Evidence of functional duplicity of Nestin expression in the adult mouse midbrain.

Whether or not neurogenesis occurs in the adult substantia nigra pars compacta (SNc) is an important question relevant for developing better treatments for the motor symptoms of Parkinson's disease (PD). Although controversial, it is generally believed that dividing cells here remain undifferentiated or differentiate into glia, not neurons. However, there is a suggestion that Nestin-expressing neural precursor cells (NPCs) in the adult SNc have a propensity to differentiate into neurons, which we sought to confirm in the present study. Adult (>8-weeks old) transgenic NesCreERT2/GtROSA or NesCreERT2/R26eYFP mice were used to permanently label Nestin-expressing cells and their progeny with ß-galactosidase (ß-gal) or enhanced yellow fluorescent protein (eYFP), respectively. Most ß-gal+ or eYFP+ cells were found in the ependymal lining of the midbrain aqueduct (Aq) and in the midline ventral to Aq. Smaller but significant numbers were in the periaqueductal gray (PAG), the ventral tegmental area (VTA), and in SNc. Low-level basal proliferation was evidenced by a modest increase in number of ß-gal+ or eYFP+ cells over time, fewer ß-gal+ or eYFP+ cells when mice were administered the anti-mitotic agent Cytarabine, and incorporation of the proliferation marker bromodeoxyuridine (BrdU) in a very small number of ß-gal+ cells. No evidence of migration was found, including no immunoreactivity against the migration markers doublecortin (DCX) or polysialic acid neural cell adhesion molecule (PSA-NCAM), and no dispersal of ß-gal+ or eYFP+ cells through the midbrain parenchyma over time. However, ß-gal+ or eYFP+ cells did increase in size and express higher levels of mature neuronal genes over time, indicating growth and neuronal differentiation. In mice whose SNc dopamine neurons had been depleted with 6-hydroxy-dopamine, a model of PD, there were ~2-fold more ß-gal+ cells in SNc specifically, although the proportion that were also NeuN+ was not affected. Remarkably, as early as 4days following putative Nestin-expression, many ß-gal+ or eYFP+ cells had mature neuronal morphology and were NeuN+. Furthermore, mature neuronal ß-gal+ cells were immunoreactive against the self-renewal or pluripotency marker sex determining region Y-box 2 (Sox2). Overall, our data support the notion that some Nestin-expressing, presumably NPCs, have a limited capacity for proliferation, no capacity for migration, and a propensity to generate new neurons within the microenvironment of the adult midbrain. However, our data also suggest that significant numbers of extant midbrain neurons express Nestin and other classical neurogenesis markers in contexts that are presumably not neurogenic. These findings foreshadow duplicitous roles for Nestin and other molecules that are traditionally associated with neurogenesis in the adult midbrain, which should be considered in future PD research.

Combined prediction model of death toll for road traffic accidents based on independent and dependent variables.

In order to build a combined model which can meet the variation rule of death toll data for road traffic accidents and can reflect the influence of multiple factors on traffic accidents and improve prediction accuracy for accidents, the Verhulst model was built based on the number of death tolls for road traffic accidents in China from 2002 to 2011; and car ownership, population, GDP, highway freight volume, highway passenger transportation volume, and highway mileage were chosen as the factors to build the death toll multivariate linear regression model. Then the two models were combined to be a combined prediction model which has weight coefficient. Shapley value method was applied to calculate the weight coefficient by assessing contributions. Finally, the combined model was used to recalculate the number of death tolls from 2002 to 2011, and the combined model was compared with the Verhulst and multivariate linear regression models. The results showed that the new model could not only characterize the death toll data characteristics but also quantify the degree of influence to the death toll by each influencing factor and had high accuracy as well as strong practicability.