Investigating the Diversity of Radial Glia Fates in the Rat Neocortex

Radial Glia (RG) are a mitotically active population of cells which reside within the ventricular zone at the lateral ventricle and give rise to the pyramidal neurons and astrocytes of the neocortex. Through cellular divisions, RG produce two daughter cells, one which resides in the ventricular zone and becomes another RG while the other is an immature progenitor which migrates away from the ventricle and populates the growing cortex. RG have been found to be a heterogeneous population of cells which express different surface antigens and genetic promoters which may influence the cellular fate of their progeny. In this study we have investigated the progenitor profiles of two promoters, nestin (a neural intermediate filament) and GLAST (astrocyte specific glutamate transporter) within the RG. In-utero electroporation was used to transfect reporter plasmids under the control of promoter driven Cre-Recombinase into the RG lining the lateral ventricle during mid-neurogensesis (E14). It was found that there was a large amount of overlap between the nestin and GLAST expressing populations of RG, however, there was still a small subset of cells which exclusively expressed GLAST. This prompted us to investigate the lineage of these two promoters using the PiggyBac transposon system which uses promoter driven episomal plasmids to incorporate a reporter gene into the genome of the transfected cells, allowing use to trace their full progeny. Our data shows that nestin expressing RG generate mostly neurons and few astrocytes while the GLAST expressing RG generate a greater proportion of astrocytes to neurons.

Wage Premia in Employment Clusters: Agglomeration Economies or Worker Heterogeneity?

The correlation between wage premia and concentrations of firm activity may arise due to agglomeration economies or workers sorting by unobserved productivity. A worker's residential location is used as a proxy for their unobservable productivity attributes in order to test whether estimated work location wage premia are robust to the inclusion of these controls. Further, in a locational equilibrium, identical workers must receive equivalent compensation so that after controlling for residential location (housing prices) and commutes workers must be paid the same wages and only wage premia arising from unobserved productivity differences should remain unexplained. The models in this paper are estimated using a sample of male workers residing in 33 large metropolitan areas drawn from the 5% Public Use Microdata Sample (PUMS) from the 2000 U.S. Decennial Census. We find that wages are higher when an individual works in a location that has more workers or a greater density of workers. These agglomeration effects are robust to the inclusion of residential location controls and disappear with the inclusion of commute time suggesting that the effects are not caused by unobserved differences in worker productivity. Extended model specifications suggest that wages increase with the education level of nearby workers and the concentration of workers in an individual's own industry or occupation.