REGIONALIZATION DEFECTS IN THE WEAVER MOUSE CEREBELLUM

The mammalian cerebellum consists of parasagittal bands and transverse zones that are laid down early in development. When the adult cerebel lum is immunostained for the Purkinje cell-specific antigen zebrin II (i.e., aldolase C), compartmentation is reflected in alternating zebri n II+ (P+) and zebrin II- bands (P-). The zebrin II phenotype is Purki nje cell autonomous; thus, disruptions in the zebrin pattern may refle ct early problems in pattern formation. Zebrin II expression has been examined in the weaver (wv) mouse cerebellum. Both zebrin II+ and zebr in II- Purkinje cells are present in the homozygous weaver (wu/wv) mou se, but they are not distributed normally. In the posterior vermis, al though the zebrin II+ bands are wider and multilaminate, the standard compartmentation is present. However, a large zebrin II+ cell mass is absent from the central vermis, and analysis of the anterior lobe reve als several missing zebrin II+ bands. The cytoarchitectonic defects in wv mice are not simply related to the Purkinje cell abnormalities. In stead, serial reconstruction reveals two transverse boundaries-one ros trally in lobule VI and the other caudally in lobule IX-that delineate cytoarchitectonic transverse zones important in cerebellar developmen t. The abnormal zebrin expression pattern in wv/vv mice may be seconda ry to the deletion of a transverse zone. This is the first demonstrati on that Purkinje cell compartmentation can be altered by mutation; the refore, the wv mutation should prove valuable in understanding cerebel lar regionalization. J. Comp. Neurol. 394:431-444, 1998. (C) 1998 Wile y-Liss, Inc.