Fig. 8. Retroviral modification of the EphA-ephrin-A interaction in the cerebellum disrupts the olivocerebellar mapping. (A-E) Ligand and receptor activity detected by affinity probe in situ, in virus-infected explants. Rostral is at the top. Cb, cerebellum. Asterisk, inferior olive. (A) In an uninfected control cerebellum, parasagittal patterns of endogenous ligand activity are seen. (B) The cerebellum of an RCAS-ephrin-A2-infected embryo shows massive expression of ephrin-A2. (C) Following infection with the RCAS-EphA3C virus, EphA3-AP fails to detect endogenous ligand activity. (D) Receptor activity in an uninfected control cerebellum. (E) Ectopic EphA3C expression induced by the RCAS-EphA3C virus. (F-O) Retrograde axon tracing in retrovirus-infected explants. (F) Dye insertion sites in the cerebellum of the organotypic hindbrain culture. The capital letters indicate domain names. The rostral domain C and the caudal domain B are labeled with DiA (green star) and DiI (red star), respectively. (G-I) Labeling pattern in the IO of an embryo infected with the RCAS-AP virus. The caudal domain B and the rostral domain C receive axons from Area Ml and Area L, respectively. (J-L) Representative labeling pattern of IO following infection with the RCAS-ephrin-A2 virus. The caudal domain B is invaded by axons from more lateral parts of the IO. The rostral domain C is innervated by axons from Area L. (M-O) In explants infected with the RCAS-EphA3C virus, the caudal domain B receives axons from Area Ml. In contrast, the rostral domain C receives axons from broad areas of the IO. (P-T) Anterograde tracing of Area Ml axons in virus-infected explants. (P) DiI insertion site (Area Ml) in the IO. (Q-R) In explants infected with RCAS-ephrin-A2 virus, labeled axons stop at the border of ectopic expression domains (arrowheads), and fail to project to their normal target domain. (S-T) Following the RCAS-EphA3C virus infection, Area Ml axons project to most parts of the cerebellum, including the domains with high endogenous ligand expression. Virus-derived expression was detected by affinity probe in situ (R,T). Scale bars, 500 µm.

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