DISTRIBUTION OF A REELER GENE-RELATED ANTIGEN IN THE DEVELOPING CEREBELLUM - AN IMMUNOHISTOCHEMICAL STUDY WITH AN ALLOGENEIC ANTIBODY CR-50ON NORMAL AND REELER MICE

We have immunohistochemically investigated the expression of a reeler gene-related antigen in the mouse cerebellum by using a monoclonal ant ibody, CR-50. This antibody probes a distinct allelic antigen present in normal but not in reeler mutant mice, and this antigen is localized in the brain regions in which morphological abnormalities occur in re eler mice (Ogawa et al., Neuron 14: 899-912, 1995). The developing nor mal cerebellum showed transient immunoreactivity to CR-50 in a limited set of neurons and in the extracellular space near the pial surface. An early population of CR-50-labeled cells emerged on embryonic day (E ) 13 along the dorsal cerebellar surface, comprising the nuclear trans itory zone (NTZ). Bromodeoxyuridine labeling revealed the time of orig in of these cells to be at E11-12. From E14 to E18, some CR-50-labeled cells were stacked in the inner border of the external granular layer (EGL), whereas others were scattered in deep areas, such as the cereb ellar nuclei and the surrounding intermediate zone or white matter. In the first postnatal week, these subcortical structures became immunon egative. However, CR-50 antigen was continuously produced until the se cond postnatal week by another population of cells occupying i) the pr emigratory zone (PMZ), the inner half of the EGL, and ii) the internal granular layer (IGL). These later CR-50-positive cells were smaller t han the earlier type and showed the morphology typical of granule neur ons. Both types of CR-50-labeled cells were positive for a DNA-binding protein, tie. By treating living cerebellar slices with CR-50, the ex tracellular antigen was localized as a puncutate staining pattern in t he NTZ, PMZ, and molecular layer (ML), but not in the subcortical regi ons and IGL. Purkinje cells were negative for CR-50 and aligned as a m onolayer adjacent to the PMZ, though their dendritic trees were closel y associated with the extracellular CR-50-antigen in the PMZ and ML. S taining of dissociated cells suggested that the extracellular antigen is initially present throughout the surfaces of the CR-50/anti-zic dou ble positive neurons, acid is then rearranged to concentrate on their processes contacting with Purkinje cells. The spatiotemporal expressio ns of the CR-50 antigen in the cerebellum are consistent with the poss ibility that this antigen is involved in cell-cell interactions relate d to the histogenetic assembly of Purkinje cells. (C) 1996 Wiley-Liss, Inc.