Fig. 8. In situ immunohistochemical analysis of ERK activation in 32-cell stage Ciona embryos. (A,B) Vegetal view of early 32-cell stage. (C,D) Animal view of late 32-cell stage. (A,C) Control embryos. (B,D) Embryos treated with PD184352. A-line vegetal blastomeres (A6.4, A6.2) are shown outlined in yellow; a-line neural precursors (a6.5) in red; and b6.5, which also contains neural fate, in green.