Late Embryonic Neurogenic Differentiation in the Ventral Neural Tube

CARCAGNO, A; DI BELLA, D; GOULDING, M; GUILLEMOT, F; LANUZA, G.M.

Montevideo

Congreso; 6th International Meeting of the Latin American Society of Developmental Biology; 2012

Latin American Society of Developmental Biology

The regulatory networks that control lineage specification in the developing central nervous system are not completely understood. Studies from the last decade have shown that positional identity of progenitor cells in the neural tube is important in generating neuronal diversity. According to this model, different neuronal cell types are initially determined by unique genetic programs largely controlled by combinatorial action of transcription factors expressed in discrete domains of precursors along the dorsal-ventral axis. We have recently identified a new population of neurons that originate from ventral neural tube progenitors at developmental stages when spinal cord neuroepithelium is committed to glial fate. These neurons consist of a late-born subset of V2 cells and were identified as CerebroSpinal Fluid-contacting Neurons (CSF-cN). The objective of this work is to determine the mechanisms involved in the differentiation of CSF-cN. Lineage tracking in vivo experiments and gene expression analysis indicate that CSF-cN progenitors express the proneural transcription factor Ascl1. We have found that CSF-cN are missing in Ascl1 knockout mice, while other cell types generated earlier from the same domain remain unaffected. This phenotype is not rescued by the proneural protein Neurogenin2 (Ascl1Neurog2 knock-in mouse), suggesting that Ascl1 activity is specifically required for generation of CSF-cN. In order to assess when Ascl1 is required for CSF-cN, we took advantage of the temporally restricted expression of Ascl1 in Foxn4 null mice and in tamoxifen-induced Ascl1 conditional mutants. These experiments indicate that Ascl1 exerts its critical actions around the time of CSF-cN differentiation. Finally, pharmacological in vivo manipulations of Notch receptor processing, using a specific inhibitor of g-secretase complex, suggested that Notch signaling is involved in the regulation of Ascl1 expression in ventral neural tube progenitors. In summary, our results show that Ascl1 expression in the late embryonic ventral neural tube is regulated by Notch signaling, and that Ascl1 plays an essential and specific role in the differentiation of CSF-cNs.