Functional categories of the identified proteins. The relative composition of the functional categories varies between the subventricular zone group and the olfactory bulb group. This shift in protein categories may be associated with increased differentiation and integration towards the olfactory bulb. Proteins which have a function in differentiation are highly expressed in undifferentiated cells where differentiation is already initiated. Their expression decreases in terminally differentiated cells, since cellular differentiation programs are not active any more. Therefore, we interpret the decrease in differentiation-related proteins as sign for differentiated, not differentiating cells.