Fig. 2. Emx2 is expressed in acutely isolated stem cells and in ANSCs and is down regulated during differentiation. (A,B) Primary cultures from the adult PVR were obtained by differential adhesion on PDK-treated plastic (Lim and Alvarez-Buylla, 1999) in order to establish two distinct cell fractions, the type B/C cell fraction and the PSA-NCAM-positive fraction, called type A. By means of in situ hybridization, Emx2 was shown to be expressed in (A) type B and (B) type A cells. (C) High levels of Emx2 expression were also detected in undifferentiated adult CNS stem/progenitors. (D) A faint signal was observed in the terminally differentiated progeny of ANSCs, restricted to cells morphologically identifiable as immature neurons. Bar in C, 15 µm. (E) A high frequency of cells expressing Emx2 messenger can be observed when cells are highly undifferentiated. The onset of differentiation and maturation is coincident with a decrease in the number of Emx2-positive cells that drops to 8% of the total cell number by 7 days following induction of differentiation. (F) Semi-quantitative RT-PCR shows high levels of Emx2 messenger in undifferentiated multipotent neural stem cells (ANSCs), while in stem cell-derived terminally differentiated progeny (DCs) lower expression could be detected. No such change was observed in the level of the Emx2 paralog Emx1, or of Otx1, Otx2 and Mash1. Quantitative comparison was made with the housekeeper gene glyceraldehyde-3-phosphate dehydrogenase (GAPDH).