Comparison of ncam, stx and polysialic acid (PSA) expression in the differentiating cerebellum during stages of neuronal migration. A-L: High magnification of lateral (A-C,G-I) and transverse (D-F,J-L) sections of the anterior hindbrain are shown at 30 hpf (A-F) and 48 hpf (G-L). The anterior cerebellar border at the midbrain-hindbrain boundary (MHB) and the posterior edge of the cerebellum are marked with a dashed and solid line, respectively. The mRNA in situ analysis was performed for ncam (A,D,G,J) and stx expression (B,E,H,K), while PSA immunoreactivity was detected using the mAb735 antibody (C,F,I,L). At 30 hours postfertilization (hpf), ncam expression was found to be strong and uniform in the cerebellum (A,D) similar to stx expression showing strongest expression at the ventricle (B,E). Moderate PSA levels can also be detected in this domain (C,F) during onset of rhombic lip derived neuronal migration (compare areas of dashed oval circles demarcating one cerebellar half). G,J: At 48 hpf, ncam expression is still uniform in the cerebellum. H,I: In contrast, stx and PSA expression have become restricted to the rostral cerebellar region along the MHB and are not longer detectable along the ventricle (red dashed circle). K,L: Transverse views of stx and PSA expression in the anterior cerebellum delineating the anteroventral migration route of neuronal progenitors. Scale bars = 50 μm.
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