DISTINCT ADHESIVE BEHAVIORS OF NEURONS AND NEURAL PRECURSOR CELLS DURING REGIONAL DIFFERENTIATION IN THE MAMMALIAN FOREBRAIN

Prior to the emergence of the major functional subdivisions of the mam malian forebrain-the neocortex, hippocampus, olfactory bulb, basal gan glia, and basal forebrain-the lateral aspect of the telencephalic vesi cle is distinguished by early neuronal differentiation assessed by MAP 2 and GAP43 expression and increased expression of the Ca2+-independen t/immunoglobulin superfamily cell adhesion molecules (CAMs) NCAM, L1, and TAG-1. In contrast, the ventral and medial aspects of the vesicle show little early neuronal differentiation and intermediate or undetec table levels of CAM expression. We asked whether cells from these thre e regions acquire distinct adhesive and recognition properties that re flect their position, state of neuronal differentiation, and level of CAM expression. In a dissociation/reaggregation assay, cells from the lateral telencephalic vesicle form the largest reaggregates while vent ral reaggregates are of intermediate size and medial reaggregates are the smallest. This differential adhesion has a Ca2+-independent compon ent, and cells in reaggregates from each region maintain expression of CAMs and other neuronal markers consistent with their region of origi n. Furthermore, cells from the lateral telencephalon can specifically sort out from medial cells. Little adhesivity is observed prior to ear ly neuronal differentiation and the expression of Ca2+-independent CAM s, when the forebrain is still a prosencephalic vesicle, nor does it f ollow the pattern of detectable CAM expression once forebrain rudiment s are formed. Thus, cells in the early developing forebrain acquire di stinct adhesive and recognition properties that reflect the concurrent emergence of regional differences in neuronal differentiation and CAM expression. These differences are transient and can only be detected in the telencephalic vesicle before and during the morphogenesis of ru diments of major forebrain subdivisions. (C) 1995 Academic Press, Inc.