Aim: 

Down syndrome (DS) is a high-incidence pathology that represents the most common genetic cause of mental retardation. Defects in neurogenesis appear to be a major determinant of the severe hypoplasia that characterizes the DS brain. In this study we took advantage of neural stem cells from the Ts65Dn mouse model for DS to dissect the molecular mechanisms underlying proliferation impairment.

Methods: 

Neural stem cells, derived from the rostral telencephalon of newborn Ts65Dn and control mice, were grown in culture as neurospheres. Proliferation rate was evaluated based on BrdU incorporation, neurosphere-forming efficiency and neurosphere diameters. Flow cytometry analysis (FACS) was performed to assess differences in cell cycle dynamics and finally expression levels of critical cell cycle regulators were quantified by Real time PCR analysis.

Results: 

We found that proliferation rate, assessed by BrdU incorporation, was significantly reduced (-20%) in Ts65Dn neurospheres compared to controls. Differences of the same magnitude were found in neurosphere-forming efficiency and neurosphere dimensions. FACS results showed that the percentage of cells in the G₂ phase of cell cycle was larger (+17%) in Ts65Dn neurospheres compared to controls. Moreover, screening of cell cycle regulatory genes showed that Ts65Dn neurospheres had a decreased expression of Skp2, a key regulator of G₂/M and G₁/S transition.

Conclusion: 

Current results in neurospheres from the rostral telencephalon are in agreement with previous in vivo evidence in the cerebellum and hippocampus of Ts65Dn mice, indicating that neuronal stem cell cultures are a good model to unravel the molecular mechanisms underlying neurogenesis impairment in DS. The ensemble of our data additionally suggests that neuronal precursors from different neurogenic regions of the Ts65Dn brain share similar proliferation defects.