Ectopic neurons are present at areas of disrupted basement membrane. Immunofluorescent detection of transient axonal glycoprotein 1 (TAG1), microtubule-associated protein 2 (MAP2), paired box 6 (pax6), neuronal nuclear protein (NeuN), and GABAA receptor α6 (GABARA6) (all red) and laminin (LM; green) in control cerebella at P8 (A, C, E), P16 (F), P21 (G) and in age-matched nestin-Cre/DG-null (B, D, H-J). At P8, the EGL in the control cerebellum consists of an outer and inner layer, corresponding to proliferating and post-mitotic GC, respectively. Toward the end of cerebellar development at P16, the EGL ceases to exist as differented GCs migrate inward to form the IGL. In the absence of dystroglycan, ectopic GC differentiate yet remain trapped at the cerebellar surface where the basement membrane is highly disrupted. DAPI (blue) was used as a nuclear counter stain. Carets (^) denote the continuous basement membrane; tildes (~) indicate areas of disrupted basement membrane; asterisks (*) represent ectopic cells. Solid lines in panels E-G demarcate the continuous basal lamina. EGLi = inner external granule cell layer; EGLo = outer external granule cell layer. GCL = granule cell layer; IGL = internal granule cell layer; ML = molecular layer. Scale bar: 20 μm.