen to make multiple contacts with CC GAD67-GFP+ guidepost
neurons <b>(</b>t:20 min, t:60 min and
t:100 min, arrowheads<b>)</b>. Contacts
either promote axonal growth <b>(</b>t:20
min -t:60 min<b>)</b> or lead to growth
cone retraction <b>(</b>t.80 min -t:100 min<b>)</b> and formation of a new branch <b>(</b>t:80 min -t:100 min, open arrowhead<b>)</b>.</p><p> <b>Supplementary Figure 1. <i>MGE- and CGE-derived GABAergic precursors
give birth each to half of the CC GABAergic neurons, accounting together for
all CC GABAergic neurons</i></b></p>
<p><b>(A</b> and <b>B)</b> Graphs represent
the comparison of neuronal density
at E16.5 <b>(A)</b> and E18.5 <b>(B)</b> between MGE-derived Lhx6-GFP<sup>+</sup> <b>(</b>Lhx6<b>)</b>, LGE/CGE-derived Venus<sup>+</sup> <b>(</b>Venus<b>)</b> and CGE-derived <i>5-HTR3a</i>-GFP<sup>+</sup>
<b>(</b>5-HTR3a<b>)</b> neurons in the medial <b>(</b>mid<b>)</b>, lateral <b>(</b>lat<b>)</b> and entire <b>(</b>tot<b>)</b> CC of <i>Lhx6-Cre/R26R-YFP,</i>
<i>Nkx2.1-Cre/Dlx1-Venus<sup>fl </sup></i>and<i> 5-HTR3a-GFP </i>mice,<i> </i>respectively<i>.</i><b> (C</b> and <b>D</b>) Graphs represent the comparison between densities at E16.5 <b>(C)</b>
and E18.5 <b>(D)</b> between the MGE<sup>+</sup> LGE/CGE-derived <b>(</b>Lhx6<sup>+</sup>
Venus<b>)</b> neurons, the MGE<sup>+</sup> CGE-derived <b>(</b>Lhx6<sup>+</sup> 5-HTR3a<b>)</b> neurons and all GABAergic neurons
labelled for GAD67-GFP in the medial <b>(</b>mid<b>)</b>, lateral <b>(</b>lat<b>) </b>and entire <b>(</b>tot<b>)</b> CC. </p>
<p>Comparison between density values were made at E16.5 and at E18.5 in
similar portions of the CC using a <i>t</i>-test.
After making the quantification at E16.5 and E18.5, the GABAergic neurons of
the medial and the entire CC at both ages are found to be generated in equal
proportion by the MGE and the LGE/CGE. The CGE however generates higher
proportion of GABAergic neurons in the lateral CC compared to the MGE <b>(A </b>and<b> B,*)</b>. The values for the density of CC 5-HTR3a-GFP<sup>+</sup> neurons originating specifically from
the CGE and of CC LGE/CGE-derived Venus<sup>+</sup> neurons are not
significantly different <b>(A </b>and<b> B)</b> suggesting that CC GABAergic
neurons originate from the MGE and the CGE but not the LGE. Finally, the comparison of the global
neuronal population originating from both the MGE and the CGE with the
GAD67-GFP<sup>+</sup> population <b>(C</b>
and <b>D)</b> indicates that the MGE- and
CGE-derived populations together generate the whole population of CC GABAergic
guidepost neurons.</p>
<p> </p
The serotonin 6 receptor controls neuronal migration during corticogenesis via a ligand-independent Cdk5-dependent mechanism
No full textThe formation of a laminar structure such as the mammalian neocortex relies on the coordinated migration of different subtypes of excitatory pyramidal neurons in specific layers. Cyclin-dependent kinase 5 (Cdk5) is a master regulator of pyramidal neuron migration. Recently, we have shown that Cdk5 binds to the serotonin 6 receptor (5-HT6R), a G protein-coupled receptor (GPCR). Here, we investigated the role of 5-HT6R in the positioning and migration of pyramidal neurons during mouse corticogenesis. We report that constitutive expression of 5-HT6R controls pyramidal neuron migration through an agonist-independent mechanism that requires Cdk5 activity. These data provide the first in vivo evidence of a role for constitutive activity at a GPCR in neocortical radial migration
PlexinA4-Semaphorin3A-mediated crosstalk between main cortical interneuron classes is required for superficial interneuron lamination
No full textIn the mammalian cerebral cortex, the developmental events governing allocation of different classes of inhibitory interneurons (INs) to distinct cortical layers are poorly understood. Here we report that the guidance receptor PlexinA4 (PLXNA4) is upregulated in serotonin receptor 3a-expressing (HTR3A+) cortical INs (hINs) as they invade the cortical plate, and that it regulates their laminar allocation to superficial cortical layers. We find that the PLXNA4 ligand Semaphorin3A (SEMA3A) acts as a chemorepulsive factor on hINs migrating into the nascent cortex and demonstrate that SEMA3A specifically controls their laminar positioning through PLXNA4. We identify deep-layer INs as a major source of SEMA3A in the developing cortex and demonstrate that targeted genetic deletion of Sema3a in these INs specifically affects laminar allocation of hINs. These data show that, in the neocortex, deep-layer INs control laminar allocation of hINs into superficial layers
Neurogliaform cortical interneurons derive from cells in the preoptic area
No full textExcel document containing the raw dataset used in each figures and links to morphology reconstructions</p
