Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

The mature central nervous system contains precursor cells in the subventricular zone of the lateral ventricle. In this study we examined the possibility to affect fate of precursor cells through exogenous manipulations. The results indicate that administration of thyroid hormone and retinoic acid increases the expression of Ki67, a nuclear antigen associated with cell proliferation, and of nestin, a marker protein for precursor cells in the subventricular zone of adult male rats. Moreover, retinoic acid increases polysialated-neural cell adhesion molecules (PSA-NCAM)-immunoreactivity. These data suggest that nuclear receptor ligands are potential candidates for fate determination of precursor cells in the subventricular zone also in the adult brain.
Which intermediate filament (IF) protein can be used as a non-specific marker of the neuronal precursor cells of the subventricular zone?