A new strategy for analysis of phenotype marker antigens in hollow neurospheres

Changes in expression of phenotypic markers characterizing the cells comprising intact neurospheres are difficult to determine easily and accurately. The problem is compounded by the diversity of cell populations and phenotypes involved, and consequent non-uniform protein expression across the neurosphere wall, or around the circumference. Therefore, interpreting the effects of phenotype modifying conditions has been a complex and demanding task. Here, we report a novel direct method for measuring protein expression in immunofluoerescently labeled intact neurospheres by densitometric image analysis of optical cross-sections, obtained by scanning laser confocal microscopy. To demonstrate our methodology, hollow human neurospheres were exposed to basic fibroblast growth factor (FGF2), which reportedly induces neuronal commitment in monolayer cultures of neuroprogenitor cells derived from neurospheres. We determined that this treatment downregulated nestin and vimentin, protein markers accepted to indicate an immature, uncommitted phenotype. Neuron specific enolase was only marginally affected. Our strategy allows quantitation of changes in expression of marker proteins that is comparable to Western blot analysis. In addition to discriminating heterogeneity in protein expression, suitable optics may allow the resolution down to single cell level. We propose that this novel strategy, with or without confocal microscopy, may be applied to other biological systems. Analysis of protein expression by the cells comprising tubular or cylindrical cellular structures, or approximately spherical cell aggregates, can be performed efficiently using a small sample size.