Expression of cell adhesion molecules from the L2/HNK-1 family in cerebellar isografts in mice

The expression of cell adhesion molecules and glial fibrillary acid protein (GFAP) was examined in isografts of embryonic mouse cerebellum. Donor embryonic cerebella with the meninges removed were implanted into the lateral cerebral ventricles of adult host animals and examined after 2-6 weeks. Indirect immunofluorescence staining was performed on fresh frozen sections, using antibodies against the cell adhesion molecules L1, N-CAM, J1, myelin associated glycoprotein (MAG), and their shared L2/HNK-1 carbohydrate epitope, as well as GFAP. Nissl staining revealed that a normal trilaminar cytoarchitecture developed in some areas of implanted cerebella. Antibodies against cell adhesion molecules showed patterns of immunoreactivity generally similar to those present during normal cerebellar development. Expression of the L2 epitope in normal cerebellum is transiently observed in the molecular layer and is primarily seen in the substantia medullaris of mature cerebellum. This pattern was altered in the grafts, with a persistent expression of the L2 epitope in the molecular layer and less pronounced L2 immunoreactivity in the substantia medullaris cerebelli. These results may reflect a retardation of granule neuron differentiation due to abnormal or missing efferents and afferents in transplanted cerebellum. Also, the characteristic GFAP-positive radially oriented elongated fibers of Bergmann glia were not detected, even though passage of granule cells from their germinating zone to the internal granular layer was observed. The data presented here suggest that the developmental appearance and pattern of expression of cell adhesion molecules during morphogenesis of the cerebellum occurs largely independently of the normal complement of afferent and efferent connections.