Selective purkinje cell ectopia in the cerebellum of the weaver mouse

The adult mouse cerebellar vermis consists of four transverse zones, each o f which is further subdivided into parasagittal stripes. In the adult weave r (wv/wv) mouse, the zebrin II expression pattern in the cerebellar vermis is abnormal, consistent with the absence of a central zone (similar to lobu les VI/VII). Because the small, heat shock protein HSP25 is a constitutive marker of parasagittal bands of Purkinje cells in the caudal central zone a nd the nodular zone (similar to lobules IX/X), we used HSP25 immunocytochem istry to show that the patterning abnormalities in wv/wv reflect selective Purkinje cell ectopia rather than the absence of the central zone. A specif ic HSP25-immunopositive Purkinje cell ectopia within the central zone was i dentified. Symmetrical clusters of HSP25-immunopositive Purkinje cells, whi ch presumably would have formed the parasagittal stripes in the wild type, are present ectopically on either side of the midline in wv/wv. In contrast , in the nodular zone, HSP25-immunopositive Purkinje cells form a near-mono layer and are organized into parasagittal stripes. We therefore conclude th at specific Purkinje cell clusters in the wv/wv cerebellum fail to disperse and that this ectopia contributes to the topographical abnormalities. (C) 2001 Wiley-Liss, Inc.