Forcing neural progenitor cells to cycle is insufficient to alter cell-fate decision and timing of neuronal differentiation in the spinal cord

<p>Abstract</p> <p>Background</p> <p>During the development of the nervous system, neural progenitor cells can either stay in the pool of proliferating undifferentiated cells or exit the cell cycle and differentiate. Two main factors will determine the fate of a neural progenitor cell: its position within the neuroepithelium and the time at which the cell initiates differentiation. In this paper we investigated the importance of the timing of cell cycle exit on cell-fate decision by forcing neural progenitors to cycle and studying the consequences on specification and differentiation programs.</p> <p>Results</p> <p>As a model, we chose the spinal progenitors of motor neurons (pMNs), which switch cell-fate from motor neurons to oligodendrocytes with time. To keep pMNs in the cell cycle, we forced the expression of G1-phase regulators, the D-type cyclins. We observed that keeping neural progenitor cells cycling is not sufficient to retain them in the progenitor domain (ventricular zone); transgenic cells instead migrate to the differentiating field (mantle zone) regardless of cell cycle exit. Cycling cells located in the mantle zone do not retain markers of neural progenitor cells such as Sox2 or Olig2 but upregulate transcription factors involved in motor neuron specification, including MNR2 and Islet1/2. These cycling cells also progress through neuronal differentiation to axonal extension. We also observed mitotic cells displaying all the features of differentiating motor neurons, including axonal projection via the ventral root. However, the rapid decrease observed in the proliferation rate of the transgenic motor neuron population suggests that they undergo only a limited number of divisions. Finally, quantification of the incidence of the phenotype in young and more mature neuroepithelium has allowed us to propose that once the transcriptional program assigning neural progenitor cells to a subtype of neurons is set up, transgenic cells progress in their program of differentiation regardless of cell cycle exit.</p> <p>Conclusion</p> <p>Our findings indicate that maintaining neural progenitor cells in proliferation is insufficient to prevent differentiation or alter cell-fate choice. Furthermore, our results indicate that the programs of neuronal specification and differentiation are controlled independently of cell cycle exit.</p

Epilepsy Caused by an Abnormal Alternative Splicing with Dosage Effect of the SV2A Gene in a Chicken Model

Photosensitive reflex epilepsy is caused by the combination of an individual's enhanced sensitivity with relevant light stimuli, such as stroboscopic lights or video games. This is the most common reflex epilepsy in humans; it is characterized by the photoparoxysmal response, which is an abnormal electroencephalographic reaction, and seizures triggered by intermittent light stimulation. Here, by using genetic mapping, sequencing and functional analyses, we report that a mutation in the acceptor site of the second intron of SV2A (the gene encoding synaptic vesicle glycoprotein 2A) is causing photosensitive reflex epilepsy in a unique vertebrate model, the Fepi chicken strain, a spontaneous model where the neurological disorder is inherited as an autosomal recessive mutation. This mutation causes an aberrant splicing event and significantly reduces the level of SV2A mRNA in homozygous carriers. Levetiracetam, a second generation antiepileptic drug, is known to bind SV2A, and SV2A knock-out mice develop seizures soon after birth and usually die within three weeks. The Fepi chicken survives to adulthood and responds to levetiracetam, suggesting that the low-level expression of SV2A in these animals is sufficient to allow survival, but does not protect against seizures. Thus, the Fepi chicken model shows that the role of the SV2A pathway in the brain is conserved between birds and mammals, in spite of a large phylogenetic distance. The Fepi model appears particularly useful for further studies of physiopathology of reflex epilepsy, in comparison with induced models of epilepsy in rodents. Consequently, SV2A is a very attractive candidate gene for analysis in the context of both mono- and polygenic generalized epilepsies in humans

Premiers evenements de la neurogenese chez un vertebre (amphibien) : emergence precoce de sous-populations neuronales in vitro

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Régionalisation du tube neural des vertébrés (identification des mécanismes d'activation du régulateur de la transcription, Pax6, dans le tube neural d'embryon de poulet)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Contrôle de la prolifération cellulaire et développement du tube neural (régulation de l'expression des acteurs du cycle cellulaire Cycline D1 et CDC25B par le morphogène Shh)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Schematic representation showing the age of the embryo at the time of electroporation and the different times after electroporation at which the embryos were fixed to evaluate the phenotype

For each experimental condition, 23 to 48 sections from 2 to 3 electroporated embryos were analyzed and the percentage of sections displaying ectopic P-H3 cells on the transgenic side determined. The corresponding values are reported for each experimental condition. Cross-sections of the spinal cord showing the phenotype 24 h after electroporation at E1.5 (b,c) and E2.5 (d), respectively. Tuj1 (b) marks the differentiating neurons. The arrows in (c,d) mark mitotic cells in ectopic positions. (b-d) Images obtained with an epifluorescent microscope.<p><b>Copyright information:</b></p><p>Taken from "Forcing neural progenitor cells to cycle is insufficient to alter cell-fate decision and timing of neuronal differentiation in the spinal cord"</p><p>http://www.neuraldevelopment.com/content/3/1/4</p><p>Neural Development 2008;3():4-4.</p><p>Published online 13 Feb 2008</p><p>PMCID:PMC2265710.</p><p></p

Co-immunodetection of Islet1/2 (a-i, green) or MNR2 (j,k, green) with P-H3 (red)

(a,b) Maximum projections; the electroporated side is on the left. (c) Single optical section showing a high magnification view at the level of the cell marked with an arrow in (a,b). (d-g) Orthogonal sections along the cell marked with an arrow in (c). (h-k) Single optical sections taken with a 63× objective. Dotted lines mark the limit of the mitotic transgenic cell. Co-immunodetection of BrdU (red) and Islet1/2 (green). All the pictures are single optical sections. (n-q) Orthogonal projections along the cell marked with an arrow in (m).<p><b>Copyright information:</b></p><p>Taken from "Forcing neural progenitor cells to cycle is insufficient to alter cell-fate decision and timing of neuronal differentiation in the spinal cord"</p><p>http://www.neuraldevelopment.com/content/3/1/4</p><p>Neural Development 2008;3():4-4.</p><p>Published online 13 Feb 2008</p><p>PMCID:PMC2265710.</p><p></p

Forty-eight hours following forced expression of a tagged-CyclinD2 version, cells expressing GFP (green) and the transgenic protein detected with an anti-Tag-V5 antibody (blue) are observed in the ventricular zone and differentiating field

Detection of the cells in S phase visualized following a 30 minute pulse of BrdU (red). Detection of the phospho-histone H3 (P-H3) on a cross-section of the spinal cord 48 h after overexpression of CyclinD2 (e,f, red) or D1 (g-i, blue). (h,i) Magnifications of the cell in anaphase shown in (g) (arrowhead). (a-f) Maximum projections of eight optical sections acquired at 5 μm Z steps; (g-i) single optical sections.<p><b>Copyright information:</b></p><p>Taken from "Forcing neural progenitor cells to cycle is insufficient to alter cell-fate decision and timing of neuronal differentiation in the spinal cord"</p><p>http://www.neuraldevelopment.com/content/3/1/4</p><p>Neural Development 2008;3():4-4.</p><p>Published online 13 Feb 2008</p><p>PMCID:PMC2265710.</p><p></p