6 research outputs found
Basal progenitor cells in the embryonic mouse thalamus - their molecular characterization and the role of neurogenins and Pax6
<p>Abstract</p> <p>Background</p> <p>The size and cell number of each brain region are influenced by the organization and behavior of neural progenitor cells during embryonic development. Recent studies on developing neocortex have revealed the presence of neural progenitor cells that divide away from the ventricular surface and undergo symmetric divisions to generate either two neurons or two progenitor cells. These 'basal' progenitor cells form the subventricular zone and are responsible for generating the majority of neocortical neurons. However, not much has been studied on similar types of progenitor cells in other brain regions.</p> <p>Results</p> <p>We have identified and characterized basal progenitor cells in the embryonic mouse thalamus. The progenitor domain that generates all of the cortex-projecting thalamic nuclei contained a remarkably high proportion of basally dividing cells. Fewer basal progenitor cells were found in other progenitor domains that generate non-cortex projecting nuclei. By using intracellular domain of Notch1 (NICD) as a marker for radial glial cells, we found that basally dividing cells extended outside the lateral limit of radial glial cells, indicating that, similar to the neocortex and ventral telencephalon, the thalamus has a distinct subventricular zone. Neocortical and thalamic basal progenitor cells shared expression of some molecular markers, including <it>Insm1</it>, Neurog1, Neurog2 and NeuroD1. Additionally, basal progenitor cells in each region also expressed exclusive markers, such as Tbr2 in the neocortex and Olig2 and Olig3 in the thalamus. In <it>Neurog1</it>/<it>Neurog2 </it>double mutant mice, the number of basally dividing progenitor cells in the thalamus was significantly reduced, which demonstrates the roles of neurogenins in the generation and/or maintenance of basal progenitor cells. In <it>Pax6 </it>mutant mice, the part of the thalamus that showed reduced Neurog1/2 expression also had reduced basal mitosis.</p> <p>Conclusions</p> <p>Our current study establishes the existence of a unique and significant population of basal progenitor cells in the thalamus and their dependence on neurogenins and Pax6. These progenitor cells may have important roles in enhancing the generation of neurons within the thalamus and may also be critical for generating neuronal diversity in this complex brain region.</p
Ascl1 (Mash1) Defines Cells with Long-Term Neurogenic Potential in Subgranular and Subventricular Zones in Adult Mouse Brain
Ascl1 (Mash1) is a bHLH transcription factor essential for neural differentiation
during embryogenesis but its role in adult neurogenesis is less clear. Here we
show that in the adult brain Ascl1 is dynamically expressed during neurogenesis
in the dentate gyrus subgranular zone (SGZ) and more rostral subventricular zone
(SVZ). Specifically, we find Ascl1 levels low in SGZ Type-1 cells and SVZ B
cells but increasing as the cells transition to intermediate progenitor stages.
In vivo genetic lineage tracing with a tamoxifen (TAM) inducible
Ascl1CreERT2 knock-in mouse strain shows
that Ascl1 lineage cells continuously generate new neurons over extended periods
of time. There is a regionally-specific difference in neuron generation, with
mice given TAM at postnatal day 50 showing new dentate gyrus neurons through 30
days post-TAM, but showing new olfactory bulb neurons even 180 days post-TAM.
These results show that Ascl1 is not restricted to transit amplifying
populations but is also found in a subset of neural stem cells with long-term
neurogenic potential in the adult brain
Ascl1 is present in a subpopulation of Type-1 stem cells and Type-2 progenitors in adult hippocampus.
<p>(A–D) Ascl1 is weakly detected in
Nestin::GFP<sup>+</sup>GFAP<sup>+</sup> Type-1 stem cells
(arrowhead) or strongly detected in
Nestin::GFP<sup>+</sup>GFAP<sup>−</sup> Type-2
progenitors (arrow) in SGZ of adult <i>Nestin::GFP</i> mice.
(E) Percentage of Ascl1<sup>High</sup> or Ascl1<sup>Low</sup> cells that
express the markers Nestin::GFP and GFAP (Type-1) (dark shaded bars) or
just the marker Nestin::GFP (Type-2) (grey shaded bars). 50
Ascl1<sup>+</sup> cells were counted per mouse,
n = 3 <i>Nestin::GFP</i> mice. (F) Ascl1
is in Type-1 and early Type-2 cells based on a current model of adult
hippocampal neurogenesis <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0018472#pone.0018472-Kempermann1" target="_blank">[14]</a>. Scale bar
 = 20 µm.</p
A subset of Ascl1 lineage cells continue to produce new granule neurons 30 days after initial Ascl1 expression in adult hippocampus.
<p>(A) Targeting strategy for
<i>Ascl1<sup>CreERT2/+</sup></i> knock-in mice. (B)
Quantification of the percentage of YFP<sup>+</sup> cells
co-labeled with stage-specific markers in hippocampus of adult
<i>Ascl1<sup>CreERT2/+</sup>;R26R<sup>YFP/YFP</sup></i>
mice 7, 30, or 180 days post-TAM. 150–500 YFP<sup>+</sup>
cells per mouse were counted for each marker, n = 2
<i>Ascl1<sup>CreERT2/+</sup>;R26R<sup>YFP/YFP</sup></i>
mice per time point. (C–F′) 7 days post-TAM
YFP<sup>+</sup> cells co-express GFAP (and have Type-1
morphology), Sox2, or NeuroD1, but not NeuN. (G–J′) 30 days
post-TAM YFP<sup>+</sup> cells overlap with NeuN, but also can
co-express GFAP or NeuroD1. (K–N′) 180 days post-TAM a
subpopulation of YFP<sup>+</sup> cells are still Type-1 cells by
morphology and express GFAP and Sox2, whereas the majority of
YFP<sup>+</sup> cells express NeuN but not NeuroD1. (O–V)
Neurogenesis in the SGZ dramatically decreases between 12 weeks and 34
weeks of age as seen in the decrease in DCX (P,T), NeuroD1 (Q,U) and
Ki67 (R,V). Arrowheads indicate the few cells positive for these markers
in the 34 week old mice. Notably, Sox2 does not decrease (O,S) so may
label quiescent Type-1 like cells. Scale bars  = 50
µm (C,G,K), 10 µm (D–F′, H–J′,
I–V).</p
A subset of Ascl1 lineage cells in adult SVZ have long term self renewing properties in the generation of olfactory bulb neurons.
<p>(A–D) Ascl1 is detected in
Nestin::GFP<sup>+</sup>GFAP<sup>+</sup> cells (B cells) in
the SVZ (A–B′) and in
Nestin::GFP<sup>+</sup>GFAP<sup>−</sup> C cells in SVZ
(A–B′) and RMS (C,C′) in 8 week old
<i>Nestin::GFP</i> transgenic mice. (D) Percentage of
Ascl1<sup>High</sup> or Ascl1<sup>Low</sup> cells that express the
markers Nestin::GFP and GFAP (dark shaded bars) or just Nestin::GFP
(grey shaded bars) in the RMS and the SVZ. 25 Ascl1<sup>+</sup>
cells per mouse were counted in the RMS; 60 Ascl1<sup>+</sup> cells
per mouse in the SVZ, n = 3
<i>Nestin::GFP</i> mice. (E–E′) mRNA in situ
with Ascl1 (E) or Cre (E′) probes in the adult SVZ.
(F–T′) Immunofluorescence in
<i>Ascl1<sup>CreERT2/+</sup></i>;<i>R26R<sup>YFP/YFP</sup></i>
mouse brain sections harvested 7, 30, or 180 days post-TAM demonstrates
Ascl1 derived cells along the SVZ-RMS-OB pathway (F–N). 7 days
post-TAM most YFP<sup>+</sup> cells were located in the SVZ, or
along the RMS (F–H) and express Sox2 (O–O′) or DCX
(P–P′). 30 or 180 days post-TAM YFP<sup>+</sup> cells
mature into neurons in the granule cell layer or the periglomerular
layer of the OB (I, L, R–R′, and data not shown). However,
many YFP<sup>+</sup> cells remain as Sox2<sup>+</sup> or
DCX<sup>+</sup> progenitors in the RMS or SVZ (J–K,
M–N, Q–Q′, S–T′). Scale bars
 = 50 µm (F–N), 10 µm
(O–T′).</p
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Genomic analyses implicate noncoding de novo variants in congenital heart disease.
A genetic etiology is identified for one-third of patients with congenital heart disease (CHD), with 8% of cases attributable to coding de novo variants (DNVs). To assess the contribution of noncoding DNVs to CHD, we compared genome sequences from 749 CHD probands and their parents with those from 1,611 unaffected trios. Neural network prediction of noncoding DNV transcriptional impact identified a burden of DNVs in individuals with CHD (n = 2,238 DNVs) compared to controls (n = 4,177; P = 8.7 × 10-4). Independent analyses of enhancers showed an excess of DNVs in associated genes (27 genes versus 3.7 expected, P = 1 × 10-5). We observed significant overlap between these transcription-based approaches (odds ratio (OR) = 2.5, 95% confidence interval (CI) 1.1-5.0, P = 5.4 × 10-3). CHD DNVs altered transcription levels in 5 of 31 enhancers assayed. Finally, we observed a DNV burden in RNA-binding-protein regulatory sites (OR = 1.13, 95% CI 1.1-1.2, P = 8.8 × 10-5). Our findings demonstrate an enrichment of potentially disruptive regulatory noncoding DNVs in a fraction of CHD at least as high as that observed for damaging coding DNVs