The mouse cerebellar cortex is subdivided by an elaborate array of parasagittal and transverse boundaries. The relationship between these two orthogonal patterns of compartmentation is understood poorly. We have combined the use of adult and perinatal molecular markers of compartmentation-zebrin II, calbindin, and an L7/pcp-2-lacZ transgene-to resolve some of these issues. Our results indicate that the adult cerebellar vermis is divided along the rostrocaudal axis by three transverse boundaries: through the rostral face of lobule VI, in the caudal half of lobule VII, and across the posterolateral fissure between lobules IX and X. These three boundaries subdivide the vermis into four transverse zones: the anterior zone (lobules I-V), the central zone (lobules VI-VII), the posterior zone (lobules VIII-IX), and the nodular zone (lobule X). The same zones and boundaries also can be identified in the newborn cerebellum. The parasagittal organization is different in each zone: a unique combination of Purkinje cell phenotypes is found in each transverse zone both in the neonate and the adult, and different zones have distinct developmental time tables. Furthermore, the parasagittal bands of Purkinje cells revealed in the adult cerebellar cortex by using antizebrin II immunocytochemistry are discontinuous across the transverse boundaries. These data suggest that the transverse zones of the vermis form first during development and that parasagittal compartmentation develops independently in each transverse zone.
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