Fig. 3. Irx4 specifically downregulates the expression of Slit1 in GCL. (A) Replication-competent retroviral constructs for expressing full-length Irx4 protein (RCAS-Irx4) or dominant-negative Irx4 protein (RCAS-DN-Irx4). (B-G) Retinas infected with the RCAS-Irx4 virus were hybridized with the Slit1 probe (B) or Robo1 probe (D), or stained with anti-Islet 1 antibody (F). All samples were also stained with the anti-viral GAG antibody to show the area of infection (C,E,G). Note the RCAS-Irx4-infected areas had few Slit1-expressing cells (marked with red broken lines). The samples infected with the dominant-negative Irx4 virus (H,I) or the control virus expressing only the Engrailed repressor domain (J,K) were similarly hybridized with the Slit1 probe (H,J) and stained with the anti-viral GAG antibody (I,K). Note the Slit1 expression was activated in the areas infected with the RCAS-DN-Irx4 virus (arrowheads in H,I) but not the control virus. Scale bar: 100 µm.