Developmental expression, pattern of distribution, and effect on cell aggregation implicate a neuron-glial junctional domain protein in neuronal migration.

We developed a panel of monoclonal antibodies to cerebellar astroglial cells and selected for study those that revealed microdomain structures on the cell surface of neocortical and cerebellar astrocytes. One antibody, 15D7-AD7, recognized the approximately 72 kDa polypeptide doublet that was identified previously by the polyclonal antibody D4 as a component of the microdomain structure formed between migrating neurons and radial glial cell processes (Cameron and Rakic [1994] J. Neurosci. 14:3139-3155). Immunofluorescent localization studies reveal a spatial and temporal pattern of 15D7 immunoreactivity in multiple brain regions that correlates well with time periods when neuronal cell migration is a prominent morphogenetic event. In areas where the process of migration is underway, 15D7 immunoreactivity is detected simultaneously in both radial glial cells and cells that have the positional and morphologic features characteristic of migrating neurons. Subsequent to the completion of migration, immunoreactivity is detected in the transitional forms of radial glial cells and mature astrocytes, but not in neurons. Cell aggregation analyses reveal that 15D7 antibodies perturb the rate of aggregation for astrocyte-astrocyte, neuron-neuron, and mixed cell-cell combinations. Taken together, the present studies suggest that the polypeptides recognized by the 15D7 antibodies likely participate in an adhesive process, principally within the ventricular and subventricular zones, that is essential at the onset of the cell migration process.