Fig. 2. The development of oligodendrocytes in E9.5- and E10.5-derived telencephalic explants is not restricted to caudal telencephalon. Telencephalon of embryos at E9.5 or E10.5 was carefully split into caudal (CT), rostral (RT) and dorsal (DT) territories. (A) The plane of dissection of an E9.5 embryo used to separate the caudal, rostral and dorsal telencephalon. Explants were cultivated for various periods of time before being analyzed after immunolabeling with O4 mAb. (B) At E9.5, none of the telencephalic explants contained O4⁺ cells after 11 days in vitro (equivalent to E20). After 13 days in vitro (equivalent to P2), 47% and 56% of caudal and rostral telencephalic explants, respectively, contained O4⁺ cells. By contrast, more than 85% of dorsal explants were negative for O4⁺ cells at 13 days in vitro. (C) At E10.5, both caudal and rostral territories were able to generate O4⁺ cells after 10 or 12 days in vitro (P2). The data represent the mean proportion of explants in each category±s.e.m. The number of explants analyzed in each category is indicated above the bars. White bars, fewer than 10 O4⁺ cells per explant; hatched bars, 10 to 100 O4⁺ cells per explant; black bars, more than 100 O4⁺ cells per explant. di, diencephalon; epa, entopeduncular area; mge, medial ganglionic eminence; os, optic stalk.